U.S. patent application number 12/716598 was filed with the patent office on 2010-08-19 for apparatus and method for coding an information signal into a data stream, converting the data stream and decoding the data stream.
Invention is credited to Thomas Wiegand.
Application Number | 20100208791 12/716598 |
Document ID | / |
Family ID | 34887081 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100208791 |
Kind Code |
A1 |
Wiegand; Thomas |
August 19, 2010 |
Apparatus and Method for Coding an Information Signal into a Data
Stream, Converting the Data Stream and Decoding the Data Stream
Abstract
More customization and adaptation of coded data streams may be
achieved by processing the information signal such that the various
syntax structures obtained by pre-coding the information signal are
placed into logical data packets, each of which being associated
with a specific data packet type of a predetermined set of data
packet types, and by defining a predetermined order of data packet
types within one access unit of data packets. The consecutive
access units in the data stream may, for example, correspond to
different time portions of the information signal. By defining the
predetermined order among the data packet types it is possible, at
decoder's side, to detect the borders between successive access
units even when removable data packets are removed from the data
stream on the way from the data stream source to the decoder
without incorporation of any hints into the reminder of the data
stream. Due to this, decoders surely detect the beginnings and
endings of access units and therefore are not liable to a buffer
overflow despite a removal of data packets from the data stream
before arrival at the decoder.
Inventors: |
Wiegand; Thomas; (Berlin,
DE) |
Correspondence
Address: |
GLENN PATENT GROUP
3475 EDISON WAY, SUITE L
MENLO PARK
CA
94025
US
|
Family ID: |
34887081 |
Appl. No.: |
12/716598 |
Filed: |
March 3, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12422169 |
Apr 10, 2009 |
|
|
|
12716598 |
|
|
|
|
10788776 |
Feb 27, 2004 |
7586924 |
|
|
12422169 |
|
|
|
|
Current U.S.
Class: |
375/240.01 |
Current CPC
Class: |
H04N 21/6336 20130101;
H04L 29/06027 20130101; H04N 21/8451 20130101; H04L 65/607
20130101; H04N 7/26 20130101; H04N 21/23406 20130101; H04N 21/236
20130101; H04N 21/44004 20130101 |
Class at
Publication: |
375/240.01 |
International
Class: |
H04N 11/02 20060101
H04N011/02 |
Claims
1. A computer readable medium containing instructions that causes a
computer to perform a method for decoding a data stream
representing a coded version of an information signal, the data
stream comprising consecutive access units of consecutive data
packets, each data packet being of a data packet type of a
predetermined set of data packet types, at least one of the data
packet types being a removable data packet type, and the data
packet within each access unit being arranged in accordance with a
predetermined order among the data packet types, in accordance with
which a second data packet type precedes a first data packet type,
such that, even when a data packet of the removable data packet
type is removed from the data stream, borders between successive
access units are still detectable from the data stream by use of
the predetermined order and all data packets remain associated with
the respective access unit they originally belonged to before
removal of any data packet of the removable data packet type, with
the detection by use of the predetermined order involving detecting
an existence of a border between two successive access units each
time a data packet of the first data packet type precedes a data
packet of the second data packet type, the method comprising the
following steps: detecting a border between successive access units
by use of the predetermined order by detecting an existence of a
border between two successive access units each time a data packet
of the first data packet type precedes a data packet of the second
data packet type; and decoding the successive access units.
2. The computer readable medium of claim 1, wherein the
predetermined set of data packet types further comprises at least
one non-removable data packet type, and the predetermined order at
least defines as to whether the data packets of the removable data
packet type have to precede or follow data packets of the
non-removable data packet type, and wherein the step of detecting
comprises detecting the beginning of a new access unit if, either,
1) a preceding data packet is of a non-removable data packet type
and a current data packet is of the removable data packet type,
and, in accordance with the predetermined order, data packets of
the removable data packet type have to precede data packets of the
non-removable data packet type; or 2) a preceding data packet is of
the removable data packet type and the current data packet is of a
non-removable data packet type, and, in accordance with the
predetermined order, data packets of the removable data packet type
have to succeed data packets of the non-removable data packet
type.
3. The computer readable medium of claim 1, wherein the
predetermined set of data packet types comprises at least a first
removable data packet type for which the predetermined order
defines that data packets of that type have to precede data packets
of the non-removable data packet type, and at least a second
removable data packet type for which the predetermined order
defines that data packets of that type have to succeed data packets
of the non-removable data packet type, and wherein the step of
detecting comprises detecting the beginning of a new access unit
further if a data packet is of the second removable data packet
type preceeds a data packet of the first removable data packet
type.
4. The computer readable medium of claim 1, wherein each data
packet comprises a type number indicating of which data packet type
same data packet is, and the method further comprising receiving
the data stream, data packet by data packet, at an input; and
investigating the type number of a current data packet in order to
obtain the data packet type of the current data packet.
5. The method of claim 1, wherein the information signal is a video
signal, an audio signal or a multimedia signal.
6. The computer readable medium of claim 1, wherein each access
unit belongs to a picture from a video.
7. The computer readable medium of claim 1, the method further
comprising receiving the data stream at an input; and buffering the
received data packets and discarding buffered data packets access
unit-wise.
8. The computer readable medium of claim 1, wherein the information
signal comprises a video, and the step of detecting is performed
such that the data packet types which are arranged according to the
predetermined order comprise a supplemental enhancement information
data packet type, comprising supplemental enhancement information
including timing information or supplemental data that enhances
usability of a version of the information signal obtained by
decoding the successive access units but are not necessary for
obtaining the version of the information signal by decoding the
successive access units; and a coded picture data packet type
comprising syntax elements of slice header data and/or syntax
elements concerning slice transform coefficients of one or more
slices of a picture of the video, with, according to the
predetermined order, data packets of the supplemental enhancement
information data packet type preceding data packets of the coded
picture data packet type.
9. The computer readable medium of claim 1, wherein the information
signal comprises a video, and the step of detecting is performed
such that the data packet types which are arranged according to the
predetermined order comprise a sequence parameter set data packet
type comprising sequence parameter sets which apply to a series of
consecutive pictures of the video; and a picture parameter set data
packet type comprising picture parameter sets which apply to the
one or more individual pictures of the video within a series of
consecutive pictures of the video, a coded picture data packet type
comprising syntax elements of slice header data and/or syntax
elements concerning slice transform coefficients of one or more
slices of a picture of the video, with, according to the
predetermined order, data packets of the sequence parameter set
data packet type and data packets of the picture parameter set data
packet type preceding the last data packet of the coded picture
data packet type within the same access unit to which same
belong.
10. The computer readable medium of claim 9, wherein either one or
both of data packets of the sequence parameter set data packet type
and picture parameter set data packet type are conveyed separate
from the data stream by an extra transmission link such that,
according to the predetermined order, data packets of the sequence
parameter set data packet type and data packets of the picture
parameter set data packet type are received earlier than the last
data packet of the coded picture data packet type within the same
access unit to which same belong.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent application
Ser. No. 12/422,169, entitled APPARATUS AND METHOD FOR CODING AN
INFORMATION SIGNAL INTO A DATA STREAM, CONVERTING THE DATA STREAM
AND DECODING THE DATA STREAM, filed Apr. 10, 2009 which claims
priority to U.S. patent application Ser. No. 10/788,776, entitled
APPARATUS AND METHOD FOR CODING AN INFORMATION SIGNAL INTO A DATA
STREAM, CONVERTING THE DATA STREAM AND DECODING THE DATA STREAM,
filed Feb. 27, 2004, now U.S. Pat. No. 7,586,924.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field of the Invention
[0003] The present invention relates to information signal coding
schemes in general and, in particular, to coding schemes suitable
for single media or multimedia signal coding, such as video coding
or audio coding.
[0004] 2. Description of the Prior Art
[0005] The MPEG-2 video coding standard, which was developed about
10 years ago primarily as an extension of prior MPEG-1 video
capability with support of interlaced video coding, was an enabling
technology for digital television systems worldwide. It is widely
used for the transmission of standard definition (SD) and High
Definition (HD) TV signals over satellite, cable, and terrestrial
emission and the storage of high-quality SD video signals onto
DVDs.
[0006] However, an increasing number of services and growing
popularity of high definition TV are creating greater needs for
higher coding efficiency. Moreover, other transmission media such
as Cable Modem, xDSL or UMTS offer much lower data rates than
broadcast channels, and enhanced coding efficiency can enable the
transmission of more video channels or higher quality video
representations within existing digital transmission
capacities.
[0007] Video coding for telecommunication applications has evolved
through the development of the MPEG-2 coding standard, and has
diversified from ISDN and T1/E1 service to embrace PSTN, mobile
wireless networks, and LAN/Internet network delivery. Despite this
evolution, there is still a need to maximize coding efficiency
while dealing with the diversification of network types and their
characteristic formatting and loss/error robustness
requirements.
[0008] Recently, the MPEG-4 Visual standard has also begun to
emerge in use in some application domains of the prior coding
standards. It has provided video shape coding capability, and has
similarly worked toward broadening the range of environments for
digital video use.
[0009] However, the video schemes available today have in common,
that it is difficult to adapt an already coded video stream during
its way from its creation to the arrival at a receiver in order,
for example, to adapt the performance level of the coded video
stream to the performance of the receiver or to the performance of
the transmission link connecting the coded video streams source and
the receiver.
[0010] For example, a MPEG-4 data stream may be provided at a video
server in Dolby surround, thus providing a relatively large number
of audio channels. However, the receiver may be a device capable of
only reproducing mono-audio information. In this case, transferring
the video-coded stream with full performance level, i.e.
incorporating all audio channels, would mean waste of
transfer-linked capacity. Thus, it would be advantageous if a
gateway between the coded video stream source and the receiver
could convert the coded video stream from its initial performance
level to a lower performance level. However, in available video
coding schemes, the gateway may not convert a video data stream
from a higher performance level to a lower performance level merely
by discarding the portion of the coded video data stream pertaining
the excessive channels without manipulating the reminder of the
coded video stream, i.e. the portion concerning both the higher
performance level as well as the lower performance level.
[0011] Therefore, there is a need for a video coding scheme, which
allows a higher "network friendliness" to enable simple and
effective customization for a broad variety of systems. To be more
specific, the video coding scheme should allow a greater
customization of carrying the video content in a manner appropriate
for each specific network.
[0012] Moreover, the customization and adaptation of coded video
streams should be possible with reasonable efforts.
SUMMARY OF THE INVENTION
[0013] It is the object of the present invention to provide an
information signal coding scheme which enables more customization
and adaptation of the coded data stream with reasonable
efforts.
[0014] In accordance with a first aspect of the present invention,
this object is achieved by an apparatus for coding an information
signal, the apparatus comprising means for processing the
information signal in order to obtain data packets, each data
packet being of a data packet type of a predetermined set of data
packet types, at least one of the data packet types being a
removable data packet type; and means for arranging the data
packets into a data stream so that the data stream comprises
consecutive access units of consecutive data packets, so that the
data packets within each access unit are arranged in accordance
with a predetermined order among the data packet types, wherein the
means for processing and the means for arranging are adapted so
that even when a data packet of the removable data packet type is
removed from the data stream, borders between successive access
units are detectable from the dato stream by use of the
predetermined order.
[0015] In accordance with a second aspect of the present invention,
this object is achieved by an apparatus for converting a data
stream representing a coded version of an information signal from a
first performance level to a second performance level, the data
stream comprising consecutive access units of consecutive data
packets, each data packet being of a data packet type of a
predetermined set of data packet types, at least one of the data
packet types being a removable data packet type, and the data
packets within each access unit being arranged in accordance to a
predetermined order among the data packet types such that even when
a data packet of the removable data packet type is removed from the
data stream, borders between successive access units are detectable
from the data stream by use of the predetermined order, the
apparatus comprising means for removing at least one data block of
the removable data packet type from the bit stream without
manipulating the reminder of the data stream.
[0016] In accordance with a third aspect of the present invention,
this object is achieved by an apparatus for decoding a data stream
representing a coded version of an information signal, the data
stream comprising consecutive access units of consecutive data
packets, each data packet being of a data packet type of a
predetermined set of data packet types, at least one of the data
packet types being a removable data packet type, and the data
packet within each access unit being arranged in accordance with a
predetermined order among the data packet types, such that even
when a data packet of the removable data packet type is removed
from the data stream, borders between successive access units are
detectable from the data stream by use of the predetermined order,
the apparatus comprising means for detecting a border between
successive access units by use of the predetermined order; and
means for decoding the successive access units.
[0017] In accordance with a forth aspect of the present invention,
this object is achieved by a method for coding an information
signal, the method comprising processing the information signal in
order to obtain data packets, each data packet being of a data
packet type of a predetermined set of data packet types, at least
one of the data packet types being a removable data packet type;
and arranging the data packets into a data stream so that the data
stream comprises consecutive access units of consecutive data
packets, so that the data packets within each access unit are
arranged in accordance with a predetermined order among the data
packet types, wherein the steps of processing and arranging are
adapted so that even when a data packet of the removable data
packet type is removed from the data stream, borders between
successive access units are detectable from the data stream by use
of the predetermined order.
[0018] In accordance with a fifth aspect of the present invention,
this object is achieved by a method for converting a data stream
representing a coded version of an information signal from a first
performance level to a second performance level, the data stream
comprising consecutive access units of consecutive data packets,
each data packet being of a data packet type of a predetermined set
of data packet types, at least one of the data packet types being a
removable data packet type, and the data packets within each access
unit being arranged in accordance to a predetermined order among
the data packet types such that even when a data packet of the
removable data packet type is removed from the data stream, borders
between successive access units are detectable from the data stream
by use of the predetermined order, the method comprising removing
at least one data block of the removable data packet type from the
bit stream without manipulating the reminder of the data
stream.
[0019] In accordance with a sixth aspect of the present invention,
this object is achieved by a method for decoding a data stream
representing a coded version of an information signal, the data
stream comprising consecutive access units of consecutive data
packets, each data packet being of a data packet type of a
predetermined set of data packet types, at least one of the data
packet types being a removable data packet type, and the data
packet within each access unit being arranged in accordance with a
predetermined order among the data packet types, such that even
when a data packet of the removable data packet type is removed
from the data stream, borders between successive access units are
detectable from the data stream by use of the predetermined order,
the method comprising detecting a border between successive access
units by use of the predetermined order; and decoding the
successive access units.
[0020] In accordance with a sixth aspect of the present invention,
this object is achieved by a data stream representing a coded
version of a video or audio signal, the data stream comprising
consecutive access units of consecutive data packets, each data
packet being of a data packet type of a predetermined set of data
packet types, at least one of the data packet types being a
removable data packet type, and the data packets within each access
unit being arranged in accordance with a predetermined order among
the data packet types such that even when a data packet of the
removable data packet type is removed from the data stream, borders
between successive access units or detectable from the data stream
by use of the predetermined order.
[0021] The present invention is based on the finding that a
customization and adaptation of coded data streams may be achieved
by processing the information signal such that the various syntax
structures obtained by pre-coding the information signal are placed
into logical data packets, each of which being associated with a
specific data packet type of a predetermined set of data packet
types, and by defining a predetermined order of data packet types
within one access unit of data packets. The consecutive access
units in the data stream may, for example, correspond to different
time portions of the information signal. By defining the
predetermined order among the data packet types it is possible, at
decoder's side, to detect the borders between successive access
units even when removable data packets are removed from the data
stream on the way from the data stream source to the decoder
without incorporation of any hints into the reminder of the data
stream. Due to this, decoders surely detect the beginnings and
endings of access units and therefore are not liable to a buffer
overflow despite a removal of data packets from the data stream
before arrival at the decoder.
[0022] The removable data packets may be data packets which are
negligible or not necessary for decoding the values of the samples
in the information signal. In this case, the removable data packets
may contain redundant information concerning the video content.
Alternatively, such removable data packets may contain supplemental
enhancement information, such as timing information and other
supplemental data that may enhance usability of the decoded
information signal obtained from the data stream but are not
necessary for decoding the values of the samples of the
informations signal.
[0023] However, the removable data packets may also contain
parameters sets, such as important header data, that can apply to a
large number of other data packets. In this case, such removable
data packets contain information necessary for retrieval of the
video content from the data stream. Therefore, in case of removal
of such data packets, same are transferred to the receiver in
another way, for example, by use of a different transmission link
or by inserting thus removed data packet somewhere else into the
data stream in accordance with the predetermined order among the
data packet types in order not to accidentally create a condition
in the data stream defining the beginning of a new access unit
although being in the middle of an access unit.
[0024] Thus, it is an advantage of the present invention that an
information signal may be coded into a data stream composed of
consecutive data packets, and that removable data packets may be
removed from the data stream without having to manipulate the
reminder of the data stream and with, despite this, the order among
the data packet types within access units being maintained so that
boarders between successive access units are still derivable by use
of the order, preferably merely by the knowledge of the order.
[0025] Moreover, another advantage of the present invention is the
higher flexibility in arranging the data packets in the data stream
as long as the arrangement complies with the predetermined order
among the data packet types. This allows duplicating data packets
for redundancy enhancement and purposes as well as adapting the
performance level of the data stream to the receiving or
transmission environment.
SHORT DESCRIPTION OF THE DRAWINGS
[0026] Preferred embodiment of the present invention are described
in more detail below with respect to the Figures.
[0027] FIG. 1 shows a schematic diagram illustrating a creation,
conversion and decoding of a data stream in accordance with an
embodiment of the present invention.
[0028] FIG. 2 shows a block diagram of a system in which the
procedures of FIG. 1 may be realized in accordance with an
embodiment of the present invention.
[0029] FIG. 3 shows a block diagram of an encoder environment in
accordance with an embodiment of the present invention.
[0030] FIG. 4 shows a schematic diagram illustrating the structure
of a data stream in accordance with a specific embodiment of the
present invention.
[0031] FIG. 5 shows a syntax diagram for illustrating the structure
of an access unit in accordance with the specific embodiment of
FIG. 4.
[0032] FIG. 6 shows a flow diagram for illustrating a possible mode
of operation in the gateway of FIG. 2 in accordance with an
embodiment of the present invention.
[0033] FIG. 7 shows a schematic diagram illustrating the parameter
set transmission via an extra transmission link between encoder and
decoder in accordance with an embodiment of the present
invention.
[0034] FIG. 8 shows a flow diagram illustrating the operation of
the decoder of FIG. 2 in accordance with the specific embodiment of
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT
INVENTION
[0035] Before describing preferred embodiments of the present
invention with respect to the figures, it is noted that like
elements in the figures are designated by like reference numbers,
and that a repeated explanation of these elements is left-out.
[0036] FIG. 1 shows the creation, conversion and decoding of a data
stream in accordance with an embodiment of the present invention,
the data stream representing a coded version of an information
signal, such as an audio, video or multimedia signal.
[0037] In FIG. 1, the information signal is indicated by reference
number 10. Although the information signal 10 could be any
time-domain or time-dependent information signal, the information
10 is illustrated as a multimedia signal comprised of a video
signal or video content 10a and an audio signal or audio content
10b. The video content 10a is illustrated as being composed of a
sequence of pictures 12, while the audio signal 10b is illustrated
as comprising a sequence of audio samples 14, the sequence
extending along the time axis t.
[0038] Although the information signal 10 could be handled, such as
stored and transferred, in an un-coded digital manner, the
information signal 10 is encoded in order to compress the
information signal, i.e. to reduce the amount of data necessary in
order to represent the information signal. This encoding process is
indicated in FIG. 1 by arrow 16, while an encoder performing the
encoding process 16 is indicated at 18 in FIG. 2 which is also
referred to in the following and which shows an example for a
possible environment in which the processes of FIG. 1 could be
employed.
[0039] By the encoding process 16 a bit stream 20 is obtained. The
bit stream 20 is composed of a sequence of consecutive data packets
22, with the data stream 20 being illustrated as an arrow. The
direction of the arrow indicates which of the data packets 22
precedes which data packet 22 of the data stream 20. The data
packets are indicated by individual rectangles inside the arrow 20
and are labeled by A-F. Each data packet is uniquely associated
with one of a predetermined set of data packet types, each data
packet type being illustrated by A-F. The data packets 22 are, for
example, associated with a respective data packet type by a type
number in a header of the data packets 22. Each data packet type
would by uniquely associated with a different type number.
[0040] Several consecutive data packets 22 are grouped into an
access unit, as illustrated by braces 24. In this way, the data
stream 20 is composed of immediately consecutive access units 24
which are themselves composed of immediately consecutive data
packets 22.
[0041] Although access units 24 could have any meaning, in the
following it will be assumed that each access unit 24 belongs to a
specific time portion of the information signal 10. In the case of
a multimedia signal, as illustrated at 10, each access unit 24
could, for example, represent a coded version of a specific of the
pictures 12 and the corresponding portion of the audio signal 14 of
the information signal 10.
[0042] As will be described in more detail below with respect to
FIG. 3, the encoding process 16 could be composed of several steps.
For example, as a first step the encoding process 16 could involve
a pre-coding step in which samples of the information signal are
pre-coded in order to obtain syntax elements of various syntax
element types, each syntax element either applying to a portion of
one picture 12 or a portion of the audio signal 14, to a whole
picture 12 or to a sequence of pictures 12. As a second step, the
encoding process 16 could then involve a step of grouping syntax
elements being of the like syntax element type and applying to the
same pictures 12 to obtain the individual data packets 22. In a
further, last step, these data packets 22 would then be arranged in
a sequence in order to obtain the data stream 20 the
characteristics if which will be described in more detail
below.
[0043] In the following, the encoding process 16 is assumed to be
optimized in order to achieve a high-performance level coded
version of the information signal 10. In other words, the encoding
process 16 is assumed to be adjustable in the sense that the
encoding process creates, beside others, syntax elements and
corresponding data packets 22 which are not essential or absolutely
necessary for retrieval of the information signal from the
resulting data stream 20. In particular, it is assumed that the
encoder 18 creates a dato stream 20 being composed of the data
packets of all possible or envisaged data packet types A-F. Of
course, due to the high-performance level of the data stream 20,
same involves a greater amount of data than a data stream of a
lower-performance level.
[0044] As shown in FIG. 2, it is assumed that the data stream 20 is
firstly stored in a store 26 such as a video server or the like,
with which the encoder 18 is connected. Now, in order to enable the
transmission of the data stream 20 to a receiver 28 via a
transmission link 30 in an efficient way, a gateway 32 is connected
between the store 26 and the receiver 28, and preferably between
the store 26 and the transmission link 30. This gateway 32 performs
an adaptation or conversion of the data stream 20 from the
high-performance level as it is provided in the server 26 to a
lower performance level which is adapted to the capacity and
performance of the transmission line 30 and receiver 28,
respectively. For example, the transmission link 30 may be a
transmission link with a very low error bit rate. In this case, the
gateway 32 would convert the data stream 20 into a data stream
having less or no redundancy information.
[0045] In order to enable this conversion which is illustrated in
FIG. 1 by an arrow 34, in an effective and very simple way, the
encoding process 16 is performed such that the data packets 22
within one access unit 24 are arranged in accordance with a
predetermined order among the data packet types A-F. For
illustrating purposes only, it is assumed in FIG. 1 that the
predetermined order among the data packet types A-F is equivalent
to the alphabetical order. Thus, as can be seen from FIG. 1, in
each access unit 24 the consecutive data packets 22 are arranged in
alphabetical order with respect to their type. It is emphasized,
that there is possibly more than one data packet of a specific data
package type in an access unit, although such circumstances are not
depicted in FIG. 1, and that the order among such data packets of
the same data packet type may or may not be prescribed by a
predetermined ordering rule. Moreover, even though it is assumed
that the present data stream 20 is of highest performance level,
there may exist access units 24 in the data stream 20 which do not
contain data packets of all the data packet types A-F, although
such an access unit is not shown in FIG. 1. Moreover, it is noted
that for the purpose of enabling adaptation and converting the data
stream in a simple way, a more relaxed predetermined order among
the data packet types A-F could be sufficient as will be described
in the following with respect to FIGS. 4 to 8. To be more precise,
it is not necessary that the predetermined order is such strict
that each data packet type is fixed to a position in front of all
other data packet types, between two other data packet types or
after all other data packet types. Rather, it could be sufficient
if the predetermined order contains just one or more ordering rules
such as "data packets of the removable data packet type X (X=A, . .
. , F) have to precede or succeed data packets of data packet type
Y (Y.noteq.X and Y=A, . . . , F)". In particular, it would be
possible that instead of the strict alphabetic order, the
predetermined order could allow the mixing-up of data packets of
the data packet types C and D, for example.
[0046] Due to the prescribed order among the data packet types A-F,
the gateway 32 can convert the data stream 20 having a
high-performance level to a data stream 36 having a lower
performance level merely by removing some of the removable data
packet types which, for example, contain redundant picture
information or supplemental enhancement information which is not
necessary for retrieval of the pictures 12 or audio signal 14 from
the data stream 20. Moreover, the removed data packets of the
removable data packet types could as well concern essential
information. In this case, the gateway 32 would, for example,
transmit this information of these data packets via a different
transmission link to the receiver 28 as will be described in more
detail below.
[0047] As can be seen in FIG. 1, it is assumed that in the
conversion process 34 performed by gateway 32 all data packets 22
of the data packet types A, B, and E have been removed from the
data stream 20 in order to obtain a shortened data stream 36. As
can easily be understood, the borders between successive access
units can still easily be detected in the data stream 36 by means
of the predetermined order: Each time a data packet of a specific
data packet type X precedes a data of a data packet type Y that, in
accordance with the predetermined order, precedes the data packet
type X of the preceding data packet, between these data packets two
successive access units 38 abut or a border between two successive
access 38 units exists. In the exemplary case of FIG. 1, this
condition applies all times when the data packet of the data packet
type F precedes a data packet of the data packet type C. Thus, the
extension of each access unit 38 in the converted data stream 36
can still easily be obtained at decoder's side by use of the
knowledge of the predetermined order among data packet types even
though, at decoder's side, it is unknown which if the removable
data packet types have been removed. Thus, each access unit of the
access units in the converted data stream 36 which are indicated by
braces 38 corresponds with one of the access units 24 in the data
stream 20. In particular, the access units 24 and access units 38
are equal in number and order. Moreover, since the borders between
successive access units are detectable even in the modified data
stream 36 and are arranged at the same places, removal of data
packets merely results reducing the size of access units 38 of data
stream 36 relative to the access units 24 in data stream 22.
[0048] After transmission of the data stream 36 via a transmission
link 30 to receiver 28, the converter data stream 36 is decoded at
the receiver 28 in a decoding process 40. The receiver 28 may
decode the data stream 36 solely by use of the data stream itself
if the data packets removed at the converting process 34 merely
contained information not being necessary for retrieval of the
original information signal 10. In the other case, the receiver 28
decodes the converted data stream 36 based on information contained
in the data packets having been removed in the converting process
34 and having been transmitted to receiver 28 via an extra
transmission link, for example.
[0049] The result of the decoding process 40 is a decoded
information signal 42 in a quality as it would be obtained by
directly decoding the data stream 20. Alternatively, the quality of
the decoded information signal 42 is somewhat reduced in comparison
to the quality of a decoded information signal as obtained directly
by decoding data stream 20.
[0050] To summarize, by defining the predetermined order among the
data packet types, it is possible not only to maintain the
correspondence between access units in the original data stream 20
and the access units 38 in the converted data stream 36 but also to
enable the receiver 28 to associate each data packet with the
access unit it originally belonged to in the original data stream
20. The latter guaranties that a receiver 28 buffering the incoming
data packets and emptying the buffer in units of access units is
not liable to a buffer overflow as will be described in more detail
below.
[0051] In the following, a specific embodiment of the present
invention will be described in view of a video signal as the
information signal. In the following, reference will also be made
to FIG. 2, in order to illustrate the following specific embodiment
in view of an exemplary application environment.
[0052] FIG. 3 shows an embodiment of an encoder 18 for encoding a
video signal into a data stream. The encoder 18 comprises a
precoder 50, an encoder 52 and an arranging unit 54 all being
connected in series between an input 56 and an output 58 of the
encoder 18. At the input 56 the encoder 18 receives the video
signal, wherein in FIG. 3 illustratively one picture 12 of the
video signal is shown. All pictures 12 of the video signal are
composed of a plurality of pixels or picture samples arranged in
rows and columns.
[0053] The video signal or pictures 12 are fed via input 56 to the
video precoder 50. The video precoder 50 treats the pictures 12 in
units of so-called macroblocks 12a, i.e. a block of, for example,
4.times.4 pixel samples. On each macroblock 12a precoder 50
performs a transformation into spectral transformation coefficients
followed by a quantization into transform coefficient levels.
Moreover, intra-frame prediction or motion-compensation is used in
order not to perform the afore-mentioned steps directly on the
pixel data but on the differences of same to predicted pixel
values, thereby achieving small values which may more easily be
compressed.
[0054] The macroblocks into which the picture 12 is partitioned are
grouped into several slices. For each slice a number of syntax
elements are generated which form a coded version of the
macroblocks of the slice. For illustration purposes, in FIG. 3 the
picture 12 is shown as being partitioned into three slice groups or
slices 12b.
[0055] The syntax elements output by precoder 50 are dividable into
several categories or types. The encoder 52 collects the syntax
elements of the same category and belonging to the same slice of
the same picture 12 of a sequence of pictures and groups them to
obtain data packets. In particular, in order to obtain a data
packet, the encoder 52 forms a compressed representation of the
syntax elements belonging to a specific data packet to obtain
payload data. To this payload data encoder 52 attaches a type
number indicating the data packet type to obtain a data packet. The
precoder 50 and the encoder 52 of the encoder 18 form a so-called
video coding layer (VCL) for efficiently representing the video
content.
[0056] The data packets output by encoder 52 are arranged into a
data stream by arranging unit 55 as will be described in more
detail with respect to FIG. 4. The arranging unit 55 represents the
network abstraction layer (NAL) of encoder 18 for formatting the
VCL representation of the video and providing header information in
a manner appropriate for conveyance by a variety of transport
layers of a storage media.
[0057] The structure of the data stream output by encoder 18 of
FIG. 3 is described in more detail below with respect to FIG. 4. In
FIG. 4, the data stream output at output 58 is shown at 70. The
data stream 70 is organized in consecutive blocks 72 of coded video
sequences of consecutive pictures of a video. The coded video
sequence blocks 72 internally consist of a series of access units
74 that are sequential in the data stream 70. Each coded video
sequence 72 can be decoded independently of any other coded video
sequence 72 from the data stream 70, given the necessary parameter
set information, which may be conveyed "in-band" or "out-ofband" as
will be described in more detail below. Each coded video sequence
72 uses only one sequence parameter set.
[0058] At the beginning of a coded video sequence 72 is an access
unit 74 of a special type, called instantaneous decoding refresh
(IDR) access unit. An IDR access unit contains an intra picture,
i.e. a coded picture that can be decoded without decoding any
previous pictures in the data stream 70. The presence of an IDR
access unit in the data stream 70 indicates that no subsequent
picture in the stream 70 will require reference to pictures prior
to the intra picture it contains in order to be decoded. The data
stream 70 may contain one or more coded video sequences 72.
[0059] An access unit 74 is a set of NAL units 76 in a specified
form, the specified form being explained in more detail below. The
decoding of each access unit 74 results in one decoded picture. In
the following, the data stream 70 is also sometimes called NAL unit
stream 70.
[0060] The NAL units 76 correspond with the data packets mentioned
above with respect to FIG. 3. In other words, the coded video data
is organized by encoder 52 in NAL units 76. Each NAL unit 76 is
effectively a packet that contains an integer number of bytes. The
first byte of each NAL unit is a header byte 78 that contains an
indication of the type of data in the NAL unit, and the remaining
bytes contain payload 80 data of the type indicated by header
78.
[0061] The payload data 80 in the NAL units 76 may be interleaved,
as necessary, with emulation prevention bytes. Emulation prevention
bytes are bytes inserted with a specific value to prevent a
particular pattern of data called a start co-prefix from being
accidentally generated inside the payload.
[0062] The NAL unit structure definition specifies a generic format
for use in both packet-oriented and bit stream-oriented transport
systems, at a series of NAL units generated by an encoder as
referred to as the NAL unit stream 70.
[0063] For example, some systems require delivery of the entire or
partial NAL unit stream 70 as an ordered stream of bytes or bits
within which the locations of NAL unit boundaries 82 need to be
identifiable from patterns with the coded data itself.
[0064] For use in such systems, encoder 18 creates data stream 70
in a byte stream format. In the byte stream format each NAL unit 76
is prefixed by a specific pattern of, for example, three bytes,
called a start code prefix. This start code prefix is not shown in
FIG. 4 since it is optionally. If present, the start code prefix
within an NAL unit precedes the header byte 78. The boundaries of
the NAL 76 can then be identified by searching the coded data for
the unique start code prefix pattern. Moreover, the NAL data stream
output by encoder 18 of FIG. 3 may be interleaved by emulation
prevention bytes within the payload data blocks 80 of the NAL units
76 in order to guarantee that start code prefixes are unique
identifiers of a start of a new NAL unit 76. A small amount of
additional data (one byte per video picture) may also be added to
allow decoders that operate in systems that provide streams of bits
without alignment to byte boundaries to recover the necessary
alignment from the data in the stream.
[0065] Additional data could also be inserted into the byte stream
format that allows expansion of the amount of data to be sent and
can aid in achieving more rapid byte alignment recovery, if
desired.
[0066] In other systems, like internet protocol or RTP systems, the
coded data or data stream 70 is carried in packets that are framed
by the system transport protocol, an identification of the
boundaries of NAL units within the packets can be established
without use of start code prefix patterns. In such systems, the
inclusion of start code prefixes in the data of NAL units 76 would
be a waste of data-carrying capacity, so instead the NAL units 76
can be carried in data packets without start code prefixes.
[0067] NAL units are classified into VCL and non-VCL NAL units. The
VCL NAL units contain the data that represents the values of the
samples in the video pictures 12 and are, therefore, necessary for
decoding, and the non-VCL NAL units contain any associated
additional information such as parameter sets, i.e. important
header data that can apply to a large number of VCL NAL units, and
supplemental enhancement information, such as timing information
and other supplemental data that may enhance usability of the
decoded video signal (42 in FIG. 1) but are not necessary for
decoding the values of the samples in the video pictures 12.
[0068] A parameter set is supposed to contain information that is
expected to rarely change and offers the decoding of a large number
of VCL NAL units. There are two types of parameter sets: [0069]
sequence parameter sets, which apply to a series of consecutive
coded video pictures called a coded video sequence, and [0070]
picture parameter sets, which apply to the decoding of one or more
individual pictures 12 within a coded video sequence 72.
[0071] The sequence and picture parameter set mechanism which is
described in more detail below decouples the transmission of
infrequently changing information from the transmission of coded
representations of the values of the samples in the video pictures
12. Each VCL NAL unit 76 contains in its payload data portion 80 an
identifier that refers to the content of the relevant picture
parameter set, and each picture parameter set non-VCL NAL unit
contains in its payload data portion 80 an identifier that refers
to the content of the relevant sequence parameter set. In this
manner, a small amount of data, i.e. the identifier, can be used to
refer to a larger amount of information, i.e. the parameter set,
without repeating that information within each VCL NAL unit.
[0072] Sequence and picture parameter sets can be sent well ahead
of the VCL NAL units that they apply to, and can be repeated to
provide robustness against data loss, as will be described in more
detail below. In some applications, parameter sets may be sent
within the channel that carries the VCL NAL units termed "in-band"
transmission. In other applications, it can be advantageous to
convey the parameter sets "out-of-band" using a more reliable
transport mechanism or transmission link than the video channel for
transmitting the NAL data stream 70 itself as will be described in
the following with respect to FIGS. 6 and 7.
[0073] Now, before explaining in detail the predetermined order
among the NAL unit types in accordance with the present embodiment,
in the following the different NAL unit types are listed in Table 1
below along with their associated NAL unit type number for reasons
of completeness.
TABLE-US-00001 TABLE NAL units Nal unit type Content of NAL unit
and RBSP syntax structure C 0 Unspecified 1 coded slice of a
non-IDR picture 2, 3, 4 slice_layer_without_partitioning_NAL unit(
) 2 Coded slice data partition A 2 slice_data_partition_a_layer_NAL
unit( ) 3 Coded slice data partition B 3
slice_data_partition_b_layer-_NAL unit( ) 4 Coded slice data
partition C 4 slice_data_partition_c_layer_NAL unit( ) 5 Coded
slice of an IDR picture 2, 3 slice_layer_without_partitioning_NAL
unit( ) 6 Supplemental enhancement information (SEI) 5 sei_NAL
unit( ) 7 Sequence parameter set 0 seq_parameter_set_NAL unit( ) 8
Picture parameter set 1 pic_parameter_set_NAL unit( ) 9 Access unit
delimiter 6 access_unit_delimiter_NAL unit( ) 10 End of sequence 7
end_of_seq_NAL unit( ) 11 End of stream 8 end_of_stream_NAL unit( )
12 Filler data 9 filler_data_NAL unit3( ) 13 . . . 23 Reserved 24 .
. . 31 Unspecified
[0074] As can be seen from Table 1, NAL units 76 having a NAL unit
type 1 as its header byte 78 belong to one of the non-IDR access
units, i.e. one of the access units 74 which succeed the first
access unit of each coded video sequence 72, which is the IDR
access unit as mentioned before. Moreover, as indicated in Table 1,
a NAL unit 76 of NAL unit type 1 represent coded versions of a
slice of a non-IDR picture, i.e. a picture other than the first
picture of a coded video sequence 72. As is shown in the last
column of Table 1, in NAL units 76 of NAL unit type 1 syntax
elements of categories C=2, 3 and 4 are combined.
[0075] At the side of the encoder, it may have been decided not to
combine the syntax elements of category 2, 3 and 4 of one slice in
one common NAL unit 76. In this case, partitioning is used in order
to distribute the syntax elements of different categories 2, 3 and
4 to NAL units of different NAL unit types, i.e. NAL unit type 2, 3
and 4 for categories C 2, 3 and 4, respectively. To be more
specific, partition A contains all syntax elements of category 2.
Category 2 syntax elements include all syntax elements in the slice
header and slice data syntax structures other than the syntax
elements concerning single transform coefficients. Generally
spoken, partition A syntax elements as contained in NAL units of
the NAL unit type 2 are more important than the syntax elements
contained in NAL units 76 of NAL unit type 3 and 4. These latter
NAL units contain syntax elements of category 3 and 4, which
include syntax elements concerning transform coefficients.
[0076] As can be seen, slice data partitioning is not possible
within the first picture of a video sequence so that coded versions
of slices of an IDR picture are conveyed by NAL units 76 of a NAL
unit type 5.
[0077] NAL units 76 of NAL unit type 6 contain in its payload data
portion 80 supplemental enhancement information (SEI) with the
afore-mentioned examples.
[0078] NAL units 76 of NAL unit type 7 contain in its payload data
80 a sequence parameters set, while NAL units 76 of NAL unit type 8
contain in its payload data 80 a picture parameter set.
[0079] NAL units 76 of NAL unit type 9 are called an access unit
delimiter and indicate the beginning of an access unit. As it will
turn out from the following description, access unit delimiter are
optional and not necessary for parsing of the NAL data stream
70.
[0080] NAL units of NAL unit types 10 and 11 are NAL units
indicating the end of a sequence and the end of the whole data
stream, respectively. NAL units 76 of NAL unit type 12 contain in
its payload portion 80 filler data as may be necessary for some
networks. NAL unit types 13 to 23 and 24 to 31 pertain reserved or
unspecified NAL unit types for specific applications.
[0081] Now, after having described rather broadly the structure of
the NAL unit stream 70 generated by the encoder 18 of FIG. 3, the
constrains on the order of the NAL units 76 in the bit stream 70
are described in more detail with reference to Table 1 and FIG. 4.
Any order of NAL units 76 and the data or bit stream 70 obeying the
below mentioned constrains are, in accordance with the present
embodiment of the present invention, in conformity with parsing
rules used by a decoder of interest in order to retrieve the coded
information, i.e. the video signal. Decoders using that parsing
rules shall be capable of receiving NAL units in this parsing or
decoding order and retrieving the syntax elements.
[0082] In the following, the positioning of sequence and picture
parameter set NAL units, i.e. NAL units of NAL unit type 7 and 8,
is specified first. Then, the order of access units 74 is
specified. Then, the order of NAL unit 76 and coded pictures 12 and
their association to access units 74 is specified. Finally, the
order of VCL NAL units and association to coded pictures is
described.
[0083] As mentioned before, NAL units 76 are classified into VCL
and non-VCL NAL units. The VCL NAL units contain the data that
represent the values of the samples and the video pictures, and the
non-VCL NAL units contain any associated additional information
such as parameter sets and supplemental enhancement information,
such as timing information and other supplemental data that may
enhance usability of the decoded video signal but are not necessary
for decoding the values of the samples and the video pictures. With
reference to Table 1, which specifies the type of RBSP data
structure contained in the NAL unit 76, VCL NAL units are specified
as those NAL units having NAL_unit_type=1, 2, 3, 4, 5 or 12, all
remaining NAL units are called non-VCL NAL units.
[0084] The NAL units having NAL unit type other than 1-5 and NAL
units having NAL unit type 1-5 and, concurrently, having a syntax
element indicating that they are concerning redundant pictures are
removable NAL units.
[0085] In the following, the payload data 80 is sometimes called
Raw Bata Sequence Payload or RBSP. The RBSP 80 is a syntax
structure containing an integer number of bytes that is
encapsulated in a NAL unit 76. An RBSP is either empty or has the
form of a string of data bytes containing syntax elements followed
by an RBSP stop bit and followed by a zero and more subsequent
bytes equal to zero.
[0086] In this way, a NAL unit 76 is a syntax structure containing
an indication of the type of data to follow, i.e. the header byte
78, and bytes 80 containing the data in the form of an RBSP
interspersed as necessary with emulation prevention bytes as
already noted above.
[0087] On the other hand, an access unit 74 represents any primary
coded picture, zero or more corresponding redundant coded pictures,
and zero or more non-VCL NAL units. The association of VCL NAL
units to primary or redundant coded pictures or access units is
described below.
[0088] In order to allow the removal of removable NAL units 76 from
data stream 70 with remaining the decoding or parsing order, the
format of the access unit 74 is like shown in FIG. 5. The NAL units
76 that can be removed are all types except VCL NAL units of a
primary coded picture, i.e. all NAL unit types except NAL unit
types 1 to 5.
[0089] As shown in FIG. 5, each access unit contains in any case a
set of VCL NAL units that together compose a primary coded picture
100. An access unit may be prefixed with an access unit delimiter
102, i.e. a NAL unit having NAL_unit_type 9 to 8 to aid in locating
the start of the access unit 74. Some supplemental enhancement
information SEI in form of SEI NAL units of NAL unit type 6
containing data such as picture timing information may also precede
the primary coded picture 100, this SEI block being indicated by
reference number 104.
[0090] The primary coded picture consists of a set of VCL NAL units
76 consisting of slices or sliced data partitions that represent
samples of the video picture.
[0091] Following the primary coded picture 100 may be some
additional VCL NAL units that contain redundant representations of
areas of the same video picture. These are referred to as redundant
coded pictures 106, and are available for use by a decoder in
recovering from loss or correction of the data in the primary coded
pictures 100. Decoders are not required to decode redundant coded
pictures if they are present. Finally, if the coded picture the
access unit 74 is associated with is the last picture of a coded
video sequence 72, wherein a sequence of pictures is independently
decodable and uses only one sequence parameter set, an end of
sequence NAL unit 108 may be present to indicate the end of the
sequence 72. And if the coded picture is the last coded picture in
the entire NAL unit stream 70, an end of stream NAL unit 110 may be
present to indicate that the stream 70 is ending.
[0092] FIG. 5 shows the structure of access units not containing
any NAL units with NAL_unit_type=0, 7, 8 or in the range of 12 to
31, inclusive. The reason for having limited the illustration of
access units to cases where NAL units of the aforementioned have
been removed is, that, as already noted above, sequence and picture
parameter sets in NAL units of NAL unit type 7 and 8 may, in some
applications, be conveyed "out-of-band" using a reliable transport
mechanism or, in an redundant manner, in-band. Thus, an encoder 18
may output the sequence and picture parameter sets in-band i.e. in
the data stream 70, or out-of-band i.e. using an extra output
terminal.
[0093] Anyway, the encoder 18 or any means in between the encoder
18 and the decoder 28 has to guarantee that the following
constrains on the order of sequence and parameter set RBSPs and
their activation are obeyed.
[0094] A picture parameter set RBSP includes parameters that can be
referred to by decoded slice A NAL units or coded slice data
partition NAL units of one or more coded pictures. [0095] I) When a
picture parameter set RBSP having a particular value of
PIC_parameter_set_id, i.e. the header byte 78, 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. Picture parameter set RBSP, with that
particular value of PIC_parameter_set_id, shall be available to the
decoding process at decoder 28 prior to its activation. Thus, the
encoder 18 has to take this into account when transmitting sequence
and picture parameter set in-band or out-of-band.
[0096] Any picture parameter set NAL unit containing the value of
pic_parameter_set_id for the active picture parameter set RBSP
shall have the same content as that of the active picture parameter
set RBSP unless it follows the last VCL NAL unit of a coded picture
and precedes the first VCL NAL unit of another coded picture.
[0097] 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.
[0098] II) When a sequence parameter set RBSP (with a particular
value of seq_parameter_set_id) 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 et
RBSP. A sequence parameter set RBSP, with that particular value of
seq_parameter_set_id, shall be available to the decoding process
prior to its activation. An activated sequence parameter set RBSP
shall remain active for the entire coded video sequence.
[0099] Any sequence parameter set NAL unit containing the value of
seq_parameter_set_id for the active sequence parameter set RBSP
shall have the same content as that of the active sequence
parameter set RBSP unless it follows the last access unit of a
coded video sequence and precedes the first VCL NAL unit and the
first SEI NAL unit containing a buffering period SEI message (when
present) of another coded video sequence.
[0100] In the following, the order of NAL units and coded pictures
and their association to access units is described in more detail
as before with reference to FIG. 5.
[0101] An access unit 74 consists of one primary coded picture 100,
zero or more corresponding redundant coded pictures 106, and zero
or more one-VCL NAL units 102, 104, 108 and 110, as already
mentioned above.
[0102] The association of VCL NAL units to primary or redundant
coded pictures is described below.
[0103] The first of any of the following NAL units 76 after the
last VCL NAL unit of a primary coded picture 100 specifies the
start of a new access unit. [0104] a) Access unit delimiter NAL
unit (NAL unit type 9) (when present) [0105] b) sequence parameter
set NAL unit (NAL unit type 7) (when present) [0106] c) picture
parameter set NAL unit (NAL unit type 8) (when present) [0107] d)
SEI NAL unit (NAL unit type 6) (when present) [0108] e) NAL units
with nal_unit_type in the range of 13 to 18, inclusive [0109] f)
first VCL NAL unit of a primary coded picture (NAL unit type 1-5)
(always present)
[0110] The constraints for the detection of the first VCL NAL unit
of a primary coded picture are specified further below and can be
used given the above claimed restriction to distinguish access
units even if NAL units that are allowed to be removed are removed.
The NAL units that can be removed are all types except VCL NAL unit
of a primary coded picture.
[0111] The following constraints shall be obeyed by the order of
the coded pictures and non-VCL NAL units within an access unit.
[0112] g) When an access unit delimiter NAL unit (NAL unit type 9)
is present, it shall be the first NAL unit. There shall be at most
one access unit delimiter NAL unit in any access unit. [0113] h)
When any SEI NAL units (NAL unit type 6) are present, they shall
precede the primary coded picture. [0114] i) When an SEI NAL unit
containing a buffering period SEI message shall be the first SEI
message payload of the first SEI NAL unit in the access unit,
wherein a buffering period SEI NAL unit is for controlling the
buffering management at decoder's side. [0115] j) The primary coded
picture (consisting of NAL units of NAL unit types 1-5 and having
redundant picture count value being equal to zero) shall precede
the corresponding redundant coded pictures. [0116] k) When
redundant coded pictures (consisting of NAL units of NAL unit types
1-5 and having redundant picture count value being not equal to
zero) are present, they shall be ordered in ascending order of the
value of redundant picture count value redundant_pic_cnt. [0117] l)
When an end of sequence NAL unit (NAL unit type 10) is present, it
shall follow the primary coded picture and all redundant coded
pictures (if any). [0118] m) When an end of stream NAL (NAL unit
type 11) unit is present, it shall be the last NAL unit. [0119] n)
NAL units having nal_unit_type equal to 0, 12, or in the range of
19 to 31, inclusive, shall not precede the first VCL NAL unit of
the primary coded picture. [0120] o) Sequence parameter set NAL
units or picture parameter set NAL units may be present in an
access unit, but cannot follow the last VCL NAL unit of the primary
coded picture within the access unit, as this condition would
specify the start of a new access unit (see constraint b)). [0121]
p) When a NAL unit having nal_unit_type equal to 7 or 8 is present
in an access unit, it may not be referred to in the coded pictures
of the access unit in which it is present, and may be referred to
in coded pictures of subsequent access units.
[0122] In the following, the order of VCL NAL units and the
association to coded pictures is described in more detail below.
[0123] q) Each VCL NAL unit is part of a coded picture. [0124] r)
The order of the VCL NAL units within a coded IDR picture is
constrained as follows. [0125] If arbitrary slice order is allowed
as specified by a certain syntax element, coded slice of an IDR
picture NAL units may have any order relative to each other. [0126]
Otherwise (arbitrary slice order is not allowed), the order of
coded slice of an IDR picture NAL units shall be in the order of
increasing macroblock address for the first macroblock of each
coded slice of an IDR picture NAL unit. [0127] s) The order of the
VCL NAL units within a coded non-IDR picture is constrained as
follows. [0128] If arbitrary slice order is allowed as specified by
a specific syntax element, coded slice of a non-IDR picture NAL
units or coded slice data partition A NAL units may have any order
relative to each other. A coded slice data partition A NAL unit
with a particular value of slice_id shall precede any present coded
slice data partition B NAL unit with the same value of slice_id. A
coded slice data partition A NAL unit with a particular value of
slice_id shall precede any present coded slice data partition C NAL
unit with the same value of slice_id. When a coded slice data
partition B NAL unit with particular value of slice_id is present,
it shall precede any present coded slice data partition C NAL unit
with the same value of slice_id. [0129] Otherwise (arbitrary slice
order is not allowed), the order of coded slice of a non-IDR
picture NAL units or coded slice data partition A NAL units shall
be in the order of increasing macroblock address for the first
macroblock of each coded slice of a non-IDR picture NAL unit or
coded slice data partition A NAL unit. A coded slice data partition
A NAL unit with a particular value of slice_id shall immediately
precede any present coded slice data partition B NAL unit with the
same value of slice_id. A coded slice data partition A NAL unit
with a particular value of slice_id shall immediately precede any
present coded slice data partition C NAL unit with the same value
of slice_id, when a coded slice data partition B NAL unit with the
same value of slice_id is present; it shall immediately precede any
present coded slice data partition C NAL unit with the same value
of slice_id [0130] t) NAL units having nal_unit_type equal to 12
may be present in the access unit but shall not precede the first
VCL NAL unit of the primary coded picture within the access unit.
[0131] u) NAL units having nal_unit_type equal to 0 or in the range
of 24 to 31, inclusive, which are unspecified, may be present in
the access unit but shall not precede the first VCL NAL unit of the
primary coded picture within the access unit. [0132] v) NAL units
having nal_unit_type in the range of 19 to 3, inclusive, which are
reserved, shall not precede the first VCL NAL unit of the primary
coded picture within the access unit.
[0133] The creation of the data stream 70 is further restricted by
the following constraints in order to enable the detection of the
first VCL NAL unit of a primary coded picture: [0134] w) Any coded
slice NAL unit or coded slice data partition A NAL unit of the
primary coded picture of the current access unit shall be different
from any coded slice NAL unit or coded slice data partition A NAL
unit of the primary coded picture of the previous access unit in
one or more of the following ways. [0135] frame num differs in
value. frame_num is an identifier in each VCL NAL unit indicating
the picture 12 of the video 10a it belongs to. A value of frame_num
may be assigned to more than one picture or access unit, but the
value of frame_num in the payload data of the VCL NAL unit of
successive access units 74 may not be the same. In other words,
frame_num is used as a unique identifier for each short-term
reference frame. For example, when the current picture is an IDR
picture, frame_num shall be equal to zero. [0136] field_pic_flag
differs in value. field_pic_flag as contained in the payload data
80 of VCL NAL units specifies, if equal to one, that the slice is
associated to a coded field, i.e. a field of an interlaced frame,
and, if equal to zero specifies that the picture which the VCL NAL
unit having that field_pic_flag is a coded frame, i.e. a coded
interleaved or coded progressive frame. [0137] bottom_field_flag is
present in both and differs in value. bottom_field_flag as
contained in the payload data 80 of a VCL NAL unit specifies, if
equal to one, that the slice is associated to a coded bottom field,
whereas bottom_field_flag equal to zero specifies that the picture
is a coded top field. To be more specific, a coded video sequence
consists of a sequence of coded pictures, wherein a coded picture
may represent either an entire frame or a single field. Generally,
a frame of video can be considered to contain two interleaved
fields, a top and a bottom field. The top field contains
even-numbered rows, whereas the bottom field contains the
oddnumbered rows, for example. Frames in which the two fields of a
frame are kept at a different time instance, are referred to as
interlaced frames. Otherwise, a frame is referred to as a
progressive frame. [0138] nal_ref_idc differs in value with one of
the nal_ref_idc values being equal to 0. nal_ref_idc is an
identifier that may be contained in a payload data 80 of a NAL
unit. nal_ref_idc not equal to zero specifies that the content of
the NAL unit contains a sequence parameter set or a picture
parameter set or a slice of a reference picture or a slice data
partition of a reference picture. Therefore, nal_ref_idc equal to
zero for a NAL unit containing a slice or slice data partition
indicates that a slice or slice data partition is part of a
non-reference picture. Any nal_ref_idc shall not be equal to zero
for a sequence parameter set or a picture parameter set in a NAL
unit. If nal_ref_idc is equal to zero for one slice or slice data
partition in a NAL unit of a particular picture, it shall be equal
to zero for all slice and slice data partition NAL units of the
picture. nal_ref_idc is, therefore, not equal to zero for IDR NAL
units, i.e. NAL units with a nal_unit_type equal to 5. A
nal_ref_idc is equal to zero for all NAL units having an
nal_unit_type equal to 6, 9, 10, 11 or 12. Picture_order_cnt_type
is an syntax element contained in payload data 80 in order to
specify the method to code the syntax element picture_order_count.
The value of pic_order_cnt_type shall be in the range of 0 to 2,
inclusive. pic_order_cnt_type shall not be equal to 2 in a sequence
that contains two or more consecutive non-reference frames,
complementary non-reference field pairs or non-paired non-reference
fields in decoding order. pic_order_cnt_lsb specifies, when
contained in a payload data 80 of a VCL NAL unit, the picture order
count coded for the field of a coded frame or for a coded field. An
IDR picture shall, for example, have pic_order_cnt_lsb equal to
zero. Data_pic_order_cnt_bottoms is a syntax element that
specifies, when contained in a payload data 80 of a VCL NAL unit,
the picture order count difference from the expected picture order
count for the top field in a coded frame of a coded field. [0139]
frame_num is the same for both and pic_order_cnt_type is equal to 1
for both and either delta_pic_order_cnt[0] differs in value, or
delta_pic_order_cnt[1] differs in value. pic_order_cnt[0] specifies
the picture order count difference from the expected picture order
count for the top field in a coded frame or for a coded field.
delta_pic_order_cnt[1] specifies the picture order count difference
from the expected picture order count for the bottom field and the
coded frame. [0140] nal_unit_type is equal to 5 for both and
idr_pic_id differs in value. idr_pic_id is a syntax element
contained in payload data 80 of IDR picture in a VCL NAL unit and
indicates an identifier for different IDR pictures of different
coded video sequences 72.
[0141] After having described an embodiment for an encoder 18 and
its constraints for creation of a data stream 70, in the following
there is described a possible functionality of a gateway 32
suitable for parsing the data stream 70 of encoder of FIG. 3 to a
receiver 28.
[0142] The gateway 32 receives the data stream 70 NAL unit-wise at
step 120. At step 122, the gateway 32 investigates the type number,
i.e. nal_unit_type, of the current NAL unit 76 just received in
order to determine at step 124 as to whether this NAL unit is of a
NAL unit type to be removed. For example, the NAL data stream 70 is
of high performance and has several redundant coded pictures 106.
In this case, it could be, that gateway 32 decides to lower the
redundancy level of the data stream 70 and removes all NAL units 76
from data stream 70 having NAL unit types 1 to 5 and concurrently
having a syntax element in the payload data called
redundant_pic_cnt being different to 0, wherein redundant_pic_cnt,
in accordance with the present embodiment, equal to 0 indicates
slice and slice data partitions belonging to the primary coded
picture of an access unit. The reduction in redundancy is
advantageous if the transmission link 30 between gateway 32 and
receiver 28 has a low bit error rate.
[0143] Alternatively, gateway 32 decides to transmit sequence and
picture parameter set NAL units via an extra transmission link (not
shown in FIG. 2) to receiver 28. In this case, gateway 32 removes
all NAL units of NAL unit types 7 and 8. Of course, it is possible
that gateway 32 removes any combination of NAL unit types being
removable.
[0144] If the NAL unit 76 received at step 120 is to be removed,
gateway 32 performs the removal of the current NAL unit from the
data stream 70 and discards this NAL unit at step 126. Otherwise,
gateway 32 determines at step 128 as to whether the NAL unit
received at step 120 has to be transmitted to the receiver 28
safely or has to be left unchanged. For example, if the NAL unit
just received is a parameter set NAL unit it has to be transferred
to the receiver 28. In this case, there are two possibilities for
gateway 32. In the first case, gateway 32 decides to transmit the
parameter set NAL unit via an extra transmission link. In this
case, gateway 32 removes, in step 130, the NAL unit from the data
stream 70 and, then, transmits, in step 132, the NAL unit via the
extra transmission link. In particular, gateway 32 can perform the
transmission of step 132 several times. Gateway 32 just has to
comply with the constraints on the order of sequence and picture
parameter set RBSPs and their activation at decoder side as
mentioned above (see I and II).
[0145] Alternatively, gateway 32 decides to transmit NAL units
containing the parameter sets in-band. In this case, gateway 32
inserts, at step 134, the current NAL unit at another position of
the data stream 70 to be more precise, at a preceding position of
the NAL data stream 70. Of course, step 134 may be performed
several times. Gateway 32 thus has to guarantee that the
constraints on the order of sequence and picture parameters at
RBSPs and their activation at receiver 28 are obeyed (see
constraints o and p).
[0146] After any of steps 126, 128, 132 and 134, gateway 32 checks,
at step 136, as to whether there are NAL units left in the data
stream 70. If this is the case, the next NAL unit is received at
step 120. Otherwise, the process of FIG. 6 and gateway 32 awaits
the reception of the next NAL data stream 70.
[0147] In order to illustrate the decoupling of the transmission of
infrequently changing information from the transmission of coded
representations of the values of the samples in the video pictures
the sequence and picture parameter set mechanism is illustrated in
FIG. 7. FIG. 7 shows the encoder 18 and the receiving decoder 28.
The data stream 70 is represented by an arrow. The data stream 70
passed from encoder 18 to decoder 28 comprises a NAL unit with VCL
data that is encoded by means of a parameter set having a
pic_parameter_set_id of 3 as an address or index in the slice
header. As can be seen, the encoder 18 has generated several
picture parameter sets, wherein in FIG. 7, the picture parameter
set having pic_parameter_set_id 1, 2 and 3, respectively, are shown
representatively by small boxes 140. The transmission of the
parameter set NAL unit is performed via an extra transmission link
142 which is illustrated by an double-headed arrow indicated
"reliable parameter set exchange". In particular, the content of
the picture parameter set having pic_parameter_set_id of 3 is shown
at 144 in more detail for illustration purposes. The picture
parameter set having pic_parameter_set_id 3 contains information
such as the video format used, i.e. PIL, and the entropy coding
scheme used, such as one of a context adaptive binary arithmetic
coding or a context adaptive variable length (Huffman) coding. So,
the NAL unit with VCL data having pic_parameter_set_id as an index
to the parameter set NAL unit 144 does not have to contain all the
content of the parameter set NAL unit 144. Therefore, the amount of
data contained in the stream 70 can be reduced. As mentioned above,
the decoder 28 buffers the incoming parameter sets and indexes same
by the pic_parameter_set_id in the current NAL units by use of the
above explained activation mechanism (see I and II).
[0148] With respect to FIG. 8, in the following an embodiment for
the functionality of receiver or decoder 28 is described. At step
160 decoder 28 receives a NAL unit 76 of a NAL unit data stream 70
which may have been modified by the gateway 32 by the process
described with respect to FIG. 6 relative to the original version
of the data stream as created by encoder 18. At step 162, the
decoder 28 buffers the NAL unit 76 in a buffer having a
predetermined buffer space exceeding a predetermined standardized
minimum buffer size known to the encoder. Next, at step 164, the
decoder 28 detects the beginning of a new access unit. In other
words, the decoder 28 checks as to whether the NAL unit just
received at step 160 is the first of a new access unit.
[0149] The detection in step 164 is performed by use of the
afore-mentioned constraints on the order of NAL units and coded
pictures and the association to access units (see a-f). In
particular, the decoder 28 detects the beginning of a new access
unit if the NAL unit received at step 160 is the first of any of
the following NAL units after the last VCL NAL unit of a primary
coded picture of the current access unit: [0150] Access unit
delimiter NAL unit (when present) [0151] sequence parameter set NAL
unit (when present) [0152] picture parameter set NAL unit (when
present) [0153] SEI NAL unit (when present) [0154] NAL units with
nal_unit_type in the range of 13 to 18, inclusive [0155] first VCL
NAL unit of a primary coded picture (always present)
[0156] It is noted that the decoder 28 can detect the presence of a
last VCL NAL unit of a primary coded picture 100 by means of the
assumption that the payload data of all the VCL NAL units of the
primary coded picture 100 have to yield a complete pre-coded
version of one picture as well as by means of the constraints
mentioned above at (w).
[0157] When a new access unit has been detected (step 166), the
decoder 28 deallocates or flushes buffer space at step 168 by
removing an odd access unit stored in the buffer. Thereupon, the
decoder 28 makes available the picture derived from the current
access unit, i.e. the access unit which precedes the new access
unit, just detected in step 164.
[0158] Otherwise, i.e. if no new access unit has been detected
(step 166), or after step 170, the decoder 28 decodes the NAL unit
received at step 160 in order to receive the syntax elements
contained therein.
[0159] The process then loops back to step 160. As may have become
clear from the foregoing description, the decoder 28 is not liable
to a buffer overflow as long as (1) the encoder 18 has created an
NAL unit data stream 70 with access unit sizes that comply with the
maximum buffer size and (2) gateway 32 lets the data stream 70
unchanged, merely removes and discards removable and negligible NAL
units from the data stream 70, merely removes removable but
essential NAL units from the data stream 70 with transmitting them
via an extra transmission link or, alternatively, inserts NAL units
merely in access units so that the resulting access unit size does
not result in an buffer overflow at decoder's side. Anyway, by the
above-described constraints on the creation of the data stream, the
decoder 28 is in any way capable of detecting the beginning of a
new access unit in an unitary and exact way. Therefore, it is
possible for the encoder 18 and the gateway 32 to forecast the
buffer space consumption at decoder side and, therefore, to avoid
buffer spacer overflow, provided the decoder has the minimum amount
of buffer space.
[0160] As may be clear from the above, the present invention is not
restricted to multimedia, video or audio signals. Moreover, it is
noted with respect to FIG. 2, that other constellations in which
the present invention could be used are also possible. For example,
more than one gateway 32 could be interposed between the data
stream presentation (encoder) and the decoder. With respect to FIG.
6 it is noted, that the gateway 32 does not have to influence all
of the options shown in FIG. 6. For example, a gateway could be
designed to implement merely the removal of NAL units from the data
stream without implementing steps 128 to 134. Alternatively, a
gateway could implement all steps of FIG. 6 except step 134 or all
steps except 130 and 132.
[0161] With regard to decoder of FIG. 8, it is noted that the
buffering management described there helps in standardizing the
data stream format of the data stream 70 of that embodiment.
Nevertheless, the buffer management may be realized in a different
way, for example with de-allocating buffer space in other units
than access units.
[0162] In other words, in accordance with the above embodiments
each syntax element is placed into a logical packet called a NAL
unit. Rather than forcing a specific bitstream interface to the
system as in prior video standards, the NAL unit syntax structure
allows greater customization of the method of carrying the video
content in a manner appropriate for each specific network. In
particular, the above embodiment defines how NAL units are to be
ordered within in access units. The constraints formulated on the
order of NAL units specify the decoding order that must by accepted
by an standard-conform decoder allowing a novel degree of freedom.
Moreover, the ordering of the NAL units and their arrangement
specifies access units and makes the distinction between various
access units possible even if NAL units that are allowed to be
removed from the bitstream are removed.
[0163] The above embodiments permit, by their new way of defining
the decoding order, an increased degree of flexibility that is
especially important in internet applications where each NAL unit
is typically transported in one packet and shuffling is likely to
occur. This permits simpler decoder implementations.
[0164] The distinction between various access units even if units
that are allowed to be removed from the bitstream are removed
permits a flexible rate shaping and transcoding of data and makes
the method robust the transmission errors. The automatic
distinction method also increases coding efficiency by making start
codes or delimiter codes superfluous.
[0165] Depending on an actual implementation, the inventive
encoding/decoding/converting methods can be implemented in hardware
or in software. Therefore, the present invention also relates to a
computer program, which can be stored on a computer-readable medium
such as a CD, a disk or any other data carrier. The present
invention is, therefore, also a computer program having a program
code which, when executed on a computer, performs the inventive
method of encoding, converting or decoding described in connection
with the above figures.
[0166] While this invention has been described in terms of several
preferred embodiments, there are alterations, permutations, and
equivalents which fall within the scope of this invention. It
should also be noted that there are many alternative ways of
implementing the methods and compositions of the present invention.
It is therefore intended that the following appended claims be
interpreted as including all such alterations, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
[0167] Furthermore, it is noted that all steps indicated in the
flow diagrams are implemented by respective means in the encoder,
gateway or decoder, respectively, an that the implementations may
comprise subroutines running on a CPU, circuit parts of an ASIC or
the like.
* * * * *