U.S. patent number 9,270,989 [Application Number 13/928,713] was granted by the patent office on 2016-02-23 for method and apparatus for video coding.
This patent grant is currently assigned to Nokia Technologies Oy. The grantee listed for this patent is Nokia Technologies Oy. Invention is credited to Miska Hannuksela.
United States Patent |
9,270,989 |
Hannuksela |
February 23, 2016 |
Method and apparatus for video coding
Abstract
A method, apparatus and computer program product are provided
that permit values of certain parameters or syntax elements, such
as the HRD parameters and/or a level indicator, to be taken from a
syntax structure, such as a sequence parameter set. In this regard,
values of certain parameters or syntax elements, such as the HRD
parameters and/or a level indicator, may be taken from a syntax
structure of a certain other layer, such as the highest layer,
present in an access unit, coded video sequence and/or bitstream
even if the other layer, such as the highest layer, were not
decoded. The syntax element values from the other layer, such as
the highest layer, may be semantically valid and may be used for
conformance checking, while the values of the respective syntax
elements from other respective syntax structures, such as sequence
parameter sets, may be active or valid otherwise.
Inventors: |
Hannuksela; Miska (Tampere,
FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nokia Technologies Oy |
Espoo |
N/A |
FI |
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Assignee: |
Nokia Technologies Oy (Espoo,
FI)
|
Family
ID: |
49778129 |
Appl.
No.: |
13/928,713 |
Filed: |
June 27, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140003489 A1 |
Jan 2, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61667085 |
Jul 2, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N
19/187 (20141101); H04N 19/70 (20141101); H04N
19/30 (20141101) |
Current International
Class: |
H04N
19/187 (20140101); H04N 19/70 (20140101); H04N
19/30 (20140101) |
Field of
Search: |
;375/240.01,240.02 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
International Search Report received for corresponding Patent
Cooperation Treaty Application No. PCT/FI2013/050661, dated Oct.
16, 2013, 6 pages. cited by applicant .
Written Opinion received for corresponding Patent Cooperation
Treaty Application No. PCT/FI2013/050661, dated Oct. 16, 2013, 6
pages. cited by applicant .
Amon, P. et al. "File format for scalable video coding", IEEE
Trans, on Circuits and Systems for Video Technology, vol. 17 No. 9,
Sep. 2007, pp. 1174-1185. cited by applicant.
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Primary Examiner: Patel; Jay
Assistant Examiner: Sun; Yulin
Attorney, Agent or Firm: Nokia Technologies Oy
Claims
The invention claimed is:
1. A method comprising: producing, with a processor, two or more
scalability layers of a scalable data stream, wherein each of said
two or more scalability layers has a different coding property, is
associated with a scalability layer identifier and is characterized
by a first set of syntax elements comprising at least a profile and
a second set of syntax elements comprising at least one of a level
or hypothetical reference decoder (HRD) parameters; inserting a
first scalability layer identifier value in a first elementary unit
including data from a first of two or more scalability layers;
causing the first of said two or more scalability layers to be
signaled with said first and second set of syntax elements in a
first parameter set elementary unit such that the first parameter
set elementary unit is readable by a decoder to determine the
values of the first and second set of syntax elements without
decoding a scalability layer of said scalable data stream;
inserting the first scalability layer identifier value in the first
parameter set elementary unit; inserting a second scalability layer
identifier value in a second elementary unit including data from a
second of two or more scalability layers; causing the second of
said two or more scalability layers to be signaled with said first
and second set of syntax elements in a second parameter set
elementary unit such that the second parameter set elementary unit
is readable by the decoder to determine the coding property without
decoding the scalability layer of said scalable data stream;
inserting the second scalability layer identifier value in the
second parameter set elementary unit, wherein values of the first
set of syntax elements in the first parameter set elementary unit
are valid in an instance in which the first elementary unit is
processed and the second elementary unit is ignored or removed,
wherein values of the second set of syntax elements in the first
parameter set elementary unit are valid in an instance in which the
first elementary unit is processed and the second elementary unit
is removed, wherein values of the first set of syntax elements in
the second parameter set elementary unit are valid in an instance
in which the second elementary unit is processed, and wherein
values of the second set of syntax elements in the second parameter
set elementary unit are valid in an instance in which the second
elementary unit is processed.
2. A method according to claim 1 wherein the first and second sets
of syntax elements are included in a syntax structure of a highest
layer that is present in an access unit, a coded video sequence or
a bitstream.
3. A method according to claim 1 wherein the level comprises a
level indicator.
4. An apparatus comprising at least one processor and at least one
memory including computer program code, the memory and the computer
program code configured to, with the at least one processor, cause
the apparatus to: produce two or more scalability layers of a
scalable data stream, wherein each of said two or more scalability
layers has a different coding property, is associated with a
scalability layer identifier and is characterized by a first set of
syntax elements comprising at least a profile and a second set of
syntax elements comprising at least one of a level or hypothetical
reference decoder (HRD) parameters; insert a first scalability
layer identifier value in a first elementary unit including data
from a first of two or more scalability layers; cause the first of
said two or more scalability layers to be signaled with said first
and second set of syntax elements in a first parameter set
elementary unit such that the first parameter set elementary unit
is readable by a decoder to determine the values of the first and
second set of syntax elements without decoding a scalability layer
of said scalable data stream; insert the first scalability layer
identifier value in the first parameter set elementary unit; insert
a second scalability layer identifier value in a second elementary
unit including data from a second of two or more scalability
layers; cause the second of said two or more scalability layers to
be signaled with said first and second set of syntax elements in a
second parameter set elementary unit such that the second parameter
set elementary unit is readable by the decoder to determine the
coding property without decoding the scalability layer of said
scalable data stream; insert the second scalability layer
identifier value in the second parameter set elementary unit,
wherein values of the first set of syntax elements in the first
parameter set elementary unit are valid in an instance in which the
first elementary unit is processed and the second elementary unit
is ignored or removed, wherein values of the second set of syntax
elements in the first parameter set elementary unit are valid in an
instance in which the first elementary unit is processed and the
second elementary unit is removed, wherein values of the first set
of syntax elements in the second parameter set elementary unit are
valid in an instance in which the second elementary unit is
processed, and wherein values of the second set of syntax elements
in the second parameter set elementary unit are valid in an
instance in which the second elementary unit is processed.
5. An apparatus according to claim 4 wherein the first and second
sets of syntax elements are included in a syntax structure of a
highest layer that is present in an access unit, a coded video
sequence or a bitstream.
6. An apparatus according to claim 4 wherein the level comprises a
level indicator.
7. A method comprising: receiving a first scalable data stream
comprising two or more scalability layers having different coding
properties, wherein each of said two or more scalability layers is
associated with a scalability layer identifier and is characterized
by a first set of syntax elements comprising at least a profile and
a second set of syntax elements comprising at least one of a level
or hypothetical reference decoder (HRD) parameters; a first
scalability layer identifier value residing in a first elementary
unit including data from a first of two or more scalability layers;
the first and second set of syntax elements being signaled in a
first parameter set elementary unit for the first of said two or
more scalability layers such that a first parameter set is readable
by a decoder to determine the values of the first and second set of
syntax elements without decoding a scalability layer of said
scalable data stream; the first scalability layer identifier value
residing in the first parameter set elementary unit; a second
scalability layer identifier value residing in a second elementary
unit including data from a second of two or more scalability
layers; the first and second set of syntax elements being signaled
in a second parameter set elementary unit for the second of said
two or more scalability layers such that a second parameter set is
readable by the decoder to determine the coding property without
decoding the scalability layer of said scalable data stream; the
second scalability layer identifier value residing in the second
parameter set elementary unit; and removing, with a processor, from
the received first scalable data stream the second elementary unit
and the second parameter set elementary unit on the basis of the
second elementary unit and the second parameter set elementary unit
including the second scalability layer identifier value.
8. A method according to claim 7 wherein the first and second sets
of syntax elements are included in a syntax structure of a highest
layer that is present in an access unit, a coded video sequence or
a bitstream.
9. A method according to claim 7 wherein the level comprises a
level indicator.
10. An apparatus comprising at least one processor and at least one
memory including computer program code, the memory and the computer
program code configured to, with the at least one processor, cause
the apparatus to: receive a first scalable data stream comprising
two or more scalability layers having different coding properties,
wherein each of said two or more scalability layers is associated
with a scalability layer identifier and is characterized by a first
set of syntax elements comprising at least a profile and a second
set of syntax elements comprising at least one of a level or
hypothetical reference decoder (HRD) parameters; a first
scalability layer identifier value residing in a first elementary
unit including data from a first of two or more scalability layers;
the first and second set of syntax elements being signaled in a
first parameter set elementary unit for the first of said two or
more scalability layers such that a first parameter set is readable
by a decoder to determine the values of the first and second set of
syntax elements without decoding a scalability layer of said
scalable data stream; the first scalability layer identifier value
residing in the first parameter set elementary unit; a second
scalability layer identifier value residing in a second elementary
unit including data from a second of two or more scalability
layers; the first and second set of syntax elements being signaled
in a second parameter set elementary unit for the second of said
two or more scalability layers such that a second parameter set is
readable by the decoder to determine the coding property without
decoding the scalability layer of said scalable data stream; the
second scalability layer identifier value residing in the second
parameter set elementary unit; and remove from the received first
scalable data stream the second elementary unit and the second
parameter set elementary unit on the basis of the second elementary
unit and the second parameter set elementary unit including the
second scalability layer identifier value.
11. An apparatus according to claim 10 wherein the first and second
sets of syntax elements are included in a syntax structure of a
highest layer that is present in an access unit, a coded video
sequence or a bitstream.
12. An apparatus according to claim 10 wherein the level comprises
a level indicator.
13. A method comprising: receiving a first scalable data stream two
or more scalability layers having different coding properties,
wherein each of said two or more scalability layers is associated
with a scalability layer identifier and is characterized by a
coding property; a first scalability layer identifier value
residing in a first elementary unit including data from a first of
two or more scalability layers; the first of said two or more
scalability layers with said coding property being signaled in a
first parameter set elementary unit such that the coding property
is readable by a decoder to determine the coding property without
decoding a scalability layer of said scalable data stream; the
first scalability layer identifier value residing in the first
parameter set elementary unit; a second scalability layer
identifier value residing in a second elementary unit including
data from a second of two or more scalability layers; the first and
second sets of syntax elements being signaled in a second parameter
set elementary unit for the second of said two or more scalability
layers such that a first parameter set is readable by the decoder
to determine the values of the first and second sets of syntax
elements without decoding a scalability layer of said scalable data
stream; the second scalability layer identifier value residing in
the second parameter set elementary unit; receiving a set of
scalability layer identifier values indicating scalability layers
to be decoded, and removing from the received first scalable data
stream, with the processor, the second elementary unit and the
second parameter set elementary unit on the basis of the second
elementary unit and the second parameter set elementary unit
including the second scalability layer identifier value not being
among the set of scalability layer identifier values.
14. A method according to claim 13 wherein the first set of syntax
elements comprises at least a profile and the second set of syntax
elements comprises at least one of a level or hypothetical
reference decoder (HRD) parameters.
15. A method according to claim 14 wherein the level comprises a
level indicator.
16. A method according to claim 13 wherein the first and second
sets of syntax elements are included in a syntax structure of a
highest layer that is present in an access unit, a coded video
sequence or a bitstream.
17. An apparatus comprising at least one processor and at least one
memory including computer program code, the memory and the computer
program code configured to, with the at least one processor, cause
the apparatus to: receive a first scalable data stream two or more
scalability layers having different coding properties, wherein each
of said two or more scalability layers is associated with a
scalability layer identifier and is characterized by a coding
property; a first scalability layer identifier value residing in a
first elementary unit including data from a first of two or more
scalability layers; the first of said two or more scalability
layers with said coding property being signaled in a first
parameter set elementary unit such that the coding property is
readable by a decoder to determine the coding property without
decoding a scalability layer of said scalable data stream; the
first scalability layer identifier value residing in the first
parameter set elementary unit; a second scalability layer
identifier value residing in a second elementary unit including
data from a second of two or more scalability layers; the first and
second sets of syntax elements being signaled in a second parameter
set elementary unit for the second of said two or more scalability
layers such that a first parameter set is readable by the decoder
to determine the values of the first and second sets of syntax
elements without decoding a scalability layer of said scalable data
stream; the second scalability layer identifier value residing in
the second parameter set elementary unit; receive a set of
scalability layer identifier values indicating scalability layers
to be decoded, and remove from the received first scalable data
stream the second elementary unit and the second parameter set
elementary unit on the basis of the second elementary unit and the
second parameter set elementary unit including the second
scalability layer identifier value not being among the set of
scalability layer identifier values.
18. An apparatus according to claim 17 wherein the first set of
syntax elements comprises at least a profile and the second set of
syntax elements comprises at least one of a level or hypothetical
reference decoder (HRD) parameters.
19. An apparatus according to claim 18 wherein the level comprises
a level indicator.
20. An apparatus according to claim 17 wherein the first and second
sets of syntax elements are included in a syntax structure of a
highest layer that is present in an access unit, a coded video
sequence or a bitstream.
Description
TECHNICAL FIELD
The present application relates generally to an apparatus, a method
and a computer program product for video coding and decoding.
BACKGROUND
This section is intended to provide a background or context to the
invention that is recited in the claims. The description herein may
include concepts that could be pursued, but are not necessarily
ones that have been previously conceived or pursued. Therefore,
unless otherwise indicated herein, what is described in this
section is not prior art to the description and claims in this
application and is not admitted to be prior art by inclusion in
this section.
Typical audio and video coding standards specify "profiles" and
"levels." A "profile" may be defined as a subset of algorithmic
features of the standard and a "level" may be defined as a set of
limits to the coding parameters that impose a set of constraints in
decoder resource consumption. Indicated profile and level can be
used to signal properties of a media stream and to signal the
capability of a media decoder.
In many video coding standards the syntax structures may be
arranged in different layers, where a layer may be defined as one
of a set of syntactical structures in a non-branching hierarchical
relationship. Generally, higher layers may contain lower layers.
The coding layers may consist for example of the coded video
sequence, picture, slice, and treeblock layers. Some video coding
standards introduce a concept of a parameter set. An instance of a
parameter set may include all picture, group of pictures (GOP), and
sequence level data such as picture size, display window, optional
coding modes employed, macroblock allocation map, and others. Each
parameter set instance may include a unique identifier. Each slice
header may include a reference to a parameter set identifier, and
the parameter values of the referred parameter set may be used when
decoding the slice. Parameter sets may be used to decouple the
transmission and decoding order of infrequently changing picture,
GOP, and sequence level data from sequence, GOP, and picture
boundaries. Parameter sets can be transmitted out-of-band using a
reliable transmission protocol as long as they are decoded before
they are referred. If parameter sets are transmitted in-band, they
can be repeated multiple times to improve error resilience compared
to conventional video coding schemes. The parameter sets may be
transmitted at a session set-up time. However, in some systems,
mainly broadcast ones, reliable out-of-band transmission of
parameter sets may not be feasible, but rather parameter sets are
conveyed in-band in Parameter Set NAL units.
SUMMARY
A method, apparatus and computer program product are provided
according to example embodiments of the present invention that
permit values of certain parameters or syntax elements, such as the
HRD parameters and/or a level indicator, to be taken from a syntax
structure, such as a sequence parameter set. In this regard, values
of certain parameters or syntax elements, such as the HRD
parameters and/or a level indicator, may be taken from a syntax
structure of a certain other layer, such as the highest layer,
present in an access unit, coded video sequence and/or bitstream
even if the other layer, such as the highest layer, were not
decoded. The syntax element values from the other layer, such as
the highest layer, may be semantically valid and may be used for
conformance checking, while the values of the respective syntax
elements from other respective syntax structures, such as sequence
parameter sets, may be active or valid otherwise.
In one embodiment, a method is provided that includes producing,
with a processor, two or more scalability layers of a scalable data
stream. Each of the two or more scalability layers may have a
different coding property, is associated with a scalability layer
identifier and is characterized by a first set of syntax elements
that includes at least a profile and a second set of syntax
elements that includes at least one of a level or hypothetical
reference decoder (HRD) parameters. The method of this embodiment
also inserts a first scalability layer identifier value in a first
elementary unit including data from a first of two or more
scalability layers. The method may also cause the first of the two
or more scalability layers to be signaled with the first and second
set of syntax elements in a first parameter set elementary unit
such that the first parameter set elementary unit is readable by a
decoder to determine the values of the first and second set of
syntax elements without decoding a scalability layer of the
scalable data stream. The method of this embodiment also inserts a
first scalability layer identifier value in the first parameter set
elementary unit and inserts a second scalability layer identifier
value in the second elementary unit including data from a first of
two or more scalability layers. The method of this embodiment also
causes the second of the two or more scalability layers to be
signaled with the first and second set of syntax elements in a
second parameter set elementary units such that the second
parameter set elementary unit is readable by a decoder to determine
the coding property without decoding the scalability layer of the
data stream. The method may also insert the second scalability
layer identifier value in the second parameter set elementary
unit.
In this embodiment, the values of the first set of syntax elements
in the first parameter set elementary unit are valid in an instance
in which the first elementary unit is processed and the second
elementary unit is ignored or removed. Additionally, the values of
the second set of syntax elements in the first parameter set
elementary unit may be valid in an instance in which the first
elementary unit is processed and the second elementary unit is
removed. The values of the first set of syntax elements in the
second parameter set elementary unit may be valid in an instance in
which the second elementary unit is processed and the values of the
second set of syntax elements in the second parameter set
elementary unit may be valid in an instance in which the second
elementary unit is ignored or processed.
In another embodiment, an apparatus is provided that includes at
least one processor and at least one memory including computer
program code with the memory and the computer program code
configured to, with the at least one processor, cause the apparatus
to produce two or more scalability layers of a scalable data
stream. Each of the two or more scalability layers may have a
different coding property, is associated with a scalability layer
identifier and is characterized by a first set of syntax elements
that includes at least a profile and a second set of syntax
elements that includes at least one of a level or hypothetical
reference decoder (HRD) parameters. The memory and the computer
program code are also configured to, with the at least one
processor, cause the apparatus to insert a first scalability layer
identifier value in a first elementary unit including data from a
first of two or more scalability layers. The memory and the
computer program code may also be configured to, with the at least
one processor, cause the apparatus to also cause the first of the
two or more scalability layers to be signaled with the first and
second set of syntax elements in a first parameter set elementary
unit such that the first parameter set elementary unit is readable
by a decoder to determine the values of the first and second set of
syntax elements without decoding a scalability layer of the
scalable data stream. The memory and the computer program code may
be configured to, with the at least one processor, cause the
apparatus to insert a first scalability layer identifier value in
the first parameter set elementary unit and insert a second
scalability layer identifier value in the second elementary unit
including data from a first of two or more scalability layers. The
memory and the computer program code are also configured to, with
the at least one processor, cause the apparatus to cause the second
of the two or more scalability layers to be signaled with the first
and second set of syntax elements in a second parameter set
elementary units such that the second parameter set elementary unit
is readable by a decoder to determine the coding property without
decoding the scalability layer of the data stream. The memory and
the computer program code may also be configured to, with the at
least one processor, cause the apparatus to insert the second
scalability layer identifier value in the second parameter set
elementary unit.
In this embodiment, the values of the first set of syntax elements
in the first parameter set elementary unit are valid in an instance
in which the first elementary unit is processed and the second
elementary unit is ignored or removed. Additionally, the values of
the second set of syntax elements in the first parameter set
elementary unit may be valid in an instance in which the first
elementary unit is processed and the second elementary unit is
removed. The values of the first set of syntax elements in the
second parameter set elementary unit may be valid in an instance in
which the second elementary unit is processed and the values of the
second set of syntax elements in the second parameter set
elementary unit may be valid in an instance in which the second
elementary unit is ignored or processed.
In a further embodiment, a computer program product is provided
that includes at least one non-transitory computer-readable storage
medium having computer-executable program code portions stored
therein with the computer-executable program code portions
including program code instructions for producing two or more
scalability layers of a scalable data stream. Each of the two or
more scalability layers may have a different coding property, is
associated with a scalability layer identifier and is characterized
by a first set of syntax elements that includes at least a profile
and a second set of syntax elements that includes at least one of a
level or hypothetical reference decoder (HRD) parameters. The
computer-executable program code portions of one embodiment may
also include program code instructions for inserting a first
scalability layer identifier value in a first elementary unit
including data from a first of two or more scalability layers. The
computer-executable program code portions of one embodiment may
also include program code instructions for causing the first of the
two or more scalability layers to be signaled with the first and
second set of syntax elements in a first parameter set elementary
unit such that the first parameter set elementary unit is readable
by a decoder to determine the values of the first and second set of
syntax elements without decoding a scalability layer of the
scalable data stream. The computer-executable program code portions
of one embodiment may also include program code instructions for
inserting a first scalability layer identifier value in the first
parameter set elementary unit and inserting a second scalability
layer identifier value in the second elementary unit including data
from a first of two or more scalability layers. The
computer-executable program code portions of one embodiment may
also include program code instructions for the second of the two or
more scalability layers to be signaled with the first and second
set of syntax elements in a second parameter set elementary units
such that the second parameter set elementary unit is readable by a
decoder to determine the coding property without decoding the
scalability layer of the data stream. The computer-executable
program code portions of one embodiment may also include program
code instructions for inserting the second scalability layer
identifier value in the second parameter set elementary unit.
In this embodiment, the values of the first set of syntax elements
in the first parameter set elementary unit are valid in an instance
in which the first elementary unit is processed and the second
elementary unit is ignored or removed. Additionally, the values of
the second set of syntax elements in the first parameter set
elementary unit may be valid in an instance in which the first
elementary unit is processed and the second elementary unit is
removed. The values of the first set of syntax elements in the
second parameter set elementary unit may be valid in an instance in
which the second elementary unit is processed and the values of the
second set of syntax elements in the second parameter set
elementary unit may be valid in an instance in which the second
elementary unit is ignored or processed.
In yet another embodiment, an apparatus is provided that includes
means for producing two or more scalability layers of a scalable
data stream. Each of the two or more scalability layers may have a
different coding property, is associated with a scalability layer
identifier and is characterized by a first set of syntax elements
that includes at least a profile and a second set of syntax
elements that includes at least one of a level or hypothetical
reference decoder (HRD) parameters. The apparatus of this
embodiment also includes means for inserting a first scalability
layer identifier value in a first elementary unit including data
from a first of two or more scalability layers. The apparatus may
also include means for causing the first of the two or more
scalability layers to be signaled with the first and second set of
syntax elements in a first parameter set elementary unit such that
the first parameter set elementary unit is readable by a decoder to
determine the values of the first and second set of syntax elements
without decoding a scalability layer of the scalable data stream.
The apparatus of this embodiment also includes means for inserting
a first scalability layer identifier value in the first parameter
set elementary unit and means for inserting a second scalability
layer identifier value in the second elementary unit including data
from a first of two or more scalability layers. The apparatus of
this embodiment also includes means for causing the second of the
two or more scalability layers to be signaled with the first and
second set of syntax elements in a second parameter set elementary
units such that the second parameter set elementary unit is
readable by a decoder to determine the coding property without
decoding the scalability layer of the data stream. The apparatus
may also include means for inserting the second scalability layer
identifier value in the second parameter set elementary unit.
In this embodiment, the values of the first set of syntax elements
in the first parameter set elementary unit are valid in an instance
in which the first elementary unit is processed and the second
elementary unit is ignored or removed. Additionally, the values of
the second set of syntax elements in the first parameter set
elementary unit may be valid in an instance in which the first
elementary unit is processed and the second elementary unit is
removed. The values of the first set of syntax elements in the
second parameter set elementary unit may be valid in an instance in
which the second elementary unit is processed and the values of the
second set of syntax elements in the second parameter set
elementary unit may be valid in an instance in which the second
elementary unit is ignored or processed.
In one embodiment, a method is provided that includes receiving a
first scalable data stream including scalability layers having
different coding properties. Each of the two or more scalability
layers is associated with a scalability layer identifier and is
characterized by a first of syntax elements comprising at least a
profile and a second set of syntax elements including at least one
of a level or Hypothetical Reference Decoder (HRD) parameters. A
first scalability layer identifier value may reside in a first
elementary unit including data from the first of two or more
scalability layers. A first and second set of syntax elements may
be signaled in a first parameter set elementary unit for the first
of the two or more scalability layers such that a first parameter
set is readable by a decoder to determine the values of the first
and second set of syntax elements without decoding a scalability
layer of the scalable data stream. The first scalability layer
identifier value may reside in the first parameter set elementary
unit. A second scalability layer identifier value may reside in a
second elementary unit including data from a second of two or more
scalability layers. The first and second set of syntax elements may
be signaled in a second parameter set elementary unit for the
second of the two or more scalability layers such that a second
parameter set is readable by the decoder to determine the coding
property without decoding the scalability layer of the scalable
data stream. The second scalability layer identifier value may
reside in the second parameter set elementary unit. The method of
this embodiment may also include removing, with a processor, from
the first scalable data stream the second elementary unit and the
second parameter set elementary unit on the basis of the second
elementary unit and the second parameter set elementary unit
including the second scalability layer identifier value.
In another embodiment, an apparatus is provided that includes at
least one processor and at least one memory including computer
program code with the memory and the computer program code
configured to, with the at least one processor, cause the apparatus
to receive a first scalable data stream including scalability
layers having different coding properties. Each of the two or more
scalability layers is associated with a scalability layer
identifier and is characterized by a first of syntax elements
comprising at least a profile and a second set of syntax elements
including at least one of a level or Hypothetical Reference Decoder
(HRD) parameters. A first scalability layer identifier value may
reside in a first elementary unit including data from the first of
two or more scalability layers. A first and second set of syntax
elements may be signaled in a first parameter set elementary unit
for the first of the two or more scalability layers such that a
first parameter set is readable by a decoder to determine the
values of the first and second set of syntax elements without
decoding a scalability layer of the scalable data stream. The first
scalability layer identifier value may reside in the first
parameter set elementary unit. A second scalability layer
identifier value may reside in a second elementary unit including
data from a second of two or more scalability layers. The first and
second set of syntax elements may be signaled in a second parameter
set elementary unit for the second of the two or more scalability
layers such that a second parameter set is readable by the decoder
to determine the coding property without decoding the scalability
layer of the scalable data stream. The second scalability layer
identifier value may reside in the second parameter set elementary
unit. The apparatus of this embodiment may also include the memory
and the computer program code configured to, with the at least one
processor, cause the apparatus to remove from the first scalable
data stream the second elementary unit and the second parameter set
elementary unit on the basis of the second elementary unit and the
second parameter set elementary unit including the second
scalability layer identifier value.
In a further embodiment, a computer program product is provided
that includes at least one non-transitory computer-readable storage
medium having computer-executable program code portions stored
therein with the computer-executable program code portions
including program code instructions for receiving a first scalable
data stream including scalability layers having different coding
properties. Each of the two or more scalability layers is
associated with a scalability layer identifier and is characterized
by a first of syntax elements comprising at least a profile and a
second set of syntax elements including at least one of a level or
Hypothetical Reference Decoder (HRD) parameters. A first
scalability layer identifier value may reside in a first elementary
unit including data from the first of two or more scalability
layers. A first and second set of syntax elements may be signaled
in a first parameter set elementary unit for the first of the two
or more scalability layers such that a first parameter set is
readable by a decoder to determine the values of the first and
second set of syntax elements without decoding a scalability layer
of the scalable data stream. The first scalability layer identifier
value may reside in the first parameter set elementary unit. A
second scalability layer identifier value may reside in a second
elementary unit including data from a second of two or more
scalability layers. The first and second set of syntax elements may
be signaled in a second parameter set elementary unit for the
second of the two or more scalability layers such that a second
parameter set is readable by the decoder to determine the coding
property without decoding the scalability layer of the scalable
data stream. The second scalability layer identifier value may
reside in the second parameter set elementary unit. The
computer-executable program code portions of this embodiment may
also include program code instructions for removing from the first
scalable data stream the second elementary unit and the second
parameter set elementary unit on the basis of the second elementary
unit and the second parameter set elementary unit including the
second scalability layer identifier value.
In yet another embodiment, an apparatus is provided that includes
means for receiving a first scalable data stream including
scalability layers having different coding properties. Each of the
two or more scalability layers is associated with a scalability
layer identifier and is characterized by a first of syntax elements
comprising at least a profile and a second set of syntax elements
including at least one of a level or Hypothetical Reference Decoder
(HRD) parameters. A first scalability layer identifier value may
reside in a first elementary unit including data from the first of
two or more scalability layers. A first and second set of syntax
elements may be signaled in a first parameter set elementary unit
for the first of the two or more scalability layers such that a
first parameter set is readable by a decoder to determine the
values of the first and second set of syntax elements without
decoding a scalability layer of the scalable data stream. The first
scalability layer identifier value may reside in the first
parameter set elementary unit. A second scalability layer
identifier value may reside in a second elementary unit including
data from a second of two or more scalability layers. The first and
second set of syntax elements may be signaled in a second parameter
set elementary unit for the second of the two or more scalability
layers such that a second parameter set is readable by the decoder
to determine the coding property without decoding the scalability
layer of the scalable data stream. The second scalability layer
identifier value may reside in the second parameter set elementary
unit. The apparatus of this embodiment may also include means for
removing from the first scalable data stream the second elementary
unit and the second parameter set elementary unit on the basis of
the second elementary unit and the second parameter set elementary
unit including the second scalability layer identifier value.
In one embodiment, a method is provided that includes receiving a
first scalable data stream including scalability layers having
different coding properties. Each of the two or more scalability
layers is associated with a scalability layer identifier and is
characterized by a coding property. A first scalability layer
identifier value may reside in a first elementary unit including
data from a first of two or more scalability layers. The first of
the two or more scalability layers with decoding properties are
signals in a first parameter set elementary unit such that the
coding property is readable by a decoder to determine the coding
property without decoding a scalability layer of a scalable data
stream. The first scalability layer identifier value may reside in
the first parameter set elementary unit. A second scalability layer
identifier value may reside in a second elementary unit including
data from a second of two or more scalability layers. The first and
second sets of syntax elements may be signaled in a second
parameter set elementary unit for the second of the two or more
scalability layers such that a first parameter set is readable by a
decoder to determine the values of first and second sets of syntax
elements without decoding the scalability layer of the scalable
data stream. The second scalability layer identifier value may
reside in the second parameter set elementary unit. The method of
this embodiment may also receive a set of scalability layer
identifier values indicating scalability layers to be decoded and
may remove from the received first scalable data stream, with the
processor, the second elementary unit and the second parameter set
elementary unit on the basis of the second elementary unit and the
second parameter set elementary unit including the second
scalability layer identifier value not being among the set of
scalability layer identifier values.
In another embodiment, an apparatus is provided that includes at
least one processor and at least one memory including computer
program code with the memory and computer program code configured
to, with the at least one processor, cause the apparatus to receive
a first scalable data stream including scalability layers having
different coding properties. Each of the two or more scalability
layers is associated with a scalability layer identifier and is
characterized by a coding property. A first scalability layer
identifier value may reside in a first elementary unit including
data from a first of two or more scalability layers. The first of
the two or more scalability layers with decoding properties are
signals in a first parameter set elementary unit such that the
coding property is readable by a decoder to determine the coding
property without decoding a scalability layer of a scalable data
stream. The first scalability layer identifier value may reside in
the first parameter set elementary unit. A second scalability layer
identifier value may reside in a second elementary unit including
data from a second of two or more scalability layers. The first and
second sets of syntax elements may be signaled in a second
parameter set elementary unit for the second of the two or more
scalability layers such that a first parameter set is readable by a
decoder to determine the values of first and second sets of syntax
elements without decoding the scalability layer of the scalable
data stream. The second scalability layer identifier value may
reside in the second parameter set elementary unit. The memory and
computer program code may also be configured to, with the at least
one processor, cause the apparatus to receive a set of scalability
layer identifier values indicating scalability layers to be decoded
and to remove from the received first scalable data stream the
second elementary unit and the second parameter set elementary unit
on the basis of the second elementary unit and the second parameter
set elementary unit including the second scalability layer
identifier value not being among the set of scalability layer
identifier values.
In a further embodiment, a computer program product is provided
that includes at least one non-transitory computer-readable storage
medium having computer-executable program code portions stored
therein with the computer-executable program code portions
including program code instructions for receiving a first scalable
data stream including scalability layers having different coding
properties. Each of the two or more scalability layers is
associated with a scalability layer identifier and is characterized
by a coding property. A first scalability layer identifier value
may reside in a first elementary unit including data from a first
of two or more scalability layers. The first of the two or more
scalability layers with decoding properties are signals in a first
parameter set elementary unit such that the coding property is
readable by a decoder to determine the coding property without
decoding a scalability layer of a scalable data stream. The first
scalability layer identifier value may reside in the first
parameter set elementary unit. A second scalability layer
identifier value may reside in a second elementary unit including
data from a second of two or more scalability layers. The first and
second sets of syntax elements may be signaled in a second
parameter set elementary unit for the second of the two or more
scalability layers such that a first parameter set is readable by a
decoder to determine the values of first and second sets of syntax
elements without decoding the scalability layer of the scalable
data stream. The second scalability layer identifier value may
reside in the second parameter set elementary unit. The
computer-executable program code portions may also include program
code instructions for receiving a set of scalability layer
identifier values indicating scalability layers to be decoded and
program code instructions for removing from the received first
scalable data stream the second elementary unit and the second
parameter set elementary unit on the basis of the second elementary
unit and the second parameter set elementary unit including the
second scalability layer identifier value not being among the set
of scalability layer identifier values.
In yet another embodiment, an apparatus is provided that includes
means for receiving a first scalable data stream including
scalability layers having different coding properties. Each of the
two or more scalability layers is associated with a scalability
layer identifier and is characterized by a coding property. A first
scalability layer identifier value may reside in a first elementary
unit including data from a first of two or more scalability layers.
The first of the two or more scalability layers with decoding
properties are signals in a first parameter set elementary unit
such that the coding property is readable by a decoder to determine
the coding property without decoding a scalability layer of a
scalable data stream. The first scalability layer identifier value
may reside in the first parameter set elementary unit. A second
scalability layer identifier value may reside in a second
elementary unit including data from a second of two or more
scalability layers. The first and second sets of syntax elements
may be signaled in a second parameter set elementary unit for the
second of the two or more scalability layers such that a first
parameter set is readable by a decoder to determine the values of
first and second sets of syntax elements without decoding the
scalability layer of the scalable data stream. The second
scalability layer identifier value may reside in the second
parameter set elementary unit. The apparatus may also include means
for receiving a set of scalability layer identifier values
indicating scalability layers to be decoded and means for removing
from the received first scalable data stream the second elementary
unit and the second parameter set elementary unit on the basis of
the second elementary unit and the second parameter set elementary
unit including the second scalability layer identifier value not
being among the set of scalability layer identifier values.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of example embodiments of the
present invention, reference is now made to the following
descriptions taken in connection with the accompanying drawings in
which:
FIG. 1 shows schematically an electronic device employing some
embodiments of the invention;
FIG. 2 shows schematically a user equipment suitable for employing
some embodiments of the invention;
FIG. 3 further shows schematically electronic devices employing
embodiments of the invention connected using wireless and wired
network connections;
FIG. 4a shows schematically an embodiment of the invention as
incorporated within an encoder;
FIG. 4b shows schematically an embodiment of an inter predictor
according to some embodiments of the invention;
FIG. 5 shows a simplified model of a DIBR-based 3DV system;
FIG. 6 shows a simplified 2D model of a stereoscopic camera
setup;
FIG. 7 shows an example of definition and coding order of access
units;
FIG. 8 shows a high level flow chart of an embodiment of an encoder
capable of encoding texture views and depth views;
FIG. 9 shows a high level flow chart of an embodiment of a decoder
capable of decoding texture views and depth views; and
FIGS. 10-12 are flow charts illustrating operations performed in
accordance with an example embodiment of the present invention.
DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS
Some embodiments of the present invention will now be described
more fully hereinafter with reference to the accompanying drawings,
in which some, but not all embodiments of the invention are shown.
Indeed, various embodiments of the invention may be embodied in
many different forms and should not be construed as limited to the
embodiments set forth herein; rather, these embodiments are
provided so that this disclosure will satisfy applicable legal
requirements. Like reference numerals refer to like elements
throughout. As used herein, the terms "data," "content,"
"information" and similar terms may be used interchangeably to
refer to data capable of being transmitted, received and/or stored
in accordance with embodiments of the present invention. Thus, use
of any such terms should not be taken to limit the spirit and scope
of embodiments of the present invention.
Additionally, as used herein, the term `circuitry` refers to (a)
hardware-only circuit implementations (e.g., implementations in
analog circuitry and/or digital circuitry); (b) combinations of
circuits and computer program product(s) comprising software and/or
firmware instructions stored on one or more computer readable
memories that work together to cause an apparatus to perform one or
more functions described herein; and (c) circuits, such as, for
example, a microprocessor(s) or a portion of a microprocessor(s),
that require software or firmware for operation even if the
software or firmware is not physically present. This definition of
`circuitry` applies to all uses of this term herein, including in
any claims. As a further example, as used herein, the term
`circuitry` also includes an implementation comprising one or more
processors and/or portion(s) thereof and accompanying software
and/or firmware. As another example, the term `circuitry` as used
herein also includes, for example, a baseband integrated circuit or
applications processor integrated circuit for a mobile phone or a
similar integrated circuit in a server, a cellular network device,
other network device, and/or other computing device.
As defined herein, a "computer-readable storage medium," which
refers to a non-transitory, physical storage medium (e.g., volatile
or non-volatile memory device), can be differentiated from a
"computer-readable transmission medium," which refers to an
electromagnetic signal.
In the following, several embodiments of the invention will be
described in the context of one video coding arrangement. It is to
be noted, however, that the invention is not limited to this
particular arrangement. In fact, the different embodiments have
applications widely in any environment where improvement of
reference picture handling is required. For example, the invention
may be applicable to video coding systems like streaming systems,
DVD players, digital television receivers, personal video
recorders, systems and computer programs on personal computers,
handheld computers and communication devices, as well as network
elements such as transcoders and cloud computing arrangements where
video data is handled.
The H.264/AVC standard was developed by the Joint Video Team (JVT)
of the Video Coding Experts Group (VCEG) of the Telecommunications
Standardization Sector of International Telecommunication Union
(ITU-T) and the Moving Picture Experts Group (MPEG) of
International Organisation for Standardization (ISO)/International
Electrotechnical Commission (IEC). The H.264/AVC standard is
published by both parent standardization organizations, and it is
referred to as ITU-T Recommendation H.264 and ISO/IEC International
Standard 14496-10, also known as MPEG-4 Part 10 Advanced Video
Coding (AVC). There have been multiple versions of the H.264/AVC
standard, each integrating new extensions or features to the
specification. These extensions include Scalable Video Coding (SVC)
and Multiview Video Coding (MVC).
There is a currently ongoing standardization project of High
Efficiency Video Coding (HEVC) by the Joint Collaborative
Team-Video Coding (JCT-VC) of VCEG and MPEG.
Some key definitions, bitstream and coding structures, and concepts
of H.264/AVC and HEVC are described in this section as an example
of a video encoder, decoder, encoding method, decoding method, and
a bitstream structure, wherein the embodiments may be implemented.
Some of the key definitions, bitstream and coding structures, and
concepts of H.264/AVC are the same as in a draft HEVC
standard--hence, they are described below jointly. The aspects of
the invention are not limited to H.264/AVC or HEVC, but rather the
description is given for one possible basis on top of which the
invention may be partly or fully realized.
Similarly to many earlier video coding standards, the bitstream
syntax and semantics as well as the decoding process for error-free
bitstreams are specified in H.264/AVC and HEVC. The encoding
process is not specified, but encoders must generate conforming
bitstreams. Bitstream and decoder conformance can be verified with
the Hypothetical Reference Decoder (HRD). The standards contain
coding tools that help in coping with transmission errors and
losses, but the use of the tools in encoding is optional and no
decoding process has been specified for erroneous bitstreams.
Common notation for arithmetic operators, logical operators,
relational operators, bit-wise operators, assignment operators, and
range notation e.g. as specified in H.264/AVC or a draft HEVC may
be used. Furthermore, common mathematical functions e.g. as
specified in H.264/AVC or a draft HEVC may be used and a common
order of precedence and execution order (from left to right or from
right to left) of operators e.g. as specified in H.264/AVC or a
draft HEVC may be used.
In the description of existing standards as well as in the
description of example embodiments, a syntax element may be defined
as an element of data represented in the bitstream. A syntax
structure may be defined as zero or more syntax elements present
together in the bitstream in a specified order. The following
descriptors may be used to specify the parsing process of each
syntax element. b(8): byte having any pattern of bit string (8
bits). se(v): signed integer Exp-Golomb-coded syntax element with
the left bit first. u(n): unsigned integer using n bits. When n is
"v" in the syntax table, the number of bits varies in a manner
dependent on the value of other syntax elements. The parsing
process for this descriptor is specified by n next bits from the
bitstream interpreted as a binary representation of an unsigned
integer with the most significant bit written first. ue(v):
unsigned integer Exp-Golomb-coded syntax element with the left bit
first.
An Exp-Golomb bit string may be converted to a code number
(codeNum) for example using the following table:
TABLE-US-00001 Bit string codeNum 1 0 0 1 0 1 0 1 1 2 0 0 1 0 0 3 0
0 1 0 1 4 0 0 1 1 0 5 0 0 1 1 1 6 0 0 0 1 0 0 0 7 0 0 0 1 0 0 1 8 0
0 0 1 0 1 0 9 . . . . . .
A code number corresponding to an Exp-Golomb bit string may be
converted to se(v) for example using the following table:
TABLE-US-00002 codeNum syntax element value 0 0 1 1 2 -1 3 2 4 -2 5
3 6 -3 . . . . . .
Syntax structures, semantics of syntax elements, and decoding
process may be specified as follows. Syntax elements in the
bitstream are represented in bold type. Each syntax element is
described by its name (all lower case letters with underscore
characters), optionally its one or two syntax categories, and one
or two descriptors for its method of coded representation. The
decoding process behaves according to the value of the syntax
element and to the values of previously decoded syntax elements.
When a value of a syntax element is used in the syntax tables or
the text, it appears in regular (i.e., not bold) type. In some
cases the syntax tables may use the values of other variables
derived from syntax elements values. Such variables appear in the
syntax tables, or text, named by a mixture of lower case and upper
case letter and without any underscore characters. Variables
starting with an upper case letter are derived for the decoding of
the current syntax structure and all depending syntax structures.
Variables starting with an upper case letter may be used in the
decoding process for later syntax structures without mentioning the
originating syntax structure of the variable. Variables starting
with a lower case letter are only used within the context in which
they are derived. In some cases, "mnemonic" names for syntax
element values or variable values are used interchangeably with
their numerical values. Sometimes "mnemonic" names are used without
any associated numerical values. The association of values and
names is specified in the text. The names are constructed from one
or more groups of letters separated by an underscore character.
Each group starts with an upper case letter and may contain more
upper case letters.
A syntax structure may be specified using the following. A group of
statements enclosed in curly brackets is a compound statement and
is treated functionally as a single statement. A "while" structure
specifies a test of whether a condition is true, and if true,
specifies evaluation of a statement (or compound statement)
repeatedly until the condition is no longer true. A "do . . .
while" structure specifies evaluation of a statement once, followed
by a test of whether a condition is true, and if true, specifies
repeated evaluation of the statement until the condition is no
longer true. An "if . . . else" structure specifies a test of
whether a condition is true, and if the condition is true,
specifies evaluation of a primary statement, otherwise, specifies
evaluation of an alternative statement. The "else" part of the
structure and the associated alternative statement is omitted if no
alternative statement evaluation is needed. A "for" structure
specifies evaluation of an initial statement, followed by a test of
a condition, and if the condition is true, specifies repeated
evaluation of a primary statement followed by a subsequent
statement until the condition is no longer true.
A profile may be defined as a subset of the entire bitstream syntax
that is specified by a decoding/coding standard or specification.
Within the bounds imposed by the syntax of a given profile it is
still possible to require a very large variation in the performance
of encoders and decoders depending upon the values taken by syntax
elements in the bitstream such as the specified size of the decoded
pictures. In many applications, it might be neither practical nor
economic to implement a decoder capable of dealing with all
hypothetical uses of the syntax within a particular profile. In
order to deal with this issues, levels may be used. A level may be
defined as a specified set of constraints imposed on values of the
syntax elements in the bitstream and variables specified in a
decoding/coding standard or specification. These constraints may be
simple limits on values. Alternatively or in addition, they may
take the form of constraints on arithmetic combinations of values
(e.g., picture width multiplied by picture height multiplied by
number of pictures decoded per second). Other means for specifying
constraints for levels may also be used. Some of the constraints
specified in a level may for example relate to the maximum picture
size, maximum bitrate and maximum data rate in terms of coding
units, such as macroblocks, per a time period, such as a second.
The same set of levels may be defined for all profiles. It may be
preferable for example to increase interoperability of terminals
implementing different profiles that most or all aspects of the
definition of each level may be common across different
profiles.
The elementary unit for the input to an H.264/AVC or HEVC encoder
and the output of an H.264/AVC or HEVC decoder, respectively, is a
picture. In H.264/AVC and HEVC, a picture may either be a frame or
a field. A frame comprises a matrix of luma samples and
corresponding chroma samples. A field is a set of alternate sample
rows of a frame and may be used as encoder input, when the source
signal is interlaced. Chroma pictures may be subsampled when
compared to luma pictures. For example, in the 4:2:0 sampling
pattern the spatial resolution of chroma pictures is half of that
of the luma picture along both coordinate axes.
In H.264/AVC, a macroblock is a 16.times.16 block of luma samples
and the corresponding blocks of chroma samples. For example, in the
4:2:0 sampling pattern, a macroblock contains one 8.times.8 block
of chroma samples per each chroma component. In H.264/AVC, a
picture is partitioned to one or more slice groups, and a slice
group contains one or more slices. In H.264/AVC, a slice consists
of an integer number of macroblocks ordered consecutively in the
raster scan within a particular slice group.
In a draft HEVC standard, video pictures are divided into coding
units (CU) covering the area of the picture. A CU consists of one
or more prediction units (PU) defining the prediction process for
the samples within the CU and one or more transform units (TU)
defining the prediction error coding process for the samples in the
CU. Typically, a CU consists of a square block of samples with a
size selectable from a predefined set of possible CU sizes. A CU
with the maximum allowed size is typically named as LCU (largest
coding unit) or a coding tree unit (CTU) and the video picture is
divided into non-overlapping LCUs. An LCU can be further split into
a combination of smaller CUs, e.g. by recursively splitting the LCU
and resultant CUs. Each resulting CU typically has at least one PU
and at least one TU associated with it. Each PU and TU can further
be split into smaller PUs and TUs in order to increase granularity
of the prediction and prediction error coding processes,
respectively. The PU splitting can be realized by splitting the CU
into four equal size square PUs or splitting the CU into two
rectangle PUs vertically or horizontally in a symmetric or
asymmetric way. The division of the image into CUs, and division of
CUs into PUs and TUs is typically signalled in the bitstream
allowing the decoder to reproduce the intended structure of these
units.
In a draft HEVC standard, a picture can be partitioned in tiles,
which are rectangular and contain an integer number of LCUs. In a
draft HEVC standard, the partitioning to tiles forms a regular
grid, where heights and widths of tiles differ from each other by
one LCU at the maximum. In a draft HEVC, a slice consists of an
integer number of CUs. The CUs are scanned in the raster scan order
of LCUs within tiles or within a picture, if tiles are not in use.
Within an LCU, the CUs have a specific scan order.
In a Working Draft (WD) 5 of HEVC, some key definitions and
concepts for picture partitioning are defined as follows. A
partitioning is defined as the division of a set into subsets such
that each element of the set is in exactly one of the subsets.
A basic coding unit in a HEVC WD5 is a treeblock. A treeblock is an
N.times.N block of luma samples and two corresponding blocks of
chroma samples of a picture that has three sample arrays, or an
N.times.N block of samples of a monochrome picture or a picture
that is coded using three separate colour planes. A treeblock may
be partitioned for different coding and decoding processes. A
treeblock partition is a block of luma samples and two
corresponding blocks of chroma samples resulting from a
partitioning of a treeblock for a picture that has three sample
arrays or a block of luma samples resulting from a partitioning of
a treeblock for a monochrome picture or a picture that is coded
using three separate colour planes. Each treeblock is assigned a
partition signalling to identify the block sizes for intra or inter
prediction and for transform coding. The partitioning is a
recursive quadtree partitioning. The root of the quadtree is
associated with the treeblock. The quadtree is split until a leaf
is reached, which is referred to as the coding node. The coding
node is the root node of two trees, the prediction tree and the
transform tree. The prediction tree specifies the position and size
of prediction blocks. The prediction tree and associated prediction
data are referred to as a prediction unit. The transform tree
specifies the position and size of transform blocks. The transform
tree and associated transform data are referred to as a transform
unit. The splitting information for luma and chroma is identical
for the prediction tree and may or may not be identical for the
transform tree. The coding node and the associated prediction and
transform units form together a coding unit.
In a HEVC WD5, pictures are divided into slices and tiles. A slice
may be a sequence of treeblocks but (when referring to a so-called
fine granular slice) may also have its boundary within a treeblock
at a location where a transform unit and prediction unit coincide.
Treeblocks within a slice are coded and decoded in a raster scan
order. For the primary coded picture, the division of each picture
into slices is a partitioning.
In a HEVC WD5, a tile is defined as an integer number of treeblocks
co-occurring in one column and one row, ordered consecutively in
the raster scan within the tile. For the primary coded picture, the
division of each picture into tiles is a partitioning. Tiles are
ordered consecutively in the raster scan within the picture.
Although a slice contains treeblocks that are consecutive in the
raster scan within a tile, these treeblocks are not necessarily
consecutive in the raster scan within the picture. Slices and tiles
need not contain the same sequence of treeblocks. A tile may
comprise treeblocks contained in more than one slice. Similarly, a
slice may comprise treeblocks contained in several tiles.
In H.264/AVC and HEVC, in-picture prediction may be disabled across
slice boundaries. Thus, slices can be regarded as a way to split a
coded picture into independently decodable pieces, and slices are
therefore often regarded as elementary units for transmission. In
many cases, encoders may indicate in the bitstream which types of
in-picture prediction are turned off across slice boundaries, and
the decoder operation takes this information into account for
example when concluding which prediction sources are available. For
example, samples from a neighboring macroblock or CU may be
regarded as unavailable for intra prediction, if the neighboring
macroblock or CU resides in a different slice.
The elementary unit for the output of an H.264/AVC or HEVC encoder
and the input of an H.264/AVC or HEVC decoder, respectively, is a
Network Abstraction Layer (NAL) unit. For transport over
packet-oriented networks or storage into structured files, NAL
units may be encapsulated into packets or similar structures. A
bytestream format has been specified in H.264/AVC and HEVC for
transmission or storage environments that do not provide framing
structures. The bytestream format separates NAL units from each
other by attaching a start code in front of each NAL unit. To avoid
false detection of NAL unit boundaries, encoders run a
byte-oriented start code emulation prevention algorithm, which adds
an emulation prevention byte to the NAL unit payload if a start
code would have occurred otherwise. In order to enable
straightforward gateway operation between packet- and
stream-oriented systems, start code emulation prevention may always
be performed regardless of whether the bytestream format is in use
or not. A NAL unit may be defined as a syntax structure containing
an indication of the type of data to follow and bytes containing
that data in the form of an RBSP interspersed as necessary with
emulation prevention bytes. A raw byte sequence payload (RBSP) may
be defined as a syntax structure containing an integer number of
bytes that is encapsulated in a NAL unit. An RBSP is either empty
or has the form of a string of data bits containing syntax elements
followed by an RB SP stop bit and followed by zero or more
subsequent bits equal to 0.
NAL units consist of a header and payload. In H.264/AVC and HEVC,
the NAL unit header indicates the type of the NAL unit and whether
a coded slice contained in the NAL unit is a part of a reference
picture or a non-reference picture.
H.264/AVC NAL unit header includes a 2-bit nal_ref_idc syntax
element, which when equal to 0 indicates that a coded slice
contained in the NAL unit is a part of a non-reference picture and
when greater than 0 indicates that a coded slice contained in the
NAL unit is a part of a reference picture. A draft HEVC standard
includes a 1-bit nal_ref_idc syntax element, also known as
nal_ref_flag, which when equal to 0 indicates that a coded slice
contained in the NAL unit is a part of a non-reference picture and
when equal to 1 indicates that a coded slice contained in the NAL
unit is a part of a reference picture. The header for SVC and MVC
NAL units may additionally contain various indications related to
the scalability and multiview hierarchy.
In a draft HEVC standard, a two-byte NAL unit header is used for
all specified NAL unit types. The first byte of the NAL unit header
contains one reserved bit, a one-bit indication nal_ref_flag
primarily indicating whether the picture carried in this access
unit is a reference picture or a non-reference picture, and a
six-bit NAL unit type indication. The second byte of the NAL unit
header includes a three-bit temporal_id indication for temporal
level and a five-bit reserved field (called reserved_one.sub.--5
bits) required to have a value equal to 1 in a draft HEVC standard.
The temporal_id syntax element may be regarded as a temporal
identifier for the NAL unit.
In a draft HEVC standard, the NAL unit syntax is specified as
follows:
TABLE-US-00003 nal_unit( NumBytesInNALunit ) { Descriptor
forbidden_zero_bit f(1) nal_ref_flag u(1) nal_unit_type u(6)
temporal_id u(3) reserved_one_5bits u(5) NumBytesInRBSP = 0 for( i
= 2; i < NumBytesInNALunit; i++ ) { if( i + 2 <
NumBytesInNALunit && next_bits( 24 ) = = 0x000003 ) {
rbsp_byte[ NumBytesInRBSP++ ] b(8) rbsp_byte[ NumBytesInRBSP++ ]
b(8) i += 2 emulation_prevention_three_byte /* equal to 0x03 */
f(8) } else rbsp_byte[ NumBytesInRBSP++ ] b(8) } }
The five-bit reserved field is expected to be used by extensions
such as a future scalable and 3D video extension. It is expected
that these five bits would carry information on the scalability
hierarchy, such as quality_id or similar, dependency_id or similar,
any other type of layer identifier, view order index or similar,
view identifier, an identifier similar to priority_id of SVC
indicating a valid sub-bitstream extraction if all NAL units
greater than a specific identifier value are removed from the
bitstream. Without loss of generality, in some example embodiments
a variable LayerId is derived from the value of
reserved_one.sub.--5 bits, which may also be referred to as
layer_id_plus1, for example as follows:
LayerId=reserved_one.sub.--5 bits-1. reserved_one.sub.--5 bits may
represent a layer identifier in scalable extensions of HEVC, for
example using the following syntax:
TABLE-US-00004 nal_unit( NumBytesInNALunit ) { Descriptor
forbidden_zero_bit f(1) nal_ref_flag u(1) nal_unit_type u(6)
temporal_id u(3) layer_id_plus1 u(5) . . .
NAL units can be categorized into Video Coding Layer (VCL) NAL
units and non-VCL NAL units. VCL NAL units are typically coded
slice NAL units. In H.264/AVC, coded slice NAL units contain syntax
elements representing one or more coded macroblocks, each of which
corresponds to a block of samples in the uncompressed picture. In
HEVC, coded slice NAL units contain syntax elements representing
one or more CU. In H.264/AVC and HEVC a coded slice NAL unit can be
indicated to be a coded slice in an Instantaneous Decoding Refresh
(IDR) picture or coded slice in a non-IDR picture. In HEVC, a coded
slice NAL unit can be indicated to be a coded slice in a Clean
Decoding Refresh (CDR) picture (which may also be referred to as a
Clean Random Access picture or a CRA picture).
A non-VCL NAL unit may be for example one of the following types: a
sequence parameter set, a picture parameter set, a supplemental
enhancement information (SEI) NAL unit, an access unit delimiter,
an end of sequence NAL unit, an end of stream NAL unit, or a filler
data NAL unit. Parameter sets may be needed for the reconstruction
of decoded pictures, whereas many of the other non-VCL NAL units
are not necessary for the reconstruction of decoded sample
values.
Parameters that remain unchanged through a coded video sequence may
be included in a sequence parameter set. In addition to the
parameters that may be needed by the decoding process, the sequence
parameter set may optionally contain video usability information
(VUI), which includes parameters that may be important for
buffering, picture output timing, rendering, and resource
reservation. There are three NAL units specified in H.264/AVC to
carry sequence parameter sets: the sequence parameter set NAL unit
containing all the data for H.264/AVC VCL NAL units in the
sequence, the sequence parameter set extension NAL unit containing
the data for auxiliary coded pictures, and the subset sequence
parameter set for MVC and SVC VCL NAL units. In a draft HEVC
standard a sequence parameter set RBSP includes parameters that can
be referred to by one or more picture parameter set RBSPs or one or
more SEI NAL units containing a buffering period SEI message. A
picture parameter set contains such parameters that are likely to
be unchanged in several coded pictures. A picture parameter set
RBSP may include parameters that can be referred to by the coded
slice NAL units of one or more coded pictures.
In a draft HEVC, there is also a third type of parameter sets, here
referred to as an Adaptation Parameter Set (APS), which includes
parameters that are likely to be unchanged in several coded slices
but may change for example for each picture or each few pictures.
In a draft HEVC, the APS syntax structure includes parameters or
syntax elements related to quantization matrices (QM), adaptive
sample offset (SAO), adaptive loop filtering (ALF), and deblocking
filtering. In a draft HEVC, an APS is a NAL unit and coded without
reference or prediction from any other NAL unit. An identifier,
referred to as aps_id syntax element, is included in APS NAL unit,
and included and used in the slice header to refer to a particular
APS. In another draft HEVC standard, an APS syntax structure only
contains ALF parameters. In a draft HEVC standard, an adaptation
parameter set RBSP includes parameters that can be referred to by
the coded slice NAL units of one or more coded pictures when at
least one of sample_adaptive_offset_enabled_flag or
adaptive_loop_filter_enabled_flag are equal to 1.
A draft HEVC standard also includes a fourth type of a parameter
set, called a video parameter set (VPS), which was proposed for
example in document JCTVC-H0388
(http://phenix.int-evry.fr/jct/doc_end_user/documents/8_San
%20Jose/wg11/JCTVC-H0388-v4.zip). A video parameter set RBSP may
include parameters that can be referred to by one or more sequence
parameter set RBSPs.
The relationship and hierarchy between VPS, SPS, and PPS may be
described as follows. VPS resides one level above SPS in the
parameter set hierarchy and in the context of scalability and/or
3DV. VPS may include parameters that are common for all slices
across all (scalability or view) layers in the entire coded video
sequence. SPS includes the parameters that are common for all
slices in a particular (scalability or view) layer in the entire
coded video sequence, and may be shared by multiple (scalability or
view) layers. PPS includes the parameters that are common for all
slices in a particular layer representation (the representation of
one scalability or view layer in one access unit) and are likely to
be shared by all slices in multiple layer representations.
VPS may provide information about the dependency relationships of
the layers in a bitstream, as well as many other information that
are applicable to all slices across all (scalability or view)
layers in the entire coded video sequence. In a scalable extension
of HEVC, VPS may for example include a mapping of the LayerId value
derived from the NAL unit header to one or more scalability
dimension values, for example correspond to dependency_id,
quality_id, view_id, and depth_flag for the layer defined similarly
to SVC and MVC. VPS may include profile and level information for
one or more layers as well as the profile and/or level for one or
more temporal sub-layers (consisting of VCL NAL units at and below
certain temporal_id values) of a layer representation.
H.264/AVC and HEVC syntax allows many instances of parameter sets,
and each instance is identified with a unique identifier. In order
to limit the memory usage needed for parameter sets, the value
range for parameter set identifiers has been limited. In H.264/AVC
and a draft HEVC standard, each slice header includes the
identifier of the picture parameter set that is active for the
decoding of the picture that contains the slice, and each picture
parameter set contains the identifier of the active sequence
parameter set. In a HEVC standard, a slice header additionally
contains an APS identifier. Consequently, the transmission of
picture and sequence parameter sets does not have to be accurately
synchronized with the transmission of slices. Instead, it is
sufficient that the active sequence and picture parameter sets are
received at any moment before they are referenced, which allows
transmission of parameter sets "out-of-band" using a more reliable
transmission mechanism compared to the protocols used for the slice
data. For example, parameter sets can be included as a parameter in
the session description for Real-time Transport Protocol (RTP)
sessions. If parameter sets are transmitted in-band, they can be
repeated to improve error robustness.
A parameter sets may be activated by a reference from a slice or
from another active parameter set or in some cases from another
syntax structure such as a buffering period SEI message. In the
following, non-limiting examples of activation of parameter sets in
a draft HEVC standard are given.
Each adaptation parameter set RBSP is initially considered not
active at the start of the operation of the decoding process. At
most one adaptation parameter set RBSP is considered active at any
given moment during the operation of the decoding process, and the
activation of any particular adaptation parameter set RBSP results
in the deactivation of the previously-active adaptation parameter
set RBSP (if any).
When an adaptation parameter set RB SP (with a particular value of
aps_id) is not active and it is referred to by a coded slice NAL
unit (using that value of aps_id), it is activated. This adaptation
parameter set RBSP is called the active adaptation parameter set
RBSP until it is deactivated by the activation of another
adaptation parameter set RBSP. An adaptation parameter set RBSP,
with that particular value of aps_id, is available to the decoding
process prior to its activation, included in at least one access
unit with temporal_id equal to or less than the temporal_id of the
adaptation parameter set NAL unit, unless the adaptation parameter
set is provided through external means.
Each picture parameter set RBSP is initially considered not active
at the start of the operation of the decoding process. At most one
picture parameter set RBSP is considered active at any given moment
during the operation of the decoding process, and the activation of
any particular picture parameter set RB SP results in the
deactivation of the previously-active picture parameter set RB SP
(if any).
When a picture parameter set RBSP (with a particular value of
pic_parameter_set_id) is not active and it is referred to by a
coded slice NAL unit or coded slice data partition A NAL unit
(using that value of pic_parameter_set_id), it is activated. This
picture parameter set RBSP is called the active picture parameter
set RBSP until it is deactivated by the activation of another
picture parameter set RBSP. A picture parameter set RBSP, with that
particular value of pic_parameter_set_id, is available to the
decoding process prior to its activation, included in at least one
access unit with temporal_id equal to or less than the temporal_id
of the picture parameter set NAL unit, unless the picture parameter
set is provided through external means.
Each sequence parameter set RBSP is initially considered not active
at the start of the operation of the decoding process. At most one
sequence parameter set RBSP is considered active at any given
moment during the operation of the decoding process, and the
activation of any particular sequence parameter set RBSP results in
the deactivation of the previously-active sequence parameter set
RBSP (if any).
When a sequence parameter set RBSP (with a particular value of
seq_parameter_set_id) is not already active and it is referred to
by activation of a picture parameter set RBSP (using that value of
seq_parameter_set_id) or is referred to by an SEI NAL unit
containing a buffering period SEI message (using that value of
seq_parameter_set_id), it is activated. This sequence parameter set
RBSP is called the active sequence parameter set RBSP until it is
deactivated by the activation of another sequence parameter set
RBSP. A sequence parameter set RBSP, with that particular value of
seq_parameter_set_id is available to the decoding process prior to
its activation, included in at least one access unit with
temporal_id equal to 0, unless the sequence parameter set is
provided through external means. An activated sequence parameter
set RBSP remains active for the entire coded video sequence.
Each video parameter set RBSP is initially considered not active at
the start of the operation of the decoding process. At most one
video parameter set RBSP is considered active at any given moment
during the operation of the decoding process, and the activation of
any particular video parameter set RBSP results in the deactivation
of the previously-active video parameter set RBSP (if any).
When a video parameter set RBSP (with a particular value of
video_parameter_set_id) is not already active and it is referred to
by activation of a sequence parameter set RBSP (using that value of
video_parameter_set_id), it is activated. This video parameter set
RBSP is called the active video parameter set RBSP until it is
deactivated by the activation of another video parameter set RBSP.
A video parameter set RBSP, with that particular value of
video_parameter_set_id is available to the decoding process prior
to its activation, included in at least one access unit with
temporal_id equal to 0, unless the video parameter set is provided
through external means. An activated video parameter set RBSP
remains active for the entire coded video sequence.
During operation of the decoding process in a draft HEVC standard,
the values of parameters of the active video parameter set, the
active sequence parameter set, the active picture parameter set
RBSP and the active adaptation parameter set RBSP are considered in
effect. For interpretation of SEI messages, the values of the
active video parameter set, the active sequence parameter set, the
active picture parameter set RB SP and the active adaptation
parameter set RB SP for the operation of the decoding process for
the VCL NAL units of the coded picture in the same access unit are
considered in effect unless otherwise specified in the SEI message
semantics.
A SEI NAL unit may contain one or more SEI messages, which are not
required for the decoding of output pictures but may assist in
related processes, such as picture output timing, rendering, error
detection, error concealment, and resource reservation. Several SEI
messages are specified in H.264/AVC and HEVC, and the user data SEI
messages enable organizations and companies to specify SEI messages
for their own use. H.264/AVC and HEVC contain the syntax and
semantics for the specified SEI messages but no process for
handling the messages in the recipient is defined. Consequently,
encoders are required to follow the H.264/AVC standard or the HEVC
standard when they create SEI messages, and decoders conforming to
the H.264/AVC standard or the HEVC standard, respectively, are not
required to process SEI messages for output order conformance. One
of the reasons to include the syntax and semantics of SEI messages
in H.264/AVC and HEVC is to allow different system specifications
to interpret the supplemental information identically and hence
interoperate. It is intended that system specifications can require
the use of particular SEI messages both in the encoding end and in
the decoding end, and additionally the process for handling
particular SEI messages in the recipient can be specified.
In H.264/AVC, the following NAL unit types and their categorization
to VCL and non-VCL NAL units have been specified:
TABLE-US-00005 Annex G and Annex A Annex H NAL unit NAL unit
nal_unit_type Content of NAL unit and RBSP syntax structure C type
class type class 0 Unspecified non-VCL non-VCL 1 Coded slice of a
non-IDR picture 2, 3, 4 VCL VCL
slice_layer_without_partitioning_rbsp( ) 2 Coded slice data
partition A 2 VCL not slice_data_partition_a_layer_rbsp( )
applicable 3 Coded slice data partition B 3 VCL not
slice_data_partition_b_layer_rbsp( ) applicable 4 Coded slice data
partition C 4 VCL not slice_data_partition_c_layer_rbsp( )
applicable 5 Coded slice of an IDR picture 2, 3 VCL VCL
slice_layer_without_partitioning_rbsp( ) 6 Supplemental enhancement
information (SEI) 5 non-VCL non-VCL sei_rbsp( ) 7 Sequence
parameter set 0 non-VCL non-VCL seq_parameter_set_rbsp( ) 8 Picture
parameter set 1 non-VCL non-VCL pic_parameter_set_rbsp( ) 9 Access
unit delimiter 6 non-VCL non-VCL access_unit_delimiter_rbsp( ) 10
End of sequence 7 non-VCL non-VCL end_of_seq_rbsp( ) 11 End of
stream 8 non-VCL non-VCL end_of_stream_rbsp( ) 12 Filler data 9
non-VCL non-VCL filler_data_rbsp( ) 13 Sequence parameter set
extension 10 non-VCL non-VCL seq_parameter_set_extension_rbsp( ) 14
Prefix NAL unit 2 non-VCL suffix prefix_nal_unit_rbsp( ) dependent
15 Subset sequence parameter set 0 non-VCL non-VCL
subset_seq_parameter_set_rbsp( ) 16 . . . 18 Reserved non-VCL
non-VCL 19 Coded slice of an auxiliary coded picture without
partitioning 2, 3, 4 non-VCL non-VCL
slice_layer_without_partitioning_rbsp( ) 20 Coded slice extension
2, 3, 4 non-VCL VCL slice_layer_extension_rbsp( ) 21 . . . 23
Reserved non-VCL non-VCL 24 . . . 31 Unspecified non-VCL
non-VCL
In a draft HEVC standard, the following NAL unit types and their
categorization to VCL and non-VCL NAL units have been
specified:
TABLE-US-00006 Content of NAL NAL unit nal_unit_type unit and RBSP
syntax structure type class 0 Unspecified non-VCL 1 Coded slice of
a non-RAP, non-TFD and VCL non-TLA picture slice_layer_rbsp( ) 2
Coded slice of a TFD picture VCL slice_layer_rbsp( ) 3 Coded slice
of a non-TFD TLA picture VCL slice_layer_rbsp( ) 4, 5 Coded slice
of a CRA picture VCL slice_layer_rbsp( ) 6, 7 Coded slice of a BLA
picture VCL slice_layer_rbsp( ) 8 Coded slice of an IDR picture VCL
slice_layer_rbsp( ) 9 . . . 24 Reserved n/a 25 Video parameter set
non-VCL video_parameter_set_rbsp( ) 26 Sequence parameter set
non-VCL seq_parameter_set_rbsp( ) 27 Picture parameter set non-VCL
pic_parameter_set_rbsp( ) 28 Adaptation parameter set non-VCL
aps_rbsp( ) 29 Access unit delimiter non-VCL
access_unit_delimiter_rbsp( ) 30 Filler data non-VCL
filler_data_rbsp( ) 31 Supplemental enhancement non-VCL information
(SEI) sei_rbsp( ) 32 . . . 47 Reserved n/a 48 . . . 63 Unspecified
non-VCL
A coded picture is a coded representation of a picture. A coded
picture in H.264/AVC comprises the VCL NAL units that are required
for the decoding of the picture. In H.264/AVC, a coded picture can
be a primary coded picture or a redundant coded picture. A primary
coded picture is used in the decoding process of valid bitstreams,
whereas a redundant coded picture is a redundant representation
that should only be decoded when the primary coded picture cannot
be successfully decoded. In a draft HEVC, no redundant coded
picture has been specified.
In H.264/AVC and HEVC, an access unit comprises a primary coded
picture and those NAL units that are associated with it. In
H.264/AVC, the appearance order of NAL units within an access unit
is constrained as follows. An optional access unit delimiter NAL
unit may indicate the start of an access unit. It is followed by
zero or more SEI NAL units. The coded slices of the primary coded
picture appear next. In H.264/AVC, the coded slice of the primary
coded picture may be followed by coded slices for zero or more
redundant coded pictures. A redundant coded picture is a coded
representation of a picture or a part of a picture. A redundant
coded picture may be decoded if the primary coded picture is not
received by the decoder for example due to a loss in transmission
or a corruption in physical storage medium.
In H.264/AVC, an access unit may also include an auxiliary coded
picture, which is a picture that supplements the primary coded
picture and may be used for example in the display process. An
auxiliary coded picture may for example be used as an alpha channel
or alpha plane specifying the transparency level of the samples in
the decoded pictures. An alpha channel or plane may be used in a
layered composition or rendering system, where the output picture
is formed by overlaying pictures being at least partly transparent
on top of each other. An auxiliary coded picture has the same
syntactic and semantic restrictions as a monochrome redundant coded
picture. In H.264/AVC, an auxiliary coded picture contains the same
number of macroblocks as the primary coded picture.
A coded video sequence is defined to be a sequence of consecutive
access units in decoding order from an IDR access unit, inclusive,
to the next IDR access unit, exclusive, or to the end of the
bitstream, whichever appears earlier.
A group of pictures (GOP) and its characteristics may be defined as
follows. A GOP can be decoded regardless of whether any previous
pictures were decoded. An open GOP is such a group of pictures in
which pictures preceding the initial intra picture in output order
might not be correctly decodable when the decoding starts from the
initial intra picture of the open GOP. In other words, pictures of
an open GOP may refer (in inter prediction) to pictures belonging
to a previous GOP. An H.264/AVC decoder can recognize an intra
picture starting an open GOP from the recovery point SEI message in
an H.264/AVC bitstream. An HEVC decoder can recognize an intra
picture starting an open GOP, because a specific NAL unit type, CRA
NAL unit type, is used for its coded slices. A closed GOP is such a
group of pictures in which all pictures can be correctly decoded
when the decoding starts from the initial intra picture of the
closed GOP. In other words, no picture in a closed GOP refers to
any pictures in previous GOPs. In H.264/AVC and HEVC, a closed GOP
starts from an IDR access unit. As a result, closed GOP structure
has more error resilience potential in comparison to the open GOP
structure, however at the cost of possible reduction in the
compression efficiency. Open GOP coding structure is potentially
more efficient in the compression, due to a larger flexibility in
selection of reference pictures.
The bitstream syntax of H.264/AVC and HEVC indicates whether a
particular picture is a reference picture for inter prediction of
any other picture. Pictures of any coding type (I, P, B) can be
reference pictures or non-reference pictures in H.264/AVC and HEVC.
The NAL unit header indicates the type of the NAL unit and whether
a coded slice contained in the NAL unit is a part of a reference
picture or a non-reference picture.
Many hybrid video codecs, including H.264/AVC and HEVC, encode
video information in two phases. In the first phase, pixel or
sample values in a certain picture area or "block" are predicted.
These pixel or sample values can be predicted, for example, by
motion compensation mechanisms, which involve finding and
indicating an area in one of the previously encoded video frames
that corresponds closely to the block being coded. Additionally,
pixel or sample values can be predicted by spatial mechanisms which
involve finding and indicating a spatial region relationship.
Prediction approaches using image information from a previously
coded image can also be called as inter prediction methods which
may also be referred to as temporal prediction and motion
compensation. Prediction approaches using image information within
the same image can also be called as intra prediction methods.
The second phase is one of coding the error between the predicted
block of pixels or samples and the original block of pixels or
samples. This may be accomplished by transforming the difference in
pixel or sample values using a specified transform. This transform
may be a Discrete Cosine Transform (DCT) or a variant thereof.
After transforming the difference, the transformed difference is
quantized and entropy encoded.
By varying the fidelity of the quantization process, the encoder
can control the balance between the accuracy of the pixel or sample
representation (i.e. the visual quality of the picture) and the
size of the resulting encoded video representation (i.e. the file
size or transmission bit rate).
The decoder reconstructs the output video by applying a prediction
mechanism similar to that used by the encoder in order to form a
predicted representation of the pixel or sample blocks (using the
motion or spatial information created by the encoder and stored in
the compressed representation of the image) and prediction error
decoding (the inverse operation of the prediction error coding to
recover the quantized prediction error signal in the spatial
domain).
After applying pixel or sample prediction and error decoding
processes the decoder combines the prediction and the prediction
error signals (the pixel or sample values) to form the output video
frame.
The decoder (and encoder) may also apply additional filtering
processes in order to improve the quality of the output video
before passing it for display and/or storing as a prediction
reference for the forthcoming pictures in the video sequence.
In many video codecs, including H.264/AVC and HEVC, motion
information is indicated by motion vectors associated with each
motion compensated image block. Each of these motion vectors
represents the displacement of the image block in the picture to be
coded (in the encoder) or decoded (at the decoder) and the
prediction source block in one of the previously coded or decoded
images (or pictures). H.264/AVC and HEVC, as many other video
compression standards, divide a picture into a mesh of rectangles,
for each of which a similar block in one of the reference pictures
is indicated for inter prediction. The location of the prediction
block is coded as a motion vector that indicates the position of
the prediction block relative to the block being coded.
Inter prediction process may be characterized using one or more of
the following factors.
The Accuracy of Motion Vector Representation.
For example, motion vectors may be of quarter-pixel accuracy, and
sample values in fractional-pixel positions may be obtained using a
finite impulse response (FIR) filter.
Block Partitioning for Inter Prediction.
Many coding standards, including H.264/AVC and HEVC, allow
selection of the size and shape of the block for which a motion
vector is applied for motion-compensated prediction in the encoder,
and indicating the selected size and shape in the bitstream so that
decoders can reproduce the motion-compensated prediction done in
the encoder.
Number of Reference Pictures for Inter Prediction.
The sources of inter prediction are previously decoded pictures.
Many coding standards, including H.264/AVC and HEVC, enable storage
of multiple reference pictures for inter prediction and selection
of the used reference picture on a block basis. For example,
reference pictures may be selected on macroblock or macroblock
partition basis in H.264/AVC and on PU or CU basis in HEVC. Many
coding standards, such as H.264/AVC and HEVC, include syntax
structures in the bitstream that enable decoders to create one or
more reference picture lists. A reference picture index to a
reference picture list may be used to indicate which one of the
multiple reference pictures is used for inter prediction for a
particular block. A reference picture index may be coded by an
encoder into the bitstream is some inter coding modes or it may be
derived (by an encoder and a decoder) for example using neighboring
blocks in some other inter coding modes.
Motion Vector Prediction.
In order to represent motion vectors efficiently in bitstreams,
motion vectors may be coded differentially with respect to a
block-specific predicted motion vector. In many video codecs, the
predicted motion vectors are created in a predefined way, for
example by calculating the median of the encoded or decoded motion
vectors of the adjacent blocks. Another way to create motion vector
predictions is to generate a list of candidate predictions from
adjacent blocks and/or co-located blocks in temporal reference
pictures and signalling the chosen candidate as the motion vector
predictor. In addition to predicting the motion vector values, the
reference index of previously coded/decoded picture can be
predicted. The reference index is typically predicted from adjacent
blocks and/or co-located blocks in temporal reference picture.
Differential coding of motion vectors is typically disabled across
slice boundaries.
Multi-Hypothesis Motion-Compensated Prediction.
H.264/AVC and HEVC enable the use of a single prediction block in P
slices (herein referred to as uni-predictive slices) or a linear
combination of two motion-compensated prediction blocks for
bi-predictive slices, which are also referred to as B slices.
Individual blocks in B slices may be bi-predicted, uni-predicted,
or intra-predicted, and individual blocks in P slices may be
uni-predicted or intra-predicted. The reference pictures for a
bi-predictive picture may not be limited to be the subsequent
picture and the previous picture in output order, but rather any
reference pictures may be used. In many coding standards, such as
H.264/AVC and HEVC, one reference picture list, referred to as
reference picture list 0, is constructed for P slices, and two
reference picture lists, list 0 and list 1, are constructed for B
slices. For B slices, when prediction in forward direction may
refer to prediction from a reference picture in reference picture
list 0, and prediction in backward direction may refer to
prediction from a reference picture in reference picture list 1,
even though the reference pictures for prediction may have any
decoding or output order relation to each other or to the current
picture.
Weighted Prediction.
Many coding standards use a prediction weight of 1 for prediction
blocks of inter (P) pictures and 0.5 for each prediction block of a
B picture (resulting into averaging). H.264/AVC allows weighted
prediction for both P and B slices. In implicit weighted
prediction, the weights are proportional to picture order counts,
while in explicit weighted prediction, prediction weights are
explicitly indicated.
In many video codecs, the prediction residual after motion
compensation is first transformed with a transform kernel (like
DCT) and then coded. The reason for this is that often there still
exists some correlation among the residual and transform can in
many cases help reduce this correlation and provide more efficient
coding.
In a draft HEVC, each PU has prediction information associated with
it defining what kind of a prediction is to be applied for the
pixels within that PU (e.g. motion vector information for inter
predicted PUs and intra prediction directionality information for
intra predicted PUs). Similarly each TU is associated with
information describing the prediction error decoding process for
the samples within the TU (including e.g. DCT coefficient
information). It may be signalled at CU level whether prediction
error coding is applied or not for each CU. In the case there is no
prediction error residual associated with the CU, it can be
considered there are no TUs for the CU.
In some coding formats and codecs, a distinction is made between
so-called short-term and long-term reference pictures. This
distinction may affect some decoding processes such as motion
vector scaling in the temporal direct mode or implicit weighted
prediction. If both of the reference pictures used for the temporal
direct mode are short-term reference pictures, the motion vector
used in the prediction may be scaled according to the picture order
count (POC) difference between the current picture and each of the
reference pictures. However, if at least one reference picture for
the temporal direct mode is a long-term reference picture, default
scaling of the motion vector may be used, for example scaling the
motion to half may be used. Similarly, if a short-term reference
picture is used for implicit weighted prediction, the prediction
weight may be scaled according to the POC difference between the
POC of the current picture and the POC of the reference picture.
However, if a long-term reference picture is used for implicit
weighted prediction, a default prediction weight may be used, such
as 0.5 in implicit weighted prediction for bi-predicted blocks.
Some video coding formats, such as H.264/AVC, include the frame_num
syntax element, which is used for various decoding processes
related to multiple reference pictures. In H.264/AVC, the value of
frame_num for IDR pictures is 0. The value of frame_num for non-IDR
pictures is equal to the frame_num of the previous reference
picture in decoding order incremented by 1 (in modulo arithmetic,
i.e., the value of frame_num wrap over to 0 after a maximum value
of frame_num).
H.264/AVC and HEVC include a concept of picture order count (POC).
A value of POC is derived for each picture and is non-decreasing
with increasing picture position in output order. POC therefore
indicates the output order of pictures. POC may be used in the
decoding process for example for implicit scaling of motion vectors
in the temporal direct mode of bi-predictive slices, for implicitly
derived weights in weighted prediction, and for reference picture
list initialization. Furthermore, POC may be used in the
verification of output order conformance. In H.264/AVC, POC is
specified relative to the previous IDR picture or a picture
containing a memory management control operation marking all
pictures as "unused for reference".
H.264/AVC specifies the process for decoded reference picture
marking in order to control the memory consumption in the decoder.
The maximum number of reference pictures used for inter prediction,
referred to as M, is determined in the sequence parameter set. When
a reference picture is decoded, it is marked as "used for
reference". If the decoding of the reference picture caused more
than M pictures marked as "used for reference", at least one
picture is marked as "unused for reference". There are two types of
operation for decoded reference picture marking: adaptive memory
control and sliding window. The operation mode for decoded
reference picture marking is selected on picture basis. The
adaptive memory control enables explicit signaling which pictures
are marked as "unused for reference" and may also assign long-term
indices to short-term reference pictures. The adaptive memory
control may require the presence of memory management control
operation (MMCO) parameters in the bitstream. MMCO parameters may
be included in a decoded reference picture marking syntax
structure. If the sliding window operation mode is in use and there
are M pictures marked as "used for reference", the short-term
reference picture that was the first decoded picture among those
short-term reference pictures that are marked as "used for
reference" is marked as "unused for reference". In other words, the
sliding window operation mode results into first-in-first-out
buffering operation among short-term reference pictures.
One of the memory management control operations in H.264/AVC causes
all reference pictures except for the current picture to be marked
as "unused for reference". An instantaneous decoding refresh (IDR)
picture contains only intra-coded slices and causes a similar
"reset" of reference pictures.
In a draft HEVC standard, reference picture marking syntax
structures and related decoding processes are not used, but instead
a reference picture set (RPS) syntax structure and decoding process
are used instead for a similar purpose. A reference picture set
valid or active for a picture includes all the reference pictures
used as reference for the picture and all the reference pictures
that are kept marked as "used for reference" for any subsequent
pictures in decoding order. There are six subsets of the reference
picture set, which are referred to as namely RefPicSetStCurr0,
RefPicSetStCurr1, RefPicSetStFoll0, RefPicSetStFoll1,
RefPicSetLtCurr, and RefPicSetLtFoll. The notation of the six
subsets is as follows. "Curr" refers to reference pictures that are
included in the reference picture lists of the current picture and
hence may be used as inter prediction reference for the current
picture. "Foll" refers to reference pictures that are not included
in the reference picture lists of the current picture but may be
used in subsequent pictures in decoding order as reference
pictures. "St" refers to short-term reference pictures, which may
generally be identified through a certain number of least
significant bits of their POC value. "Lt" refers to long-term
reference pictures, which are specifically identified and generally
have a greater difference of POC values relative to the current
picture than what can be represented by the mentioned certain
number of least significant bits. "0" refers to those reference
pictures that have a smaller POC value than that of the current
picture. "1" refers to those reference pictures that have a greater
POC value than that of the current picture. RefPicSetStCurr0,
RefPicSetStCurr1, RefPicSetStFoll0 and RefPicSetStFoll1 are
collectively referred to as the short-term subset of the reference
picture set. RefPicSetLtCurr and RefPicSetLtFoll are collectively
referred to as the long-term subset of the reference picture
set.
In a draft HEVC standard, a reference picture set may be specified
in a sequence parameter set and taken into use in the slice header
through an index to the reference picture set. A reference picture
set may also be specified in a slice header. A long-term subset of
a reference picture set is generally specified only in a slice
header, while the short-term subsets of the same reference picture
set may be specified in the picture parameter set or slice header.
A reference picture set may be coded independently or may be
predicted from another reference picture set (known as inter-RPS
prediction). When a reference picture set is independently coded,
the syntax structure includes up to three loops iterating over
different types of reference pictures; short-term reference
pictures with lower POC value than the current picture, short-term
reference pictures with higher POC value than the current picture
and long-term reference pictures. Each loop entry specifies a
picture to be marked as "used for reference". In general, the
picture is specified with a differential POC value. The inter-RPS
prediction exploits the fact that the reference picture set of the
current picture can be predicted from the reference picture set of
a previously decoded picture. This is because all the reference
pictures of the current picture are either reference pictures of
the previous picture or the previously decoded picture itself. It
is only necessary to indicate which of these pictures should be
reference pictures and be used for the prediction of the current
picture. In both types of reference picture set coding, a flag
(used_by_curr_pic_X_flag) is additionally sent for each reference
picture indicating whether the reference picture is used for
reference by the current picture (included in a *Curr list) or not
(included in a *Foll list). Pictures that are included in the
reference picture set used by the current slice are marked as "used
for reference", and pictures that are not in the reference picture
set used by the current slice are marked as "unused for reference".
If the current picture is an IDR picture, RefPicSetStCurr0,
RefPicSetStCurr1, RefPicSetStFoll0, RefPicSetStFoll1,
RefPicSetLtCurr, and RefPicSetLtFoll are all set to empty.
A Decoded Picture Buffer (DPB) may be used in the encoder and/or in
the decoder. There are two reasons to buffer decoded pictures, for
references in inter prediction and for reordering decoded pictures
into output order. As H.264/AVC and HEVC provide a great deal of
flexibility for both reference picture marking and output
reordering, separate buffers for reference picture buffering and
output picture buffering may waste memory resources. Hence, the DPB
may include a unified decoded picture buffering process for
reference pictures and output reordering. A decoded picture may be
removed from the DPB when it is no longer used as a reference and
is not needed for output.
In many coding modes of H.264/AVC and HEVC, the reference picture
for inter prediction is indicated with an index to a reference
picture list. The index may be coded with variable length coding,
which usually causes a smaller index to have a shorter value for
the corresponding syntax element. In H.264/AVC and HEVC, two
reference picture lists (reference picture list 0 and reference
picture list 1) are generated for each bi-predictive (B) slice, and
one reference picture list (reference picture list 0) is formed for
each inter-coded (P) slice. In addition, for a B slice in HEVC, a
combined list (List C) is constructed after the final reference
picture lists (List 0 and List 1) have been constructed. The
combined list may be used for uni-prediction (also known as
uni-directional prediction) within B slices.
A reference picture list, such as reference picture list 0 and
reference picture list 1, is typically constructed in two steps:
First, an initial reference picture list is generated. The initial
reference picture list may be generated for example on the basis of
frame_num, POC, temporal_id, or information on the prediction
hierarchy such as GOP structure, or any combination thereof.
Second, the initial reference picture list may be reordered by
reference picture list reordering (RPLR) commands, also known as
reference picture list modification syntax structure, which may be
contained in slice headers. The RPLR commands indicate the pictures
that are ordered to the beginning of the respective reference
picture list. This second step may also be referred to as the
reference picture list modification process, and the RPLR commands
may be included in a reference picture list modification syntax
structure. If reference picture sets are used, the reference
picture list 0 may be initialized to contain RefPicSetStCurr0
first, followed by RefPicSetStCurr1, followed by RefPicSetLtCurr.
Reference picture list 1 may be initialized to contain
RefPicSetStCurr1 first, followed by RefPicSetStCurr0. The initial
reference picture lists may be modified through the reference
picture list modification syntax structure, where pictures in the
initial reference picture lists may be identified through an entry
index to the list.
Many high efficiency video codecs such as a draft HEVC codec employ
an additional motion information coding/decoding mechanism, often
called merging/merge mode/process/mechanism, where all the motion
information of a block/PU is predicted and used without any
modification/correction. The aforementioned motion information for
a PU may comprise 1) The information whether `the PU is
uni-predicted using only reference picture list0` or `the PU is
uni-predicted using only reference picture list1` or `the PU is
bi-predicted using both reference picture list0 and list1`; 2)
Motion vector value corresponding to the reference picture list0;
3) Reference picture index in the reference picture list0; 4)
Motion vector value corresponding to the reference picture list1;
and 5) Reference picture index in the reference picture list1.
Similarly, predicting the motion information is carried out using
the motion information of adjacent blocks and/or co-located blocks
in temporal reference pictures. A list, often called as a merge
list, may be constructed by including motion prediction candidates
associated with available adjacent/co-located blocks and the index
of selected motion prediction candidate in the list is signalled
and the motion information of the selected candidate is copied to
the motion information of the current PU. When the merge mechanism
is employed for a whole CU and the prediction signal for the CU is
used as the reconstruction signal, i.e. prediction residual is not
processed, this type of coding/decoding the CU is typically named
as skip mode or merge based skip mode. In addition to the skip
mode, the merge mechanism may also be employed for individual PUs
(not necessarily the whole CU as in skip mode) and in this case,
prediction residual may be utilized to improve prediction quality.
This type of prediction mode is typically named as an inter-merge
mode.
The merge list may be generated on the basis of reference picture
list 0 and/or reference picture list 1 for example using the
reference picture lists combination syntax structure included in
the slice header syntax. There may be a reference picture lists
combination syntax structure, created into the bitstream by an
encoder and decoded from the bitstream by a decoder, which
indicates the contents of the merge list. The syntax structure may
indicate that the reference picture list 0 and the reference
picture list 1 are combined to be an additional reference picture
lists combination used for the prediction units being
uni-directional predicted. The syntax structure may include a flag
which, when equal to a certain value, indicates that the reference
picture list 0 and reference picture list 1 are identical thus
reference picture list 0 is used as the reference picture lists
combination. The syntax structure may include a list of entries,
each specifying a reference picture list (list 0 or list 1) and a
reference index to the specified list, where an entry specifies a
reference picture to be included in the merge list.
A syntax structure for decoded reference picture marking may exist
in a video coding system. For example, when the decoding of the
picture has been completed, the decoded reference picture marking
syntax structure, if present, may be used to adaptively mark
pictures as "unused for reference" or "used for long-term
reference". If the decoded reference picture marking syntax
structure is not present and the number of pictures marked as "used
for reference" can no longer increase, a sliding window reference
picture marking may be used, which basically marks the earliest (in
decoding order) decoded reference picture as unused for
reference.
In scalable video coding, a video signal can be encoded into a base
layer and one or more enhancement layers. An enhancement layer may
enhance the temporal resolution (i.e., the frame rate), the spatial
resolution, or simply the quality of the video content represented
by another layer or part thereof. Each layer together with all its
dependent layers is one representation of the video signal at a
certain spatial resolution, temporal resolution and quality level.
In this document, we refer to a scalable layer together with all of
its dependent layers as a "scalable layer representation". The
portion of a scalable bitstream corresponding to a scalable layer
representation can be extracted and decoded to produce a
representation of the original signal at certain fidelity.
Some coding standards allow creation of scalable bit streams. A
meaningful decoded representation can be produced by decoding only
certain parts of a scalable bit stream. Scalable bit streams can be
used for example for rate adaptation of pre-encoded unicast streams
in a streaming server and for transmission of a single bit stream
to terminals having different capabilities and/or with different
network conditions. A list of some other use cases for scalable
video coding can be found in the ISO/IEC JTC1 SC29 WG11 (MPEG)
output document N5540, "Applications and Requirements for Scalable
Video Coding", the 64.sup.th MPEG meeting, Mar. 10 to 14, 2003,
Pattaya, Thailand.
In some cases, data in an enhancement layer can be truncated after
a certain location, or even at arbitrary positions, where each
truncation position may include additional data representing
increasingly enhanced visual quality. Such scalability is referred
to as fine-grained (granularity) scalability (FGS). FGS was
included in some draft versions of the SVC standard, but it was
eventually excluded from the final SVC standard. FGS is
subsequently discussed in the context of some draft versions of the
SVC standard. The scalability provided by those enhancement layers
that cannot be truncated is referred to as coarse-grained
(granularity) scalability (CGS). It collectively includes the
traditional quality (SNR) scalability and spatial scalability. The
SVC standard supports the so-called medium-grained scalability
(MGS), where quality enhancement pictures are coded similarly to
SNR scalable layer pictures but indicated by high-level syntax
elements similarly to FGS layer pictures, by having the quality_id
syntax element greater than 0.
SVC uses an inter-layer prediction mechanism, wherein certain
information can be predicted from layers other than the currently
reconstructed layer or the next lower layer. Information that could
be inter-layer predicted includes intra texture, motion and
residual data. Inter-layer motion prediction includes the
prediction of block coding mode, header information, etc., wherein
motion from the lower layer may be used for prediction of the
higher layer. In case of intra coding, a prediction from
surrounding macroblocks or from co-located macroblocks of lower
layers is possible. These prediction techniques do not employ
information from earlier coded access units and hence, are referred
to as intra prediction techniques. Furthermore, residual data from
lower layers can also be employed for prediction of the current
layer.
SVC specifies a concept known as single-loop decoding. It is
enabled by using a constrained intra texture prediction mode,
whereby the inter-layer intra texture prediction can be applied to
macroblocks (MBs) for which the corresponding block of the base
layer is located inside intra-MBs. At the same time, those
intra-MBs in the base layer use constrained intra-prediction (e.g.,
having the syntax element "constrained_intra_pred_flag" equal to
1). In single-loop decoding, the decoder performs motion
compensation and full picture reconstruction only for the scalable
layer desired for playback (called the "desired layer" or the
"target layer"), thereby greatly reducing decoding complexity. All
of the layers other than the desired layer do not need to be fully
decoded because all or part of the data of the MBs not used for
inter-layer prediction (be it inter-layer intra texture prediction,
inter-layer motion prediction or inter-layer residual prediction)
is not needed for reconstruction of the desired layer.
A single decoding loop is needed for decoding of most pictures,
while a second decoding loop is selectively applied to reconstruct
the base representations, which are needed as prediction references
but not for output or display, and are reconstructed only for the
so called key pictures (for which "store_ref base_pic_flag" is
equal to 1).
The scalability structure in the SVC draft is characterized by
three syntax elements: "temporal_id," "dependency_id" and
"quality_id." The syntax element "temporal_id" is used to indicate
the temporal scalability hierarchy or, indirectly, the frame rate.
A scalable layer representation comprising pictures of a smaller
maximum "temporal_id" value has a smaller frame rate than a
scalable layer representation comprising pictures of a greater
maximum "temporal_id". A given temporal layer typically depends on
the lower temporal layers (i.e., the temporal layers with smaller
"temporal_id" values) but does not depend on any higher temporal
layer. The syntax element "dependency_id" is used to indicate the
CGS inter-layer coding dependency hierarchy (which, as mentioned
earlier, includes both SNR and spatial scalability). At any
temporal level location, a picture of a smaller "dependency_id"
value may be used for inter-layer prediction for coding of a
picture with a greater "dependency_id" value. The syntax element
"quality_id" is used to indicate the quality level hierarchy of a
FGS or MGS layer. At any temporal location, and with an identical
"dependency_id" value, a picture with "quality_id" equal to QL uses
the picture with "quality_id" equal to QL-1 for inter-layer
prediction. A coded slice with "quality_id" larger than 0 may be
coded as either a truncatable FGS slice or a non-truncatable MGS
slice.
For simplicity, all the data units (e.g., Network Abstraction Layer
units or NAL units in the SVC context) in one access unit having
identical value of "dependency_id" are referred to as a dependency
unit or a dependency representation. Within one dependency unit,
all the data units having identical value of "quality_id" are
referred to as a quality unit or layer representation.
A base representation, also known as a decoded base picture, is a
decoded picture resulting from decoding the Video Coding Layer
(VCL) NAL units of a dependency unit having "quality_id" equal to 0
and for which the "store_ref base_pic_flag" is set equal to 1. An
enhancement representation, also referred to as a decoded picture,
results from the regular decoding process in which all the layer
representations that are present for the highest dependency
representation are decoded.
As mentioned earlier, CGS includes both spatial scalability and SNR
scalability. Spatial scalability is initially designed to support
representations of video with different resolutions. For each time
instance, VCL NAL units are coded in the same access unit and these
VCL NAL units can correspond to different resolutions. During the
decoding, a low resolution VCL NAL unit provides the motion field
and residual which can be optionally inherited by the final
decoding and reconstruction of the high resolution picture. When
compared to older video compression standards, SVC's spatial
scalability has been generalized to enable the base layer to be a
cropped and zoomed version of the enhancement layer.
MGS quality layers are indicated with "quality_id" similarly as FGS
quality layers. For each dependency unit (with the same
"dependency_id"), there is a layer with "quality_id" equal to 0 and
there can be other layers with "quality_id" greater than 0. These
layers with "quality_id" greater than 0 are either MGS layers or
FGS layers, depending on whether the slices are coded as
truncatable slices.
In the basic form of FGS enhancement layers, only inter-layer
prediction is used. Therefore, FGS enhancement layers can be
truncated freely without causing any error propagation in the
decoded sequence. However, the basic form of FGS suffers from low
compression efficiency. This issue arises because only low-quality
pictures are used for inter prediction references. It has therefore
been proposed that FGS-enhanced pictures be used as inter
prediction references. However, this may cause encoding-decoding
mismatch, also referred to as drift, when some FGS data are
discarded.
One feature of a draft SVC standard is that the FGS NAL units can
be freely dropped or truncated, and a feature of the SVCV standard
is that MGS NAL units can be freely dropped (but cannot be
truncated) without affecting the conformance of the bitstream. As
discussed above, when those FGS or MGS data have been used for
inter prediction reference during encoding, dropping or truncation
of the data would result in a mismatch between the decoded pictures
in the decoder side and in the encoder side. This mismatch is also
referred to as drift.
To control drift due to the dropping or truncation of FGS or MGS
data, SVC applied the following solution: In a certain dependency
unit, a base representation (by decoding only the CGS picture with
"quality_id" equal to 0 and all the dependent-on lower layer data)
is stored in the decoded picture buffer. When encoding a subsequent
dependency unit with the same value of "dependency_id," all of the
NAL units, including FGS or MGS NAL units, use the base
representation for inter prediction reference. Consequently, all
drift due to dropping or truncation of FGS or MGS NAL units in an
earlier access unit is stopped at this access unit. For other
dependency units with the same value of "dependency_id," all of the
NAL units use the decoded pictures for inter prediction reference,
for high coding efficiency.
Each NAL unit includes in the NAL unit header a syntax element
"use_ref base_pic_flag." When the value of this element is equal to
1, decoding of the NAL unit uses the base representations of the
reference pictures during the inter prediction process. The syntax
element "store_ref base_pic_flag" specifies whether (when equal to
1) or not (when equal to 0) to store the base representation of the
current picture for future pictures to use for inter
prediction.
NAL units with "quality_id" greater than 0 do not contain syntax
elements related to reference picture lists construction and
weighted prediction, i.e., the syntax elements
"num_refactive_lx_minus1" (x=0 or 1), the reference picture list
reordering syntax table, and the weighted prediction syntax table
are not present. Consequently, the MGS or FGS layers have to
inherit these syntax elements from the NAL units with "quality_id"
equal to 0 of the same dependency unit when needed.
In SVC, a reference picture list consists of either only base
representations (when "use_ref base_pic_flag" is equal to 1) or
only decoded pictures not marked as "base representation" (when
"use_ref base_pic_flag" is equal to 0), but never both at the same
time.
The value of variable DQId for the decoding process of SVC may be
set equal to dependency_id.times.16+quality_id, or equivalently
(dependency_id<<4)+quality_id, where << is the
bit-shift operation to left. The value of variable DQIdMax in SVC
may be set equal to greatest DQId value for any VCL NAL unit in the
access unit being decoded. The variable DependencyIdMax may be set
equal to (DQIdMax>>4) where >> is the bit-shift
operation to right. In conforming SVC coded video sequences,
DependencyIdMax is the same for all access units of the coded video
sequence.
A scalable nesting SEI message has been specified in SVC. The
scalable nesting SEI message provides a mechanism for associating
SEI messages with subsets of a bitstream. A scalable nesting SEI
message contains one or more SEI messages that are not scalable
nesting SEI messages themselves. An SEI message contained in a
scalable nesting SEI message is referred to as a nested SEI
message. An SEI message not contained in a scalable nesting SEI
message is referred to as a non-nested SEI message. The scope to
which the nested SEI message applies is indicated by the syntax
elements all_layer_representations_in_au_flag,
num_layer_representations_minus1, sei_dependency_id[i],
sei_quality_id[i], and sei_temporal_id, when present in the
scalable nesting SEI message. all_layer_representations_in_au_flag
equal to 1 specifies that the nested SEI message applies to all
layer representations of the access unit.
all_layer_representations_in_au_flag equal to 0 specifies that the
scope of the nested SEI message is specified by the syntax elements
num_layer_representations_minus1, sei_dependency_id[i],
sei_quality_id[i], and sei_temporal_id.
num_layer_representations_minus1 plus 1 specifies, when
num_layer_representations_minus1 is present, the number of syntax
element pairs sei_dependency_id[i] and sei_quality_id[i] that are
present in the scalable nesting SEI message. When
num_layer_representations_minus1 is not present, it is inferred to
be equal to (numSVCLayers-1) with numSVCLayers being the number of
layer representations that are present in the primary coded picture
of the access unit. sei_dependency_id[i] and sei_quality_id[i]
indicate the dependency_id and the quality_id values, respectively,
of the layer representations to which the nested SEI message
applies. The access unit may or may not contain layer
representations with dependency_id equal to sei_dependency_id[i]
and quality_id equal to sei_quality_id[i]. When
num_layer_representations_minus1 is not present, the values of
sei_dependency_id[i] and sei_quality_id[i] for i in the range of 0
to num_layer_representations_minus 1 (with
num_layer_representations_minus 1 being the inferred value),
inclusive, are inferred as specified in the following: 1. Let
setDQId be the set of the values DQId for all layer representations
that are present in the primary coded picture of the access unit.
2. For i proceeding from 0 to num_layer_representations_minus1,
inclusive, the following applies: a. sei_dependency_id[i] and
sei_quality_id[i] are inferred to be equal to (minDQId>>4)
and (minDQId & 15), respectively, with minDQId being the
smallest value (smallest value of DQId) in the set setDQId. b. The
smallest value (smallest value of DQId) of the set setDQId is
removed from setDQId and thus the number of elements in the set
setDQId is decreased by 1.
sei_temporal_id indicates the temporal_id value of the bitstream
subset to which the nested SEI message applies. When
sei_temporal_id is not present, it shall be inferred to be equal to
temporal_id of the access unit.
In SVC, in addition to the active picture parameter set RBSP, zero
or more picture parameter set RBSPs may be specifically active for
layer representations (with a particular value of DQId less than
DQIdMax) that may be referred to through inter-layer prediction in
decoding the target layer representation. Such a picture parameter
set RBSP is referred to as active layer picture parameter set RBSP
for the particular value of DQId (less than DQIdMax). The
restrictions on active picture parameter set RBSPs also apply to
active layer picture parameter set RBSPs with a particular value of
DQId.
In SVC, when a picture parameter set RBSP (with a particular value
of pic_parameter_set_id) is not the active picture parameter set
RBSP and it is referred to by a coded slice NAL unit with DQId
equal to DQIdMax (using that value of pic_parameter_set_id), it is
activated. This picture parameter set RBSP is called the active
picture parameter set RBSP until it is deactivated when another
picture parameter set RBSP becomes the active picture parameter set
RBSP. A picture parameter set RBSP, with that particular value of
pic_parameter_set_id, is available to the decoding process prior to
its activation.
In SVC, when a picture parameter set RBSP (with a particular value
of pic_parameter_set_id) is not the active layer picture parameter
set for a particular value of DQId less than DQIdMax and it is
referred to by a coded slice NAL unit with the particular value of
DQId (using that value of pic_parameter_set_id), it is activated
for layer representations with the particular value of DQId. This
picture parameter set RBSP is called the active layer picture
parameter set RBSP for the particular value of DQId until it is
deactivated when another picture parameter set RBSP becomes the
active layer picture parameter set RBSP for the particular value of
DQId or when decoding an access unit with DQIdMax less than or
equal to the particular value of DQId. A picture parameter set
RBSP, with that particular value of pic_parameter_set_id, is
available to the decoding process prior to its activation.
In SVC, an SVC sequence parameter set RBSP may be defined as a
collective term for sequence parameter set RBSP or subset sequence
parameter set RBSP.
In SVC, when an SVC sequence parameter set RBSP with a particular
value of seq_parameter_set_id is not already the active SVC
sequence parameter set RBSP and it is referred to by activation of
a picture parameter set RB SP (using that value of
seq_parameter_set_id) as an active picture parameter set RBSP, the
SVC sequence parameter set RBSP is activated. The active SVC
sequence parameter set RBSP remains active until it is deactivated
when another SVC sequence parameter set RBSP becomes the active SVC
sequence parameter set RBSP. A sequence parameter set RBSP, with
that particular value of seq_parameter_set_id, is available to the
decoding process prior to its activation.
In SVC, profile_idc and level_idc in an SVC sequence parameter set
RBSP indicate the profile and level to which the coded video
sequence conforms when the SVC sequence parameter set RB SP is the
active SVC sequence parameter set RBSP.
In addition to the active SVC sequence parameter set RBSP, zero or
more SVC sequence parameter set RBSPs may be specifically active
for layer representations (with a particular value of DQId less
than DQIdMax) that may be referred to through inter-layer
prediction in decoding the target layer representation. Such an SVC
sequence parameter set RBSP is referred to as active layer SVC
sequence parameter set RBSP for the particular value of DQId (less
than DQIdMax). The restrictions on active SVC sequence parameter
set RBSPs also apply to active layer SVC sequence parameter set
RBSPs with a particular value of DQId.
In SVC, when a sequence parameter set RBSP with a particular value
of seq_parameter_set_id is not already the active layer SVC
sequence parameter set RBSP for DQId equal to 0 and it is referred
to by activation of a picture parameter set RBSP (using that value
of seq_parameter_set_id) and the picture parameter set RBSP is
activated by a base-layer coded slice NAL unit or buffering period
SEI message and DQIdMax is greater than 0 (the picture parameter
set RBSP becomes the active layer picture parameter set RBSP for
DQId equal to 0), the sequence parameter set RBSP is activated for
layer representations with DQId equal to 0. This sequence parameter
set RBSP is called the active layer SVC sequence parameter set RBSP
for DQId equal to 0 until it is deactivated when another SVC
sequence parameter set RBSP becomes the active layer SVC sequence
parameter set RBSP for DQId equal to 0 or when decoding an access
unit with DQIdMax equal to 0. A sequence parameter set RBSP, with
that particular value of seq_parameter_set_id, is available to the
decoding process prior to its activation.
In SVC, when a subset sequence parameter set RBSP with a particular
value of seq_parameter_set_id is not already the active layer SVC
sequence parameter set RBSP for a particular value of DQId less
than DQIdMax and it is referred to by an activating layer buffering
period SEI message for the particular value of DQId (using that
value of seq_parameter_set_id) that is included in a scalable
nesting SEI message, the subset sequence parameter set RBSP is
activated for layer representations with the particular value of
DQId. This subset sequence parameter set RBSP is called the active
layer SVC sequence parameter set RBSP for the particular value of
DQId until it is deactivated when another SVC sequence parameter
set RBSP becomes the active layer SVC sequence parameter set RBSP
for the particular value of DQId or when decoding an access unit
with DQIdMax less than or equal to the particular value of DQId. A
subset sequence parameter set RBSP, with that particular value of
seq_parameter_set_id, is available to the decoding process prior to
its activation.
Let spsA and spsB be two SVC sequence parameter set RBSPs with one
of the following properties: spsA is the SVC sequence parameter set
RBSP that is referred to by the coded slice NAL units (via the
picture parameter set) of a layer representation with a particular
value of dependency_id and quality_id equal to 0 and spsB is the
SVC sequence parameter set RBSP that is referred to by the coded
slice NAL units (via the picture parameter set) of another layer
representation, in the same access unit, with the same value of
dependency_id and quality_id greater than 0, spsA is the active SVC
sequence parameter set RBSP for an access unit and spsB is the SVC
sequence parameter set RBSP that is referred to by the coded slice
NAL units (via the picture parameter set) of the layer
representation with DQId equal to DQIdMax, spsA is the active SVC
sequence parameter set RBSP for an IDR access unit and spsB is the
active SVC sequence parameter set RBSP for any non-IDR access unit
of the same coded video sequence.
The SVC sequence parameter set RBSPs spsA and spsB are restricted
with regards to their contents as specified in the following. The
values of the syntax elements in the sequence parameter set data
syntax structure of spsA and spsB may only differ for the following
syntax elements and is the same otherwise: profile_idc,
constraint_setX_flag (with X being equal to 0 to 5, inclusive),
reserved_zero.sub.--2 bits, level_idc, seq_parameter_set_id,
timing_info_present_flag, num_units_in_tick, time_scale,
fixed_frame_rate_flag, nal_hrd_parameters_present_flag,
vcl_hrd_parameters_present_flag, low_delay_hrd_flag,
pic_struct_present_flag, and the hrd_parameters( ) syntax
structures. In summary, only the profile and level related
indications, profile compatibility indications, HRD parameters, and
picture timing related indications may differ. When spsA is the
active SVC sequence parameter set RBSP and spsB is the SVC sequence
parameter set RBSP that is referred to by the coded slice NAL units
of the layer representation with DQId equal to DQIdMax, the level
specified by level_idc (or level_idc and constraint_set3_flag) in
spsA is not less than the level specified by level_idc (or
level_idc and constraint_set3_flag) in spsB. When the
seq_parameter_set_svc_extension( ) syntax structure is present in
both spsA and spsB, the values of all syntax elements in the
seq_parameter_set_svc_extension( ) syntax structure are the
same.
In SVC, the scalability information SEI message provides
scalability information for subsets of the bitstream. A scalability
information SEI message is not be included in a scalable nesting
SEI message. A scalability information SEI message may be present
in an access unit where all dependency representations are IDR
dependency representations. The set of access units consisting of
the access unit associated with the scalability information SEI
message and all succeeding access units in decoding order until,
but excluding, the next access unit where all dependency
representations are IDR dependency representations (if present) or
the end of the bitstream (otherwise) is referred to as the target
access unit set. The scalability information SEI message applies to
the target access unit set. The scalability information SEI message
provides information for subsets of the target access unit set.
These subsets are referred to as scalable layers. A scalable layer
represents a set of NAL units, inside the target access unit set,
that consists of VCL NAL units with the same values of
dependency_id, quality_id, and temporal_id, as indicated by the
scalability information SEI message, and associated non-VCL NAL
units. The representation of a particular scalable layer is the set
of NAL units that represents the set union of the particular
scalable layer and all scalable layers on which the particular
scalable layer directly or indirectly depends. The representation
of a scalable layer is also referred to as scalable layer
representation. Terms representation of a scalable layer and
scalable layer representation may also be used for referring to the
access unit set that can be constructed from the NAL units of the
scalable layer representation. A scalable layer representation can
be decoded independently of all NAL units that do not belong to the
scalable layer representation. The decoding result of a scalable
layer representation is the set of decoded pictures that are
obtained by decoding the access unit set of the scalable layer
representation.
Among other things, the scalability information SEI message in SVC
may specify one or more scalable layers through a set of
dependency_id, quality_id, and temporal_id values. Specifically,
the scalability information SEI message may include for each
scalable layer i the syntax elements dependency_id[i],
quality_id[i], and temporal_id[i] that are equal to the values of
dependency_id, quality_id, and temporal_id, respectively, of the
VCL NAL units of the scalable layer. All VCL NAL units of a
scalable layer have the same values of dependency_id, quality_id,
and temporal_id.
Among other things, the scalability information SEI message in SVC
may include layer_profile_level_idc[i] for scalable layer i that
indicates the conformance point of the representation of the
scalable layer. layer_profile_level_idc[i] is the exact copy of the
three bytes comprised of profile_idc, constraint_set0_flag,
constraint_set1_flag, constraint_set2_flag, constraint_set3_flag,
constraint_set4_flag, constraint_set5_flag, reserved_zero.sub.--2
bits and level_idc, as if these syntax elements were used to
specify the profile and level conformance of the representation of
the current scalable layer.
As indicated earlier, MVC is an extension of H.264/AVC. Many of the
definitions, concepts, syntax structures, semantics, and decoding
processes of H.264/AVC apply also to MVC as such or with certain
generalizations or constraints. Some definitions, concepts, syntax
structures, semantics, and decoding processes of MVC are described
in the following.
An access unit in MVC is defined to be a set of NAL units that are
consecutive in decoding order and contain exactly one primary coded
picture consisting of one or more view components. In addition to
the primary coded picture, an access unit may also contain one or
more redundant coded pictures, one auxiliary coded picture, or
other NAL units not containing slices or slice data partitions of a
coded picture. The decoding of an access unit results in one
decoded picture consisting of one or more decoded view components,
when decoding errors, bitstream errors or other errors which may
affect the decoding do not occur. In other words, an access unit in
MVC contains the view components of the views for one output time
instance.
A view component in MVC is referred to as a coded representation of
a view in a single access unit.
Inter-view prediction may be used in MVC and refers to prediction
of a view component from decoded samples of different view
components of the same access unit. In MVC, inter-view prediction
is realized similarly to inter prediction. For example, inter-view
reference pictures are placed in the same reference picture list(s)
as reference pictures for inter prediction, and a reference index
as well as a motion vector are coded or inferred similarly for
inter-view and inter reference pictures.
An anchor picture is a coded picture in which all slices may
reference only slices within the same access unit, i.e., inter-view
prediction may be used, but no inter prediction is used, and all
following coded pictures in output order do not use inter
prediction from any picture prior to the coded picture in decoding
order. Inter-view prediction may be used for IDR view components
that are part of a non-base view. A base view in MVC is a view that
has the minimum value of view order index in a coded video
sequence. The base view can be decoded independently of other views
and does not use inter-view prediction. The base view can be
decoded by H.264/AVC decoders supporting only the single-view
profiles, such as the Baseline Profile or the High Profile of
H.264/AVC.
In the MVC standard, many of the sub-processes of the MVC decoding
process use the respective sub-processes of the H.264/AVC standard
by replacing term "picture", "frame", and "field" in the
sub-process specification of the H.264/AVC standard by "view
component", "frame view component", and "field view component",
respectively. Likewise, terms "picture", "frame", and "field" are
often used in the following to mean "view component", "frame view
component", and "field view component", respectively.
In scalable multiview coding, the same bitstream may contain coded
view components of multiple views and at least some coded view
components may be coded using quality and/or spatial
scalability.
A texture view refers to a view that represents ordinary video
content, for example has been captured using an ordinary camera,
and is usually suitable for rendering on a display. A texture view
typically comprises pictures having three components, one luma
component and two chroma components. In the following, a texture
picture typically comprises all its component pictures or color
components unless otherwise indicated for example with terms luma
texture picture and chroma texture picture.
Depth-enhanced video refers to texture video having one or more
views associated with depth video having one or more depth views. A
number of approaches may be used for representing of depth-enhanced
video, including the use of video plus depth (V+D), multiview video
plus depth (MVD), and layered depth video (LDV). In the video plus
depth (V+D) representation, a single view of texture and the
respective view of depth are represented as sequences of texture
picture and depth pictures, respectively. The MVD representation
contains a number of texture views and respective depth views. In
the LDV representation, the texture and depth of the central view
are represented conventionally, while the texture and depth of the
other views are partially represented and cover only the
dis-occluded areas required for correct view synthesis of
intermediate views.
Depth-enhanced video may be coded in a manner where texture and
depth are coded independently of each other. For example, texture
views may be coded as one MVC bitstream and depth views may be
coded as another MVC bitstream. Alternatively depth-enhanced video
may be coded in a manner where texture and depth are jointly coded.
When joint coding texture and depth views is applied for a
depth-enhanced video representation, some decoded samples of a
texture picture or data elements for decoding of a texture picture
are predicted or derived from some decoded samples of a depth
picture or data elements obtained in the decoding process of a
depth picture. Alternatively or in addition, some decoded samples
of a depth picture or data elements for decoding of a depth picture
are predicted or derived from some decoded samples of a texture
picture or data elements obtained in the decoding process of a
texture picture.
It has been found that a solution for some multiview 3D video (3DV)
applications is to have a limited number of input views, e.g. a
mono or a stereo view plus some supplementary data, and to render
(i.e. synthesize) all required views locally at the decoder side.
From several available technologies for view rendering, depth
image-based rendering (DIBR) has shown to be a competitive
alternative.
A simplified model of a DIBR-based 3DV system is shown in FIG. 5.
The input of a 3D video codec comprises a stereoscopic video and
corresponding depth information with stereoscopic baseline b0. Then
the 3D video codec synthesizes a number of virtual views between
two input views with baseline (bi<b0). DIBR algorithms may also
enable extrapolation of views that are outside the two input views
and not in between them. Similarly, DIBR algorithms may enable view
synthesis from a single view of texture and the respective depth
view. However, in order to enable DIBR-based multiview rendering,
texture data should be available at the decoder side along with the
corresponding depth data.
In such 3DV system, depth information is produced at the encoder
side in a form of depth pictures (also known as depth maps) for
each video frame. A depth map is an image with per-pixel depth
information. Each sample in a depth map represents the distance of
the respective texture sample from the plane on which the camera
lies. In other words, if the z axis is along the shooting axis of
the cameras (and hence orthogonal to the plane on which the cameras
lie), a sample in a depth map represents the value on the z
axis.
Depth information can be obtained by various means. For example,
depth of the 3D scene may be computed from the disparity registered
by capturing cameras. A depth estimation algorithm takes a
stereoscopic view as an input and computes local disparities
between the two offset images of the view. Each image is processed
pixel by pixel in overlapping blocks, and for each block of pixels
a horizontally localized search for a matching block in the offset
image is performed. Once a pixel-wise disparity is computed, the
corresponding depth value z is calculated by equation (1):
.DELTA..times..times. ##EQU00001##
where f is the focal length of the camera and b is the baseline
distance between cameras, as shown in FIG. 6. Further, d refers to
the disparity observed between the two cameras, and the camera
offset .DELTA.d reflects a possible horizontal misplacement of the
optical centers of the two cameras. However, since the algorithm is
based on block matching, the quality of a depth-through-disparity
estimation is content dependent and very often not accurate. For
example, no straightforward solution for depth estimation is
possible for image fragments that are featuring very smooth areas
with no textures or large level of noise.
Disparity or parallax maps, such as parallax maps specified in
ISO/IEC International Standard 23002-3, may be processed similarly
to depth maps. Depth and disparity have a straightforward
correspondence and they can be computed from each other through
mathematical equation.
The coding and decoding order of texture and depth view components
within an access unit is typically such that the data of a coded
view component is not interleaved by any other coded view
component, and the data for an access unit is not interleaved by
any other access unit in the bitstream/decoding order. For example,
there may be two texture and depth views (T0.sub.t, T1.sub.t,
T0.sub.t+1, T1.sub.t+1, T0.sub.t+2, T1.sub.t+2, D0.sub.t, D1.sub.t,
D0.sub.t+1, D1.sub.t+1, D0.sub.t+2, D1.sub.t+2) in different access
units (t, t+1, t+2), as illustrated in FIG. 7, where the access
unit t consisting of texture and depth view components
(T0.sub.t,T1.sub.t, D0.sub.t,D1.sub.t) precedes in bitstream and
decoding order the access unit t+1 consisting of texture and depth
view components (T0.sub.t+1, T1.sub.t+1, D0.sub.t+1,
D1.sub.t+1).
The coding and decoding order of view components within an access
unit may be governed by the coding format or determined by the
encoder. A texture view component may be coded before the
respective depth view component of the same view, and hence such
depth view components may be predicted from the texture view
components of the same view. Such texture view components may be
coded for example by MVC encoder and decoder by MVC decoder. An
enhanced texture view component refers herein to a texture view
component that is coded after the respective depth view component
of the same view and may be predicted from the respective depth
view component. The texture and depth view components of the same
access units are typically coded in view dependency order. Texture
and depth view components can be ordered in any order with respect
to each other as long as the ordering obeys the mentioned
constraints.
Texture views and depth views may be coded into a single bitstream
where some of the texture views may be compatible with one or more
video standards such as H.264/AVC and/or MVC. In other words, a
decoder may be able to decode some of the texture views of such a
bitstream and can omit the remaining texture views and depth
views.
In this context an encoder that encodes one or more texture and
depth views into a single H.264/AVC and/or MVC compatible bitstream
is also called as a 3DV-ATM encoder. Bitstreams generated by such
an encoder can be referred to as 3DV-ATM bitstreams. The 3DV-ATM
bitstreams may include some of the texture views that H.264/AVC
and/or MVC decoder cannot decode, and depth views. A decoder
capable of decoding all views from 3DV-ATM bitstreams may also be
called as a 3DV-ATM decoder.
3DV-ATM bitstreams can include a selected number of AVC/MVC
compatible texture views. The depth views for the AVC/MVC
compatible texture views may be predicted from the texture views.
The remaining texture views may utilize enhanced texture coding and
depth views may utilize depth coding.
Many video coding standards specify buffering models and buffering
parameters for the bit streams. Such buffering models may be called
Hypothetical Reference Decoder (HRD) or Video Buffer Verifier
(VBV). A standard compliant bit stream complies with the buffering
model with a set of buffering parameters specified in the
corresponding standard. Such buffering parameters for a bit stream
may be explicitly or implicitly signaled. `Implicitly signaled`
means that the default buffering parameter values according to the
profile and level apply. The HRD/VBV parameters are used, among
other things, to impose constraints on the bit rate variations of
compliant bit streams.
HRD conformance checking may concern for example the following two
types of bitstreams: The first such type of bitstream, called Type
I bitstream, is a NAL unit stream containing only the VCL NAL units
and filler data NAL units for all access units in the bitstream.
The second type of bitstream, called a Type II bitstream, may
contain, in addition to the VCL NAL units and filler data NAL units
for all access units in the bitstream, additional non-VCL NAL units
other than filler data NAL units and/or syntax elements such as
leading_zero.sub.--8 bits, zero_byte, start_code_prefix_one.sub.--3
bytes, and trailing_zero.sub.--8 bits that form a byte stream from
the NAL unit stream.
Two types of HRD parameters (NAL HRD parameters and VCL HRD
parameters) may be used. The HRD parameter may be indicated through
video usability information included in the sequence parameter set
syntax structure.
Sequence parameter sets and picture parameter sets referred to in
the VCL NAL units, and corresponding buffering period and picture
timing SEI messages may be conveyed to the HRD, in a timely manner,
either in the bitstream (by non-VCL NAL units), or by out-of-band
means externally from the bitstream e.g. using a signalling
mechanism, such as media parameters included in the media line of a
session description formatted e.g. according to the Session
Description Protocol (SDP). For the purpose of counting bits in the
HRD, only the appropriate bits that are actually present in the
bitstream may be counted. When the content of a non-VCL NAL unit is
conveyed for the application by some means other than presence
within the bitstream, the representation of the content of the
non-VCL NAL unit may or may not use the same syntax as would be
used if the non-VCL NAL unit were in the bitstream.
The HRD may contain a coded picture buffer (CPB), an instantaneous
decoding process, a decoded picture buffer (DPB), and output
cropping.
The CPB may operate on decoding unit basis. A decoding unit may be
an access unit or it may be a subset of an access unit, such as an
integer number of NAL units. The selection of the decoding unit may
be indicated by an encoder in the bitstream.
The HRD may operate as follows. Data associated with decoding units
that flow into the CPB according to a specified arrival schedule
may be delivered by the Hypothetical Stream Scheduler (HSS). The
arrival schedule may be determined by the encoder and indicated for
example through picture timing SEI messages, and/or the arrival
schedule may be derived for example based on a bitrate which may be
indicated for example as part of HRD parameters in video usability
information. The HRD parameter in video usability information may
contain many sets of parameters, each for different bitrate or
delivery schedule. The data associated with each decoding unit may
be removed and decoded instantaneously by the instantaneous
decoding process at CPB removal times. A CPB removal time may be
determined for example using an initial CPB buffering delay, which
may be determined by the encoder and indicated for example through
a buffering period SEI message, and differential removal delays
indicated for each picture for example though picture timing SEI
messages. Each decoded picture is placed in the DPB. A decoded
picture may be removed from the DPB at the later of the DPB output
time or the time that it becomes no longer needed for
inter-prediction reference. Thus, the operation of the CPB of the
HRD may comprise timing of bitstream arrival, timing of decoding
unit removal and decoding of decoding unit, whereas the operation
of the DPB of the HRD may comprise removal of pictures from the
DPB, picture output, and current decoded picture marking and
storage.
The HRD may be used to check conformance of bitstreams and
decoders.
Bitstream conformance requirements of the HRD may comprise for
example the following and/or alike. The CPB is required not to
overflow (relative to the size which may be indicated for example
within HRD parameters of video usability information) or underflow
(i.e. the removal time of a decoding unit cannot be smaller than
the arrival time of the last bit of that decoding unit). The number
of pictures in the DPB may be required to be smaller than or equal
to a certain maximum number, which may be indicated for example in
the sequence parameter set. All pictures used as prediction
references may be required to be present in the DPB. It may be
required that the interval for outputting consecutive pictures from
the DPB is not smaller than a certain minimum.
Decoder conformance requirements of the HRD may comprise for
example the following and/or alike. A decoder claiming conformance
to a specific profile and level may be required to decode
successfully all conforming bitstreams specified for decoder
conformance provided that all sequence parameter sets and picture
parameter sets referred to in the VCL NAL units, and appropriate
buffering period and picture timing SEI messages are conveyed to
the decoder, in a timely manner, either in the bitstream (by
non-VCL NAL units), or by external means. There may be two types of
conformance that can be claimed by a decoder: output timing
conformance and output order conformance.
To check conformance of a decoder, test bitstreams conforming to
the claimed profile and level may be delivered by a hypothetical
stream scheduler (HSS) both to the HRD and to the decoder under
test (DUT). All pictures output by the HRD may also be required to
be output by the DUT and, for each picture output by the HRD, the
values of all samples that are output by the DUT for the
corresponding picture may also be required to be equal to the
values of the samples output by the HRD.
For output timing decoder conformance, the HSS may operate e.g.
with delivery schedules selected from those indicated in the HRD
parameters of video usability information, or with "interpolated"
delivery schedules. The same delivery schedule may be used for both
the HRD and DUT. For output timing decoder conformance, the timing
(relative to the delivery time of the first bit) of picture output
may be required to be the same for both HRD and the DUT up to a
fixed delay.
For output order decoder conformance, the HSS may deliver the
bitstream to the DUT "by demand" from the DUT, meaning that the HSS
delivers bits (in decoding order) only when the DUT requires more
bits to proceed with its processing. The HSS may deliver the
bitstream to the HRD by one of the schedules specified in the
bitstream such that the bit rate and CPB size are restricted. The
order of pictures output may be required to be the same for both
HRD and the DUT.
In SVC, a buffering period SEI message that initiates the HRD is
chosen as follows. When an access unit contains one or more
buffering period SEI messages that are included in scalable nesting
SEI messages and are associated with values of DQId in the range of
((DQIdMax>>4)<<4) to
(((DQIdMax>>4)<<4)+15), inclusive, the last of these
buffering period SEI messages in decoding order is the buffering
period SEI message that initialises the HRD. Let hrdDQId be the
largest value of 16*sei_dependency_id[i]+sei_quality_id[i] that is
associated with the scalable nesting SEI message containing the
buffering period SEI message that initialises the HRD, let hrdDId
and hrdQId be equal to hrdDQId>>4 and hrdDQId & 15,
respectively, and let hrdTId be the value of sei_temporal_id that
is associated with the scalable nesting SEI message containing the
buffering period SEI message that initialises the HRD. In SVC, the
picture timing SEI messages that specify the removal timing of
access units from the CPB and output timing from the DPB are the
picture timing SEI messages that are included in scalable nesting
SEI messages associated with values of sei_dependency_id[i],
sei_quality_id[i], and sei_temporal_id equal to hrdDId, hrdQId, and
hrdTId, respectively. In SVC, the HRD parameter sets that are used
for conformance checking are the HRD parameter sets included in the
SVC video usability information extension of the active SVC
sequence parameter set that are associated with values of
vui_ext_dependency_id[i], vui_ext_quality_id[i], and
vui_ext_temporal_id[i] equal to hrdDId, hrdQId, and hrdTId,
respectively.
In SVC, the video usability information is extended to selectively
include timing information, HRD parameter sets, and the presence of
picture structure information for bitstream subsets of coded video
sequences (including the complete coded video sequences). Any
number of bitstream subsets for which the extended VUI is provided
may be selected by the encoder and indicated in the VUI parameters
extension. Each such bitstream subset is characterized by values of
dependency_id, quality_id and temporal_id, which are included in
the vui_ext_dependency_id[i], vui_ext_quality[i] and
vui_ext_temporal_id[i] syntax elements, respectively, where i is an
index for a bitstream subset. The bitstream subset with index i for
which the timing information, HRD parameter sets, and the presence
of picture structure information may be given can be obtained by
applying the sub-bitstream extraction process with
vui_ext_dependency_id[i], vui_ext_quality[i] and
vui_ext_temporal_id[i] as inputs.
A high level flow chart of an embodiment of an encoder 200 capable
of encoding texture views and depth views is presented in FIG. 8
and a decoder 210 capable of decoding texture views and depth views
is presented in FIG. 9. On these figures solid lines depict general
data flow and dashed lines show control information signaling. The
encoder 200 may receive texture components 201 to be encoded by a
texture encoder 202 and depth map components 203 to be encoded by a
depth encoder 204. When the encoder 200 is encoding texture
components according to AVC/MVC a first switch 205 may be switched
off. When the encoder 200 is encoding enhanced texture components
the first switch 205 may be switched on so that information
generated by the depth encoder 204 may be provided to the texture
encoder 202. The encoder of this example also comprises a second
switch 206 which may be operated as follows. The second switch 206
is switched on when the encoder is encoding depth information of
AVC/MVC views, and the second switch 206 is switched off when the
encoder is encoding depth information of enhanced texture views.
The encoder 200 may output a bitstream 207 containing encoded video
information.
The decoder 210 may operate in a similar manner but at least partly
in a reversed order. The decoder 210 may receive the bitstream 207
containing encoded video information. The decoder 210 comprises a
texture decoder 211 for decoding texture information and a depth
decoder 212 for decoding depth information. A third switch 213 may
be provided to control information delivery from the depth decoder
212 to the texture decoder 211, and a fourth switch 214 may be
provided to control information delivery from the texture decoder
211 to the depth decoder 212. When the decoder 210 is to decode
AVC/MVC texture views the third switch 213 may be switched off and
when the decoder 210 is to decode enhanced texture views the third
switch 213 may be switched on. When the decoder 210 is to decode
depth of AVC/MVC texture views the fourth switch 214 may be
switched on and when the decoder 210 is to decode depth of enhanced
texture views the fourth switch 214 may be switched off. The
Decoder 210 may output reconstructed texture components 215 and
reconstructed depth map components 216.
Many video encoders utilize the Lagrangian cost function to find
rate-distortion optimal coding modes, for example the desired
macroblock mode and associated motion vectors. This type of cost
function uses a weighting factor or 2 to tie together the exact or
estimated image distortion due to lossy coding methods and the
exact or estimated amount of information required to represent the
pixel/sample values in an image area. The Lagrangian cost function
may be represented by the equation: C=D+.lamda.R
where C is the Lagrangian cost to be minimised, D is the image
distortion (for example, the mean-squared error between the
pixel/sample values in original image block and in coded image
block) with the mode and motion vectors currently considered,
.lamda. is a Lagrangian coefficient and R is the number of bits
needed to represent the required data to reconstruct the image
block in the decoder (including the amount of data to represent the
candidate motion vectors).
A coding standard or specification may include a sub-bitstream
extraction process, and such is specified for example in SVC, MVC,
and HEVC. The sub-bitstream extraction process relates to
converting a bitstream by removing NAL units to a sub-bitstream.
The sub-bitstream still remains conforming to the standard. For
example, in a draft HEVC standard, the bitstream created by
excluding all VCL NAL units having a temporal_id greater than or
equal to a selected value and including all other VCL NAL units
remains conforming. Consequently, a picture having temporal_id
equal to TID does not use any picture having a temporal_id greater
than TID as inter prediction reference.
A first profile of a coding standard or specification, such as the
Baseline Profile of H.264/AVC, may be specified to include only
certain types of pictures or coding modes, such as intra (I) and
inter (P) pictures or coding modes. A second profile of the coding
standard or specification, such as the High Profile of H.264/AVC,
may be specified to include a greater variety of types of pictures
or coding modes, such as intra, inter, and bi-predictive (B)
pictures or coding modes. A bitstream conform to the second
profile, while a bitstream comprising a subset of the pictures may
also conform to the first profile. For example, a common group of
pictures pattern is IBBP, i.e., between each intra (I) or inter (P)
reference frame, there are two non-reference (B) frames. The base
layer in this case may consist of reference frames. The entire bit
stream may comply with the High Profile (which includes the B
picture feature), whereas the base layer bit stream may also comply
with the Baseline Profile (which excludes the B picture
feature).
A sub-bitstream extraction process may be used for multiple
purposes, some of which are described as examples below. In the
first example, a multimedia message is created for which the entire
bit stream complies to particular profile and level and the
bitstream subset consisting of the base layer complies with another
profile and level. At the time of creation, the originating
terminal does not know the capability of the receiving terminal. A
Multimedia Messaging Service Center (MMSC) or alike, in contrast,
knows the capability of the receiving terminal and is responsible
of adapting the message accordingly. In this example, the receiving
terminal is capable of decoding the bitstream subset consisting of
the base layer but not the entire bitstream. Consequently, the
adaptation process using the present invention requires merely
stripping off or removing the NAL units with a scalability layer
identifier indicating a higher layer than the base layer according
to a sub-bitstream extraction process.
In a second example, a scalable bit stream is coded and stored in a
streaming server. Profile and level and possibly also the HRD/VBV
parameters of each layer are signaled in the stored file. When
describing the available session, the server can create a
description e.g. according to the Session Description Protocol
(SDP) or Media Presentation Description (MPD) or alike for each
layer or alternative of the scalable bit stream in the same file
such that a streaming client can conclude whether there is an ideal
layer and choose an ideal layer for streaming playback according to
the SDP descriptions or alike. If the server has no prior knowledge
on receiver capabilities, it is advantageous to create multiple SDP
descriptions or alike from the same content, and these descriptions
are then called alternate. The client can then pick the description
that suits its capabilities the best. If the server knows the
receiver capabilities (e.g., using the UAProf mechanism specified
in 3GPP TS 26.234), the server preferably chooses the most suitable
profile and level for the receiver among the profiles and levels of
the entire bit stream and all substreams. A sub-bitstream
extraction process may be carried out to conclude data to be
transmitted such that it matches the chosen SDP description or
alike.
In a third example, a stream such as that described in the second
example, is multicast or broadcast to multiple terminals. The
multicast/broadcast server can announce all the available layers or
decoding and playback alternatives, each of which is characterized
by a combination of profile and level and possibly also HRD/VBV
parameters. The client can then know from the broadcast/multicast
session announcement whether there is an ideal layer for it and
choose an ideal layer for playback. A sub-bitstream extraction
process can be used to conclude the elementary data units, such as
NAL units, to be transmitted within each multicast group or
alike.
In a fourth example of the use of the present invention, for local
playback applications, even though the entire signaled stream
cannot be decoded, it is still possible to decode and enjoy part of
the stream. Typically if the player gets to know that the entire
stream is of a set of profile and level and HRD/VBV parameters it
is not capable to decode, it just gives up the decoding and
playback. Alternatively or in addition, a user may have selected a
fast-forward or fast-backward play operation, and the player may
choose a level such that it can decode the data faster than
real-time. A sub-bitstream extraction process may be carried out
when the player has chosen a layer that is not the highest layer of
the bitstream.
FIG. 1 shows a block diagram of a video coding system according to
an example embodiment as a schematic block diagram of an exemplary
apparatus or electronic device 50, which may incorporate a codec
according to an embodiment of the invention. FIG. 2 shows a layout
of an apparatus according to an example embodiment. The elements of
FIGS. 1 and 2 will be explained next.
The electronic device 50 may for example be a mobile terminal or
user equipment of a wireless communication system. However, it
would be appreciated that embodiments of the invention may be
implemented within any electronic device or apparatus which may
require encoding and decoding or encoding or decoding video images.
For example, in some embodiments, the apparatus may be embodied as
a chip or chip set (which may in turn be employed at one of the
devices mentioned above). In other words, the apparatus may
comprise one or more physical packages (e.g., chips) including
materials, components and/or wires on a structural assembly (e.g.,
a baseboard). The structural assembly may provide physical
strength, conservation of size, and/or limitation of electrical
interaction for component circuitry comprised thereon. The
apparatus may therefore, in some cases, be configured to implement
an embodiment of the present invention on a single chip or as a
single "system on a chip." As such, in some cases, a chip or
chipset may constitute means for performing one or more operations
for providing the functionalities described herein.
The apparatus 50 may comprise a housing 30 for incorporating and
protecting the device. The apparatus 50 further may comprise a
display 32 in the form of a liquid crystal display. In other
embodiments of the invention the display may be any suitable
display technology suitable to display an image or video. The
apparatus 50 may further comprise a keypad 34. In other embodiments
of the invention any suitable data or user interface mechanism may
be employed. For example the user interface may be implemented as a
virtual keyboard or data entry system as part of a touch-sensitive
display. The apparatus may comprise a microphone 36 or any suitable
audio input which may be a digital or analogue signal input. The
apparatus 50 may further comprise an audio output device which in
embodiments of the invention may be any one of: an earpiece 38,
speaker, or an analogue audio or digital audio output connection.
The apparatus 50 may also comprise a battery 40 (or in other
embodiments of the invention the device may be powered by any
suitable mobile energy device such as solar cell, fuel cell or
clockwork generator). The apparatus may further comprise an
infrared port 42 for short range line of sight communication to
other devices. In other embodiments the apparatus 50 may further
comprise any suitable short range communication solution such as
for example a Bluetooth wireless connection or a USB/firewire wired
connection.
The apparatus 50 may comprise a controller or processor (with
controller and processor being used synonomously herein with either
or both being designated as 56) for controlling the apparatus 50.
The controller 56 may be connected to memory 58 which in
embodiments of the invention may store both data in the form of
image and audio data and/or may also store instructions for
implementation on the controller 56. The controller 56 may further
be connected to codec circuitry 54 suitable for carrying out coding
and decoding of audio and/or video data or assisting in coding and
decoding carried out by the controller 56.
The processor 56 may be embodied in a number of different ways. For
example, the processor may be embodied as one or more of various
hardware processing means such as a coprocessor, a microprocessor,
a controller, a digital signal processor (DSP), a processing
element with or without an accompanying DSP, or various other
processing circuitry including integrated circuits such as, for
example, an ASIC (application specific integrated circuit), an FPGA
(field programmable gate array), a microcontroller unit (MCU), a
hardware accelerator, a special-purpose computer chip, or the like.
As such, in some embodiments, the processor may comprise one or
more processing cores configured to perform independently. A
multi-core processor may enable multiprocessing within a single
physical package. Additionally or alternatively, the processor may
comprise one or more processors configured in tandem via the bus to
enable independent execution of instructions, pipelining and/or
multithreading.
In an example embodiment, the processor 56 may be configured to
execute instructions stored in the memory device 58 or otherwise
accessible to the processor. Alternatively or additionally, the
processor may be configured to execute hard coded functionality. As
such, whether configured by hardware or software methods, or by a
combination thereof, the processor may represent an entity (e.g.,
physically embodied in circuitry) capable of performing operations
according to an embodiment of the present invention while
configured accordingly. Thus, for example, when the processor is
embodied as an ASIC, FPGA or the like, the processor may be
specifically configured hardware for conducting the operations
described herein. Alternatively, as another example, when the
processor is embodied as an executor of software instructions, the
instructions may specifically configure the processor to perform
the algorithms and/or operations described herein when the
instructions are executed. However, in some cases, the processor
may be a processor of a specific device (e.g., a computing device)
adapted for employing an embodiment of the present invention by
further configuration of the processor by instructions for
performing the algorithms and/or operations described herein. The
processor may comprise, among other things, a clock, an arithmetic
logic unit (ALU) and logic gates configured to support operation of
the processor.
The memory 58 may comprise, for example, a non-transitory memory,
such as one or more volatile and/or non-volatile memories. In other
words, for example, the memory device may be an electronic storage
device (e.g., a computer readable storage medium) comprising gates
configured to store data (e.g., bits) that may be retrievable by a
machine (e.g., a computing device like the processor). The memory
device may be configured to store information, data, applications,
instructions or the like for enabling the apparatus to carry out
various functions in accordance with example embodiments of the
present invention. For example, the memory device could be
configured to buffer input data for processing by the processor.
Additionally or alternatively, the memory device could be
configured to store instructions for execution by the processor 56.
The apparatus 50 may further comprise a card reader 48 and a smart
card 46, for example a UICC and UICC reader for providing user
information and being suitable for providing authentication
information for authentication and authorization of the user at a
network.
The apparatus 50 may comprise a communication interface which may
be any means such as a device or circuitry embodied in either
hardware or a combination of hardware and software that is
configured to receive and/or transmit data from/to the apparatus.
In this regard, the communication interface may comprise, for
example, radio interface circuitry 52 connected to the controller
56 and suitable for generating wireless communication signals for
example for communication with a cellular communications network, a
wireless communications system or a wireless local area network.
The communication interface of the apparatus 50 may further
comprise an antenna 44 connected to the radio interface circuitry
52 for transmitting radio frequency signals generated at the radio
interface circuitry 52 to other apparatus(es) and for receiving
radio frequency signals from other apparatus(es). In some
environments, the communication interface may alternatively or also
support wired communication. As such, for example, the
communication interface may comprise a communication modem and/or
other hardware/software for supporting communication via cable,
digital subscriber line (DSL), USB or other mechanisms.
In some embodiments of the invention, the apparatus 50 comprises a
camera capable of recording or detecting individual frames which
are then passed to the codec 54 or controller for processing. In
some embodiments of the invention, the apparatus may receive the
video image data for processing from another device prior to
transmission and/or storage. In some embodiments of the invention,
the apparatus 50 may receive either wirelessly or by a wired
connection the image for coding/decoding.
FIG. 3 shows an arrangement for video coding comprising a plurality
of apparatuses, networks and network elements according to an
example embodiment. With respect to FIG. 3, an example of a system
within which embodiments of the present invention can be utilized
is shown. The system 10 comprises multiple communication devices
which can communicate through one or more networks. The system 10
may comprise any combination of wired or wireless networks
including, but not limited to a wireless cellular telephone network
(such as a GSM, UMTS, CDMA network etc), a wireless local area
network (WLAN) such as defined by any of the IEEE 802.x standards,
a Bluetooth personal area network, an Ethernet local area network,
a token ring local area network, a wide area network, and the
Internet.
The system 10 may include both wired and wireless communication
devices or apparatus 50 suitable for implementing embodiments of
the invention. For example, the system shown in FIG. 3 shows a
mobile telephone network 11 and a representation of the internet
28. Connectivity to the internet 28 may include, but is not limited
to, long range wireless connections, short range wireless
connections, and various wired connections including, but not
limited to, telephone lines, cable lines, power lines, and similar
communication pathways.
The example communication devices shown in the system 10 may
include, but are not limited to, an electronic device or apparatus
50, a combination of a personal digital assistant (PDA) and a
mobile telephone 14, a PDA 16, an integrated messaging device (IMD)
18, a desktop computer 20, a notebook computer 22. The apparatus 50
may be stationary or mobile when carried by an individual who is
moving. The apparatus 50 may also be located in a mode of transport
including, but not limited to, a car, a truck, a taxi, a bus, a
train, a boat, an airplane, a bicycle, a motorcycle or any similar
suitable mode of transport.
Some or further apparatuses may send and receive calls and messages
and communicate with service providers through a wireless
connection 25 to a base station 24. The base station 24 may be
connected to a network server 26 that allows communication between
the mobile telephone network 11 and the internet 28. The system may
include additional communication devices and communication devices
of various types.
The communication devices may communicate using various
transmission technologies including, but not limited to, code
division multiple access (CDMA), global systems for mobile
communications (GSM), universal mobile telecommunications system
(UMTS), time divisional multiple access (TDMA), frequency division
multiple access (FDMA), transmission control protocol-internet
protocol (TCP-IP), short messaging service (SMS), multimedia
messaging service (MMS), email, instant messaging service (IMS),
Bluetooth, IEEE 802.11 and any similar wireless communication
technology. A communications device involved in implementing
various embodiments of the present invention may communicate using
various media including, but not limited to, radio, infrared,
laser, cable connections, and any suitable connection.
FIGS. 4a and 4b show block diagrams for video encoding and decoding
according to an example embodiment.
FIG. 4a shows the encoder as comprising a pixel predictor 302,
prediction error encoder 303 and prediction error decoder 304. FIG.
4a also shows an embodiment of the pixel predictor 302 as
comprising an inter-predictor 306, an intra-predictor 308, a mode
selector 310, a filter 316, and a reference frame memory 318. In
this embodiment the mode selector 310 comprises a block processor
381 and a cost evaluator 382. The encoder may further comprise an
entropy encoder 330 for entropy encoding the bit stream.
FIG. 4b depicts an embodiment of the inter predictor 306. The inter
predictor 306 comprises a reference frame selector 360 for
selecting reference frame or frames, a motion vector definer 361, a
prediction list former 363 and a motion vector selector 364. These
elements or some of them may be part of a prediction processor 362
or they may be implemented by using other means.
The pixel predictor 302 receives the image 300 to be encoded at
both the inter-predictor 306 (which determines the difference
between the image and a motion compensated reference frame 318) and
the intra-predictor 308 (which determines a prediction for an image
block based only on the already processed parts of a current frame
or picture). The output of both the inter-predictor and the
intra-predictor are passed to the mode selector 310. Both the
inter-predictor 306 and the intra-predictor 308 may have more than
one intra-prediction modes. Hence, the inter-prediction and the
intra-prediction may be performed for each mode and the predicted
signal may be provided to the mode selector 310. The mode selector
310 also receives a copy of the image 300.
The mode selector 310 determines which encoding mode to use to
encode the current block. If the mode selector 310 decides to use
an inter-prediction mode it will pass the output of the
inter-predictor 306 to the output of the mode selector 310. If the
mode selector 310 decides to use an intra-prediction mode it will
pass the output of one of the intra-predictor modes to the output
of the mode selector 310.
The mode selector 310 may use, in the cost evaluator block 382, for
example Lagrangian cost functions to choose between coding modes
and their parameter values, such as motion vectors, reference
indexes, and intra prediction direction, typically on block basis.
This kind of cost function uses a weighting factor lambda to tie
together the (exact or estimated) image distortion due to lossy
coding methods and the (exact or estimated) amount of information
that is required to represent the pixel values in an image area:
C=D+lambda.times.R, where C is the Lagrangian cost to be minimized,
D is the image distortion (e.g. Mean Squared Error) with the mode
and their parameters, and R the number of bits needed to represent
the required data to reconstruct the image block in the decoder
(e.g. including the amount of data to represent the candidate
motion vectors).
The output of the mode selector is passed to a first summing device
321. The first summing device may subtract the pixel predictor 302
output from the image 300 to produce a first prediction error
signal 320 which is input to the prediction error encoder 303.
The pixel predictor 302 further receives from a preliminary
reconstructor 339 the combination of the prediction representation
of the image block 312 and the output 338 of the prediction error
decoder 304. The preliminary reconstructed image 314 may be passed
to the intra-predictor 308 and to a filter 316. The filter 316
receiving the preliminary representation may filter the preliminary
representation and output a final reconstructed image 340 which may
be saved in a reference frame memory 318. The reference frame
memory 318 may be connected to the inter-predictor 306 to be used
as the reference image against which the future image 300 is
compared in inter-prediction operations. In many embodiments the
reference frame memory 318 may be capable of storing more than one
decoded picture, and one or more of them may be used by the
inter-predictor 306 as reference pictures against which the future
images 300 are compared in inter prediction operations. The
reference frame memory 318 may in some cases be also referred to as
the Decoded Picture Buffer.
The operation of the pixel predictor 302 may be configured to carry
out any known pixel prediction algorithm known in the art.
The pixel predictor 302 may also comprise a filter 385 to filter
the predicted values before outputting them from the pixel
predictor 302.
The operation of the prediction error encoder 302 and prediction
error decoder 304 will be described hereafter in further detail. In
the following examples the encoder generates images in terms of
16.times.16 pixel macroblocks which go to form the full image or
picture. However, it is noted that FIG. 4a is not limited to block
size 16.times.16, but any block size and shape can be used
generally, and likewise FIG. 4a is not limited to partitioning of a
picture to macroblocks but any other picture partitioning to
blocks, such as coding units, may be used. Thus, for the following
examples the pixel predictor 302 outputs a series of predicted
macroblocks of size 16.times.16 pixels and the first summing device
321 outputs a series of 16.times.16 pixel residual data macroblocks
which may represent the difference between a first macroblock in
the image 300 against a predicted macroblock (output of pixel
predictor 302).
The prediction error encoder 303 comprises a transform block 342
and a quantizer 344. The transform block 342 transforms the first
prediction error signal 320 to a transform domain. The transform
is, for example, the DCT transform or its variant. The quantizer
344 quantizes the transform domain signal, e.g. the DCT
coefficients, to form quantized coefficients.
The prediction error decoder 304 receives the output from the
prediction error encoder 303 and produces a decoded prediction
error signal 338 which when combined with the prediction
representation of the image block 312 at the second summing device
339 produces the preliminary reconstructed image 314. The
prediction error decoder may be considered to comprise a
dequantizer 346, which dequantizes the quantized coefficient
values, e.g. DCT coefficients, to reconstruct the transform signal
approximately and an inverse transformation block 348, which
performs the inverse transformation to the reconstructed transform
signal wherein the output of the inverse transformation block 348
contains reconstructed block(s). The prediction error decoder may
also comprise a macroblock filter (not shown) which may filter the
reconstructed macroblock according to further decoded information
and filter parameters.
In the following the operation of an example embodiment of the
inter predictor 306 will be described in more detail. The inter
predictor 306 receives the current block for inter prediction. It
is assumed that for the current block there already exists one or
more neighboring blocks which have been encoded and motion vectors
have been defined for them. For example, the block on the left side
and/or the block above the current block may be such blocks.
Spatial motion vector predictions for the current block can be
formed e.g. by using the motion vectors of the encoded neighboring
blocks and/or of non-neighbor blocks in the same slice or frame,
using linear or non-linear functions of spatial motion vector
predictions, using a combination of various spatial motion vector
predictors with linear or non-linear operations, or by any other
appropriate means that do not make use of temporal reference
information. It may also be possible to obtain motion vector
predictors by combining both spatial and temporal prediction
information of one or more encoded blocks. These kinds of motion
vector predictors may also be called as spatio-temporal motion
vector predictors.
Reference frames used in encoding may be stored to the reference
frame memory. Each reference frame may be included in one or more
of the reference picture lists, within a reference picture list,
each entry has a reference index which identifies the reference
frame. When a reference frame is no longer used as a reference
frame it may be removed from the reference frame memory or marked
as "unused for reference" or a non-reference frame wherein the
storage location of that reference frame may be occupied for a new
reference frame.
As described above, an access unit may contain slices of different
component types (e.g. primary texture component, redundant texture
component, auxiliary component, depth/disparity component), of
different views, and of different scalable layers.
It has been proposed that at least a subset of syntax elements that
have conventionally been included in a slice header are included in
a GOS (Group of Slices) parameter set by an encoder. An encoder may
code a GOS parameter set as a NAL unit. GOS parameter set NAL units
may be included in the bitstream together with for example coded
slice NAL units, but may also be carried out-of-band as described
earlier in the context of other parameter sets.
The GOS parameter set syntax structure may include an identifier,
which may be used when referring to a particular GOS parameter set
instance for example from a slice header or another GOS parameter
set. Alternatively, the GOS parameter set syntax structure does not
include an identifier but an identifier may be inferred by both the
encoder and decoder for example using the bitstream order of GOS
parameter set syntax structures and a pre-defined numbering
scheme.
The encoder and the decoder may infer the contents or the instance
of GOS parameter set from other syntax structures already encoded
or decoded or present in the bitstream. For example, the slice
header of the texture view component of the base view may
implicitly form a GOS parameter set. The encoder and decoder may
infer an identifier value for such inferred GOS parameter sets. For
example, the GOS parameter set formed from the slice header of the
texture view component of the base view may be inferred to have
identifier value equal to 0.
A GOS parameter set may be valid within a particular access unit
associated with it. For example, if a GOS parameter set syntax
structure is included in the NAL unit sequence for a particular
access unit, where the sequence is in decoding or bitstream order,
the GOS parameter set may be valid from its appearance location
until the end of the access unit. Alternatively, a GOS parameter
set may be valid for many access units.
The encoder may encode many GOS parameter sets for an access unit.
The encoder may determine to encode a GOS parameter set if it is
known, expected, or estimated that at least a subset of syntax
element values in a slice header to be coded would be the same in a
subsequent slice header.
A limited numbering space may be used for the GOS parameter set
identifier. For example, a fixed-length code may be used and may be
interpreted as an unsigned integer value of a certain range. The
encoder may use a GOS parameter set identifier value for a first
GOS parameter set and subsequently for a second GOS parameter set,
if the first GOS parameter set is subsequently not referred to for
example by any slice header or GOS parameter set. The encoder may
repeat a GOS parameter set syntax structure within the bitstream
for example to achieve a better robustness against transmission
errors.
In many embodiments, syntax elements which may be included in a GOS
parameter set are conceptually collected in sets of syntax
elements. A set of syntax elements for a GOS parameter set may be
formed for example on one or more of the following basis: Syntax
elements indicating a scalable layer and/or other scalability
features Syntax elements indicating a view and/or other multiview
features Syntax elements related to a particular component type,
such as depth/disparity Syntax elements related to access unit
identification, decoding order and/or output order and/or other
syntax elements which may stay unchanged for all slices of an
access unit Syntax elements which may stay unchanged in all slices
of a view component Syntax elements related to reference picture
list modification Syntax elements related to the reference picture
set used Syntax elements related to decoding reference picture
marking Syntax elements related to prediction weight tables for
weighted prediction Syntax elements for controlling deblocking
filtering Syntax elements for controlling adaptive loop filtering
Syntax elements for controlling sample adaptive offset Any
combination of sets above
For each syntax element set, the encoder may have one or more of
the following options when coding a GOS parameter set:
The syntax element set may be coded into a GOS parameter set syntax
structure, i.e. coded syntax element values of the syntax element
set may be included in the GOS parameter set syntax structure. The
syntax element set may be included by reference into a GOS
parameter set. The reference may be given as an identifier to
another GOS parameter set. The encoder may use a different
reference GOS parameter set for different syntax element sets. The
syntax element set may be indicated or inferred to be absent from
the GOS parameter set.
The options from which the encoder is able to choose for a
particular syntax element set when coding a GOS parameter set may
depend on the type of the syntax element set. For example, a syntax
element set related to scalable layers may always be present in a
GOS parameter set, while the set of syntax elements which may stay
unchanged in all slices of a view component may not be available
for inclusion by reference but may be optionally present in the GOS
parameter set and the syntax elements related to reference picture
list modification may be included by reference in, included as such
in, or be absent from a GOS parameter set syntax structure. The
encoder may encode indications in the bitstream, for example in a
GOS parameter set syntax structure, which option was used in
encoding. The code table and/or entropy coding may depend on the
type of the syntax element set. The decoder may use, based on the
type of the syntax element set being decoded, the code table and/or
entropy decoding that is matched with the code table and/or entropy
encoding used by the encoder.
The encoder may have multiple means to indicate the association
between a syntax element set and the GOS parameter set used as the
source for the values of the syntax element set. For example, the
encoder may encode a loop of syntax elements where each loop entry
is encoded as syntax elements indicating a GOS parameter set
identifier value used as a reference and identifying the syntax
element sets copied from the reference GOP parameter set. In
another example, the encoder may encode a number of syntax
elements, each indicating a GOS parameter set. The last GOS
parameter set in the loop containing a particular syntax element
set is the reference for that syntax element set in the GOS
parameter set the encoder is currently encoding into the bitstream.
The decoder parses the encoded GOS parameter sets from the
bitstream accordingly so as to reproduce the same GOS parameter
sets as the encoder.
It has been proposed to have a partial updating mechanism for the
Adaptation Parameter Set in order to reduce the size of APS NAL
units and hence to spend a smaller bitrate for conveying APS NAL
units. Although the APS provides an effective approach to share
picture-adaptive information common at the slice level, coding of
APS NAL units independently may be suboptimal when only a part of
the APS parameters changes compared to one or more earlier
Adaptation Parameter Sets.
In document JCTVC-H0069
(http://phenix.int-evry.fr/jct/doc_end_user/documents/8_San
%20Jose/wg11/JCTVC-H0069-v4.zip), the APS syntax structure is
subdivided into a number of groups of syntax elements, each
associated with a certain coding technology (such as Adaptive
In-Loop Filter (ALF), or Sample Adaptive Offset (SAO)). Each of
these groups in the APS syntax structure is preceded by a flag
indicating their respective presence. The APS syntax structure also
includes a conditional reference to another APS. A ref aps_flag
signals the presence of a reference ref_aps_id referred to by the
current APS. With this link mechanism, a linked list of multiple
APSs can be created. The decoding process during APS activation
uses the reference in the slice header to address the first APS of
the linked list. Those groups of syntax elements for which the
associated flag (such as the
aps_adaptive_loop_filter_data_present_flag) is set, are decoded
from the subject APS. After this decoding, the linked list is
followed to the next linked APS (if any--as indicated by ref
aps_flag equal to 1). Only those groups which were not signaled as
present previously, but are signaled as present in the current APS,
are decoded from the current APS. The mechanism continues along the
list of linked APSs until one of three conditions are met: (1) all
required groups of syntax elements (as indicated by SPS, PPS, or
profile/level) have been decoded from the linked APS chain, (2) the
end of the list is detected, and (3) a fixed, probably
profile-dependent, number of links have been followed--the number
could be as small as one. If there are any groups that are not
signaled as present in any of the linked APSs, the related decoding
tool is not used for this picture. Condition (2) prevents circular
referencing loops. The complexity of the referencing mechanism is
further limited by the finite size of the APS table. In
JCTVC-H0069, the de-referencing, i.e. resolving the source for each
group of syntax elements, is proposed to be performed each time an
APS is activated, typically once at the beginning of decoding a
slice.
It has also been proposed in document JCTVC-H0255 to include
multiple APS identifiers in the slice header, each specifying the
source APS for certain groups of syntax elements, e.g. one APS
being the source for quantization matrices and another APS being
the source for ALF parameters. In document JCTVC-H0381, a "copy"
flag for each type of APS parameters was proposed, which allows
copying that type of APS parameters from another APS. In document
JCTVC-H0505, a Group Parameter Set (GPS) was introduced, which
collects parameter set identifiers of different types of parameter
sets (SPS, PPS, APS) and may contain multiple APS parameter set
identifiers. Furthermore, it was proposed in JCTVC-H0505 that a
slice header contains a GPS identifier to be used for decoding of
the slice instead of individual PPS, and APS identifiers.
An APS partial updating mechanism has been proposed also in
document JCTVC-I0070 as outlined in the following. The encoder
specifies the value range of aps_id values with the max_aps_id
syntax element within the sequence parameter set. In other words,
the value of aps_id may be in the range of 0 to max_aps_id,
inclusive. The encoder also specifies a range of aps_id values that
are considered "used" and indicates that range to the decoder in
max_aps_id_diff. The range is relative to the latest received APS
NAL unit and hence specifies a kind of a sliding window of valid
aps_id values. APS NAL units that have an aps_id value outside the
sliding-window range are considered "unused" and a new APS NAL unit
with the same aps_id value may be transmitted. Each received APS
NAL unit updates the position of the sliding-window range of aps_id
values considered "used". It is recommended that encoders increment
aps_id value by 1 relative to that in the previous APS NAL unit in
decoding order. As aps_id values may wrap over, modulo arithmetic
is used in determining the aps_id values within the sliding-window
range. Thanks to the controlled marking which aps_id values can be
reused for new APS NAL units, the number of APSes is limited to
(max_aps_id_diff+1) and losses of APS NAL units e.g. during
transmission can be detected. It has been proposed in JCTVC-I0070
that the APS syntax includes a possibility to copy any group of
syntax elements (QM, deblocking filter, SAO, ALF) from either the
same APS or from different APSes, indicated by their aps_id value,
while the referred APSes are required to be marked as "used". The
partial update references are proposed to be resolved at the time
of decoding the APS NAL unit, i.e. the APS is decoded by copying
the referenced data from the indicated source APS into the APS
being decoded. In other words, the references to other APS NAL
units are resolved only once.
While background has been explained above with relation to SVC, for
example when it comes to parameter set activation, SEI messages HRD
parameters, as well as buffering period and picture timing SEI
messages, it should be understood that similar processes and syntax
structures exist also for MVC.
We have discovered at least the following challenges and
shortcomings in the design of SVC and MVC: 1. In a sequence
parameter set RBSP that is referred to by the base layer, the level
has to be set to cover also the bitrate caused by the
enhancement-layer NAL units, because H.264/AVC decoders without SVC
capability will activate that sequence parameter set RBSP and hence
the bitrate inferred by the level should cover the bitrate of the
entire bitstream. Similarly, in a sequence parameter set RBSP that
is referred to by the base view, the level has to be set to cover
also the bitrate caused by the non-base-view NAL units, because
H.264/AVC decoders without MVC capability will activate that
sequence parameter set RBSP. The level may therefore be
unnecessarily high for decoders that can access the bitstream fast
enough and skip enhancement-layer NAL units or non-base-view NAL
units, e.g. typically decoders reading a bitstream from a file. A
level for the bitstream subset consisting of the base layer only
may be indicated by the scalability information SEI message (for
SVC) or view scalability information SEI message (for MVC), but
H.264/AVC decoders are unlikely to decode those SEI messages,
because they have been specified in the SVC and MVC extensions,
respectively. 2. As described above, only the profile and level
related indications, profile compatibility indications, HRD
parameters, and picture timing related indications may differ in
active SVC sequence parameter set RBSP and active layer SVC
sequence parameter set RBSPs. Similarly, most but not all syntax
elements remain unchanged in active view sequence parameter set
RBSPs when compared to active sequence parameter set RBSPs. Thus,
sequence parameter set RBSPs duplicate information, i.e. have the
same values for respective syntax elements. One approach for
reducing this overhead caused by duplicate information in sequence
parameter set RBSPs could be to re-use the same sequence parameter
set RBSPs across layers or views, i.e. to activate the same
sequence parameter set RBSP for more than one layer or view.
However, then the level would be suboptimally selected and HRD
parameters would be suboptimally selected or not present (and then
would not help the decoder in buffer initialization, buffering,
picture timing, and so on). 3. Decoder conformance to profiles is
limited to a maximum of two profiles in the following sense: the
base layer or view may conform to a profile specified in Annex A of
the H.264/AVC standard, i.e. one of the profiles for non-scalable
(and non-multiview) coding. The other layers may conform to a
profile specified in Annex G of the H.264/AVC standard, i.e. one of
the profiles for scalable coding. Similarly, the other views may
conform to a profile specified in Annex H of the H.264/AVC
standard, i.e. one of the profiles for multiview coding. The values
of profile_idc and level_idc in an SVC sequence parameter set RBSP
are those that would be valid if the SVC sequence parameter set
RBSP is the active SVC sequence parameter set. Similarly. the
values of profile_idc and level_idc in an MVC sequence parameter
set RBSP are those that would be valid if the MVC sequence
parameter set RBSP is the active MVC sequence parameter set.
However, the bitstream may, in general, contain additional types of
scalability, such as coded depth views, which a decoder conforming
to Annex G and Annex H would not be able to decode. A decoder
conforming to Annex G or Annex H is not aware whether or not NAL
units of such additional types of scalability are present in the
bitstream, as NAL units of such additional types of scalability
would use an extension mechanism, such as previously reserved NAL
unit type values, which a decoder conforming to Annex G or Annex H
would ignore. However, the NAL units of such additional types of
scalability would affect the bitrate of the bitstream and
potentially the HRD parameters, such as an initial CPB buffering
delay or time. Even if the bitstream contains NAL of such
additional type of scalability, a decoder conforming to Annex G or
Annex H would still active that SVC or MVC sequence parameter set
RBSPs according to the SVC or MVC standard and assume conformance
according to the SVC or MVC standard. Consequently, the level_idc
should be set sub-optimally to cover also the bitrate of the
non-SVC or non-MVC data in the bitstream. Moreover, the HRD
parameters should cover the non-SVC or non-MVC data in the
bitstream. 4. If sub-bitstream extraction is done according to the
process specified in Annex G or Annex H of the H.264/AVC standard
for a bitstream containing additional types of scalability that a
decoder conforming to Annex G or Annex H of the H.264/AVC standard
cannot decode, the NAL units containing data for such additional
types of scalability are kept unchanged in the resulting
sub-bitstream. However, the data for such additional types of
scalability may have some of the same scalability dimensions as
present in Annex G or Annex H. For example, in 3DV-ATM, the coded
depth views are associated with temporal_id and view_id as texture
views coded with MVC. Therefore sub-bitstream extraction based on
temporal_id and/or view_id should also concern depth views.
However, if a sub-bitstream extraction process using the existing
scalability dimensions, such as temporal_id and/or view_id, is used
also for NAL units containing such additional types of scalability,
such as depth views, the level indicator and HRD parameters present
for Annex G or Annex H would be outdated, as they assume a
sub-bitstream extraction to be done according to the process
specified in Annex G or Annex H, i.e. keeping the NAL units
containing such additional types of scalability, such as depth
views, present in the resulting sub-bitstream. 5. Decoders
conforming to a profile specified in Annex A of the H.264/AVC
standard, i.e. one of the profiles for non-scalable (and
non-multiview) coding consider coded slices of SVC and MVC (i.e.,
NAL units of nal_unit_type equal to 20) as non-VCL NAL units,
whereas decoders conforming to a profile specified in Annex G or
Annex H consider them as VCL NAL units. Therefore, the VCL and NAL
HRD parameters differ. For example, the semantics of the MVC video
usability information extension and the MVC scalable nesting SEI
message used to carry picture timing and buffering period SEI
messages rely on the sub-bitstream extraction process specified in
subclause H.8.5.3, which treats NAL units of nal_unit_type equal to
21 as non-VCL NAL units and does not perform temporal_id and
view_id based extraction for them. Hence, no proper HRD parameters
can be conveyed for sub-bitstreams consisting of texture views
only
In 3DV-ATM some of the above-mentioned shortcomings can be avoided
as follows. It is proposed that in some embodiments the texture
sub-bitstream HRD parameters are conveyed for example in a second
instance of mvc_vui_parameters_extension( ) for example within a
3DVC sequence parameter set and HRD parameters within or similar to
picture timing and buffering period SEI messages are conveyed in a
specific data structure that can be limited to be valid or pertain
to a sub-bitstream containing only texture views, such as a 3DVC
texture sub-bitstream HRD nesting SEI message. If a texture
sub-bitstream is extracted using the sub-bitstream extraction
process, these nested HRD parameters and SEI messages may replace
the respective MVC HRD parameters and SEI messages, which, as
stated above, assume the presence of NAL units of nal_unit_type 21
as non-VCL NAL units.
For example, the following subset sequence parameter syntax
structure may be used for 3DVC sequence parameter set RBSPs.
TABLE-US-00007 subset_seq_parameter_set_rbsp( ) { C Descriptor
seq_parameter_set_data( ) 0 if( profile_idc = = 83 || profile_idc =
= 86 ) { seq_parameter_set_svc_extension( ) /* specified in Annex G
*/ 0 svc_vui_parameters_present_flag 0 u(1) if(
svc_vui_parameters_present_flag = = 1 )
svc_vui_parameters_extension( ) /* specified in Annex G */ 0 } else
if( profile_idc = = 118 || profile_idc = = 128 ) { bit_equal_to_one
/* equal to 1 */ 0 f(1) seq_parameter_set_mvc_extension( ) /*
specified in Annex H */ 0 mvc_vui_parameters_present_flag 0 u(1)
if( mvc_vui_parameters_present_flag = = 1 )
mvc_vui_parameters_extension( ) /* specified in Annex H */ 0 } if(
profile_idc = = 138 ) { bit_equal_to_one /* equal to 1 */ 0 f(1)
seq_parameter_set_mvc_extension( ) /* specified in Annex H */ 0
seq_parameter_set_3dvc_extension( ) 0
3dvc_vui_parameters_present_flag 0 u(1) if(
3dvc_vui_parameters_present_flag = = 1 )
mvc_vui_parameters_extension( ) 0
texture_vui_parameters_present_flag 0 u(1) if(
texture_vui_parameters_present_flag = = 1 )
mvc_vui_parameters_extension( ) 0 } additional_extension3_flag 0
u(1) if( additional_extension3_flag = = 1 ) while( more_rbsp_data(
) ) additional_extension3_data_flag 0 u(1) rbsp_trailing_bits( ) 0
}
In the presented example syntax structure, certain syntax elements
may be specified as follows. 3dvc_vui_parameters_present_flag equal
to 0 specifies that the syntax structure
mvc_vui_parameters_extension( ) corresponding to 3DVC VUI
parameters extension is not present.
3dvc_vui_parameters_present_flag equal to 1 specifies that the
syntax structure mvc_vui_parameters_extension( ) is present and
referred to as 3DVC VUI parameters extension.
texture_vui_parameters_present_flag equal to 0 specifies that the
syntax structure mvc_vui_parameters_extension( ) corresponding to
3DVC texture sub-bitstream VUI parameters extension is not present.
texture_vui_parameters_present_flag equal to 1 specifies that the
syntax structure mvc_vui_parameters_extension( ) is present and
referred to as 3DVC texture sub-bitstream VUI parameters
extension.
In the HRD for 3DV-ATM, it may be specified that when the coded
video sequence conforms to one or more of the profiles specified in
3DV-ATM, the HRD parameter sets are signalled through the 3DVC
video usability information extension, which is part of the subset
sequence parameter set syntax structure. Furthermore, it may
specified that when the coded video sequence conforms to 3DV-ATM
and the decoding process 3DV-ATM is applied, the HRD parameters
specifically indicated for 3DV-ATM are in use.
The syntax of a 3DVC texture sub-bitstream HRD nesting SEI message
may be specified as follows.
TABLE-US-00008 De- scrip- 3dvc_texture_subbitstream_hrd_nesting(
payloadSize ) { C tor
num_texture_subbitstream_view_components_minus1 5 ue(v) for( i = 0;
i <= num_view_components_op_minus1; i++ )
texture_subbitstream_view_id[ i ] 5 u(10)
texture_subbitstream_temporal_id 5 u(3) while( !byte_aligned( ) )
sei_nesting_zero_bit /* equal to 0 */ 5 f(1) sei_message( ) 5 }
The semantics of a 3DVC texture sub-bitstream HRD nesting SEI
message may be specified as follows. A 3DVC texture sub-bitstream
HRD nesting SEI message may contain for example one SEI message of
payload type 0 or 1 (i.e. buffering period or picture timing SEI
message) or one and only one MVC scalable nesting SEI message
containing one SEI message of payload type 0 or 1. The SEI message
included in a 3DVC texture sub-bitstream HRD nesting SEI message
and not included in an MVC scalable nesting SEI message is referred
to as the nested SEI message. The semantics of the nested SEI
message apply for the sub-bitstream obtained with a 3DV-ATM
sub-bitstream extraction process with depthPresentFlagTarget equal
to 0, tIdTarget equal to texture_subbitstream_temporal_id, and
viewIdTargetList consisting of texture_subbitstream_view_id[i] for
all values of i in the range of to
num_texture_subbitstream_view_components_minus1, inclusive, as
inputs. num_texture_subbitstream_view_components_minus1 plus 1
specifies the number of view components of the operation point to
which the nested SEI message applies.
texture_subbitstream_view_id[i] specifies the view_id of the i-th
view component to which the nested SEI message applies.
texture_subbitstream_temporal_id specifies the maximum temporal_id
of the bitstream subset to which the nested SEI message applies.
sei_nesting_zero_bit is equal to 0.
In some embodiments, a 3DV-ATM sub-bitstream extraction process may
be specified as follows. Inputs to this process may be: a variable
depthPresentFlagTarget (when present), a variable pIdTarget (when
present), a variable tIdTarget (when present), a list
viewIdTargetList consisting of one or more values of viewIdTarget
(when present). Outputs of this process may be a sub-bitstream and
a list of VOIdx values VOIdxList. When depthPresentFlagTarget is
not present as input, depthPresentFlagTarget may be inferred to be
equal to 0. When pIdTarget is not present as input, pIdTarget may
be inferred to be equal to 63. When tIdTarget is not present as
input, tIdTarget may be inferred to be equal to 7. When
viewIdTargetList is not present as input, there may be one value of
viewIdTarget inferred in viewIdTargetList and the value of
viewIdTarget may be inferred to be equal to view_id of the base
view. In the sub-bitstream extraction process, if
depthPresentFlagTarget is equal to 0 or a similar indication to
remove depth views from the resulting sub-bitstream is input, the
HRD parameters specifically indicated for texture sub-bitstreams
may be converted to data structures specified in H.264/AVC and/or
MVC. For example, one or more of the following operations may be
used within a sub-bitstream extraction process to convert HRD
related data structures: Replace an SEI NAL unit in which
payloadType indicates a 3DVC texture sub-bitstream HRD nesting SEI
message with an SEI NAL unit with payload consisting of the SEI
message nested within the 3DVC texture sub-bitstream HRD nesting
SEI message. Replace mvc_vui_parameters_extension( ) syntax
structure in an active texture 3DVC sequence parameter set RBSPs
with the mvc_vui_parameters_extension( ) syntax structure of the
3DVC texture sub-bitstream VUI parameters extension.
For example, the sub-bitstream may be derived by applying the
following operations in sequential order: 1. Derive variable
VOIdxList to include all views needed for decoding all views
included in viewIdTargetList according to the inter-view
dependencies indicated in the active sequence parameter set. If
depthPresentFlagTarget is equal to 1, inter-view dependencies of
depth views may be taken into account when deriving VOIdxList. Mark
all NAL units for all view components that are not in VOIdxList as
"to be removed from the bitstream". 2. Mark all VCL NAL units and
filler data NAL units for which any of the following conditions are
true as "to be removed from the bitstream": priority_id is greater
than pIdTarget, temporal_id is greater than tIdTarget,
anchor_pic_flag is equal to 1 and view_id is not marked as
"required for anchor", anchor_pic_flag is equal to 0 and view_id is
not marked as "required for non-anchor", nal_ref_idc is equal to 0
and inter_view_flag is equal to 0 and view_id is not equal to any
value in the list viewIdTargetList, NAL units contains a coded
slice for a depth view component and depthPresentFlagTarget is
equal to 0. 3. Remove all access units for which all VCL NAL units
are marked as "to be removed from the bitstream". 4. Remove all VCL
NAL units and filler data NAL units that are marked as "to be
removed from the bitstream". 5. Remove all NAL units with
nal_unit_type equal to 6 in which the first SEI message has
payloadType equal to 0 or 1, or the first SEI message has
payloadType equal to equal to 37 (MVC scalable nesting SEI message)
and operation_point_flag in the first SEI message is equal to 1. 6.
When depthPresentFlagTarget is equal to 0, the following applies.
Replace all NAL units with nal_unit_type equal to 6 in which
payloadType indicates a 3DVC texture sub-bitstream HRD nesting SEI
message with the nal_unit_type equal to 6 with payload consisting
of the SEI message nested within 3DVC texture sub-bitstream HRD
nesting SEI message. The following applies for each active texture
3DVC sequence parameter set RBSP: Replace
mvc_vui_parameters_extension( ) syntax structure in an active
texture 3DVC sequence parameter set RBSPs with the
mvc_vui_parameters_extension( ) syntax structure of the 3DVC
texture sub-bitstream VUI parameters extension, if both
mvc_vui_parameters_extension( ) syntax structures apply to the same
views. Otherwise, remove mvc_vui_parameters_extension( ) syntax
structure in an active texture 3DVC sequence parameter set RBSP.
Remove all SEI NAL units with specified in 3DV-ATM and not
applicable for H.264/AVC or MVC. 7. Let maxTId be the maximum
temporal_id of all the remaining VCL NAL units. Remove all NAL
units with nal_unit_type equal to 6 that only contain SEI messages
that are part of an MVC scalable nesting SEI message or 3DVC
scalable nesting SEI message with any of the following properties:
operation_point_flag is equal to 0 and
all_view_components_in_au_flag is equal to 0 and none of
sei_view_id[i] for all i in the range of 0 to
num_view_components_minus1, inclusive, corresponds to a VOIdx value
included in VOIdxList, operation_point_flag is equal to 1 and
either sei_op_temporal_id is greater than maxTId or the list of
sei_op_view_id[i] for all i in the range of 0 to
num_view_components_op_minus1, inclusive, is not a subset of
viewIdTargetList (i.e., it is not true that sei_op_view_id[i] for
any i in the range of 0 to num_view_components_op_minus1,
inclusive, is equal to a value in viewIdTargetList). 8. Let maxTId
be the maximum temporal_id of all the remaining VCL NAL units.
Remove all NAL units with nal_unit_type equal to 6 that only
contain SEI messages that are part of a 3DVC texture sub-bitstream
HRD nesting SEI message with any of the following properties:
either texture_subbitstream_temporal_id is greater than maxTId or
the list of texture_subbitstream_view_id[i] for all i in the range
of 0 to num_texture_subbitstream_view_components_minus1, inclusive,
is not a subset of viewIdTargetList (i.e., it is not true that
sei_texture_subbitstream_view_id[i] for any i in the range of 0 to
num_texture_subbitstream_view_components_minus1, inclusive, is
equal to a value in viewIdTargetList). 9. Remove each view
scalability information SEI message and each operation point not
present SEI message, when present. 10. When VOIdxList does not
contain a value of VOIdx equal to minVOIdx, the view with VOIdx
equal to the minimum VOIdx value included in VOIdxList is converted
to the base view of the extracted sub-bitstream.
In some embodiments, the following may apply for buffering period
and picture timing SEI messages, that is SEI messages with
payloadType is equal to 0 or 1.
If a buffering period or picture timing SEI message is included in
a 3DVC scalable nesting SEI message and not included in an MVC
scalable nesting SEI message or a 3DVC texture sub-bitstream HRD
nesting SEI message, the following may apply. When the SEI message
and all other SEI messages with payloadType equal to 0 or 1
included in a 3DVC scalable nesting SEI message with identical
values of sei_op_temporal_id and sei_op_view_id[i] for all i in the
range of 0 to num_view_components_op_minus1, inclusive, are used as
the buffering period and picture timing SEI messages for checking
the bitstream conformance according to the HRD, the bitstream that
would be obtained by invoking the 3DV-ATM bitstream extraction
process with depthPresentTargetFlag equal to 1, tIdTarget equal to
sei_op_temporal_id and viewIdTargetList equal to sei_op_view_id[i]
for all i in the range of 0 to num_view_components_op_minus1,
inclusive, conforms to 3DV-ATM.
If a buffering period or picture timing SEI message is included in
a 3DVC texture sub-bitstream HRD nesting SEI message, the following
may apply. When the SEI message and all other SEI messages included
in a 3DVC texture sub-bitstream HRD nesting SEI message with
identical values of texture_subbitstream_temporal_id and
texture_subbitstream_view_id[i] for all i in the range of 0 to
num_texture_subbitstream_view_components_minus1, inclusive, are
used as the buffering period and picture timing SEI messages for
checking the bitstream conformance according to the HRD, the
bitstream that would be obtained by invoking the 3DV-ATM bitstream
extraction process with depthPresentTargetFlag equal to 0,
tIdTarget equal to texture_subbitstream_temporal_id and
viewIdTargetList equal to texture_subbitstream_view_id[i] for all i
in the range of 0 to
num_texture_subbitstream_view_components_minus1, inclusive,
conforms to 3DV-ATM.
As can be judged from the descriptions above, extending H.264/AVC,
SVC, and MVC with new scalability types, such as depth views, may
be complicated due to at least the following reasons: 1. The coded
slice NAL units of the new scalability types are VCL NAL units
according to the new amendment but non-VCL NAL units according to
the "old" versions of the standard. As the HRD makes a difference
between the VCL and non-VCL NAL units in its operation, different
sets of HRD parameters are needed depending on the interpretation
of the NAL unit types to either VCL or non-VCL NAL units. 2. The
sub-bitstream extraction process is specified for the NAL units and
scalability types of the "old" versions of the standard, e.g. for
dependency_id, quality_id, temporal_id and priority_id in Annex G
of H.264/AVC and for temporal_id, priority_id and view_id in Annex
H of H.264/AVC. However, new NAL unit types are introduced for new
types of scalability, such as NAL unit type 21 for coded depth
views and potentially for enhanced texture view, as specified in
3DV-ATM, and the existing sub-bitstream extraction process of SVC
or MVC leaves those new NAL unit types intact even if they would
also contain the "old" scalability dimensions, such as temporal_id
and view_id in the case of depth views.
While a draft HEVC standard does not include scalability features
beyond temporal scalability, we have identified that the design in
the draft HEVC standard could, when extended to support scalable
extensions, would have similar problems to the SVC and MVC design.
More specifically, we have identified at least the following
problems or challenges in the design of a draft HEVC standard: 1.
Sequence parameter sets associated with the different layers are
likely to be similar regardless of the type of scalability (e.g.
quality, spatial, multiview, or depth/disparity extension). For
example spatial resolution of pictures in different views may be
identical in multiview coding. In another example, the same coding
algorithms and parameters may be used across layers and may
therefore have the same values for the related syntax elements in
the sequence parameter sets. Consequently, the bitrate used for
sequence parameter sets and the storage space required for sequence
parameter sets in decoders may be unnecessarily high. Sequence
parameter sets may be transmitted once per each IDR/CRA/BLA picture
e.g. in broadcast applications. 2. No different profile and level
can be indicated for each bitstream subset resulting from a
sub-bitstream extraction process with a temporal_id value as input.
This issue applies more generally too. For example, if a bitstream
contains multiview video with associated depth views and a decoder
only capable of texture video decoding is processing the bitstream,
it activates the sequence parameter sets that apply to the texture
views. However, these sequence parameter sets are generated by the
encoder to take the bitrate used for coded depth into account in
the level and HRD parameters. In general terms, when a bitstream
contains NAL units for layers not documented by an active sequence
parameter set, the level and HRD parameter indicated in the active
sequence parameter set still cover the whole bitstream. There is no
mechanism at the moment to indicate the level for the bitstream
subset consisting of only certain layers. 3. When a bitstream
contains NAL units for non-base layers (i.e. NAL units having
reserved_one.sub.--5 bits/layer_id_plus1 not equal to 1), the SPS
for the base layer indicates the profile of the base layer, while
the level and the HRD parameters are valid for the whole bitstream
including non-base-layer NAL units. There is no mechanism at the
moment to indicate the level for the bitstream subset containing
the base-layer NAL units only.
In some embodiments, certain parameters or syntax elements values,
such as the HRD parameters and/or level indicator, may be taken
from a syntax structure, such as the sequence parameter set, of the
highest layer present in an access unit, coded video sequence,
and/or bitstream even if the highest layer were not decoded. The
highest layer may be defined for example as the greatest value of
reserved_one.sub.--5 bits or layer_id_plus1 in a scalable extension
of HEVC, although other definitions of the highest layer may also
be possible. These syntax element values from the highest layer may
be semantically valid and may be used for conformance checking e.g.
using an HRD, while the values of the respective syntax elements
from other respective syntax structures, such as sequence parameter
sets, may be active or valid otherwise.
In the following, some example embodiments are described for a
draft HEVC standard or similar. It should be understood that
similar embodiments would apply for other coding standards and
specifications.
Syntax structures, such as sequence parameter sets, may be
encapsulated as NAL units, which may include scalability layer
identifiers, such as temporal_id and/or layer_id_plus1, for example
in a header of the NAL unit.
In some embodiments, the same seq_parameter_set_id may be used for
sequence parameter set RBSPs having different syntax element
values. The sequence parameter set RBSPs having the same
seq_parameter_set_id value may be associated with each other, e.g.
such a manner that sequence parameter set RBSPs with the same value
of seq_parameter_set_id is referred from different component
pictures, such as layer representations or view components, of the
same access unit.
In some embodiments, a partial updating mechanism may be enabled in
the SPS syntax structure for example as follows. For each group of
syntax elements (e.g. profile and level indications, HRD
parameters, spatial resolution), the encoder may for example have
one or more of the following options when coding an SPS syntax
structure: The group of syntax elements may be coded into an SPS
syntax structure, i.e. coded syntax element values of the syntax
element set may be included in the sequence parameter set syntax
structure. The group of syntax elements may be included by
reference into the SPS. The reference may be given as an identifier
to another SPS or it may be implicit. If a reference identifier is
used, the encoder may in some embodiments use a different reference
APS identifier for different groups syntax elements. If an SPS is
implicitly referenced, the referenced SPS may for example have the
same seq_parameter_set_id or similar identifier and have a
scalability identifier, such as layer_id_plus1, that is immediately
preceding in the dependency order between component pictures or
layers or views, or be the active SPS for a layer or view from
which the layer or view for which the SPS being coded is the active
SPS depends on. The group of syntax elements set may be indicated
or inferred to be absent from the SPS.
The options from which the encoder is able to choose for a
particular group of syntax elements when coding an SPS may depend
on the type of the syntax element group. For example, it may be
required that syntax elements of a certain type syntax are always
present in the SPS syntax structure, while other groups of syntax
elements may be included by reference or be present in the SPS
syntax structure. The encoder may encode indications in the
bitstream, for example in an SPS syntax structure, which option was
used in encoding. The code table and/or entropy coding may depend
on the type of the group of syntax elements. The decoder may use,
based on the type of the group of syntax elements being decoded,
the code table and/or entropy decoding that is matched with the
code table and/or entropy encoding used by the encoder.
The encoder may have multiple means to indicate the association
between a group of syntax elements and the SPS used as the source
for the values of the syntax element set. For example, the encoder
may encode a loop of syntax elements where each loop entry is
encoded as syntax elements indicating an SPS identifier value used
as a reference and identifying the syntax element sets copied from
the reference SPS. In another example, the encoder may encode a
number of syntax elements, each indicating an SPS. The last SPS in
the loop containing a particular group of syntax elements is the
reference for that group of syntax elements in SPS the encoder is
currently encoding into the bitstream. The decoder parses the
encoded adaptation parameter sets from the bitstream accordingly so
as to reproduce the same adaptation parameter sets as the
encoder.
A partial updating mechanism for the SPS may for example allow
copying syntax elements other than profile and level indications
and potentially HRD parameters from another sequence parameter set
of the same seq_parameter_set_id. In some embodiments, a sequence
parameter set RBSP having temporal_id greater than 0 may inherit
values of syntax elements other than profile and level indications
and selectively also VUI parameters from the sequence parameter set
RBSP having the same seq_parameter_set_id and reserved_one.sub.--5
bits values. In some embodiments, a sequence parameter set RB SP
having reserved_one.sub.--5 bits/layer_id_plus1 greater than 1
selectively includes or inherits (as governed e.g. by the
short_sps_flag syntax element presented later) values of syntax
elements other than profile and level indications from the sequence
parameter set RBSP of the same seq_parameter_set_id and
reserved_one.sub.--5 bits equal to an indicated sequence parameter
set (as indicated by src_layer_id_plus1).
In some embodiments, a maximum temporal_id value and a set of
reserved_one.sub.--5 bits/layer_id_plus1 values to be decoded may
be provided to the decoding process for example by the receiving
process or the receiver. If not provided to the decoding process,
VCL NAL units of all temporal_id values and reserved_one.sub.--5
bits/layer_id_plus1 equal to 1 may be decoded while the other VCL
NAL units may be ignored. For example, the variable
TargetLayerIdPlus1Set may comprise a set of values for
reserved_one.sub.--5 bits of VCL NAL units to be decoded.
TargetLayerIdPlus1 may be provide for the decoding process, or,
when not for the decoding process, TargetLayerIdPlus1 contains one
value for reserved_one.sub.--5 bits, which is equal to 1. The
variable TargetTemporalId may be provided for the decoding process,
or, when not provided for the decoding process, TargetTemporalId is
equal to 7. A sub-bitstream extraction process is applied with
TargetLayerIdPlus1Set and TargetTemporalId as inputs and the output
assigned to a bitstream referred to as BitstreamToDecode. The
decoding process operates for BitstreamToDecode.
In some embodiments, a sub-bitstream extraction process with
temporal_id and a set of reserved_one.sub.--5 bits values as inputs
may be used. Sequence parameter set NAL units may be subject to
sub-bitstream extraction based on reserved_one.sub.--5
bits/layer_id_plus1 and temporal_id. For example, the inputs to the
sub-bitstream extraction process are variables tIdTarget and
layerIdPlus1Set, and the output of the process is a sub-bitstream.
For example, the sub-bitstream is derived by removing from the
bitstream all NAL units for which temporal_id is greater than
tIdTarget or for which reserved_one.sub.--5 bits is not among the
values in layerIdPlus1Set.
In some embodiments, the following syntax for sequence parameter
set RBSP may be used:
TABLE-US-00009 seq_parameter_set_rbsp( ) { Descriptor profile_space
u(3) profile_idc u(5) constraint_flags u(16) level_idc u(8) for( i
= 0; i < 32; i++ ) profile_compatability_flag[ i ] u(1)
seq_parameter_set_id ue(v) if( reserved_one_5bits != 1 &&
!temporal_id ) { short_sps_flag u(1) if( short_sps_flag )
src_layer_id_plus1 u(5) } if( !short_sps_flag ) {
video_parameter_set_id ue(v) chroma_format_idc ue(v) ...
long_term_ref_pics_present_flag u(1) sps_temporal_mvp_enable_flag
u(1) } vui_parameters_present_flag u(1) if(
vui_parameters_present_flag ) vui_parameters( ) sps_extension_flag
u(1) if( sps_extension_flag ) while( more_rbsp_data( ) )
sps_extension_data_flag u(1) rbsp_trailing_bits( ) }
In the syntax above, short_sps_flag may specify the presence and
inference of values for syntax elements of the sequence parameter
set RBSP for example as follows. When short_sps_flag is not present
and temporal_id is greater than 0, short_sps_flag is inferred to be
equal to 1 and variable SrcLayerIdPlus1 is set equal to
reserved_one.sub.--5 bits. When short_sps_flag is not present and
temporal_id is equal to 0, short_sps_flag is inferred to be equal
to 0. When short_sps_flag is present, variable SrcLayerIdPlus1 is
set equal to src_layer_id_plus1. When short_sps_flag is or is
inferred to be equal to 1 and the sequence parameter set RBSP is
activated, the values of the syntax elements in
seq_parameter_set_rbsp( ) syntax structure other than
profile_space, profile_idc, constraint_flags, level_idc,
profile_compatibility_flag[i], seq_parameter_set_id, short_sps_flag
and src_layer_id_plus1 are inferred to be identical to the values
of the respective syntax elements in the seq_parameter_set_rbsp( )
syntax structure having the same value of seq_parameter_set_id and
the value of reserved_one.sub.--5 bits equal to src_layer_id_plus
1. When short_sps_flag is or is inferred to be equal to 1 and
either the sequence parameter set RB SP is activated or used by the
hypothetical reference decoder, the values of those syntax elements
in video usability information that are not present in the sequence
parameter set RBSP are inferred to be identical to the values of
the respective syntax elements, if present, in
seq_parameter_set_rbsp( ) syntax structure having the same value of
seq_parameter_set_id and the value of reserved_one.sub.--5 bits
equal to src_layer_id_plus 1.
In some embodiments, e.g. when only temporal scalability is in use
or allowed, a sequence parameter set RBSP may be activated as
follows. When a sequence parameter set RBSP (with a particular
value of seq_parameter_set_id) is not already active and it is
referred to by activation of a picture parameter set RB SP (using
that value of seq_parameter_set_id) or is referred to by an SEI NAL
unit containing a buffering period SEI message (using that value of
seq_parameter_set_id), a sequence parameter set RBSP is activated
as follows: Let a set of sequence parameter set RBSPs,
potentialSPSSet, contain those sequence parameter set RBSPs that
have a particular value of seq_parameter_set_id and a value of
temporal_id smaller than or equal to TargetTemporalId and a value
of reserved_one.sub.--5 bits equal to 1. If there is only one
sequence parameter set RBSP among potentialSPSSet, it is activated.
Otherwise, among the set of sequence parameter set RBSPs having the
greatest value of reserved_one.sub.--5 bits in potentialSPSSet, the
sequence parameter set RBSP with the greatest value of temporal_id
is activated.
In some embodiments, e.g. when both temporal scalability indicated
with temporal_id and at least one other type of scalability
indicated with layer_id_plus1, is in use or allowed, sequence
parameter set RBSPs may be activated as follows. When a sequence
parameter set RBSP (with a particular value of
seq_parameter_set_id) is not already active and it is referred to
by activation of a picture parameter set RBSP (using that value of
seq_parameter_set_id) or is referred to by an SEI NAL unit
containing a buffering period SEI message (using that value of
seq_parameter_set_id), a sequence parameter set RBSP is activated
for a layer having reserved_one.sub.--5 bits equal to LIdPlus1, for
LIdPlus1 value equal to each value in TargetLayerIdPlus1Set as
follows: Let a set of sequence parameter set RBSPs,
potentialSPSSet, contain those sequence parameter set RBSPs that
have a particular value of seq_parameter_set_id and a value of
temporal_id smaller than or equal to TargetTemporalId and a value
of reserved_one.sub.--5 bits be among TargerLayerIdPlus1Set and be
smaller than or equal to LIdPlus1. If there is only one sequence
parameter set RBSP among potentialSPSSet, it is activated.
Otherwise, if among potentialSPSSet there is only one sequence
parameter set RBSP that has a value of reserved_one.sub.--5 bits
greater than the value of reserved_one.sub.--5 bits of any other
sequence parameter set RBSP in potentialSPSSet, that sequence
parameter set RBSP is activated. Otherwise, among the set of
sequence parameter set RBSPs having the greatest value of
reserved_one.sub.--5 bits in potentialSPSSet, the sequence
parameter set RBSP with the greatest value of temporal_id is
activated.
In some embodiments, the sequence parameter set RBSP used for HRD
parameter sets for bitstream conformance, conformanceSPS, may be
selected as follows: Let a set of sequence parameter set RBSPs,
potentialSPSSet, contain those sequence parameter set RBSPs that
have the same seq_parameter_set_id value as that of the active
sequence parameter set RBSP and a value of temporal_id smaller than
or equal to the greatest temporal_id value among the VCL NAL units
of the bitstream and a value of reserved_one.sub.--5 bits smaller
than or equal to the greatest reserved_one.sub.--5 bits value among
the VCL NAL units of the bitstream. If there is only one sequence
parameter set RBSP among potentialSPSSet, conformanceSPS is that
one sequence parameter set RBSP. Otherwise, if among
potentialSPSSet there is only one sequence parameter set RBSP that
has a value of reserved_one.sub.--5 bits greater than the value of
reserved_one.sub.--5 bits of any other sequence parameter set RBSP
in potentialSPSSet, conformanceSPS is that sequence parameter set
RB SP. Otherwise, among the set of sequence parameter set RBSPs
having the greatest value of reserved_one.sub.--5 bits in
potentialSPSSet, conformanceSPS is the sequence parameter set RBSP
with the greatest value of temporal_id.
In some embodiments, terms component sequence and component picture
may be defined and used. A component sequence can be for example a
texture view, a depth view, or an enhancement layer of
spatial/quality scalability. Each component sequence may refer to a
separate sequence parameter set, and several component sequences
may refer to the same sequence parameter set. Each component
sequence may be uniquely identified by variable CPId or LayerId,
which may be, in the context of HEVC, derived from the 5 reserved
bits (reserved_one.sub.--5 bits) in the second byte of the NAL unit
header. Temporal subsets of the coded video sequence might not be
considered to be component sequences; instead temporal_id may be
regarded as an orthogonal property. Component pictures may appear
in ascending order of CPId within the access unit. In general, a
coded video sequence may contain one or more component sequences.
An access unit may comprise one or more component pictures. In a
draft HEVC specification a component picture may be defined as the
coded picture of an access unit, and in the future scalable HEVC
extensions it would be for example a view component, a depth map,
or a layer representation.
In some embodiments, a sequence parameter set or a video parameter
set or some other syntax structure or structures may contain syntax
elements indicating dependencies, such as prediction relationship,
between component sequences. For example, The VPS syntax may
include: dependencies between component sequences and the mapping
of CPId to specific scalability properties (e.g. dependency_id,
quality_id, view order index).
In one example, referred to as cross-layer VPS, dependencies of
between layers of the entire coded video sequence and the
properties of layers are described in a VPS. A single VPS may be
active for all layers. If layers are extracted from the bitstream,
the cross-layer VPS may describe layers that are no longer present
in the bitstream. A cross-layer VPS may extend the VPS specified in
a draft HEVC standard as follows:
TABLE-US-00010 video_parameter_set_rbsp( ) { Descriptor ...
vps_extension1_flag u(1) if( vps_extension1_flag ) { for( i = 1; i
<= vps_max_layers_minus1; i++ ) { num_ref_component_seq[ i ]
ue(v) for( j = 0; j < num_ref_component_seq; j++ )
ref_component_seq_id[ i ][ j ] u(5) } num_component_seq_types ue(v)
for( i = 1; i <= num_component_seq_types; i++ ) {
component_sequence_type[ i ] ue(v) component_sequence_property_len[
i ] ue(v) len[ i ] = component_sequence_property_len[ i ] } for( i
= 1; i <= max_component_sequences_minus1; i++ ) {
component_sequence_type_idx[ i ] ue(v) tp =
component_sequence_type_idx[ i ] component_sequence_property[ i ]
u(len[tp]) } } vps_extension2_flag u(1) if( vps_extension_flag )
while( more_rbsp_data( ) ) vps_extension_data_flag u(1)
rbsp_trailing_bits( ) }
As the types of scalability and the syntax elements used to
represent them might not be known and new types of scalability may
be introduced later, the proposed syntax enables parsing of VPS
even if the scalability types were unknown for the decoder. The
decoder might be able to decode a subset of the bitstream
containing those scalability types that it is aware of.
The semantics of the cross-layer VPS may be specified as follows.
num_ref component_seq[i] specifies the number of component
sequences that the component sequence with CPId equal to i depends
on. ref_component_seq_id[i][j] specifies the vps_id values of the
component sequences that the component sequence with CPId equal to
i depends on. component_sequence_type[i] specifies the type of the
component sequence with type index equal to i.
component_sequence_type[0] is inferred to indicate HEVC base
component sequence. component_sequence_property_len[i] specifies
the size in bits of component_sequence_property[ ] syntax element
which is preceded by component_sequence_type_idx[ ] syntax element
having value equal to i. component_sequence_type_idx[i] specifies
the type index for the component sequence with CPId equal to i. The
component sequence with CPId equal to i is of type
component_sequence_type[component_sequence_type_idx [i]].
component_sequence_property[i] specifies the value or values
characterizing the component sequence with CPId equal to i. The
semantics of component_sequence_property[i] are specified according
to component_sequence_type[component_sequence_type_idx [i]].
In one example, referred to as layered VPS, a VPS NAL unit
describes the dependencies and properties of a single layer or
component sequence. The layered VPS NAL unit uses
reserved_one.sub.--5 bits and hence VPS NAL units are extracted
along with other layer-specific NAL units in sub-bitstream
extraction. A different VPS may be active for each layer, although
the same vps_id may be used in all active VPSes. The vps_id in all
active (layer/view) sequence parameter sets may be required to be
identical. A layered VPS may extend the VPS specified in a draft
HEVC standard as follows:
TABLE-US-00011 video_parameter_set_rbsp( ) { Descriptor ...
vps_extension1_flag u(1) if( vps_extension1_flag ) {
num_ref_component_seq[ i ] ue(v) for( j = 0; j <
num_ref_component_seq; j++ ) ref_component_seq_id[ i ][ j ] u(5)
component_sequence_type ue(v) component_sequence_property_len ue(v)
len = component_sequence_property_len component_sequence_property
u(len) } vps_extension2_flag u(1) if( vps_extension_flag ) while(
more_rbsp_data( ) ) vps_extension_data_flag u(1)
rbsp_trailing_bits( ) }
The semantics of the layered VPS may be specified as follows.
num_ref component_seq specifies the number of component sequences
that the component sequence depends on. ref_component_seq_id[j]
specifies the vps_id values of the component sequences that the
component sequence depends on. component_sequence_type specifies
the type of the component sequence. Values of
component_sequence_type are reserved.
component_sequence_property_len specifies the size in bits of
component_sequence_property syntax element.
component_sequence_property specifies the value or values
characterizing the component sequence. The semantics of
component_sequence_property are specified according to
component_sequence_type.
In some embodiments, a sub-bitstream extraction process may be
specified, where a set of output layers or component sequences is
provided as input. The sub-bitstream extraction process may
conclude the components sequences required for decoding the output
component sequences for example using the dependency information
provided in sequence parameter set(s) or video parameter set(s).
The output component sequences and the component sequences required
for decoding may be referred to as target component sequences and
the respective scalability layer identifier values as target
scalability layer identifier values. The sub-bitstream extraction
process may remove all NAL units, including parameter set NAL
units, where the scalability layer identifier value is not among
the target scalability layer identifier values.
Referring now to FIG. 10, the operations that may be performed by
an apparatus 50 specifically configured in accordance with an
example embodiment of the present invention are illustrated. In
this regard, an apparatus may include means, such as the processor
56 or the like, for producing two or more scalability layers of a
scalable data stream. Said means, such as the processor 56 or the
like, may for example include blocks implementing an encoding
arrangement according to FIG. 4a or the like, potentially also
including inter-layer, inter-view, and/or view-synthesis prediction
or the like (not illustrated in FIG. 4a). See block 400 of FIG. 10.
Each of the two or more scalability layers may have a different
coding property, may be associated with a scalability layer
identifier and may be characterized by a first set of syntax
elements that include at least a profile and a second set of syntax
elements including at least one of a level or HRD parameters. As
shown in block 402 of FIG. 10, the apparatus of this embodiment may
also include means, such as the processor or the like, for
inserting a first scalability layer identifier value and a first
elementary unit including data from the first of two or more
scalability layers. The apparatus of this embodiment may also
include means, such as the processor, the communication interface
or the like, for causing the first of the two or more scalability
layers to be signaled with the first and second set of syntax
elements and a first parameter set elementary unit such that the
first parameter set elementary unit is readable by a decoder to
determine the values of the first and second set of syntax elements
without decoding a scalability layer of the scalable data stream.
See block 404 of FIG. 10. The first set of syntax elements may for
example comprise a profile indicator and the second set of syntax
elements may for example comprise a level indicator and HRD
parameters. The apparatus of one embodiment may also include means,
such as the processor or the like, for inserting the first
scalability layer identifier value in the first parameter set
elementary unit, and means, such as the processor or the like, for
inserting a second scalability layer identifier value in a second
elementary unit including data from a second of two or more
scalability layers. See blocks 406 and 408 of FIG. 10. The
parameter set elementary unit may for example be a NAL unit
including a parameter set. The first and second scalability layer
identifier may for example be one or more syntax elements, such as
reserved_one.sub.--5 bits in HEVC, included in a NAL unit header.
As shown in block 410 of FIG. 10, the apparatus of one embodiment
may also include means, such as the processor, the communication
interface or the like, for causing the second of the two or more
scalability layers to be signaled with the first and second set of
syntax elements and a second parameter set elementary unit such
that the second parameter set elementary unit is readable by the
decoder to determine the coding property without decoding the
scalability layer of the scalable data stream. The apparatus of
this embodiment may also include means, such as the processor or
the like, for inserting the second scalability layer identifier
value in the second parameter set elementary unit. See Block 412 of
FIG. 10.
In this embodiment, values of the first set of syntax elements and
the first parameter set elementary unit may be valid in an instance
in which the first elementary unit is processed and the second
elementary unit is ignored or removed. The second elementary unit
may be removed in a sub-bitstream extraction process, for example,
which may remove the scalable layer or component sequence
containing the second elementary unit. In the absence of the second
elementary unit or the entire component sequence containing the
second elementary unit, the values of the first set of syntax
elements, such as a profile indicator, of the first parameter set
may be valid. Values of the second set of syntax elements in the
first parameter set elementary unit may be valid in an instance in
which the first elementary unit is processed and the second
elementary unit is removed. For example, HRD parameters and/or a
level indicator included in the second set of syntax elements, may
be valid for a sub-bitstream that contains the first elementary
unit, and in many cases the component sequence containing the first
elementary unit, but excluding the second elementary unit, and in
many cases the component sequence containing the second elementary
unit. Values of the first set of syntax elements in the second
parameter set elementary unit may be valid in an instance in which
the second elementary unit is processed. For example, if a
bitstream including the second elementary unit is decoded, the
values of the first set of syntax elements, such as the profile
indicator, may be valid and may be used in decoding. Additionally,
values of the second set of syntax elements in the second parameter
set elementary unit may be valid in an instance in which the second
elementary unit is ignored or processed. For example, if a
component sequence containing the first elementary unit is decoded
but the second elementary unit, and in many cases the component
sequence containing the second elementary unit, is ignored, HRD
parameters and/or level_idc of the second parameter set may
characterize the bitrate of the bitstream and/or buffering of the
bitstream and/or other things and hence may be valid and may be
used for decoding. In another example, if a bitstream containing
both the first and second elementary unit is decoded, HRD
parameters and/or level_idc of the second parameter set may
characterize the bitrate of the bitstream and/or buffering of the
bitstream and/or other things and hence may be valid and may be
used for decoding.
Referring now to FIG. 11, the operations performed by an apparatus
50 specifically configured in accordance with another example
embodiment of the present invention are illustrated. In this
regard, the apparatus may include means, such as the processor 56,
the communication interface or the like, for receiving a first
scalable data stream including scalability layers having different
coding properties. See block 420 of FIG. 11. Each of the two or
more scalability layers may be associated with a scalability layer
identifier and may be characterized by a first set of syntax
elements that include a least a profile and a second set of syntax
elements including at least one of a level or HRD parameters. A
first scalability layer identifier value may reside in a first
elementary unit including data from a first of two or more
scalability layers. The first and second set of syntax elements may
be signaled in a first parameter set elementary unit for the first
of the two or more scalability layers such that a first parameter
set is readable by a decoder to determine the values of the first
and second set of syntax elements without decoding a scalability
layer of a scalable data stream. The first scalability layer
identifier value may reside in the first parameter set elementary
unit. A second scalability layer identifier value may reside in a
second elementary unit including data from a second of two or more
scalability layers. The first and second set of syntax elements may
be signaled in a second parameter set elementary unit with a second
of the two or more scalability layers such that a second parameter
set is readable by the decoder to determine the decoding property
without decoding the scalability layer of the scalable data stream.
The second scalability layer identifier value may reside in the
second parameter set elementary unit. As shown in Block 422 of FIG.
11, the apparatus of this embodiment may also include means, such
as the processor or the like, for removing from the received first
scalable data stream the second elementary unit and the second
parameter set elementary unit. The second elementary unit and the
second parameter set elementary unit may be removed on the basis of
the second elementary unit and the second parameter set elementary
unit including the second scalability layer identifier value.
Referring now to FIG. 12, the operations performed by an apparatus
50 specifically configured in accordance with another example
embodiment of the present invention are illustrated. In this
regard, the apparatus may include means, such as the processor 56,
the communication interface or the like, for receiving a first
scalable data stream that includes scalability layers having
different coding properties. Each of the two or more scalability
layers may be associated with a scalability layer identifier and
may be characterized by a coding property. A first scalability
layer identifier value may reside in a first elementary unit that
includes data from a first of two or more scalability layers. The
first of the two or more scalability layers with a coding property
may be signaled in a first parameter set elementary unit such that
the coding property is readable by a decoder to determine the
coding property without decoding a scalability layer of the
scalable data stream. The first scalability layer identifier value
may reside in the first parameter set elementary unit. A second
scalability layer identifier value may reside in a second
elementary unit including data from a second of the two or more
scalability layers. The first and second sets of syntax elements
may be signaled in a second parameter set elementary unit for the
second of the two or more scalability layers such that a first
parameter set is readable by the decoder to determine the values of
the first and second sets of syntax elements without decoding the
scalability layer of the scalable data stream. The second
scalability layer identifier value may reside in the second
parameter set elementary unit. As shown in block 432, the apparatus
of this embodiment may include means, such as the processor, the
communications interface or the like, for receiving a set of
scalability layer identifier values indicating scalability layers
to be decoded. The apparatus of this embodiment may also include
means, such as the processor or the like, for removing from the
received first scalable data stream the second elementary unit and
the second parameter set elementary unit. For example, the second
elementary unit and the second parameter set elementary unit may be
removed on the basis of the second elementary unit and the second
parameter set elementary unit including the second scalability
layer identifier value not being among the set of scalability layer
identifier values. See Block 434 of FIG. 12.
In the above, the example embodiments have been described with the
help of syntax of the bitstream. It needs to be understood,
however, that the corresponding structure and/or computer program
may reside at the encoder for generating the bitstream and/or at
the decoder for decoding the bitstream. Likewise, where the example
embodiments have been described with reference to an encoder, it
needs to be understood that the resulting bitstream and the decoder
have corresponding elements in them. Likewise, where the example
embodiments have been described with reference to a decoder, it
needs to be understood that the encoder has structure and/or
computer program for generating the bitstream to be decoded by the
decoder.
In the above, embodiments have been described in relation to a
sequence parameter set. It needs to be understood, however, that
embodiments could be realized with any type of parameter set, such
as video parameter set, picture parameter, GOS parameter set, and
adaptation parameter set, and other types of syntax structures,
such as SEI NAL units and SEI messages.
Technologies involved in multimedia applications include, among
others, media coding, storage and transmission. Media types include
speech, audio, image, video, graphics and time text. While video
coding is described herein as an exemplary application for the
present invention, embodiments of the invention are not limited
thereby. Those skilled in the art will recognize that embodiments
of the present invention can be used with all media types, not only
video.
Although the above examples describe embodiments of the invention
operating within a codec within an electronic device, it would be
appreciated that embodiments of the invention as described below
may be implemented as part of any video codec. Thus, for example,
embodiments of the invention may be implemented in a video codec
which may implement video coding over fixed or wired communication
paths.
Thus, user equipment may comprise a video codec such as those
described in embodiments of the invention above. It shall be
appreciated that the term user equipment is intended to cover any
suitable type of wireless user equipment, such as mobile
telephones, portable data processing devices or portable web
browsers.
Furthermore elements of a public land mobile network (PLMN) may
also comprise video codecs as described above.
In general, the various embodiments of the invention may be
implemented in hardware or special purpose circuits, software,
logic or any combination thereof. For example, some aspects may be
implemented in hardware, while other aspects may be implemented in
firmware or software which may be executed by a controller,
microprocessor or other computing device, although the invention is
not limited thereto. While various aspects of the invention may be
illustrated and described as block diagrams, flow charts, or using
some other pictorial representation, it is well understood that
these blocks, apparatuses, systems, techniques or methods described
herein may be implemented in, as non-limiting examples, hardware,
software, firmware, special purpose circuits or logic, general
purpose hardware or controller or other computing devices, or some
combination thereof.
The various embodiments of the invention can be implemented with
the help of computer program code that resides in a memory and
causes the relevant apparatuses to carry out embodiments of the
invention. For example, a terminal device may comprise circuitry
and electronics for handling, receiving and transmitting data,
computer program code in a memory, and a processor that, when
running the computer program code, causes the terminal device to
carry out the features of an embodiment. Yet further, a network
device may comprise circuitry and electronics for handling,
receiving and transmitting data, computer program code in a memory,
and a processor that, when running the computer program code,
causes the network device to carry out the features of an
embodiment.
As noted above, the memory may be of any type suitable to the local
technical environment and may be implemented using any suitable
data storage technology, such as semiconductor-based memory
devices, magnetic memory devices and systems, optical memory
devices and systems, fixed memory and removable memory. The data
processors may be of any type suitable to the local technical
environment, and may include one or more of general purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs) and processors based on multi-core
processor architecture, as non-limiting examples and as further
described above.
Embodiments of the inventions may be practiced in various
components such as integrated circuit modules. The design of
integrated circuits is by and large a highly automated process.
Complex and powerful software tools are available for converting a
logic level design into a semiconductor circuit design ready to be
etched and formed on a semiconductor substrate.
Programs, such as those provided by Synopsys Inc., of Mountain
View, Calif. and Cadence Design, of San Jose, Calif. automatically
route conductors and locate components on a semiconductor chip
using well established rules of design as well as libraries of
pre-stored design modules. Once the design for a semiconductor
circuit has been completed, the resultant design, in a standardized
electronic format (e.g., Opus, GDSII, or the like) may be
transmitted to a semiconductor fabrication facility or "fab" for
fabrication.
As described above, FIGS. 10-12 are flowcharts of a method,
apparatus and program product according to example embodiments of
the invention. It will be understood that each block of the
flowcharts, and combinations of blocks in the flowcharts, may be
implemented by various means, such as hardware, firmware,
processor, circuitry and/or other device associated with execution
of software including one or more computer program instructions.
For example, one or more of the procedures described above may be
embodied by computer program instructions. In this regard, the
computer program instructions which embody the procedures described
above may be stored by a memory device 58 of an apparatus 50
employing an embodiment of the present invention and executed by a
processor 56 in the apparatus. As will be appreciated, any such
computer program instructions may be loaded onto a computer or
other programmable apparatus (e.g., hardware) to produce a machine,
such that the resulting computer or other programmable apparatus
embody a mechanism for implementing the functions specified in the
flowchart blocks. These computer program instructions may also be
stored in a non-transitory computer-readable storage memory (as
opposed to a transmission medium such as a carrier wave or
electromagnetic signal) that may direct a computer or other
programmable apparatus to function in a particular manner, such
that the instructions stored in the computer-readable memory
produce an article of manufacture the execution of which implements
the function specified in the flowchart blocks. The computer
program instructions may also be loaded onto a computer or other
programmable apparatus to cause a series of operations to be
performed on the computer or other programmable apparatus to
produce a computer-implemented process such that the instructions
which execute on the computer or other programmable apparatus
provide operations for implementing the functions specified in the
flowchart block(s). As such, the operations of FIGS. 10-12, when
executed, convert a computer or processing circuitry into a
particular machine configured to perform an example embodiment of
the present invention. Accordingly, the operations of FIGS. 10-12
define an algorithm for configuring a computer or processing
circuitry (e.g., processor) to perform an example embodiment. In
some cases, a general purpose computer may be configured to perform
the functions shown in FIGS. 10-12 (e.g., via configuration of the
processor), thereby transforming the general purpose computer into
a particular machine configured to perform an example
embodiment.
Accordingly, blocks of the flowcharts support combinations of means
for performing the specified functions, combinations of operations
for performing the specified functions and program instructions for
performing the specified functions. It will also be understood that
one or more blocks of the flowcharts, and combinations of blocks in
the flowcharts, can be implemented by special purpose
hardware-based computer systems which perform the specified
functions or operations, or combinations of special purpose
hardware and computer instructions.
In some embodiments, certain ones of the operations above may be
modified or further amplified. Furthermore, in some embodiments,
additional optional operations may be included. Modifications,
additions, or amplifications to the operations above may be
performed in any order and in any combination.
Many modifications and other embodiments of the inventions set
forth herein will come to mind to one skilled in the art to which
these inventions pertain having the benefit of the teachings
presented in the foregoing descriptions and the associated
drawings. Therefore, it is to be understood that the inventions are
not to be limited to the specific embodiments disclosed and that
modifications and other embodiments are intended to be included
within the scope of the appended claims. Moreover, although the
foregoing descriptions and the associated drawings describe example
embodiments in the context of certain example combinations of
elements and/or functions, it should be appreciated that different
combinations of elements and/or functions may be provided by
alternative embodiments without departing from the scope of the
appended claims. In this regard, for example, different
combinations of elements and/or functions than those explicitly
described above are also contemplated as may be set forth in some
of the appended claims. Although specific terms are employed
herein, they are used in a generic and descriptive sense only and
not for purposes of limitation.
* * * * *
References