U.S. patent application number 14/742258 was filed with the patent office on 2015-12-24 for representation format update in multi-layer codecs.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Fnu HENDRY, Adarsh Krishnan RAMASUBRAMONIAN, Ye-Kui WANG.
Application Number | 20150373343 14/742258 |
Document ID | / |
Family ID | 54870865 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150373343 |
Kind Code |
A1 |
HENDRY; Fnu ; et
al. |
December 24, 2015 |
REPRESENTATION FORMAT UPDATE IN MULTI-LAYER CODECS
Abstract
An apparatus for encoding video information according to certain
aspects includes a memory and a processor configured to: receive a
video parameter set (VPS) including one or more representation
format syntax structures, the VPS indicating a first representation
format syntax structure associated with a first layer of the
plurality of layers; receive a sequence parameter set (SPS)
including (1) a reference to a second representation format syntax
structure in the VPS or (2) a third representation format syntax
structure not included in the VPS, each representation format
syntax structure including a first flag indicative of whether to
code color components of chroma format of a layer separately; and
update a value of a first variable indicative of whether to code
color components of chroma format of a layer separately without
referring to a value of the first flag in the first representation
format syntax structure.
Inventors: |
HENDRY; Fnu; (Poway, CA)
; RAMASUBRAMONIAN; Adarsh Krishnan; (San Diego, CA)
; WANG; Ye-Kui; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
54870865 |
Appl. No.: |
14/742258 |
Filed: |
June 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62015378 |
Jun 20, 2014 |
|
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Current U.S.
Class: |
375/240.12 |
Current CPC
Class: |
H04N 19/30 20141101;
H04N 19/124 20141101; H04N 19/597 20141101; H04N 19/31 20141101;
H04N 19/105 20141101; H04N 19/51 20141101; H04N 19/70 20141101;
H04N 19/176 20141101; H04N 19/50 20141101; H04N 19/52 20141101;
H04N 19/172 20141101; H04N 19/187 20141101 |
International
Class: |
H04N 19/187 20060101
H04N019/187; H04N 19/30 20060101 H04N019/30; H04N 19/124 20060101
H04N019/124; H04N 19/176 20060101 H04N019/176; H04N 19/172 20060101
H04N019/172; H04N 19/50 20060101 H04N019/50; H04N 19/597 20060101
H04N019/597 |
Claims
1. An apparatus for encoding video information, comprising: a
memory for storing video information associated with a plurality of
layers; and a processor operationally coupled to the memory and
configured to: receive a video parameter set (VPS) including one or
more representation format syntax structures, the VPS indicating a
first representation format syntax structure of the one or more
representation format syntax structures associated with a first
layer of the plurality of layers; receive a sequence parameter set
(SPS) including (1) a reference to a second representation format
syntax structure of the one or more representation format syntax
structures in the VPS or (2) a third representation format syntax
structure not included in the one or more representation format
syntax structures in the VPS, each representation format syntax
structure including a first flag indicative of whether to code
color components of chroma format of a layer separately; and update
a value of a first variable indicative of whether to code color
components of chroma format of a layer separately without referring
to a value of the first flag in the first representation format
syntax structure, the first variable associated with the first
layer.
2. The apparatus of claim 1, wherein the SPS includes the reference
to the second representation format syntax structure, and the
processor is configured to update the value of the first variable
to be equal to the value of the first flag in the second
representation format syntax structure.
3. The apparatus of claim 2, wherein each representation format
syntax structure includes one or more second flags in addition to
the first flag, and the processor is further configured to update
values of one or more second variables corresponding to the one or
more second flags to values of the one or more second flags in the
second representation format syntax structure when the values of
one or more second flags in the second representation format syntax
structure are less than or equal to values of the one or more
second flags in the first representation format syntax structure,
the one or more second variables associated with the first
layer.
4. The apparatus of claim 1, wherein the SPS includes the third
representation format syntax structure, and the processor is
configured to update the value of the first variable to be equal to
the value of the first flag in the third representation format
syntax structure.
5. The apparatus of claim 4, wherein each representation format
syntax structure includes one or more second flags in addition to
the first flag, and the processor is further configured to update
values of one or more second variables corresponding to the one or
more second flags to values of the one or more second flags in the
third representation format syntax structure when the values of one
or more second flags in the third representation format syntax
structure are less than or equal to values of the one or more
second flags in the first representation format syntax structure,
the one or more second variables associated with the first
layer.
6. The apparatus of claim 1, wherein the VPS includes a mapping of
which of the one or more representation format syntax structures is
associated with respective layer of the plurality of layers.
7. The apparatus of claim 1, wherein the first flag indicates that
color components of chroma format of a layer should be coded
separately when the value of the first flag is equal to 1 and the
first variable indicates that color components of chroma format of
a layer should be coded separately when the value of the first
variable is equal to 1.
8. The apparatus of claim 1, wherein the first flag indicates that
color components of chroma format of a layer should not be coded
separately when the value of the first flag is equal to 0 and the
first variable indicates that color components of chroma format of
a layer should not be coded separately when the value of the first
variable is equal to 0.
9. The apparatus of claim 1, wherein the first flag comprises
separate_colour_plane_vps_flag and the first variable comprises
separate_colour_plane_flag.
10. The apparatus of claim 1, wherein the reference to the second
representation format syntax structure comprises
sps_rep_format_idx.
11. The apparatus of claim 1, wherein the VPS applies to all of the
plurality of layers and the SPS applies to a particular layer among
the plurality of layers.
12. The apparatus of claim 1, wherein the processor is further
configured to code video data associated with the VPS based on the
value of the first variable.
13. The apparatus of claim 1, wherein the apparatus comprises one
or more of: a desktop computer, a notebook computer, a laptop
computer, a tablet computer, a set-top box, a telephone handset, a
smart phone, a wireless communication device, a smart pad, a
television, a camera, a display device, a digital media player, a
video gaming console, or a video streaming device.
14. A method of encoding video information, comprising: storing
video information associated with a plurality of layers; receiving
a video parameter set (VPS) including one or more representation
format syntax structures, the VPS indicating a first representation
format syntax structure of the one or more representation format
syntax structures associated with a first layer of the plurality of
layers; receiving a sequence parameter set (SPS) including (1) a
reference to a second representation format syntax structure of the
one or more representation format syntax structures in the VPS or
(2) a third representation format syntax structure not included in
the one or more representation format syntax structures in the VPS,
each representation format syntax structure including a first flag
indicative of whether to code color components of chroma format of
a layer separately; and updating a value of a first variable
indicative of whether to code color components of chroma format of
a layer separately without referring to a value of the first flag
in the first representation format syntax structure, the first
variable associated with the first layer.
15. The method of claim 14, wherein the SPS includes the reference
to the second representation format syntax structure, and the value
of the first variable is updated to be equal to the value of the
first flag in the second representation format syntax
structure.
16. The method of claim 15, wherein each representation format
syntax structure includes one or more second flags in addition to
the first flag, the method further comprising updating values of
one or more second variables corresponding to the one or more
second flags to values of the one or more second flags in the
second representation format syntax structure when the values of
one or more second flags in the second representation format syntax
structure are less than or equal to values of the one or more
second flags in the first representation format syntax structure,
the one or more second variables associated with the first
layer.
17. The method of claim 14, wherein the SPS includes the third
representation format syntax structure, and the value of the first
variable is updated to be equal to the value of the first flag in
the third representation format syntax structure.
18. The method of claim 17, wherein each representation format
syntax structure includes one or more second flags in addition to
the first flag, the method further comprising updating values of
one or more second variables corresponding to the one or more
second flags to values of the one or more second flags in the third
representation format syntax structure when the values of one or
more second flags in the third representation format syntax
structure are less than or equal to values of the one or more
second flags in the first representation format syntax structure,
the one or more second variables associated with the first
layer.
19. The method of claim 14, wherein the VPS includes a mapping of
which of the one or more representation format syntax structures is
associated with respective layer of the plurality of layers.
20. The method of claim 14, wherein the first flag indicates that
color components of chroma format of a layer should be coded
separately when the value of the first flag is equal to 1 and the
first variable indicates that color components of chroma format of
a layer should be coded separately when the value of the first
variable is equal to 1.
21. The method of claim 14, wherein the first flag indicates that
color components of chroma format of a layer should not be coded
separately when the value of the first flag is equal to 0 and the
first variable indicates that color components of chroma format of
a layer should not be coded separately when the value of the first
variable is equal to 0.
22. The method of claim 14, wherein the first flag comprises
separate_colour_plane_vps_flag and the first variable comprises
separate_colour_plane_flag.
23. The method of claim 14, wherein the reference to the second
representation format syntax structure comprises
sps_rep_format_idx.
24. The method of claim 14, further comprising coding video data
associated with the VPS based on the value of the first
variable.
25. A non-transitory computer readable medium comprising
instructions that when executed on a processor comprising computer
hardware cause the processor to: store video information associated
with a plurality of layers; receive a video parameter set (VPS)
including one or more representation format syntax structures, the
VPS indicating a first representation format syntax structure of
the one or more representation format syntax structures associated
with a first layer of the plurality of layers; receive a sequence
parameter set (SPS) including (1) a reference to a second
representation format syntax structure of the one or more
representation format syntax structures in the VPS or (2) a third
representation format syntax structure not included in the one or
more representation format syntax structures in the VPS, each
representation format syntax structure including a first flag
indicative of whether to code color components of chroma format of
a layer separately; and update a value of a first variable
indicative of whether to code color components of chroma format of
a layer separately without referring to a value of the first flag
in the first representation format syntax structure, the first
variable associated with the first layer.
26. The computer readable medium of claim 25, wherein the SPS
includes the reference to the second representation format syntax
structure, and the instructions cause the processor to update the
value of the first variable to be equal to the value of the first
flag in the second representation format syntax structure.
27. The computer readable medium of claim 25, wherein the SPS
includes the third representation format syntax structure, and the
instructions cause the processor to update the value of the first
variable to be equal to the value of the first flag in the third
representation format syntax structure.
28. An apparatus for encoding video information, comprising: means
for storing video information associated with a plurality of
layers; means for receiving a video parameter set (VPS) including
one or more representation format syntax structures, the VPS
indicating a first representation format syntax structure of the
one or more representation format syntax structures associated with
a first layer of the plurality of layers; means for receiving a
sequence parameter set (SPS) including (1) a reference to a second
representation format syntax structure of the one or more
representation format syntax structures in the VPS or (2) a third
representation format syntax structure not included in the one or
more representation format syntax structures in the VPS, each
representation format syntax structure including a first flag
indicative of whether to code color components of chroma format of
a layer separately; and means for updating a value of a first
variable indicative of whether to code color components of chroma
format of a layer separately without referring to a value of the
first flag in the first representation format syntax structure, the
first variable associated with the first layer.
29. The apparatus of claim 28, wherein the SPS includes the
reference to the second representation format syntax structure, and
the means for updating is configured to update the value of the
first variable to be equal to the value of the first flag in the
second representation format syntax structure.
30. The apparatus of claim 28, wherein the SPS includes the third
representation format syntax structure, and the means for updating
is configured to update the value of the first variable to be equal
to the value of the first flag in the third representation format
syntax structure.
Description
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/015,378, filed Jun. 20, 2014, which is
incorporated by reference in its entirety. Any and all applications
for which a foreign or domestic priority claim is identified in the
Application Data Sheet as filed with the present application are
hereby incorporated by reference under 37 CFR 1.57.
TECHNICAL FIELD
[0002] This disclosure relates to the field of video coding and
compression, including both single-layer video coding and
multi-layer video coding. Multi-layer video coding can include
scalable video coding, multiview video coding, three-dimensional
(3D) video coding, etc.
BACKGROUND
[0003] Digital video capabilities can be incorporated into a wide
range of devices, including digital televisions, digital direct
broadcast systems, wireless broadcast systems, personal digital
assistants (PDAs), laptop or desktop computers, digital cameras,
digital recording devices, digital media players, video gaming
devices, video game consoles, cellular or satellite radio
telephones, video teleconferencing devices, and the like. Digital
video devices implement video compression techniques, such as those
described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263,
ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High
Efficiency Video Coding (HEVC) standard, and extensions of such
standards. The video devices may transmit, receive, encode, decode,
and/or store digital video information more efficiently by
implementing such video coding techniques.
[0004] Video compression techniques perform spatial (intra-picture)
prediction and/or temporal (inter-picture) prediction to reduce or
remove redundancy inherent in video sequences. For block-based
video coding, a video slice (e.g., a video frame, a portion of a
video frame, etc.) may be partitioned into video blocks, which may
also be referred to as treeblocks, coding units (CUs) and/or coding
nodes. Video blocks in an intra-coded (I) slice of a picture are
encoded using spatial prediction with respect to reference samples
in neighboring blocks in the same picture. Video blocks in an
inter-coded (P or B) slice of a picture may use spatial prediction
with respect to reference samples in neighboring blocks in the same
picture or temporal prediction with respect to reference samples in
other reference pictures. Pictures may be referred to as frames,
and reference pictures may be referred to as reference frames.
[0005] Spatial or temporal prediction results in a predictive block
for a block to be coded. Residual data represents pixel differences
between the original block to be coded and the predictive block. An
inter-coded block is encoded according to a motion vector that
points to a block of reference samples forming the predictive
block, and the residual data indicating the difference between the
coded block and the predictive block. An intra-coded block is
encoded according to an intra-coding mode and the residual data.
For further compression, the residual data may be transformed from
the pixel domain to a transform domain, resulting in residual
transform coefficients, which then may be quantized. The quantized
transform coefficients, initially arranged in a two-dimensional
array, may be scanned in order to produce a one-dimensional vector
of transform coefficients, and entropy encoding may be applied to
achieve even more compression.
SUMMARY
[0006] The systems, methods and devices of this disclosure each
have several innovative aspects, no single one of which is solely
responsible for the desirable attributes disclosed herein. The
details of one or more examples are set forth in the accompanying
drawings and the description below, which are not intended to limit
the full scope of the inventive concepts described herein. Other
features, objects, and advantages will be apparent from the
description and drawings, and from the claims.
[0007] Scalable video coding (SVC) refers to video coding in which
a base layer (BL), sometimes referred to as a reference layer (RL),
and one or more scalable enhancement layers (ELs) are used. In SVC,
the base layer can carry video data with a base level of quality.
The one or more enhancement layers can carry additional video data
to support, for example, higher spatial, temporal, and/or
signal-to-noise ratio (SNR) levels. Enhancement layers may be
defined relative to a previously encoded layer. For example, a
bottom layer may serve as a BL, while a top layer may serve as an
EL. Middle layers may serve as either ELs or RLs, or both. For
example, a middle layer (e.g., a layer that is neither the lowest
layer nor the highest layer) may be an EL for the layers below the
middle layer, such as the base layer or any intervening enhancement
layers, and at the same time serve as a RL for one or more
enhancement layers above the middle layer. Similarly, in the
Multiview or 3D extension of the HEVC standard, there may be
multiple views, and information of one view may be utilized to code
(e.g., encode or decode) the information of another view (e.g.,
motion estimation, motion vector prediction and/or other
redundancies).
[0008] An apparatus for coding video information according to
certain aspects includes a memory and a processor. The memory is
configured to store video information associated with a plurality
of layers. The processor is configured to obtain information
associated with a current access unit (AU) to be coded, the current
AU containing pictures from a plurality of layers, the plurality of
layers including a current layer to be coded, the current layer
including a current picture to be coded. The processor is further
configured to determine a value of a first flag indicative of
whether preceding pictures that precede the current picture in the
current layer in decoding order are used for temporal motion vector
prediction (TMVP) of subsequent pictures that follow the current
picture in the current layer in decoding order, the first flag
associated with the current picture. The processor is additionally
configured to refrain from using the preceding pictures in the
current layer as reference pictures for TMVP of the current
picture, in response to determining that the value of the first
flag indicates that the preceding pictures in the current layer
should not be used for TMVP of the subsequent pictures in the
current layer.
[0009] An apparatus for coding video information according to
certain aspects includes a memory and a processor. In one
embodiment, the apparatus is for encoding video information. The
memory is configured to store video information associated with a
plurality of layers. The processor is configured to receive a video
parameter set (VPS) including one or more representation format
syntax structures, the VPS indicating a first representation format
syntax structure of the one or more representation format syntax
structures associated with a first layer of the plurality of
layers. The processor is further configured to receive a sequence
parameter set (SPS) including (1) a reference to a second
representation format syntax structure of the one or more
representation format syntax structures in the VPS or (2) a third
representation format syntax structure not included in the one or
more representation format syntax structures in the VPS, each
representation format syntax structure including a first flag
indicative of whether to code color components of chroma format of
a layer separately. The processor is additionally configured to
update a value of a first variable indicative of whether to code
color components of chroma format of a layer separately without
referring to a value of the first flag in the first representation
format syntax structure, the first variable associated with the
first layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is a block diagram illustrating an example video
encoding and decoding system that may utilize techniques in
accordance with aspects described in this disclosure.
[0011] FIG. 1B is a block diagram illustrating another example
video encoding and decoding system that may perform techniques in
accordance with aspects described in this disclosure.
[0012] FIG. 2A is a block diagram illustrating an example of a
video encoder that may implement techniques in accordance with
aspects described in this disclosure.
[0013] FIG. 2B is a block diagram illustrating an example of a
video encoder that may implement techniques in accordance with
aspects described in this disclosure.
[0014] FIG. 3A is a block diagram illustrating an example of a
video decoder that may implement techniques in accordance with
aspects described in this disclosure.
[0015] FIG. 3B is a block diagram illustrating an example of a
video decoder that may implement techniques in accordance with
aspects described in this disclosure.
[0016] FIG. 4 is a block diagram illustrating an example
configuration of pictures in different layers.
[0017] FIG. 5 is a block diagram illustrating an example
configuration of pictures in different layers.
[0018] FIG. 6 is a flowchart illustrating a method of coding video
information, according to one or more aspects of the present
disclosure.
[0019] FIG. 7 is a flowchart illustrating a method of coding video
information, according to one or more aspects of the present
disclosure.
DETAILED DESCRIPTION
[0020] In general, this disclosure relates to single layer coding
as well as inter-layer prediction for scalable video coding in the
context of advanced video codecs, such as HEVC (High Efficiency
Video Coding). More specifically, the present disclosure relates to
systems and methods for temporal motion vector prediction (TMVP)
indication and representation format update in multi-layer
codecs.
[0021] In the description below, H.264/Advanced Video Coding (AVC)
techniques related to certain embodiments are described; the HEVC
standard and related techniques are also discussed. While certain
embodiments are described herein in the context of the HEVC and/or
H.264 standards, one having ordinary skill in the art may
appreciate that systems and methods disclosed herein may be
applicable to any suitable video coding standard. For example,
embodiments disclosed herein may be applicable to one or more of
the following standards: International Telecommunication Union
(ITU) Telecommunication Standardization Sector (ITU-T) H.261,
International Organization for Standardization (ISO) and the
International Electrotechnical Commission (IEC) (ISO/IEC) Moving
Picture Experts Group (MPEG) 1 (MPEG-1) Visual, ITU-T H.262 or
ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T
H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable
Video Coding (SVC) and Multiview Video Coding (MVC) extensions.
[0022] HEVC generally follows the framework of previous video
coding standards in many respects. The unit of prediction in HEVC
is different from the units of prediction (e.g., macroblock) in
certain previous video coding standards. In fact, the concept of a
macroblock does not exist in HEVC as understood in certain previous
video coding standards. A macroblock is replaced by a hierarchical
structure based on a quadtree scheme, which may provide high
flexibility, among other possible benefits. For example, within the
HEVC scheme, three types of blocks, Coding Unit (CU), Prediction
Unit (PU), and Transform Unit (TU), are defined. CU may refer to
the basic unit of region splitting. CU may be considered analogous
to the concept of macroblock, but HEVC does not restrict the
maximum size of CUs and may allow recursive splitting into four
equal size CUs to improve the content adaptivity. PU may be
considered the basic unit of inter/intra prediction, and a single
PU may contain multiple arbitrary shape partitions to effectively
code irregular image patterns. TU may be considered the basic unit
of transform. TU can be defined independently from the PU; however,
the size of a TU may be limited to the size of the CU to which the
TU belongs. This separation of the block structure into three
different concepts may allow each unit to be optimized according to
the respective role of the unit, which may result in improved
coding efficiency.
[0023] For purposes of illustration only, certain embodiments
disclosed herein are described with examples including only two
layers (e.g., a lower layer such as the base layer, and a higher
layer such as the enhancement layer) of video data. A "layer" of
video data may generally refer to a sequence of pictures having at
least one common characteristic, such as a view, a frame rate, a
resolution, or the like. For example, a layer may include video
data associated with a particular view (e.g., perspective) of
multi-view video data. As another example, a layer may include
video data associated with a particular layer of scalable video
data. Thus, this disclosure may interchangeably refer to a layer
and a view of video data. That is, a view of video data may be
referred to as a layer of video data, and a layer of video data may
be referred to as a view of video data. In addition, a multi-layer
codec (also referred to as a multi-layer video coder or multi-layer
encoder-decoder) may jointly refer to a multiview codec or a
scalable codec (e.g., a codec configured to encode and/or decode
video data using MV-HEVC, 3D-HEVC, SHVC, or another multi-layer
coding technique). Video encoding and video decoding may both
generally be referred to as video coding. It should be understood
that such examples may be applicable to configurations including
multiple base and/or enhancement layers. In addition, for ease of
explanation, the following disclosure includes the terms "frames"
or "blocks" with reference to certain embodiments. However, these
terms are not meant to be limiting. For example, the techniques
described below can be used with any suitable video units, such as
blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,
etc.
Video Coding Standards
[0024] A digital image, such as a video image, a TV image, a still
image or an image generated by a video recorder or a computer, may
consist of pixels or samples arranged in horizontal and vertical
lines. The number of pixels in a single image is typically in the
tens of thousands. Each pixel typically contains luminance and
chrominance information. Without compression, the sheer quantity of
information to be conveyed from an image encoder to an image
decoder would render real-time image transmission impossible. To
reduce the amount of information to be transmitted, a number of
different compression methods, such as JPEG, MPEG and H.263
standards, have been developed.
[0025] Video coding standards include ITU-T H.261, ISO/IEC MPEG-1
Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC
MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),
including its SVC and MVC extensions.
[0026] In addition, a new video coding standard, namely High
Efficiency Video Coding (HEVC), is being developed by the Joint
Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding
Experts Group (VCEG) and ISO/IEC Moving Picture Experts Group
(MPEG). The full citation for the HEVC Draft 10 is document
JCTVC-L1003, Bross et al., "High Efficiency Video Coding (HEVC)
Text Specification Draft 10," Joint Collaborative Team on Video
Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 12th
Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan. 23, 2013. The
multiview extension to HEVC, namely MV-HEVC, and the scalable
extension to HEVC, named SHVC, are also being developed by the
JCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video Coding
Extension Development) and JCT-VC, respectively.
Overview
[0027] Early versions of SHVC and MV-HEVC (e.g., SHVC Working Draft
6, MV-HEVC Working Draft 8, etc.) implement a restriction that
temporal motion vector from pictures that precede the current
picture in decoding order should not be used in TMVP of any
pictures that follow the current picture in decoding order when the
values of both slice_temporal_mvp_enabled_flag and temporal ID of
the current picture are equal to 0 and when the pictures belong to
the base layer (e.g., a layer having layer ID=0).
Slice_temporal_mvp_enabled_flag can indicate whether the current
picture in a slice can use TMVP, for example, based on preceding
pictures of the current picture as reference pictures (e.g.,
collocated pictures). The restriction and the condition that the
pictures belong to the base layer were introduced, for example, to
allow the enhancement layer to use TMVP. However, the enhancement
layer may use TMVP without limiting the restriction to the base
layer.
[0028] The early versions of SHVC and MV-HEVC also add a new SEI
message called TMVP constraints SEI message, which provides an
indication of whether pictures of the current layer that precede
the current picture should not be used as collocated pictures in
TMVP for any subsequent picture of the same layer. For example, the
TMVP constraints SEI message can include a flag called
prev_pics_not_used_flag that indicates whether the preceding
pictures of the current picture in the current layer in decoding
order can be used for TMVP of subsequent pictures of the current
picture in the current layer in decoding order. However, the
semantics of prev_pics_not_used_flag in the early versions of SHVC
and MV-HEVC can lead to a conflict with
slice_temporal_mvp_enabled_flag. For instance,
slice_temporal_mvp_enabled_flag in the slice header of the slice
containing the current picture is equal to 1 and indicates that the
current picture can use TMVP, referring to preceding pictures of
the current picture as collocated pictures, but
prev_pics_not_used_flag in the TMVP constraints SEI message for the
current picture is equal to 1 and indicates that subsequent
pictures of the current picture in decoding should not use
preceding pictures of the current picture for TMVP in decoding
order. In such case, any error introduced in the TMVP of the
current picture using preceding pictures may be propagated to the
subsequent pictures since the subsequent pictures could use the
current picture as a collocated picture for TMVP. Although the
subsequent pictures are not using any preceding pictures of the
current picture for TMVP, the subsequent pictures may use the
current picture itself for TMVP.
[0029] In order to address these and other challenges, the
techniques according to certain aspects can apply the restriction
that temporal motion vector from any preceding pictures of the
current picture should not be used in TMVP of any subsequent
pictures of the current picture in decoding order to all layers.
For example, the restriction can apply to pictures when
slice_temporal_mvp_enabled_flag=0 and temporal ID=0 regardless of
whether the pictures belong to the base layer or other layers. In
one example, the TMVP constraints SEI message can be used with
slice_temporal_mvp_enabled_flag to allow an enhancement layer to
use TMVP without limiting the restriction to the base layer.
[0030] Moreover, the techniques can modify the semantics of
prev_pics_not_used_flag, for example, to resolve the conflict
between slice_temporal_mvp_enabled_flag for the current picture and
prev_pics_not_used_flag for the current picture. For instance,
prev_pics_not_used_flag can take a higher precedence than
slice_temporal_mvp_enabled_flag. In one example,
prev_pics_not_used_flag is modified to indicate that preceding
pictures of the current picture should not be used for TMVP of the
current picture as well as the subsequent pictures of the current
picture in decoding order.
[0031] The restriction imposed by slice_temporal_mvp_enabled_flag
and the restriction imposed by prev_pics_not_used_flag may be
implemented for error resilience purposes. However, when both
slice_temporal_mvp_enabled_flag and prev_pics_not_used_flag are
equal to 1, any error in the TMVP of the current picture can still
be introduced in the TMVP of the subsequent pictures of the current
picture in decoding order. By disallowing both the current picture
and the subsequent pictures from using the preceding pictures of
the current picture in TMVP, error resilience can be significantly
improved and increased.
[0032] Further, in the early versions of SHVC and MV-HEVC, the
values of syntax elements or flags in a VPS are used to constrain
the values of corresponding syntax elements or flags in a SPS. The
VPS and the SPS can both include representation format information.
The representation format information can include picture width and
height (e.g., picture size), bit depth of chroma components, bit
depth of luma components, color plane information, conformance
window size. The VPS can apply to all the layers, and generally,
one VPS can be defined for a bitstream. The SPS can be specific to
a particular layer, and multiple SPSs can be present if a bitstream
includes multiple sequences. In general, the values in the VPS
represent the worst case scenario values or maximum values, and the
SPS can specify different values that are less than or equal to the
values in the VPS as appropriate. Accordingly, the values of syntax
elements or flags in the VPS can constrain the values of
corresponding syntax elements or flags in the SPS when
representation format information is updated for the SPS. However,
for certain syntax elements or flags, it is unclear whether a worst
case scenario value or a maximum value is applicable. One example
can be a flag having a value of either 0 or 1.
[0033] In order to address these and other challenges, the
techniques according to certain aspects can remove the constraint
for separate_colour_plane_flag in the representation format.
Separate_colour_plane_flag can indicate whether the three colour
components (e.g., Y, Cb, or Cr) of the chroma format are coded
separately or not. When the value of separate_colour_plane_flag is
to be updated in an SPS, the techniques does not have to check
whether the desired value of separate_colour_plane_flag is less
than or equal to the value of separate_colour_plane_flag in the
VPS. In this way, the value of separate_colour_plane_flag can be
updated in the SPS in a more flexible manner, and the update of
separate_colour_plane_flag in representation format can be more
efficient.
Video Coding System
[0034] Various aspects of the novel systems, apparatuses, and
methods are described more fully hereinafter with reference to the
accompanying drawings. This disclosure may, however, be embodied in
many different forms and should not be construed as limited to any
specific structure or function presented throughout this
disclosure. Rather, these aspects are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the disclosure to those skilled in the art. Based on the
teachings herein one skilled in the art should appreciate that the
scope of the disclosure is intended to cover any aspect of the
novel systems, apparatuses, and methods disclosed herein, whether
implemented independently of, or combined with, any other aspect of
the present disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the present
disclosure is intended to cover such an apparatus or method which
is practiced using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the present disclosure set forth herein. It should be understood
that any aspect disclosed herein may be embodied by one or more
elements of a claim.
[0035] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
of the disclosure. Although some benefits and advantages of the
preferred aspects are mentioned, the scope of the disclosure is not
intended to be limited to particular benefits, uses, or objectives.
Rather, aspects of the disclosure are intended to be broadly
applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof.
[0036] The attached drawings illustrate examples. Elements
indicated by reference numbers in the attached drawings correspond
to elements indicated by like reference numbers in the following
description. In this disclosure, elements having names that start
with ordinal words (e.g., "first," "second," "third," and so on) do
not necessarily imply that the elements have a particular order.
Rather, such ordinal words are merely used to refer to different
elements of a same or similar type.
[0037] FIG. 1A is a block diagram that illustrates an example video
coding system 10 that may utilize techniques in accordance with
aspects described in this disclosure. As used described herein, the
term "video coder" refers generically to both video encoders and
video decoders. In this disclosure, the terms "video coding" or
"coding" may refer generically to video encoding and video
decoding. In addition to video encoders and video decoders, the
aspects described in the present application may be extended to
other related devices such as transcoders (e.g., devices that can
decode a bitstream and re-encode another bitstream) and middleboxes
(e.g., devices that can modify, transform, and/or otherwise
manipulate a bitstream).
[0038] As shown in FIG. 1A, video coding system 10 includes a
source device 12 that generates encoded video data to be decoded at
a later time by a destination device 14. In the example of FIG. 1A,
the source device 12 and destination device 14 constitute separate
devices. It is noted, however, that the source and destination
devices 12, 14 may be on or part of the same device, as shown in
the example of FIG. 1B.
[0039] With reference once again, to FIG. 1A, the source device 12
and the destination device 14 may respectively comprise any of a
wide range of devices, including desktop computers, notebook (e.g.,
laptop) computers, tablet computers, set-top boxes, telephone
handsets such as so-called "smart" phones, so-called "smart" pads,
televisions, cameras, display devices, digital media players, video
gaming consoles, video streaming device, or the like. In some
cases, the source device 12 and the destination device 14 may be
equipped for wireless communication.
[0040] The destination device 14 may receive, via link 16, the
encoded video data to be decoded. The link 16 may comprise any type
of medium or device capable of moving the encoded video data from
the source device 12 to the destination device 14. In the example
of FIG. 1A, the link 16 may comprise a communication medium to
enable the source device 12 to transmit encoded video data to the
destination device 14 in real-time. The encoded video data may be
modulated according to a communication standard, such as a wireless
communication protocol, and transmitted to the destination device
14. The communication medium may comprise any wireless or wired
communication medium, such as a radio frequency (RF) spectrum or
one or more physical transmission lines. The communication medium
may form part of a packet-based network, such as a local area
network, a wide-area network, or a global network such as the
Internet. The communication medium may include routers, switches,
base stations, or any other equipment that may be useful to
facilitate communication from the source device 12 to the
destination device 14.
[0041] Alternatively, encoded data may be output from an output
interface 22 to an optional storage device 31. Similarly, encoded
data may be accessed from the storage device 31 by an input
interface 28, for example, of the destination device 14. The
storage device 31 may include any of a variety of distributed or
locally accessed data storage media such as a hard drive, flash
memory, volatile or non-volatile memory, or any other suitable
digital storage media for storing encoded video data. In a further
example, the storage device 31 may correspond to a file server or
another intermediate storage device that may hold the encoded video
generated by the source device 12. The destination device 14 may
access stored video data from the storage device 31 via streaming
or download. The file server may be any type of server capable of
storing encoded video data and transmitting that encoded video data
to the destination device 14. Example file servers include a web
server (e.g., for a website), a File Transfer Protocol (FTP)
server, network attached storage (NAS) devices, or a local disk
drive. The destination device 14 may access the encoded video data
through any standard data connection, including an Internet
connection. This may include a wireless channel (e.g., a wireless
local area network (WLAN) connection), a wired connection (e.g., a
digital subscriber line (DSL), a cable modem, etc.), or a
combination of both that is suitable for accessing encoded video
data stored on a file server. The transmission of encoded video
data from the storage device 31 may be a streaming transmission, a
download transmission, or a combination of both.
[0042] The techniques of this disclosure are not limited to
wireless applications or settings. The techniques may be applied to
video coding in support of any of a variety of multimedia
applications, such as over-the-air television broadcasts, cable
television transmissions, satellite television transmissions,
streaming video transmissions, e.g., via the Internet (e.g.,
dynamic adaptive streaming over Hypertext Transfer Protocol (HTTP),
etc.), encoding of digital video for storage on a data storage
medium, decoding of digital video stored on a data storage medium,
or other applications. In some examples, video coding system 10 may
be configured to support one-way or two-way video transmission to
support applications such as video streaming, video playback, video
broadcasting, and/or video telephony.
[0043] In the example of FIG. 1A, the source device 12 includes a
video source 18, a video encoder 20 and the output interface 22. In
some cases, the output interface 22 may include a
modulator/demodulator (modem) and/or a transmitter. In the source
device 12, the video source 18 may include a source such as a video
capture device, e.g., a video camera, a video archive containing
previously captured video, a video feed interface to receive video
from a video content provider, and/or a computer graphics system
for generating computer graphics data as the source video, or a
combination of such sources. As one example, if the video source 18
is a video camera, the source device 12 and the destination device
14 may form so-called "camera phones" or "video phones," as
illustrated in the example of FIG. 1B. However, the techniques
described in this disclosure may be applicable to video coding in
general, and may be applied to wireless and/or wired
applications.
[0044] The captured, pre-captured, or computer-generated video may
be encoded by the video encoder 20. The encoded video data may be
transmitted to the destination device 14 via the output interface
22 of the source device 12. The encoded video data may also (or
alternatively) be stored onto the storage device 31 for later
access by the destination device 14 or other devices, for decoding
and/or playback. The video encoder 20 illustrated in FIGS. 1A and
1B may comprise the video encoder 20 illustrated FIG. 2A, the video
encoder 23 illustrated in FIG. 2B, or any other video encoder
described herein.
[0045] In the example of FIG. 1A, the destination device 14
includes an input interface 28, a video decoder 30, and a display
device 32. In some cases, the input interface 28 may include a
receiver and/or a modem. The input interface 28 of the destination
device 14 may receive the encoded video data over the link 16
and/or from the storage device 31. The encoded video data
communicated over the link 16, or provided on the storage device
31, may include a variety of syntax elements generated by the video
encoder 20 for use by a video decoder, such as the video decoder
30, in decoding the video data. Such syntax elements may be
included with the encoded video data transmitted on a communication
medium, stored on a storage medium, or stored a file server. The
video decoder 30 illustrated in FIGS. 1A and 1B may comprise the
video decoder 30 illustrated FIG. 3A, the video decoder 33
illustrated in FIG. 3B, or any other video decoder described
herein.
[0046] The display device 32 may be integrated with, or external
to, the destination device 14. In some examples, the destination
device 14 may include an integrated display device and also be
configured to interface with an external display device. In other
examples, the destination device 14 may be a display device. In
general, the display device 32 displays the decoded video data to a
user, and may comprise any of a variety of display devices such as
a liquid crystal display (LCD), a plasma display, an organic light
emitting diode (OLED) display, or another type of display
device.
[0047] In related aspects, FIG. 1B shows an example video encoding
and decoding system 10' wherein the source and destination devices
12, 14 are on or part of a device 11. The device 11 may be a
telephone handset, such as a "smart" phone or the like. The device
11 may include an optional controller/processor device 13 in
operative communication with the source and destination devices 12,
14. The system 10' of FIG. 1B, and components thereof, are
otherwise similar to the system 10 of FIG. 1A, and components
thereof.
[0048] The video encoder 20 and the video decoder 30 may operate
according to a video compression standard, such as the HEVC, and
may conform to a HEVC Test Model (HM). Alternatively, the video
encoder 20 and video decoder 30 may operate according to other
proprietary or industry standards, such as the ITU-T H.264
standard, alternatively referred to as MPEG-4, Part 10, AVC, or
extensions of such standards. The techniques of this disclosure,
however, are not limited to any particular coding standard. Other
examples of video compression standards include MPEG-2 and ITU-T
H.263.
[0049] Although not shown in the examples of FIGS. 1A and 1B, the
video encoder 20 and the video decoder 30 may each be integrated
with an audio encoder and decoder, and may include appropriate
MUX-DEMUX units, or other hardware and software, to handle encoding
of both audio and video in a common data stream or separate data
streams. If applicable, in some examples, MUX-DEMUX units may
conform to the ITU H.223 multiplexer protocol, or other protocols
such as the user datagram protocol (UDP).
[0050] The video encoder 20 and the video decoder 30 each may be
implemented as any of a variety of suitable encoder circuitry, such
as one or more microprocessors, digital signal processors (DSPs),
application specific integrated circuits (ASICs), field
programmable gate arrays (FPGAs), discrete logic, software,
hardware, firmware or any combinations thereof. When the techniques
are implemented partially in software, a device may store
instructions for the software in a suitable, non-transitory
computer-readable medium and execute the instructions in hardware
using one or more processors to perform the techniques of this
disclosure. Each of the video encoder 20 and the video decoder 30
may be included in one or more encoders or decoders, either of
which may be integrated as part of a combined encoder/decoder
(CODEC) in a respective device.
Video Coding Process
[0051] As mentioned briefly above, the video encoder 20 encodes
video data. The video data may comprise one or more pictures. Each
of the pictures is a still image forming part of a video. In some
instances, a picture may be referred to as a video "frame." When
the video encoder 20 encodes the video data, the video encoder 20
may generate a bitstream. The bitstream may include a sequence of
bits that form a coded representation of the video data. The
bitstream may include coded pictures and associated data. A coded
picture is a coded representation of a picture.
[0052] To generate the bitstream, the video encoder 20 may perform
encoding operations on each picture in the video data. When the
video encoder 20 performs encoding operations on the pictures, the
video encoder 20 may generate a series of coded pictures and
associated data. The associated data may include video parameter
sets (VPS), sequence parameter sets (SPSs), picture parameter sets
(PPSs), adaptation parameter sets (APSs), and other syntax
structures. A SPS may contain parameters applicable to zero or more
sequences of pictures. A PPS may contain parameters applicable to
zero or more pictures. An APS may contain parameters applicable to
zero or more pictures. Parameters in an APS may be parameters that
are more likely to change than parameters in a PPS.
[0053] To generate a coded picture, the video encoder 20 may
partition a picture into equally-sized video blocks. A video block
may be a two-dimensional array of samples. Each of the video blocks
is associated with a treeblock. In some instances, a treeblock may
be referred to as a largest coding unit (LCU). The treeblocks of
HEVC may be broadly analogous to the macroblocks of previous
standards, such as H.264/AVC. However, a treeblock is not
necessarily limited to a particular size and may include one or
more coding units (CUs). The video encoder 20 may use quadtree
partitioning to partition the video blocks of treeblocks into video
blocks associated with CUs, hence the name "treeblocks."
[0054] In some examples, the video encoder 20 may partition a
picture into a plurality of slices. Each of the slices may include
an integer number of CUs. In some instances, a slice comprises an
integer number of treeblocks. In other instances, a boundary of a
slice may be within a treeblock.
[0055] As part of performing an encoding operation on a picture,
the video encoder 20 may perform encoding operations on each slice
of the picture. When the video encoder 20 performs an encoding
operation on a slice, the video encoder 20 may generate encoded
data associated with the slice. The encoded data associated with
the slice may be referred to as a "coded slice."
[0056] To generate a coded slice, the video encoder 20 may perform
encoding operations on each treeblock in a slice. When the video
encoder 20 performs an encoding operation on a treeblock, the video
encoder 20 may generate a coded treeblock. The coded treeblock may
comprise data representing an encoded version of the treeblock.
[0057] When the video encoder 20 generates a coded slice, the video
encoder 20 may perform encoding operations on (e.g., encode) the
treeblocks in the slice according to a raster scan order. For
example, the video encoder 20 may encode the treeblocks of the
slice in an order that proceeds from left to right across a topmost
row of treeblocks in the slice, then from left to right across a
next lower row of treeblocks, and so on until the video encoder 20
has encoded each of the treeblocks in the slice.
[0058] As a result of encoding the treeblocks according to the
raster scan order, the treeblocks above and to the left of a given
treeblock may have been encoded, but treeblocks below and to the
right of the given treeblock have not yet been encoded.
Consequently, the video encoder 20 may be able to access
information generated by encoding treeblocks above and to the left
of the given treeblock when encoding the given treeblock. However,
the video encoder 20 may be unable to access information generated
by encoding treeblocks below and to the right of the given
treeblock when encoding the given treeblock.
[0059] To generate a coded treeblock, the video encoder 20 may
recursively perform quadtree partitioning on the video block of the
treeblock to divide the video block into progressively smaller
video blocks. Each of the smaller video blocks may be associated
with a different CU. For example, the video encoder 20 may
partition the video block of a treeblock into four equally-sized
sub-blocks, partition one or more of the sub-blocks into four
equally-sized sub-sub-blocks, and so on. A partitioned CU may be a
CU whose video block is partitioned into video blocks associated
with other CUs. A non-partitioned CU may be a CU whose video block
is not partitioned into video blocks associated with other CUs.
[0060] One or more syntax elements in the bitstream may indicate a
maximum number of times the video encoder 20 may partition the
video block of a treeblock. A video block of a CU may be square in
shape. The size of the video block of a CU (e.g., the size of the
CU) may range from 8.times.8 pixels up to the size of a video block
of a treeblock (e.g., the size of the treeblock) with a maximum of
64.times.64 pixels or greater.
[0061] The video encoder 20 may perform encoding operations on
(e.g., encode) each CU of a treeblock according to a z-scan order.
In other words, the video encoder 20 may encode a top-left CU, a
top-right CU, a bottom-left CU, and then a bottom-right CU, in that
order. When the video encoder 20 performs an encoding operation on
a partitioned CU, the video encoder 20 may encode CUs associated
with sub-blocks of the video block of the partitioned CU according
to the z-scan order. In other words, the video encoder 20 may
encode a CU associated with a top-left sub-block, a CU associated
with a top-right sub-block, a CU associated with a bottom-left
sub-block, and then a CU associated with a bottom-right sub-block,
in that order.
[0062] As a result of encoding the CUs of a treeblock according to
a z-scan order, the CUs above, above-and-to-the-left,
above-and-to-the-right, left, and below-and-to-the left of a given
CU may have been encoded. CUs below and to the right of the given
CU have not yet been encoded. Consequently, the video encoder 20
may be able to access information generated by encoding some CUs
that neighbor the given CU when encoding the given CU. However, the
video encoder 20 may be unable to access information generated by
encoding other CUs that neighbor the given CU when encoding the
given CU.
[0063] When the video encoder 20 encodes a non-partitioned CU, the
video encoder 20 may generate one or more prediction units (PUs)
for the CU. Each of the PUs of the CU may be associated with a
different video block within the video block of the CU. The video
encoder 20 may generate a predicted video block for each PU of the
CU. The predicted video block of a PU may be a block of samples.
The video encoder 20 may use intra prediction or inter prediction
to generate the predicted video block for a PU.
[0064] When the video encoder 20 uses intra prediction to generate
the predicted video block of a PU, the video encoder 20 may
generate the predicted video block of the PU based on decoded
samples of the picture associated with the PU. If the video encoder
20 uses intra prediction to generate predicted video blocks of the
PUs of a CU, the CU is an intra-predicted CU. When the video
encoder 20 uses inter prediction to generate the predicted video
block of the PU, the video encoder 20 may generate the predicted
video block of the PU based on decoded samples of one or more
pictures other than the picture associated with the PU. If the
video encoder 20 uses inter prediction to generate predicted video
blocks of the PUs of a CU, the CU is an inter-predicted CU.
[0065] Furthermore, when the video encoder 20 uses inter prediction
to generate a predicted video block for a PU, the video encoder 20
may generate motion information for the PU. The motion information
for a PU may indicate one or more reference blocks of the PU. Each
reference block of the PU may be a video block within a reference
picture. The reference picture may be a picture other than the
picture associated with the PU. In some instances, a reference
block of a PU may also be referred to as the "reference sample" of
the PU. The video encoder 20 may generate the predicted video block
for the PU based on the reference blocks of the PU.
[0066] After the video encoder 20 generates predicted video blocks
for one or more PUs of a CU, the video encoder 20 may generate
residual data for the CU based on the predicted video blocks for
the PUs of the CU. The residual data for the CU may indicate
differences between samples in the predicted video blocks for the
PUs of the CU and the original video block of the CU.
[0067] Furthermore, as part of performing an encoding operation on
a non-partitioned CU, the video encoder 20 may perform recursive
quadtree partitioning on the residual data of the CU to partition
the residual data of the CU into one or more blocks of residual
data (e.g., residual video blocks) associated with transform units
(TUs) of the CU. Each TU of a CU may be associated with a different
residual video block.
[0068] The video encoder 20 may apply one or more transforms to
residual video blocks associated with the TUs to generate transform
coefficient blocks (e.g., blocks of transform coefficients)
associated with the TUs. Conceptually, a transform coefficient
block may be a two-dimensional (2D) matrix of transform
coefficients.
[0069] After generating a transform coefficient block, the video
encoder 20 may perform a quantization process on the transform
coefficient block. Quantization generally refers to a process in
which transform coefficients are quantized to possibly reduce the
amount of data used to represent the transform coefficients,
providing further compression. The quantization process may reduce
the bit depth associated with some or all of the transform
coefficients. For example, an n-bit transform coefficient may be
rounded down to an m-bit transform coefficient during quantization,
where n is greater than m.
[0070] The video encoder 20 may associate each CU with a
quantization parameter (QP) value. The QP value associated with a
CU may determine how the video encoder 20 quantizes transform
coefficient blocks associated with the CU. The video encoder 20 may
adjust the degree of quantization applied to the transform
coefficient blocks associated with a CU by adjusting the QP value
associated with the CU.
[0071] After the video encoder 20 quantizes a transform coefficient
block, the video encoder 20 may generate sets of syntax elements
that represent the transform coefficients in the quantized
transform coefficient block. The video encoder 20 may apply entropy
encoding operations, such as Context Adaptive Binary Arithmetic
Coding (CABAC) operations, to some of these syntax elements. Other
entropy coding techniques such as context adaptive variable length
coding (CAVLC), probability interval partitioning entropy (PIPE)
coding, or other binary arithmetic coding could also be used.
[0072] The bitstream generated by the video encoder 20 may include
a series of Network Abstraction Layer (NAL) units. Each of the NAL
units may be a syntax structure containing an indication of a type
of data in the NAL unit and bytes containing the data. For example,
a NAL unit may contain data representing a video parameter set, a
sequence parameter set, a picture parameter set, a coded slice,
supplemental enhancement information (SEI), an access unit
delimiter, filler data, or another type of data. The data in a NAL
unit may include various syntax structures.
[0073] The video decoder 30 may receive the bitstream generated by
the video encoder 20. The bitstream may include a coded
representation of the video data encoded by the video encoder 20.
When the video decoder 30 receives the bitstream, the video decoder
30 may perform a parsing operation on the bitstream. When the video
decoder 30 performs the parsing operation, the video decoder 30 may
extract syntax elements from the bitstream. The video decoder 30
may reconstruct the pictures of the video data based on the syntax
elements extracted from the bitstream. The process to reconstruct
the video data based on the syntax elements may be generally
reciprocal to the process performed by the video encoder 20 to
generate the syntax elements.
[0074] After the video decoder 30 extracts the syntax elements
associated with a CU, the video decoder 30 may generate predicted
video blocks for the PUs of the CU based on the syntax elements. In
addition, the video decoder 30 may inverse quantize transform
coefficient blocks associated with TUs of the CU. The video decoder
30 may perform inverse transforms on the transform coefficient
blocks to reconstruct residual video blocks associated with the TUs
of the CU. After generating the predicted video blocks and
reconstructing the residual video blocks, the video decoder 30 may
reconstruct the video block of the CU based on the predicted video
blocks and the residual video blocks. In this way, the video
decoder 30 may reconstruct the video blocks of CUs based on the
syntax elements in the bitstream.
Video Encoder
[0075] FIG. 2A is a block diagram illustrating an example of the
video encoder 20 that may implement techniques in accordance with
aspects described in this disclosure. The video encoder 20 may be
configured to process a single layer of a video frame, such as for
HEVC. Further, the video encoder 20 may be configured to perform
any or all of the techniques of this disclosure, including but not
limited to the methods of inferring NoOutputOfPriorPicsFlag and
related processes described in greater detail above and below with
respect to FIGS. 4 and 5. As one example, prediction processing
unit 100 may be configured to perform any or all of the techniques
described in this disclosure. In another embodiment, the video
encoder 20 includes an optional inter-layer prediction unit 128
that is configured to perform any or all of the techniques
described in this disclosure. In other embodiments, inter-layer
prediction can be performed by prediction processing unit 100
(e.g., inter prediction unit 121 and/or intra prediction unit 126),
in which case the inter-layer prediction unit 128 may be omitted.
However, aspects of this disclosure are not so limited. In some
examples, the techniques described in this disclosure may be shared
among the various components of the video encoder 20. In some
examples, additionally or alternatively, a processor (not shown)
may be configured to perform any or all of the techniques described
in this disclosure.
[0076] For purposes of explanation, this disclosure describes the
video encoder 20 in the context of HEVC coding. However, the
techniques of this disclosure may be applicable to other coding
standards or methods. The example depicted in FIG. 2A is for a
single layer codec. However, as will be described further with
respect to FIG. 2B, some or all of the video encoder 20 may be
duplicated for processing of a multi-layer codec.
[0077] The video encoder 20 may perform intra- and inter-coding of
video blocks within video slices. Intra coding relies on spatial
prediction to reduce or remove spatial redundancy in video within a
given video frame or picture. Inter-coding relies on temporal
prediction to reduce or remove temporal redundancy in video within
adjacent frames or pictures of a video sequence. Intra-mode (I
mode) may refer to any of several spatial based coding modes.
Inter-modes, such as uni-directional prediction (P mode) or
bi-directional prediction (B mode), may refer to any of several
temporal-based coding modes.
[0078] In the example of FIG. 2A, the video encoder 20 includes a
plurality of functional components. The functional components of
the video encoder 20 include a prediction processing unit 100, a
residual generation unit 102, a transform processing unit 104, a
quantization unit 106, an inverse quantization unit 108, an inverse
transform unit 110, a reconstruction unit 112, a filter unit 113, a
decoded picture buffer 114, and an entropy encoding unit 116.
Prediction processing unit 100 includes an inter prediction unit
121, a motion estimation unit 122, a motion compensation unit 124,
an intra prediction unit 126, and an inter-layer prediction unit
128. In other examples, the video encoder 20 may include more,
fewer, or different functional components. Furthermore, motion
estimation unit 122 and motion compensation unit 124 may be highly
integrated, but are represented in the example of FIG. 2A
separately for purposes of explanation.
[0079] The video encoder 20 may receive video data. The video
encoder 20 may receive the video data from various sources. For
example, the video encoder 20 may receive the video data from video
source 18 (e.g., shown in FIG. 1A or 1B) or another source. The
video data may represent a series of pictures. To encode the video
data, the video encoder 20 may perform an encoding operation on
each of the pictures. As part of performing the encoding operation
on a picture, the video encoder 20 may perform encoding operations
on each slice of the picture. As part of performing an encoding
operation on a slice, the video encoder 20 may perform encoding
operations on treeblocks in the slice.
[0080] As part of performing an encoding operation on a treeblock,
prediction processing unit 100 may perform quadtree partitioning on
the video block of the treeblock to divide the video block into
progressively smaller video blocks. Each of the smaller video
blocks may be associated with a different CU. For example,
prediction processing unit 100 may partition a video block of a
treeblock into four equally-sized sub-blocks, partition one or more
of the sub-blocks into four equally-sized sub-sub-blocks, and so
on.
[0081] The sizes of the video blocks associated with CUs may range
from 8.times.8 samples up to the size of the treeblock with a
maximum of 64.times.64 samples or greater. In this disclosure,
"N.times.N" and "N by N" may be used interchangeably to refer to
the sample dimensions of a video block in terms of vertical and
horizontal dimensions, e.g., 16.times.16 samples or 16 by 16
samples. In general, a 16.times.16 video block has sixteen samples
in a vertical direction (y=16) and sixteen samples in a horizontal
direction (x=16). Likewise, an N.times.N block generally has N
samples in a vertical direction and N samples in a horizontal
direction, where N represents a nonnegative integer value.
[0082] Furthermore, as part of performing the encoding operation on
a treeblock, prediction processing unit 100 may generate a
hierarchical quadtree data structure for the treeblock. For
example, a treeblock may correspond to a root node of the quadtree
data structure. If prediction processing unit 100 partitions the
video block of the treeblock into four sub-blocks, the root node
has four child nodes in the quadtree data structure. Each of the
child nodes corresponds to a CU associated with one of the
sub-blocks. If prediction processing unit 100 partitions one of the
sub-blocks into four sub-sub-blocks, the node corresponding to the
CU associated with the sub-block may have four child nodes, each of
which corresponds to a CU associated with one of the
sub-sub-blocks.
[0083] Each node of the quadtree data structure may contain syntax
data (e.g., syntax elements) for the corresponding treeblock or CU.
For example, a node in the quadtree may include a split flag that
indicates whether the video block of the CU corresponding to the
node is partitioned (e.g., split) into four sub-blocks. Syntax
elements for a CU may be defined recursively, and may depend on
whether the video block of the CU is split into sub-blocks. A CU
whose video block is not partitioned may correspond to a leaf node
in the quadtree data structure. A coded treeblock may include data
based on the quadtree data structure for a corresponding
treeblock.
[0084] The video encoder 20 may perform encoding operations on each
non-partitioned CU of a treeblock. When the video encoder 20
performs an encoding operation on a non-partitioned CU, the video
encoder 20 generates data representing an encoded representation of
the non-partitioned CU.
[0085] As part of performing an encoding operation on a CU,
prediction processing unit 100 may partition the video block of the
CU among one or more PUs of the CU. The video encoder 20 and the
video decoder 30 may support various PU sizes. Assuming that the
size of a particular CU is 2N.times.2N, the video encoder 20 and
the video decoder 30 may support PU sizes of 2N.times.2N or
N.times.N, and inter-prediction in symmetric PU sizes of
2N.times.2N, 2N.times.N, N.times.2N, N.times.N, 2N.times.nU,
nL.times.2N, nR.times.2N, or similar. The video encoder 20 and the
video decoder 30 may also support asymmetric partitioning for PU
sizes of 2N.times.nU, 2N.times.nD, nL.times.2N, and nR.times.2N. In
some examples, prediction processing unit 100 may perform geometric
partitioning to partition the video block of a CU among PUs of the
CU along a boundary that does not meet the sides of the video block
of the CU at right angles.
[0086] Inter prediction unit 121 may perform inter prediction on
each PU of the CU. Inter prediction may provide temporal
compression. To perform inter prediction on a PU, motion estimation
unit 122 may generate motion information for the PU. Motion
compensation unit 124 may generate a predicted video block for the
PU based the motion information and decoded samples of pictures
other than the picture associated with the CU (e.g., reference
pictures). In this disclosure, a predicted video block generated by
motion compensation unit 124 may be referred to as an
inter-predicted video block.
[0087] Slices may be I slices, P slices, or B slices. Motion
estimation unit 122 and motion compensation unit 124 may perform
different operations for a PU of a CU depending on whether the PU
is in an I slice, a P slice, or a B slice. In an I slice, all PUs
are intra predicted. Hence, if the PU is in an I slice, motion
estimation unit 122 and motion compensation unit 124 do not perform
inter prediction on the PU.
[0088] If the PU is in a P slice, the picture containing the PU is
associated with a list of reference pictures referred to as "list
0." Each of the reference pictures in list 0 contains samples that
may be used for inter prediction of other pictures. When motion
estimation unit 122 performs the motion estimation operation with
regard to a PU in a P slice, motion estimation unit 122 may search
the reference pictures in list 0 for a reference block for the PU.
The reference block of the PU may be a set of samples, e.g., a
block of samples, that most closely corresponds to the samples in
the video block of the PU. Motion estimation unit 122 may use a
variety of metrics to determine how closely a set of samples in a
reference picture corresponds to the samples in the video block of
a PU. For example, motion estimation unit 122 may determine how
closely a set of samples in a reference picture corresponds to the
samples in the video block of a PU by sum of absolute difference
(SAD), sum of square difference (SSD), or other difference
metrics.
[0089] After identifying a reference block of a PU in a P slice,
motion estimation unit 122 may generate a reference index that
indicates the reference picture in list 0 containing the reference
block and a motion vector that indicates a spatial displacement
between the PU and the reference block. In various examples, motion
estimation unit 122 may generate motion vectors to varying degrees
of precision. For example, motion estimation unit 122 may generate
motion vectors at one-quarter sample precision, one-eighth sample
precision, or other fractional sample precision. In the case of
fractional sample precision, reference block values may be
interpolated from integer-position sample values in the reference
picture. Motion estimation unit 122 may output the reference index
and the motion vector as the motion information of the PU. Motion
compensation unit 124 may generate a predicted video block of the
PU based on the reference block identified by the motion
information of the PU.
[0090] If the PU is in a B slice, the picture containing the PU may
be associated with two lists of reference pictures, referred to as
"list 0" and "list 1." In some examples, a picture containing a B
slice may be associated with a list combination that is a
combination of list 0 and list 1.
[0091] Furthermore, if the PU is in a B slice, motion estimation
unit 122 may perform uni-directional prediction or bi-directional
prediction for the PU. When motion estimation unit 122 performs
uni-directional prediction for the PU, motion estimation unit 122
may search the reference pictures of list 0 or list 1 for a
reference block for the PU. Motion estimation unit 122 may then
generate a reference index that indicates the reference picture in
list 0 or list 1 that contains the reference block and a motion
vector that indicates a spatial displacement between the PU and the
reference block. Motion estimation unit 122 may output the
reference index, a prediction direction indicator, and the motion
vector as the motion information of the PU. The prediction
direction indicator may indicate whether the reference index
indicates a reference picture in list 0 or list 1. Motion
compensation unit 124 may generate the predicted video block of the
PU based on the reference block indicated by the motion information
of the PU.
[0092] When motion estimation unit 122 performs bi-directional
prediction for a PU, motion estimation unit 122 may search the
reference pictures in list 0 for a reference block for the PU and
may also search the reference pictures in list 1 for another
reference block for the PU. Motion estimation unit 122 may then
generate reference indexes that indicate the reference pictures in
list 0 and list 1 containing the reference blocks and motion
vectors that indicate spatial displacements between the reference
blocks and the PU. Motion estimation unit 122 may output the
reference indexes and the motion vectors of the PU as the motion
information of the PU. Motion compensation unit 124 may generate
the predicted video block of the PU based on the reference blocks
indicated by the motion information of the PU.
[0093] In some instances, motion estimation unit 122 does not
output a full set of motion information for a PU to entropy
encoding unit 116. Rather, motion estimation unit 122 may signal
the motion information of a PU with reference to the motion
information of another PU. For example, motion estimation unit 122
may determine that the motion information of the PU is sufficiently
similar to the motion information of a neighboring PU. In this
example, motion estimation unit 122 may indicate, in a syntax
structure associated with the PU, a value that indicates to the
video decoder 30 that the PU has the same motion information as the
neighboring PU. In another example, motion estimation unit 122 may
identify, in a syntax structure associated with the PU, a
neighboring PU and a motion vector difference (MVD). The motion
vector difference indicates a difference between the motion vector
of the PU and the motion vector of the indicated neighboring PU.
The video decoder 30 may use the motion vector of the indicated
neighboring PU and the motion vector difference to determine the
motion vector of the PU. By referring to the motion information of
a first PU when signaling the motion information of a second PU,
the video encoder 20 may be able to signal the motion information
of the second PU using fewer bits.
[0094] As further discussed below with reference to FIGS. 6-7, the
prediction processing unit 100 may be configured to code (e.g.,
encode or decode) the PU (or any other reference layer and/or
enhancement layer blocks or video units) by performing the methods
illustrated in FIGS. 6-7. For example, inter prediction unit 121
(e.g., via motion estimation unit 122 and/or motion compensation
unit 124), intra prediction unit 126, or inter-layer prediction
unit 128 may be configured to perform the methods illustrated in
FIGS. 6-7, either together or separately.
[0095] As part of performing an encoding operation on a CU, intra
prediction unit 126 may perform intra prediction on PUs of the CU.
Intra prediction may provide spatial compression. When intra
prediction unit 126 performs intra prediction on a PU, intra
prediction unit 126 may generate prediction data for the PU based
on decoded samples of other PUs in the same picture. The prediction
data for the PU may include a predicted video block and various
syntax elements. Intra prediction unit 126 may perform intra
prediction on PUs in I slices, P slices, and B slices.
[0096] To perform intra prediction on a PU, intra prediction unit
126 may use multiple intra prediction modes to generate multiple
sets of prediction data for the PU. When intra prediction unit 126
uses an intra prediction mode to generate a set of prediction data
for the PU, intra prediction unit 126 may extend samples from video
blocks of neighboring PUs across the video block of the PU in a
direction and/or gradient associated with the intra prediction
mode. The neighboring PUs may be above, above and to the right,
above and to the left, or to the left of the PU, assuming a
left-to-right, top-to-bottom encoding order for PUs, CUs, and
treeblocks. Intra prediction unit 126 may use various numbers of
intra prediction modes, e.g., 33 directional intra prediction
modes, depending on the size of the PU.
[0097] Prediction processing unit 100 may select the prediction
data for a PU from among the prediction data generated by motion
compensation unit 124 for the PU or the prediction data generated
by intra prediction unit 126 for the PU. In some examples,
prediction processing unit 100 selects the prediction data for the
PU based on rate/distortion metrics of the sets of prediction
data.
[0098] If prediction processing unit 100 selects prediction data
generated by intra prediction unit 126, prediction processing unit
100 may signal the intra prediction mode that was used to generate
the prediction data for the PUs, e.g., the selected intra
prediction mode. Prediction processing unit 100 may signal the
selected intra prediction mode in various ways. For example, it may
be probable that the selected intra prediction mode is the same as
the intra prediction mode of a neighboring PU. In other words, the
intra prediction mode of the neighboring PU may be the most
probable mode for the current PU. Thus, prediction processing unit
100 may generate a syntax element to indicate that the selected
intra prediction mode is the same as the intra prediction mode of
the neighboring PU.
[0099] As discussed above, the video encoder 20 may include
inter-layer prediction unit 128. Inter-layer prediction unit 128 is
configured to predict a current block (e.g., a current block in the
EL) using one or more different layers that are available in SVC
(e.g., a base or reference layer). Such prediction may be referred
to as inter-layer prediction. Inter-layer prediction unit 128
utilizes prediction methods to reduce inter-layer redundancy,
thereby improving coding efficiency and reducing computational
resource requirements. Some examples of inter-layer prediction
include inter-layer intra prediction, inter-layer motion
prediction, and inter-layer residual prediction. Inter-layer intra
prediction uses the reconstruction of co-located blocks in the base
layer to predict the current block in the enhancement layer.
Inter-layer motion prediction uses motion information of the base
layer to predict motion in the enhancement layer. Inter-layer
residual prediction uses the residue of the base layer to predict
the residue of the enhancement layer. Each of the inter-layer
prediction schemes is discussed below in greater detail.
[0100] After prediction processing unit 100 selects the prediction
data for PUs of a CU, residual generation unit 102 may generate
residual data for the CU by subtracting (e.g., indicated by the
minus sign) the predicted video blocks of the PUs of the CU from
the video block of the CU. The residual data of a CU may include 2D
residual video blocks that correspond to different sample
components of the samples in the video block of the CU. For
example, the residual data may include a residual video block that
corresponds to differences between luminance components of samples
in the predicted video blocks of the PUs of the CU and luminance
components of samples in the original video block of the CU. In
addition, the residual data of the CU may include residual video
blocks that correspond to the differences between chrominance
components of samples in the predicted video blocks of the PUs of
the CU and the chrominance components of the samples in the
original video block of the CU.
[0101] Prediction processing unit 100 may perform quadtree
partitioning to partition the residual video blocks of a CU into
sub-blocks. Each undivided residual video block may be associated
with a different TU of the CU. The sizes and positions of the
residual video blocks associated with TUs of a CU may or may not be
based on the sizes and positions of video blocks associated with
the PUs of the CU. A quadtree structure known as a "residual quad
tree" (RQT) may include nodes associated with each of the residual
video blocks. The TUs of a CU may correspond to leaf nodes of the
RQT.
[0102] Transform processing unit 104 may generate one or more
transform coefficient blocks for each TU of a CU by applying one or
more transforms to a residual video block associated with the TU.
Each of the transform coefficient blocks may be a 2D matrix of
transform coefficients. Transform processing unit 104 may apply
various transforms to the residual video block associated with a
TU. For example, transform processing unit 104 may apply a discrete
cosine transform (DCT), a directional transform, or a conceptually
similar transform to the residual video block associated with a
TU.
[0103] After transform processing unit 104 generates a transform
coefficient block associated with a TU, quantization unit 106 may
quantize the transform coefficients in the transform coefficient
block. Quantization unit 106 may quantize a transform coefficient
block associated with a TU of a CU based on a QP value associated
with the CU.
[0104] The video encoder 20 may associate a QP value with a CU in
various ways. For example, the video encoder 20 may perform a
rate-distortion analysis on a treeblock associated with the CU. In
the rate-distortion analysis, the video encoder 20 may generate
multiple coded representations of the treeblock by performing an
encoding operation multiple times on the treeblock. The video
encoder 20 may associate different QP values with the CU when the
video encoder 20 generates different encoded representations of the
treeblock. The video encoder 20 may signal that a given QP value is
associated with the CU when the given QP value is associated with
the CU in a coded representation of the treeblock that has a lowest
bitrate and distortion metric.
[0105] Inverse quantization unit 108 and inverse transform unit 110
may apply inverse quantization and inverse transforms to the
transform coefficient block, respectively, to reconstruct a
residual video block from the transform coefficient block.
Reconstruction unit 112 may add the reconstructed residual video
block to corresponding samples from one or more predicted video
blocks generated by prediction processing unit 100 to produce a
reconstructed video block associated with a TU. By reconstructing
video blocks for each TU of a CU in this way, the video encoder 20
may reconstruct the video block of the CU.
[0106] After reconstruction unit 112 reconstructs the video block
of a CU, filter unit 113 may perform a deblocking operation to
reduce blocking artifacts in the video block associated with the
CU. After performing the one or more deblocking operations, filter
unit 113 may store the reconstructed video block of the CU in
decoded picture buffer 114. Motion estimation unit 122 and motion
compensation unit 124 may use a reference picture that contains the
reconstructed video block to perform inter prediction on PUs of
subsequent pictures. In addition, intra prediction unit 126 may use
reconstructed video blocks in decoded picture buffer 114 to perform
intra prediction on other PUs in the same picture as the CU.
[0107] Entropy encoding unit 116 may receive data from other
functional components of the video encoder 20. For example, entropy
encoding unit 116 may receive transform coefficient blocks from
quantization unit 106 and may receive syntax elements from
prediction processing unit 100. When entropy encoding unit 116
receives the data, entropy encoding unit 116 may perform one or
more entropy encoding operations to generate entropy encoded data.
For example, the video encoder 20 may perform a context adaptive
variable length coding (CAVLC) operation, a CABAC operation, a
variable-to-variable (V2V) length coding operation, a syntax-based
context-adaptive binary arithmetic coding (SBAC) operation, a
Probability Interval Partitioning Entropy (PIPE) coding operation,
or another type of entropy encoding operation on the data. Entropy
encoding unit 116 may output a bitstream that includes the entropy
encoded data.
[0108] As part of performing an entropy encoding operation on data,
entropy encoding unit 116 may select a context model. If entropy
encoding unit 116 is performing a CABAC operation, the context
model may indicate estimates of probabilities of particular bins
having particular values. In the context of CABAC, the term "bin"
is used to refer to a bit of a binarized version of a syntax
element.
Multi-Layer Video Encoder
[0109] FIG. 2B is a block diagram illustrating an example of a
multi-layer video encoder 23 (also simply referred to as video
encoder 23) that may implement techniques in accordance with
aspects described in this disclosure. The video encoder 23 may be
configured to process multi-layer video frames, such as for SHVC
and multiview coding. Further, the video encoder 23 may be
configured to perform any or all of the techniques of this
disclosure.
[0110] The video encoder 23 includes a video encoder 20A and video
encoder 20B, each of which may be configured as the video encoder
20 and may perform the functions described above with respect to
the video encoder 20. Further, as indicated by the reuse of
reference numbers, the video encoders 20A and 20B may include at
least some of the systems and subsystems as the video encoder 20.
Although the video encoder 23 is illustrated as including two video
encoders 20A and 20B, the video encoder 23 is not limited as such
and may include any number of video encoder 20 layers. In some
embodiments, the video encoder 23 may include a video encoder 20
for each picture or frame in an access unit. For example, an access
unit that includes five pictures may be processed or encoded by a
video encoder that includes five encoder layers. In some
embodiments, the video encoder 23 may include more encoder layers
than frames in an access unit. In some such cases, some of the
video encoder layers may be inactive when processing some access
units.
[0111] In addition to the video encoders 20A and 20B, the video
encoder 23 may include an resampling unit 90. The resampling unit
90 may, in some cases, upsample a base layer of a received video
frame to, for example, create an enhancement layer. The resampling
unit 90 may upsample particular information associated with the
received base layer of a frame, but not other information. For
example, the resampling unit 90 may up sample the spatial size or
number of pixels of the base layer, but the number of slices or the
POC may remain constant. In some cases, the resampling unit 90 may
not process the received video and/or may be optional. For example,
in some cases, the prediction processing unit 100 may perform
upsampling. In some embodiments, the resampling unit 90 is
configured to upsample a layer and reorganize, redefine, modify, or
adjust one or more slices to comply with a set of slice boundary
rules and/or raster scan rules. Although primarily described as
upsampling a base layer, or a lower layer in an access unit, in
some cases, the resampling unit 90 may downsample a layer. For
example, if during streaming of a video bandwidth is reduced, a
frame may be downsampled instead of upsampled.
[0112] The resampling unit 90 may be configured to receive a
picture or frame (or picture information associated with the
picture) from the decoded picture buffer 114 of the lower layer
encoder (e.g., the video encoder 20A) and to upsample the picture
(or the received picture information). This upsampled picture may
then be provided to the prediction processing unit 100 of a higher
layer encoder (e.g., the video encoder 20B) configured to encode a
picture in the same access unit as the lower layer encoder. In some
cases, the higher layer encoder is one layer removed from the lower
layer encoder. In other cases, there may be one or more higher
layer encoders between the layer 0 video encoder and the layer 1
encoder of FIG. 2B.
[0113] In some cases, the resampling unit 90 may be omitted or
bypassed. In such cases, the picture from the decoded picture
buffer 114 of the video encoder 20A may be provided directly, or at
least without being provided to the resampling unit 90, to the
prediction processing unit 100 of the video encoder 20B. For
example, if video data provided to the video encoder 20B and the
reference picture from the decoded picture buffer 114 of the video
encoder 20A are of the same size or resolution, the reference
picture may be provided to the video encoder 20B without any
resampling.
[0114] In some embodiments, the video encoder 23 downsamples video
data to be provided to the lower layer encoder using the
downsampling unit 94 before provided the video data to the video
encoder 20A. Alternatively, the downsampling unit 94 may be a
resampling unit 90 capable of upsampling or downsampling the video
data. In yet other embodiments, the downsampling unit 94 may be
omitted.
[0115] As illustrated in FIG. 2B, the video encoder 23 may further
include a multiplexor 98, or mux. The mux 98 can output a combined
bitstream from the video encoder 23. The combined bitstream may be
created by taking a bitstream from each of the video encoders 20A
and 20B and alternating which bitstream is output at a given time.
While in some cases the bits from the two (or more in the case of
more than two video encoder layers) bitstreams may be alternated
one bit at a time, in many cases the bitstreams are combined
differently. For example, the output bitstream may be created by
alternating the selected bitstream one block at a time. In another
example, the output bitstream may be created by outputting a
non-1:1 ratio of blocks from each of the video encoders 20A and
20B. For instance, two blocks may be output from the video encoder
20B for each block output from the video encoder 20A. In some
embodiments, the output stream from the mux 98 may be
preprogrammed. In other embodiments, the mux 98 may combine the
bitstreams from the video encoders 20A, 20B based on a control
signal received from a system external to the video encoder 23,
such as from a processor on a source device including the source
device 12. The control signal may be generated based on the
resolution or bitrate of a video from the video source 18, based on
a bandwidth of the link 16, based on a subscription associated with
a user (e.g., a paid subscription versus a free subscription), or
based on any other factor for determining a resolution output
desired from the video encoder 23.
Video Decoder
[0116] FIG. 3A is a block diagram illustrating an example of the
video decoder 30 that may implement techniques in accordance with
aspects described in this disclosure. The video decoder 30 may be
configured to process a single layer of a video frame, such as for
HEVC. Further, the video decoder 30 may be configured to perform
any or all of the techniques of this disclosure, including but not
limited to the methods of inferring NoOutputOfPriorPicsFlag and
related processes described in greater detail above and below with
respect to FIGS. 4 and 5. As one example, motion compensation unit
162 and/or intra prediction unit 164 may be configured to perform
any or all of the techniques described in this disclosure. In one
embodiment, the video decoder 30 may optionally include inter-layer
prediction unit 166 that is configured to perform any or all of the
techniques described in this disclosure. In other embodiments,
inter-layer prediction can be performed by prediction processing
unit 152 (e.g., motion compensation unit 162 and/or intra
prediction unit 164), in which case the inter-layer prediction unit
166 may be omitted. However, aspects of this disclosure are not so
limited. In some examples, the techniques described in this
disclosure may be shared among the various components of the video
decoder 30. In some examples, additionally or alternatively, a
processor (not shown) may be configured to perform any or all of
the techniques described in this disclosure.
[0117] For purposes of explanation, this disclosure describes the
video decoder 30 in the context of HEVC coding. However, the
techniques of this disclosure may be applicable to other coding
standards or methods. The example depicted in FIG. 3A is for a
single layer codec. However, as will be described further with
respect to FIG. 3B, some or all of the video decoder 30 may be
duplicated for processing of a multi-layer codec.
[0118] In the example of FIG. 3A, the video decoder 30 includes a
plurality of functional components. The functional components of
the video decoder 30 include an entropy decoding unit 150, a
prediction processing unit 152, an inverse quantization unit 154,
an inverse transform unit 156, a reconstruction unit 158, a filter
unit 159, and a decoded picture buffer 160. Prediction processing
unit 152 includes a motion compensation unit 162, an intra
prediction unit 164, and an inter-layer prediction unit 166. In
some examples, the video decoder 30 may perform a decoding pass
generally reciprocal to the encoding pass described with respect to
the video encoder 20 of FIG. 2A. In other examples, the video
decoder 30 may include more, fewer, or different functional
components.
[0119] The video decoder 30 may receive a bitstream that comprises
encoded video data. The bitstream may include a plurality of syntax
elements. When the video decoder 30 receives the bitstream, entropy
decoding unit 150 may perform a parsing operation on the bitstream.
As a result of performing the parsing operation on the bitstream,
entropy decoding unit 150 may extract syntax elements from the
bitstream. As part of performing the parsing operation, entropy
decoding unit 150 may entropy decode entropy encoded syntax
elements in the bitstream. Prediction processing unit 152, inverse
quantization unit 154, inverse transform unit 156, reconstruction
unit 158, and filter unit 159 may perform a reconstruction
operation that generates decoded video data based on the syntax
elements extracted from the bitstream.
[0120] As discussed above, the bitstream may comprise a series of
NAL units. The NAL units of the bitstream may include video
parameter set NAL units, sequence parameter set NAL units, picture
parameter set NAL units, SEI NAL units, and so on. As part of
performing the parsing operation on the bitstream, entropy decoding
unit 150 may perform parsing operations that extract and entropy
decode sequence parameter sets from sequence parameter set NAL
units, picture parameter sets from picture parameter set NAL units,
SEI data from SEI NAL units, and so on.
[0121] In addition, the NAL units of the bitstream may include
coded slice NAL units. As part of performing the parsing operation
on the bitstream, entropy decoding unit 150 may perform parsing
operations that extract and entropy decode coded slices from the
coded slice NAL units. Each of the coded slices may include a slice
header and slice data. The slice header may contain syntax elements
pertaining to a slice. The syntax elements in the slice header may
include a syntax element that identifies a picture parameter set
associated with a picture that contains the slice. Entropy decoding
unit 150 may perform entropy decoding operations, such as CABAC
decoding operations, on syntax elements in the coded slice header
to recover the slice header.
[0122] As part of extracting the slice data from coded slice NAL
units, entropy decoding unit 150 may perform parsing operations
that extract syntax elements from coded CUs in the slice data. The
extracted syntax elements may include syntax elements associated
with transform coefficient blocks. Entropy decoding unit 150 may
then perform CABAC decoding operations on some of the syntax
elements.
[0123] After entropy decoding unit 150 performs a parsing operation
on a non-partitioned CU, the video decoder 30 may perform a
reconstruction operation on the non-partitioned CU. To perform the
reconstruction operation on a non-partitioned CU, the video decoder
30 may perform a reconstruction operation on each TU of the CU. By
performing the reconstruction operation for each TU of the CU, the
video decoder 30 may reconstruct a residual video block associated
with the CU.
[0124] As part of performing a reconstruction operation on a TU,
inverse quantization unit 154 may inverse quantize, e.g.,
de-quantize, a transform coefficient block associated with the TU.
Inverse quantization unit 154 may inverse quantize the transform
coefficient block in a manner similar to the inverse quantization
processes proposed for HEVC or defined by the H.264 decoding
standard. Inverse quantization unit 154 may use a quantization
parameter QP calculated by the video encoder 20 for a CU of the
transform coefficient block to determine a degree of quantization
and, likewise, a degree of inverse quantization for inverse
quantization unit 154 to apply.
[0125] After inverse quantization unit 154 inverse quantizes a
transform coefficient block, inverse transform unit 156 may
generate a residual video block for the TU associated with the
transform coefficient block. Inverse transform unit 156 may apply
an inverse transform to the transform coefficient block in order to
generate the residual video block for the TU. For example, inverse
transform unit 156 may apply an inverse DCT, an inverse integer
transform, an inverse Karhunen-Loeve transform (KLT), an inverse
rotational transform, an inverse directional transform, or another
inverse transform to the transform coefficient block. In some
examples, inverse transform unit 156 may determine an inverse
transform to apply to the transform coefficient block based on
signaling from the video encoder 20. In such examples, inverse
transform unit 156 may determine the inverse transform based on a
signaled transform at the root node of a quadtree for a treeblock
associated with the transform coefficient block. In other examples,
inverse transform unit 156 may infer the inverse transform from one
or more coding characteristics, such as block size, coding mode, or
the like. In some examples, inverse transform unit 156 may apply a
cascaded inverse transform.
[0126] In some examples, motion compensation unit 162 may refine
the predicted video block of a PU by performing interpolation based
on interpolation filters. Identifiers for interpolation filters to
be used for motion compensation with sub-sample precision may be
included in the syntax elements. Motion compensation unit 162 may
use the same interpolation filters used by the video encoder 20
during generation of the predicted video block of the PU to
calculate interpolated values for sub-integer samples of a
reference block. Motion compensation unit 162 may determine the
interpolation filters used by the video encoder 20 according to
received syntax information and use the interpolation filters to
produce the predicted video block.
[0127] As further discussed below with reference to FIGS. 6-7, the
prediction processing unit 152 may code (e.g., encode or decode)
the PU (or any other reference layer and/or enhancement layer
blocks or video units) by performing the methods illustrated in
FIGS. 6-7. For example, motion compensation unit 162, intra
prediction unit 164, or inter-layer prediction unit 166 may be
configured to perform the methods illustrated in FIGS. 6-7, either
together or separately.
[0128] If a PU is encoded using intra prediction, intra prediction
unit 164 may perform intra prediction to generate a predicted video
block for the PU. For example, intra prediction unit 164 may
determine an intra prediction mode for the PU based on syntax
elements in the bitstream. The bitstream may include syntax
elements that intra prediction unit 164 may use to determine the
intra prediction mode of the PU.
[0129] In some instances, the syntax elements may indicate that
intra prediction unit 164 is to use the intra prediction mode of
another PU to determine the intra prediction mode of the current
PU. For example, it may be probable that the intra prediction mode
of the current PU is the same as the intra prediction mode of a
neighboring PU. In other words, the intra prediction mode of the
neighboring PU may be the most probable mode for the current PU.
Hence, in this example, the bitstream may include a small syntax
element that indicates that the intra prediction mode of the PU is
the same as the intra prediction mode of the neighboring PU. Intra
prediction unit 164 may then use the intra prediction mode to
generate prediction data (e.g., predicted samples) for the PU based
on the video blocks of spatially neighboring PUs.
[0130] As discussed above, the video decoder 30 may also include
inter-layer prediction unit 166. Inter-layer prediction unit 166 is
configured to predict a current block (e.g., a current block in the
EL) using one or more different layers that are available in SVC
(e.g., a base or reference layer). Such prediction may be referred
to as inter-layer prediction. Inter-layer prediction unit 166
utilizes prediction methods to reduce inter-layer redundancy,
thereby improving coding efficiency and reducing computational
resource requirements. Some examples of inter-layer prediction
include inter-layer intra prediction, inter-layer motion
prediction, and inter-layer residual prediction. Inter-layer intra
prediction uses the reconstruction of co-located blocks in the base
layer to predict the current block in the enhancement layer.
Inter-layer motion prediction uses motion information of the base
layer to predict motion in the enhancement layer. Inter-layer
residual prediction uses the residue of the base layer to predict
the residue of the enhancement layer. Each of the inter-layer
prediction schemes is discussed below in greater detail.
[0131] Reconstruction unit 158 may use the residual video blocks
associated with TUs of a CU and the predicted video blocks of the
PUs of the CU, e.g., either intra-prediction data or
inter-prediction data, as applicable, to reconstruct the video
block of the CU. Thus, the video decoder 30 may generate a
predicted video block and a residual video block based on syntax
elements in the bitstream and may generate a video block based on
the predicted video block and the residual video block.
[0132] After reconstruction unit 158 reconstructs the video block
of the CU, filter unit 159 may perform a deblocking operation to
reduce blocking artifacts associated with the CU. After filter unit
159 performs a deblocking operation to reduce blocking artifacts
associated with the CU, the video decoder 30 may store the video
block of the CU in decoded picture buffer 160. Decoded picture
buffer 160 may provide reference pictures for subsequent motion
compensation, intra prediction, and presentation on a display
device, such as display device 32 of FIG. 1A or 1B. For instance,
the video decoder 30 may perform, based on the video blocks in
decoded picture buffer 160, intra prediction or inter prediction
operations on PUs of other CUs.
Multi-Layer Decoder
[0133] FIG. 3B is a block diagram illustrating an example of a
multi-layer video decoder 33 (also simply referred to as video
decoder 33) that may implement techniques in accordance with
aspects described in this disclosure. The video decoder 33 may be
configured to process multi-layer video frames, such as for SHVC
and multiview coding. Further, the video decoder 33 may be
configured to perform any or all of the techniques of this
disclosure.
[0134] The video decoder 33 includes a video decoder 30A and video
decoder 30B, each of which may be configured as the video decoder
30 and may perform the functions described above with respect to
the video decoder 30. Further, as indicated by the reuse of
reference numbers, the video decoders 30A and 30B may include at
least some of the systems and subsystems as the video decoder 30.
Although the video decoder 33 is illustrated as including two video
decoders 30A and 30B, the video decoder 33 is not limited as such
and may include any number of video decoder 30 layers. In some
embodiments, the video decoder 33 may include a video decoder 30
for each picture or frame in an access unit. For example, an access
unit that includes five pictures may be processed or decoded by a
video decoder that includes five decoder layers. In some
embodiments, the video decoder 33 may include more decoder layers
than frames in an access unit. In some such cases, some of the
video decoder layers may be inactive when processing some access
units.
[0135] In addition to the video decoders 30A and 30B, the video
decoder 33 may include an upsampling unit 92. In some embodiments,
the upsampling unit 92 may upsample a base layer of a received
video frame to create an enhanced layer to be added to the
reference picture list for the frame or access unit. This enhanced
layer can be stored in the decoded picture buffer 160. In some
embodiments, the upsampling unit 92 can include some or all of the
embodiments described with respect to the resampling unit 90 of
FIG. 2A. In some embodiments, the upsampling unit 92 is configured
to upsample a layer and reorganize, redefine, modify, or adjust one
or more slices to comply with a set of slice boundary rules and/or
raster scan rules. In some cases, the upsampling unit 92 may be a
resampling unit configured to upsample and/or downsample a layer of
a received video frame
[0136] The upsampling unit 92 may be configured to receive a
picture or frame (or picture information associated with the
picture) from the decoded picture buffer 160 of the lower layer
decoder (e.g., the video decoder 30A) and to upsample the picture
(or the received picture information). This upsampled picture may
then be provided to the prediction processing unit 152 of a higher
layer decoder (e.g., the video decoder 30B) configured to decode a
picture in the same access unit as the lower layer decoder. In some
cases, the higher layer decoder is one layer removed from the lower
layer decoder. In other cases, there may be one or more higher
layer decoders between the layer 0 decoder and the layer 1 decoder
of FIG. 3B.
[0137] In some cases, the upsampling unit 92 may be omitted or
bypassed. In such cases, the picture from the decoded picture
buffer 160 of the video decoder 30A may be provided directly, or at
least without being provided to the upsampling unit 92, to the
prediction processing unit 152 of the video decoder 30B. For
example, if video data provided to the video decoder 30B and the
reference picture from the decoded picture buffer 160 of the video
decoder 30A are of the same size or resolution, the reference
picture may be provided to the video decoder 30B without
upsampling. Further, in some embodiments, the upsampling unit 92
may be a resampling unit 90 configured to upsample or downsample a
reference picture received from the decoded picture buffer 160 of
the video decoder 30A.
[0138] As illustrated in FIG. 3B, the video decoder 33 may further
include a demultiplexor 99, or demux. The demux 99 can split an
encoded video bitstream into multiple bitstreams with each
bitstream output by the demux 99 being provided to a different
video decoder 30A and 30B. The multiple bitstreams may be created
by receiving a bitstream and each of the video decoders 30A and 30B
receives a portion of the bitstream at a given time. While in some
cases the bits from the bitstream received at the demux 99 may be
alternated one bit at a time between each of the video decoders
(e.g., video decoders 30A and 30B in the example of FIG. 3B), in
many cases the bitstream is divided differently. For example, the
bitstream may be divided by alternating which video decoder
receives the bitstream one block at a time. In another example, the
bitstream may be divided by a non-1:1 ratio of blocks to each of
the video decoders 30A and 30B. For instance, two blocks may be
provided to the video decoder 30B for each block provided to the
video decoder 30A. In some embodiments, the division of the
bitstream by the demux 99 may be preprogrammed. In other
embodiments, the demux 99 may divide the bitstream based on a
control signal received from a system external to the video decoder
33, such as from a processor on a destination device including the
destination device 14. The control signal may be generated based on
the resolution or bitrate of a video from the input interface 28,
based on a bandwidth of the link 16, based on a subscription
associated with a user (e.g., a paid subscription versus a free
subscription), or based on any other factor for determining a
resolution obtainable by the video decoder 33.
Intra Random Access Point (IRAP) Pictures
[0139] Some video coding schemes may provide various random access
points throughout the bitstream such that the bitstream may be
decoded starting from any of those random access points without
needing to decode any pictures that precede those random access
points in the bitstream. In such video coding schemes, pictures
that follow a random access point in output order (e.g., including
those pictures that are in the same access unit as the picture
providing the random access point) can be correctly decoded without
using any pictures that precede the random access point. For
example, even if a portion of the bitstream is lost during
transmission or during decoding, a decoder can resume decoding the
bitstream starting from the next random access point. Support for
random access may facilitate, for example, dynamic streaming
services, seek operations, channel switching, etc. In some cases,
pictures that follow a random access point in output order may use
leading pictures for decoding. Leading pictures may refer to
pictures that follow the random access point in the bitstream and
are output and displayed before the random access point.
[0140] In some coding schemes, such random access points may be
provided by pictures that are referred to as IRAP pictures. For
example, a random access point (e.g., provided by an enhancement
layer IRAP picture) in an enhancement layer ("layerA") contained in
an access unit ("auA") may provide layer-specific random access
such that for each reference layer ("layerB") of layerA (e.g., a
reference layer being a layer that is used to predict layerA)
having a random access point contained in an access unit ("auB")
that is in layerB and precedes auA in decoding order (or a random
access point contained in auA), the pictures in layerA that follow
auB in output order (including those pictures located in auB), may
be correctly decodable without needing to decode any pictures in
layerA that precede auB. For example, when decoding starts from
auB, and a picture in layerB and in auB is decodable, then the
picture in layer A that is in auA and pictures in layerA that
follow auA are decodable.
[0141] IRAP pictures may be coded using intra prediction (e.g.,
coded without referring to other pictures in the same layer), and
may include, for example, instantaneous decoding refresh (IDR)
pictures, clean random access (CRA) pictures, and broken link
access (BLA) pictures. When there is an IDR picture in the
bitstream, the pictures that precede the IDR picture in decoding
order are not used for prediction by pictures that follow the IDR
picture in decoding order. When there is a CRA picture in the
bitstream, the pictures that follow the CRA picture may or may not
use pictures that precede the CRA picture in decoding order for
prediction. Those pictures that follow the CRA picture in decoding
order but use pictures that precede the CRA picture in decoding
order may be referred to as random access skipped leading (RASL)
pictures. Another type of picture that follows an IRAP picture in
decoding order and precedes the IRAP picture in output order is a
random access decodable leading (RADL) picture, which may not
contain references to any pictures that precede the IRAP picture in
decoding order. RASL pictures may be discarded by the decoder if
the pictures that precede the CRA picture are not available. RASL
pictures may or may not be present after a BLA picture. When RASL
pictures are present after BLA pictures, they should be ignored
and/or not decoded because their reference pictures may not be
available. An access unit (e.g., a group of pictures including the
coded pictures associated with the same output time across multiple
layers) containing a base layer picture (e.g., a picture having a
layer ID value of 0) that is an IRAP picture may be referred to as
an IRAP access unit.
Cross-Layer Alignment of IRAP Pictures
[0142] In SHVC extensions such as SHVC and MV-HEVC, IRAP pictures
may not be required to be aligned (e.g., contained in the same
access unit) across different layers. For example, if IRAP pictures
were required to be aligned, any access unit containing at least
one IRAP picture would only contain IRAP pictures. On the other
hand, if IRAP pictures were not required to be aligned, in a single
access unit, one picture (e.g., in a first layer) may be an IRAP
picture, and another picture (e.g., in a second layer) may be a
non-IRAP picture. Having such non-aligned IRAP pictures in a
bitstream may provide some advantages. For example, in a two-layer
bitstream, if there are more IRAP pictures in the base layer than
in the enhancement layer, in broadcast and multicast applications,
low tune-in delay and higher coding efficiency can be achieved.
[0143] In some video coding schemes, a POC may be used to keep
track of the relative order in which the decoded pictures are
displayed. Some of such coding schemes may cause the POC values to
be reset (e.g., set to zero or set to some value signaled in the
bitstream) whenever certain types of pictures appear in the
bitstream. For example, the POC values of certain IRAP pictures may
be reset, causing the POC values of other pictures preceding those
IRAP pictures in decoding order to also be reset. This may be
problematic when the IRAP pictures are not required to be aligned
across different layers. For example, when one picture ("picA") is
an IRAP picture and another picture ("picB") in the same access
unit is not an IRAP picture, the POC value of a picture ("picC"),
which is reset due to picA being an IRAP picture, in the layer
containing picA may be different from the POC value of a picture
("picD"), which is not reset, in the layer containing picB, where
picC and picD are in the same access unit. This causes picC and
picD to have different POC values even though they belong to the
same access unit (e.g., same output time). Thus, in this example,
the derivation process for deriving the POC values of picC and picD
can be modified to produce POC values that are consistent with the
definition of POC values and access units.
Temporal Motion Vector Prediction Indication and Representation
Format Update for Multi-Layer Codecs
[0144] Early versions of SHVC and MV-HEVC (e.g., SHVC Working Draft
6, MV-HEVC Working Draft 8, etc.) implement a restriction that
temporal motion vector from pictures that precede the current
picture in decoding order should not be used in TMVP of any
pictures that follow the current picture in decoding order when the
values of both slice_temporal_mvp_enabled_flag and temporal ID of
the current picture are equal to 0 and when the pictures belong to
the base layer (e.g., a layer having layer ID=0). According to
certain aspects, in this disclosure, preceding pictures of the
current picture may refer to preceding pictures in decoding order,
and subsequent pictures of the current picture may refer to
subsequent pictures in decoding order.
Slice_temporal_mvp_enabled_flag can indicate whether the current
picture in a slice can use TMVP, for example, based on preceding
pictures of the current picture as reference pictures (e.g.,
collocated pictures). A bitstream may support temporal scalability
and provide different frame rates depending on the embodiment. In
one embodiment, a temporal layer with temporal ID=0 can provide the
default frame rate. The temporal layer with temporal ID=0 can be
referred to as the base temporal sublayer. There can be one or more
temporal sublayers, and a constraint can apply for inter prediction
that pictures in a lower temporal sublayer should not use pictures
in a higher temporal sublayer as references. The restriction and
the condition that the pictures belong to the base layer were
introduced, for example, to allow the enhancement layer to use
TMVP. However, the enhancement layer may use TMVP without limiting
the restriction to the base layer. Certain details relating to the
restrictions and issues associated with the restriction are
discussed in further detail below, for example, in sections
describing semantics of slice_temporal_mvp_enabled_flag and
semantics of prev_pics_not_used_flag.
[0145] The early versions of SHVC and MV-HEVC also add a new SEI
message called TMVP constraints SEI message, which provides an
indication of whether pictures of the current layer that precede
the current picture should not be used as collocated pictures in
TMVP for any subsequent picture of the same layer. For example, the
TMVP constraints SEI message can include a flag called
prev_pics_not_used_flag that indicates whether the preceding
pictures of the current picture in the current layer in decoding
order can be used for TMVP of subsequent pictures of the current
picture in the current layer in decoding order. However, the
semantics of prev_pics_not_used_flag in the early versions of SHVC
and MV-HEVC can lead to a conflict with
slice_temporal_mvp_enabled_flag. For instance,
slice_temporal_mvp_enabled_flag in the slice header of the slice
containing the current picture is equal to 1 and indicates that the
current picture can use TMVP, referring to preceding pictures of
the current picture as collocated pictures, but
prev_pics_not_used_flag in the TMVP constraints SEI message for the
current picture is equal to 1 and indicates that subsequent
pictures of the current picture in decoding should not use
preceding pictures of the current picture for TMVP in decoding
order. In such case, any error introduced in the TMVP of the
current picture using preceding pictures may be propagated to the
subsequent pictures since the subsequent pictures could use the
current picture as a collocated picture for TMVP. Although the
subsequent pictures are not using any preceding pictures of the
current picture for TMVP, the subsequent pictures may use the
current picture itself for TMVP. Certain details relating to the
flag and the TMVP constraints SEI message and related issues are
discussed in further detail below, for example, in sections
describing Semantics of slice_temporal_mvp_enabled_flag and
semantics of prev_pics_not_used_flag.
[0146] In order to address these and other challenges, the
techniques according to certain aspects can apply the restriction
that temporal motion vector from any preceding pictures of the
current picture should not be used in TMVP of any subsequent
pictures of the current picture in decoding order to all layers.
For example, the restriction can apply to pictures when
slice_temporal_mvp_enabled_flag=0 and temporal ID=0 regardless of
whether the pictures belong to the base layer or other layers. In
one example, the TMVP constraints SEI message can be used with
slice_temporal_mvp_enabled_flag to allow an enhancement layer to
use TMVP without limiting the restriction to the base layer.
[0147] Moreover, the techniques can modify the semantics of
prev_pics_not_used_flag, for example, to resolve the conflict
between slice_temporal_mvp_enabled_flag for the current picture and
prev_pics_not_used_flag for the current picture. For instance,
prev_pics_not_used_flag can take a higher precedence than
slice_temporal_mvp_enabled_flag. In one example,
prev_pics_not_used_flag is modified to indicate that preceding
pictures of the current picture should not be used for TMVP of the
current picture as well as the subsequent pictures of the current
picture in decoding order. If the value of prev_pics_not_used_flag
is equal to 1, the preceding pictures are not used for TMVP of the
current picture or its subsequent pictures. When the preceding
pictures are not used for TMVP, motion vectors of the preceding
pictures can be removed, for example, from motion vector
storage.
[0148] The restriction imposed by slice_temporal_mvp_enabled_flag
and the restriction imposed by prev_pics_not_used_flag may be
implemented for error resilience purposes. Error resilience may
refer to preventing or reducing propagation of error to other
pictures when it is detected that an error has occurred, for
instance, in the decoding process. Not referring to pictures with
errors for prediction can stop the error from affecting the quality
of the other pictures. However, when both
slice_temporal_mvp_enabled_flag and prev_pics_not_used_flag are
equal to 1, any error in the TMVP of the current picture can still
be introduced in the TMVP of the subsequent pictures of the current
picture in decoding order. By disallowing both the current picture
and the subsequent pictures from using the preceding pictures of
the current picture in TMVP, error resilience can be significantly
improved and increased.
[0149] According to certain aspects, the condition that the
restriction imposed by slice_temporal_mvp_enabled_flag should be
limited to the base layer was implemented to allow use of error
resilience feature while still allowing enhancement layer to use
TMVP. However, the enhancement layer can still use TMVP along with
error resilience feature without the condition of limiting to the
base layer. For example, slice_temporal_mvp_enabled_flag and
prev_pics_not_used_flag can be both equal to 1. As explained above,
the modified semantics of prev_pics_not_used_flag further enhances
the error resilience aspect since any error in the prediction of
the current picture can be prevented from affecting the prediction
of the subsequent pictures of the current picture in decoding
order.
[0150] Further, in the early versions of SHVC and MV-HEVC, the
values of syntax elements or flags in a VPS are used to constrain
the values of corresponding syntax elements or flags in a SPS. The
VPS and the SPS can both include representation format information.
The representation format information can include picture width and
height (e.g., picture size), bit depth of chroma components, bit
depth of luma components, color plane information, conformance
window size. The VPS can apply to all the layers, and generally,
one VPS can be defined for a bitstream. The SPS can be specific to
a particular layer, and multiple SPSs can be present if a bitstream
includes multiple sequences. In general, the values in the VPS
represent the worst case scenario values or maximum values, and the
SPS can specify different values that are less than or equal to the
values in the VPS as appropriate. Accordingly, the values of syntax
elements or flags in the VPS can constrain the values of
corresponding syntax elements or flags in the SPS when
representation format information is updated for the SPS. Having
the worst case scenario values or maximum values in the VPS can be
important because these values can be used by the decoder to
prepare resources (e.g., memory) for decoding a bitstream; thus, it
can be important that any change of representation format made in
the SPS should not cause the required resources to exceed the
resources that have been prepared. However, for certain syntax
elements or flags, it is unclear whether a worst case scenario
value or a maximum value is applicable. One example can be a flag
having a value of either 0 or 1.
[0151] In order to address these and other challenges, the
techniques according to certain aspects can remove the constraint
for separate_colour_plane_flag in the representation format.
Separate_colour_plane_flag can indicate whether the three colour
components (e.g., Y, Cb, or Cr) of the chroma format are coded
separately or not. When the value of separate_colour_plane_flag is
to be updated in an SPS, the techniques does not have to check
whether the desired value of separate_colour_plane_flag is less
than or equal to the value of separate_colour_plane_flag in the
VPS. For example, the required resource for decoding the bitstream
is the same regardless of whether the value of separate_color_plan
flag is equal to 0 or 1.
[0152] In this way, the value of separate_colour_plane_flag can be
updated in the SPS in a more flexible manner, and the update of
separate_colour_plane_flag in representation format can be more
efficient.
[0153] Semantics of slice_temporal_mvp_enabled_flag
[0154] In the early versions of SHVC and MV-HEVC, the semantics of
slice_temporal_mvp_enabled_flag is defined as follows. The changes
are relative to prior versions of the early versions (e.g., based
on JCTVC-0189). Additions to the prior versions of SHVC and MV-HEVC
are indicated in italics.
TABLE-US-00001 TABLE 1 Semantics of slice_temporal_mvp_enabled_flag
in Early Versions of SHVC and MV-HEVC Let currLayerId be equal to
nuh_layer_id of the current NAL unit. When NumDirectRefLayers[
currLayerId ] is equal to 0, slice_temporal_mvp_enabled_flag is
equal to 0, and TemporalId is equal to 0, the syntax elements for
all coded pictures with nuh_layer_id equal to currLayerId that
follow the current picture in decoding order shall be constrained
such that no temporal motion vector from any picture that precedes
the current picture in decoding order is used in decoding of any
coded picture with nuh_layer_id equal to currLayerId that follows
the current picture in decoding order. NOTE 7--When
NumDirectRefLayers [ currLayerId ] is equal to 0 and
slice_temporal_mvp_enabled_flag is equal to 0 in an I slice, it has
no impact on the normative decoding process of the picture but
merely expresses a bitstream constraint. NOTE 8--When
NumDirectRefLayers [ currLayerId ] is equal to 0 and
slice_temporal_mvp_enabled_flag is equal to 0 in a slice with
TemporalId equal to 0, decoders may empty "motion vector storage"
for all reference pictures with nuh_layer_id equal to currLayerId
in the decoded picture buffer.
[0155] The addition of a supplemental enhancement information (SEI)
message, called TMVP constraints SEI message, provides an
indication of whether pictures of the current layer that precede,
in decoding order, the current picture shall not be used as
collocated pictures in TMVP for any subsequent picture, in decoding
order, of the same layer.
[0156] With the above two adopted changes, issues remain with
existing techniques for the indication of the use of TMVP. Such
issues are explained below.
[0157] In HEVC, the restriction imposed by
slice_temporal_mvp_enabled_flag equal to 0 for a picture with
TemporalId equal to 0 was for error resilience purpose. When the
restriction is applied, the decoder could empty the motion vectors
of earlier pictures when the current picture has both
slice_temporal_mvp_enabled_flag and TemporalId equal to 0.
[0158] The addition of the condition
"NumDirectRefLayers[currLayerId] is equal to 0" from the first
change resulted in that the restriction applies only to independent
layers. A motivation for this change was to allow TMVP for decoding
an enhancement layer picture (using motion vectors from the picture
of a reference layer in the same access unit) while at the same
time making it possible to indicate that the error resilience
constraint is applied. However, the motivation may be met without
the addition of the condition, because the enhancement layer
picture can have slice_temporal_mvp_enabled_flag equal to 1 while
at the same time have the TMVP constraints SEI message with
prev_pics_not_used_flag equal to 1. When the condition is removed,
the semantics of slice_temporal_mvp_enabled_flag would be
consistent for all layers in a way that is aligned with HEVC
version1 (i.e., the HEVC WD as cited above).
[0159] Semantics of prev_pics_not_used_flag
[0160] In the early versions of SHVC and MV-HEVC, the semantics of
prev_pics_not_used_flag in the TMVP constraints SEI message is
defined as follows:
TABLE-US-00002 TABLE 2 Semantics of prev_pics_not_used_flag in
Early Versions of SHVC and MV-HEVC prev_pics_not_used_flag equal to
1 indicates that the syntax elements for all coded pictures that
follow the access unit containing the current picture in decoding
order are constrained such that no temporal motion vector from any
picture that has nuh_layer_id equal to any value in
associatedLayerIdList and precedes the access unit containing the
current picture in decoding order is used in decoding of any coded
picture that follows the access unit containing the current picture
in decoding order. prev_pics_not_used_flag equal to 0 indicates
that the bitstream may or may not fulfill the constraints indicated
by prev_pics_not_used_flag equal to. NOTE--When
prev_pics_not_used_flag is equal to 1, decoders may empty the
"motion vector storage" for all reference pictures with
nuh_layer_id equal to any value in associatedLayerIdList in the
decoded picture buffer. prev_pics_not_used_flag shall be equal to
1, when all of the following conditions are true: --
no_intra_layer_col_pic_flag is equal to 1 in the previous motion
vector prediction constraints SEI message applying to nuh_layer_id
equal to currLayerId. -- There is no IDR or BLA picture with
nuh_layer_id equal to currLayerId following, in decoding order, the
previous motion vector prediction constraints SEI message applying
to nuh_layer_id equal to curLayerId, and preceding, in decoding
order, the current motion vector prediction constraints SEI
message. -- There is no IRAP access unit with NoClrasOutputFlag
equal to 1 following, in decoding order, the previous motion vector
prediction constraints SEI message applying to nuh_layer_id equal
to curLayerId, and preceding, in decoding order, the current motion
vector prediction constraints SEI message.
[0161] FIG. 4 illustrates an issue with the existing semantics of
prev_pics_not_used_flag. In this example, the Layer 1 picture that
is shaded is associated with a TMVP constraints SEI message with
prev_pics_not_used_flag equal to 1. When the value of the syntax
element is equal to 1 in a TMVP constraints SEI message associated
with the current picture, it is possible that the current picture
uses earlier pictures, in decoding order, from the same layer as
collocated pictures for TMVP. Also, it is possible for pictures
that succeed the current picture, in decoding order, from the same
layer to use the current picture as the collocated picture for
TMVP. Consequently, the error resilience feature, thought to be
achieved by setting prev_pics_not_used_flag equal to 1, may not be
achieved as indirect collocated reference is possible, such that if
an error occurs to an earlier picture in the same layer in decoding
order than the current picture, it is possible that the error
propagates to later pictures in the same layer in decoding
order.
[0162] Motion Vector Prediction Error Resilience in the Multi-Layer
Context
[0163] The TMVP constraints SEI message provides error resilience
(ER) feature as it can stop propagation of incorrect motion vector
prediction if there was error (e.g., picture loss). However, the ER
feature provided by the SEI message is only for layers that contain
the SEI message, not for all layers. For example, if a bitstream
has 3 layers and a TMVP constraints SEI message is present for only
layer 0 and layer 1 only, the correct motion vector prediction can
be guaranteed only for pictures with layer 0 or layer 1 that
succeed the access unit that contains the SEI message, in decoding
order, but not for pictures in layer 2 that succeed the access unit
that contains the SEI message. FIG. 5 illustrates such an example.
TMPV constraint SEI messages being contained only in layer 0 and
layer 1 within access unit (AU) E means when the value of
prev_pics_not_used_flag of the SEI message is equal to 1, all
pictures in AU F, AU G, and AU H, and so forth cannot use pictures
from layer 0 and layer 1 of AU D, AU C, AU B, and any earlier AUs.
This will only guarantee that motion vector predictions for picture
in layer 0 and layer 1 of AU F, AU G, AU H, and so forth will be
correct if there was error in one of the pictures in layer 0 or
layer 1 of AU before AU E. Layer 2 picture of AU F can, for
example, use Layer 2 picture of AU D for TMVP reference and Layer 2
picture of AU D can use Layer 1 picture of AU D for TMVP reference.
This results in indirect reference for TMVP such that ER is not
guaranteed for Layer 2 in this example.
[0164] Update of separate_color_plane_flag
[0165] In the early versions of SHVC and MV-HEVC, the
representation format syntax structure in the VPS specifies, for
each layer, the parameters that are needed to describe some
essential properties of the coded picture, including picture width,
picture height, bit depth of the luma and chroma components, as
well as chroma format and how the colour planes are coded. In SPSs
that have nuh_layer_id greater than 0, the representation format
parameters are allowed to be updated using the
update_rep_format_flag indication. For a layer that has
nuh_layer_id greater than 0 and that refers to an SPS with
nuh_layer_id greater than 0, when the SPS has
update_rep_format_flag equal to 1, the updated representation
format parameters are restricted to be less than that signaled in
the representation format parameters in the VPS corresponding to
that layer. The inference rules and constraints on these parameters
are given below, where the italicized paragraph is of relevance to
the subject of discussion:
TABLE-US-00003 TABLE 3 Updating Representation Format in Early
Versions of SHVC and MV-HEVC sps_rep_format_idx specifies the
index, into the list of rep_format( ) syntax structures in the VPS,
of the rep_format( ) syntax structure that applies to the layers
that refer to this SPS. When not present, the value of
sps_rep_format_idx is inferred to be equal to 0. The value of
sps_rep_format_idx shall be in the range of 0 to
vps_num_repformats_minus1, inclusive. When a current picture with
nuh_layer_id layerIdCurr greater than 0 refers to an SPS, the
values of chroma_format_idc, separate_colour_plane_flag,
pic_width_in_luma_samples, pic_height_in_luma_samples,
bit_depth_luma_minus8, and bit_depth_chroma_minus8 are inferred or
constrained as follows: -- The variable repFormatIdx is derived as
follows: -- If update_rep_format_flag is equal to 0, the variable
repFormatIdx is set equal to vps_rep_format_idx[ LayerIdxInVps[
layerIdCurr ] ]. -- Otherwise, (update_rep_format_flag is equal to
1), the variable repFormatIdx is set equal to sps_rep_format_idx.
-- If the nuh_layer_id of the active SPS for the layer with
nuh_layer_id equal to layerIdCurr is equal to 0, the values of
chroma_format_idc, separate_colour_plane_flag,
pic_width_in_luma_samples, pic_height_in_luma_samples,
bit_depth_luma_minus8, and bit_depth_chroma_minus8 are inferred to
be equal to chroma_format_vps_idc, separate_colour_plane_vps_flag,
pic_width_vps_in_luma_samples, pic_height_vps_in_luma_samples,
bit_depth_vps_luma_minus8, and bit_depth_vps_chroma_minus8,
respectively, of the repFormatIdx-th rep_format( ) syntax structure
in the active VPS and the values of chroma_format_idc,
separate_colour_plane_flag, pic_width_in_luma_samples,
pic_height_in_luma_samples, bit_depth_luma_minus8, and
bit_depth_chroma_minus8 of the active SPS for the layer with
nuh_layer_id equal to layerIdCurr are ignored. NOTE 2--The values
are inferred from the VPS when a non-base layer refers to an SPS
that is also referred to by the base layer, in which case the SPS
has nuh_layer_id equal to 0. For the base layer, the values of
these parameters in the active SPS for the base layer apply. --
Otherwise (the nuh_layer_id of the active SPS for the layer with
nuh_layer_id equal to layerIdCurr is greater than zero), the
following applies: -- The values of chroma_format_idc,
separate_colour_plane_flag, pic_width_in_luma_samples,
pic_height_in_luma_samples, bit_depth_luma_minus8, and
bit_depth_chroma_minus8 are inferred to be equal to
chroma_format_vps_idc, separate_colour_plane_vps_flag,
pic_width_vps_in_luma_samples, pic_height_vps_in_luma_samples,
bit_depth_vps_luma_minus8, and bit_depth_vps_chroma_minus8,
respectively, of the repFormatIdx-th rep_format( ) syntax structure
in the active VPS. -- When update rep _format _flag is equal to 1,
it is a requirement of bitstream conformance that the value of
chroma _format_idc, separate_colour_plane _flag,
pic_width_in_luma_samples, pic_height_in_luma_samples,
bit_depth_luma_minus8, or bit_depth_chroma_minus8 shall be less
than or equal to chroma _format_vps_idc, separate_colour_plane_vps
_flag, pic_width_vps_in_luma_samples,
pic_height_vps_in_luma_samples, bit_depth_vps_luma_minus8, or
bit_depth_vps_chroma_minus8, respectively, of the vps_rep
_format_idx[ j ]-th rep_format( ) syntax structure in the active
VPS, where j is equal to LayerIdxInVps [ layerIdCurr ].
[0166] Of the syntax elements included in the italicized constraint
above (chroma_format_idc, separate_colour_plane_flag,
pic_width_in_luma_samples, pic_height_in_luma_samples,
bit_depth_luma_minus8, and bit_depth_chroma_minus8), all the syntax
elements except separate_colour_plane_flag specify
parameters/variables that have a linear relationship with the value
of the syntax element. However, separate_colour_plane_flag does not
have such relationship; it describes whether the different colour
planes of a picture that refers to the SPS are coded together or
coded separately. The semantics of separate_colour_plane_flag are
given below:
TABLE-US-00004 TABLE 4 Semantics of separate_colour_plane_flag in
Early Versions of SHVC and MV-HEVC separate_colour_plane_flag equal
to 1 specifies that the three colour components of the 4:4:4 chroma
format are coded separately. separate_colour_plane_flag equal to 0
specifies that the colour components are not coded separately. When
separate_colour_plane_flag is not present, it is inferred to be
equal to 0. When separate_colour_plane_flag is equal to 1, the
coded picture consists of three separate components, each of which
consists of coded samples of one colour plane (Y, Cb, or Cr) and
uses the monochrome coding syntax. In this case, each colour plane
is associated with a specific colour_plane_id value. The value of
separate_colour_plane_flag shall be less than or equal to
separate_colour_plane_vps_flag NOTE 3--There is no dependency in
decoding processes between the colour planes having different
colour_plane_id values. For example, the decoding process of a
monochrome picture with one value of colour_plane_id does not use
any data from monochrome pictures having different values of
colour_plane_id for inter prediction. Depending on the value of
separate_colour_plane_flag, the value of the variable
ChromaArrayType is assigned as follows: -- If
separate_colour_plane_flag is equal to 0, ChromaArrayType is set
equal to chroma_format_idc. -- Otherwise
(separate_colour_plane_flag is equal to 1), ChromaArrayType is set
equal to 0.
[0167] When the representation format parameters of an SPS are
updated, and the value of separate_colour_plane_flag of the updated
representation format parameter is restricted to be less or equal
to a corresponding value in the VPS (as per the constraint above),
the following use case is allowed: the colour planes of pictures of
a particular layer are specified in the VPS to be coded separately,
but it is specified that for pictures of the same layer that refer
to a particular SPS that updates the representation format
parameters would have colour planes coded together. Use cases where
the colour planes are coded for layers differently (together and/or
independent) within the same bitstream may not be common. If such
use cases do exist where the colour planes are coded differently
(together and/or independent) for layers within the same bitstream,
then it is unclear why the following case is disallowed: the colour
planes of pictures of a layer are specified to be coded together in
the VPS, but an updated SPS specifies that the pictures referring
to the updated SPS would have the colours planes coded
separately.
[0168] A motivation of putting the italicized restriction on the
update of representation format parameters was to ensure that
resources/capabilities indicated as required by the VPS are not
exceeded by an updated SPS. However, neither value (0 or 1) of the
separate_colour_plane_flag indicates any additional data to be
signaled or processed, and hence separate_colour_plane_flag does
not need to be considered for this restriction.
[0169] TMVP Indication and Representation Format Update in
Multi-Layer Codecs
[0170] To overcome the above-described issues with existing
approaches for the indication of the use of TMVP in multi-layer
codecs, this disclosure describes improvements below. In this
disclosure, the following described techniques and approaches may
be used solely or in any combination: [0171] Extending the
constraint in the semantics of slice_temporal_mvp_enabled_flag such
that when the values of both slice_temporal_mvp_enabled_flag and
TemporalId of the current picture are equal to 0, the syntax
elements for all coded pictures that follow the current picture in
decoding order and are in the same layer as the current picture may
be constrained, such that no temporal motion vector from any
picture that precedes the current picture in decoding order is used
in the decoding of any coded picture that follows the current
picture in decoding order. [0172] This constraint may apply to
pictures belonging to any layer. [0173] This constraint may allow
the decoder to empty motion vector storage when it receives picture
with both values of slice_temporal_mvp_enabled_flag and TemporalId
are equal to 0. [0174] Modification of the semantics of
prev_pics_not_used_flag in the TMVP constraints SEI message such
that when the TMVP constraints SEI message is present and
associated with a current picture and the value of the
prev_pics_not_used_flag is equal to 1, the current picture is also
disallowed to use pictures in the same layer that precede it, in
decoding order, as collocated pictures for TMVP. [0175] In one
example approach, when a TMVP constraints SEI message is present
and associated with a current picture and the value of the
prev_pics_not_used_flag is equal to 1 and the value of
slice_temporal_mvp_enabled_flag of the current picture is equal to
1, only pictures from reference layers of the current layer that
have slice_temporal_mvp_enabled_flag equal to 0 may be used as
collocated pictures for TMVP. [0176] In another example approach,
when a TMVP constraints SEI message is present and associated with
a current picture and the value of the prev_pics_not_used_flag is
equal to 1 and the value of slice_temporal_mvp_enabled_flag of the
current picture is equal to 1, all pictures from reference layers
of the current layer may have slice_temporal_mvp_enabled_flag set
equal to 0. [0177] Addition of a constraint to the TMVP constraints
SEI message such that when a TMVP constraints SEI message with the
value of prev_pics_not_used_flag equal to 1 is present for a
particular layerA, all layers that refer to layerA directly or
indirectly may also contain the TMVP constraints SEI message with
the value of prev_pics_not_used_flag equal to 1. [0178] In one
example approach, the TMVP constraints SEI message is defined to
applies to all layers. [0179] In another example approach, when
prev_pics_not_used_flag equal to 1, prev_pics_not_used_flag may
indicate that the syntax elements for all coded pictures that are
within or follow the access unit containing the current picture in
decoding order are constrained such that no temporal motion vector
from any picture that has nuh_layer_id equal to any value in
associatedLayerIdList and precedes the access unit containing the
current picture in decoding order is used directly or indirectly in
decoding of any coded picture that are within or follows the access
unit containing the current picture in decoding order.
prev_pics_not_used_flag equal to 0 indicates that the bitstream may
or may not fulfill the constraints indicated by
prev_pics_not_used_flag equal to 1. [0180] Removal of
separate_colour_plane_flag from the restriction on update of
representation format parameters, such that when updating
representation format, there is no checking required of the value
of separate_colour_plane_flag. This allows the bitstream to have
separate_colour_plane_flag change value from 0 to 1, and vice
versa, flexibly. [0181] In one example approach, a constraint is
added such that the value of separate_colour_plane_flag shall be
the same in all the rep_format( ) syntax structures in a VPS.
[0182] In another example approach, the syntax element
separate_colour_plane_flag is signaled at most once in a VPS, e.g.,
only in the first rep_format( ) structure and the remaining
signaled rep_format( ) in the VPS shall have not the syntax element
but rather infer the value from the first structure.
EXEMPLARY EMBODIMENTS
[0183] The above mentioned techniques can be implemented as shown
in the following examples. The examples are provided in the context
of earlier versions of SHVC and MV-HEVC (e.g., SHVC WD 6 and
MV-HEVC WD 8). Additions to the earlier versions of SHVC and
MV-HEVC are indicated in italics, and deletions from the earlier
versions of SHVC and MV-HEVC are indicated in strikethrough.
Exemplary Embodiment 1
[0184] This embodiment modifies the restriction on
slice_temporal_mvp_enabled_flag. For example, the condition that
the restriction be applied to pictures that have
slice_temporal_mvp_enabled_flag=0 and temporal ID equal to 0 is
applicable to all layers, instead of only the base layer.
TABLE-US-00005 TABLE 5 Exemplary Embodiment 1 Let currLayerId be
equal to nuh_layer_id of the current NAL unit. When
slice_temporal_mvp_enabled_ flag is equal to 0-, and TemporalId is
equal to 0, the syntax elements for all coded pictures with nuh_
layer_id equal to currLayerId that follow the current picture in
decoding order shall be constrained such that no temporal motion
vector from any picture that precedes the current picture in
decoding order is used in decoding of any coded picture with
nuh_layer_id equal to currLayerId that follows the current picture
in decoding order. NOTE 7--When slice_temporal_mvp_enabled_flag is
equal to 0 in an I slice, it has no impact on the normative
decoding process of the picture but merely expresses a bitstream
constraint. NOTE 8--When slice_temporal_mvp_enabled_flag is equal
to 0 in a slice with TemporalId equal to 0, decoders may empty
"motion vector storage" for all reference pictures with
nuh_layer_id equal to currLayerId in the decoded picture
buffer.
Exemplary Embodiment 2
[0185] This embodiment modifies the semantics of
prev_pics_not_used_flag. For example, the modification adds a
constraint such that prev_pics_not_used_flag disallows using
pictures that precede the current picture in decoding order for
TMVP of the current picture when the value of the flag is set equal
to 1.
TABLE-US-00006 TABLE 6 Exemplary Embodiment 2
prev_pics_not_used_flag equal to 1 indicates that the syntax
elements for all coded pictures that are within or follow the
access unit containing the current picture in decoding order are
constrained such that no temporal motion vector from any picture
that has nuh_layer_id equal to any value in associatedLayerIdList
and precedes the access unit containing the current picture in
decoding order is used directly or indirectly in decoding of any
coded picture that are within or follows the access unit containing
the current picture in decoding order. prev_pics_not_used_flag
equal to 0 indicates that the bitstream may or may not fulfill the
constraints indicated by prev_pics_not_used_flag equal to 1.
NOTE--When prev_pics_not_used_flag is equal to 1, decoders may
empty the "motion vector storage" for all reference pictures with
nuh_layer_id equal to currLayerId in the decoded picture buffer.
prev_pics_not_used_flag shall be equal to 1, when all of the
following conditions are true: -- no_intra_layer_col_pic_flag is
equal to 1 in the previous motion vector prediction constraints SEI
message applying to nuh_layer_id equal to currLayerId. -- There is
no IDR or BLA picture with nuh_layer_id equal to currLayerId
following, in decoding order, the previous motion vector prediction
constraints SEI message applying to nuh_layer_id equal to
curLayerId, and preceding, in decoding order, the current motion
vector prediction constraints SEI message. -- There is no IRAP
access unit with NoClrasOutputFlag equal to 1 following, in
decoding order, the previous motion vector prediction constraints
SEI message applying to nuh_layer_id equal to curLayerId, and
preceding, in decoding order, the current motion vector prediction
constraints SEI message.
Exemplary Embodiment 3
[0186] This embodiment modifies the restriction for updating
representation format. For example, the restriction that the value
of a flag or syntax element in a SPS should be less than or equal
the value of corresponding flag or syntax element in a VPS is not
applied to separate_colour_plane_flag as follows:
TABLE-US-00007 TABLE 7 Exemplary Embodiment 3 When
update_rep_format_flag is equal to 1, it is a requirement of
bitstream conformance that the value of chroma_format_idc,
pic_width_in_luma_samples, pic_height_in_luma_samples,
bit_depth_luma_minus8, or bit_depth_chroma_minus8 shall be less
than or equal to chroma_format_vps_idc,
pic_width_vps_in_luma_samples, pic_height_vps_in_luma_samples,
bit_depth_vps_luma_minus8, or bit_depth_vps_chroma_minus8,
respectively, of the vps_rep_format_idx[ j ]-th rep_format( )
syntax structure in the active VPS, where j is equal to
LayerIdxInVps[ layerIdCurr ].
Method of Restricting Preceding Pictures for Temporal Motion Vector
Prediction
[0187] FIG. 6 is a flowchart illustrating a method of coding video
information, according to one or more aspects of the present
disclosure. The method relates to restricting use of preceding
pictures for TMVP. The process 600 may be performed by an encoder
(e.g., the encoder as shown in FIG. 2A, 2B, etc.), a decoder (e.g.,
the decoder as shown in FIG. 3A, 3B, etc.), or any other component,
depending on the embodiment. The blocks of the process 600 are
described with respect to the decoder 33 in FIG. 3B, but the
process 600 may be performed by other components, such as an
encoder, as mentioned above. The layer 1 video decoder 30B of the
decoder 33 and/or the layer 0 decoder 30A of the decoder 33 may
perform the process 600, depending on the embodiment. All
embodiments described with respect to FIG. 6 may be implemented
separately, or in combination with one another. Certain details
relating to the process 600 are explained above, e.g., with respect
to FIG. 4-5.
[0188] The process 600 starts at block 601. The decoder 33 can
include a memory (e.g., decoded picture buffer 160) for storing
video information associated with a plurality of layers. The
decoder 33 may obtain information associated with a current AU to
be coded. The current AU can contain pictures from a plurality of
layers. The plurality of layers can include a current layer to be
coded, and the current layer can include a current picture to be
coded.
[0189] At block 602, the decoder 33 determines the value of a first
flag indicative of whether preceding pictures that precede the
current picture in the current layer in decoding order are used for
TMVP of subsequent pictures that follow the current picture in the
current layer in decoding order. The first flag may be associated
with the current picture. In one embodiment, the first flag is
included in a SEI message. The first flag may indicate that the
preceding pictures in the current layer should not be used for TMVP
of the subsequent pictures in the current layer when the value of
the first flag is equal to 1. The first flag may indicate that the
preceding pictures in the current layer can be used for TMVP of the
current picture and/or the subsequent pictures in the current layer
when the value of the first flag is equal to 0. In one embodiment,
the first flag comprises prev_pics_not_used_flag. The preceding
pictures can precede the current picture in decoding order, and the
subsequent pictures can follow the current picture in decoding
order. In some embodiments, the current picture comprises an IDR
picture.
[0190] At block 603, the decoder 33 refrains from using the
preceding pictures in the current layer as reference pictures for
TMVP of the current picture, in response to determining that the
value of the first flag indicates that the preceding pictures in
the current layer should not be used for TMVP of the subsequent
pictures in the current layer.
[0191] In some embodiments, the decoder 33 refrains from accessing
a second flag indicative of whether TVMP is enabled. The second
flag may be included in the slice header of the slice including the
current picture, and the second flag may be associated with the
current picture. For example, the decoder 33 refrains from
accessing the second flag indicative of whether TVMP is enabled
when the value of the first flag is equal to 1. In one embodiment,
the decoder 33 refrains from accessing the second flag in response
to determining that the value of the first flag indicates that the
preceding pictures in the current layer should not be used for TMVP
of the subsequent pictures in the current layer. In another
embodiment, the second flag comprises
slice_temporal_mvp_enabled_flag. In certain embodiments, for all of
the plurality of layers in the current AU, the preceding pictures
should not be used for TMVP of the current picture when the second
flag indicates that TMVP is not enabled and when the current
picture is in the base temporal sublayer (e.g., the current picture
has a temporal ID equal to 0). In other embodiments, for all of the
plurality of layers in the current AU, the preceding pictures
should not be used for TMVP of the current picture and subsequent
pictures when the second flag indicates that TMVP is not enabled
for the current picture and when the current picture is in a base
temporal sublayer. The first flag may have a higher precedence than
the second flag. In one embodiment, the decoder 33 encodes the
video information. In another embodiment, the decoder 33 decodes
the video information.
[0192] In certain embodiments, the decoder 33 is a wireless
communication device, further comprising a receiver configured to
receive video data according to at least one radio access
technology (RAT), the video data comprising the video information
associated with the plurality of layers; and a transmitter
configured to operate in accordance with the at least one RAT. The
wireless communication device may be a cellular telephone, and the
received video data may be received by the receiver and may be
modulated according to cellular communication standard.
[0193] In some embodiments, the process 600 may be executable on a
wireless communication device comprising: a receiver configured to
receive video data according to at least one radio access
technology (RAT), the video data comprising the video information
associated with the plurality of layers; a transmitter configured
to operate in accordance with the at least one RAT; a memory
configured to store the video data; and a processor configured to
execute instructions to process the video data stored in the
memory. The wireless communication device may be a cellular
telephone, and the received video data may be received by the
receiver and may be modulated according to cellular communication
standard.
[0194] The process 600 ends at block 604. Blocks may be added
and/or omitted in the process 600, depending on the embodiment, and
blocks of the process 600 may be performed in different orders,
depending on the embodiment.
[0195] Any features and/or embodiments described with respect to
restricting use of preceding pictures for TMVP in this disclosure
may be implemented separately or in any combination thereof. For
example, any features and/or embodiments described in connection
with FIGS. 1-6 and other parts of the disclosure may be implemented
in any combination with any features and/or embodiments described
in connection with FIG. 6, and vice versa.
[0196] Method of Updating Representation Format
[0197] FIG. 7 is a flowchart illustrating a method of coding video
information, according to one or more aspects of the present
disclosure. The method relates to updating representation format.
The process 700 may be performed by an encoder (e.g., the encoder
as shown in FIG. 2A, 2B, etc.), a decoder (e.g., the decoder as
shown in FIG. 3A, 3B, etc.), or any other component, depending on
the embodiment. The blocks of the process 700 are described with
respect to the encoder 23 in FIG. 2B, but the process 700 may be
performed by other components, such as a decoder, as mentioned
above. The layer 1 video encoder 20B of the encoder 23 and/or the
layer 0 encoder 20A of the encoder 23 may perform the process 700,
depending on the embodiment. All embodiments described with respect
to FIG. 7 may be implemented separately, or in combination with one
another. Certain details relating to the process 700 are explained
above, e.g., with respect to FIG. 4-6.
[0198] The process 700 starts at block 701. The encoder 23 can
include a memory (e.g., decoded picture buffer 160) for storing
video information associated with a plurality of layers.
[0199] At block 702, the encoder 23 receives a VPS including one or
more representation format syntax structures. The VPS may indicate
a first representation format syntax structure of the one or more
representation format syntax structures associated with a first
layer of the plurality of layers.
[0200] At block 703, the encoder 23 receives a SPS including (1) a
reference to a second representation format syntax structure of the
one or more representation format syntax structures in the VPS or
(2) a third representation format syntax structure. The third
representation format syntax structure may not be included in the
one or more representation format syntax structures in the VPS.
Each representation format syntax structure may include a first
flag indicative of whether to code color components of chroma
format of a layer separately.
[0201] At block 704, the encoder 23 updates a value of a first
variable indicative of whether to code color components of chroma
format of a layer separately without referring to a value of the
first flag in the first representation format syntax structure, the
first variable associated with the first layer. The encoder 23 may
code video data associated with the VPS based on the value of the
first variable.
[0202] In some embodiments, the SPS includes the reference to the
second representation format syntax structure, and the encoder 23
updates the value of the first variable to be equal to the value of
the first flag in the second representation format syntax
structure. Each representation format syntax structure can include
one or more second flags in addition to the first flag, and the
encoder 23 can update values of one or more second variables
corresponding to the one or more second flags to values of the one
or more second flags in the second representation format syntax
structure when the values of one or more second flags in the second
representation format syntax structure are less than or equal to
values of the one or more second flags in the first representation
format syntax structure. The one or more second variables may be
associated with the first layer.
[0203] In certain embodiments, the SPS includes the third
representation format syntax structure, and the encoder 23 updates
the value of the first variable to be equal to the value of the
first flag in the third representation format syntax structure.
Each representation format syntax structure can include one or more
second flags in addition to the first flag, and the encoder 23
updates values of one or more second variables corresponding to the
one or more second flags to values of the one or more second flags
in the third representation format syntax structure when the values
of one or more second flags in the third representation format
syntax structure are less than or equal to values of the one or
more second flags in the first representation format syntax
structure. The one or more second variables may be associated with
the first layer.
[0204] The VPS may include a mapping of which of the one or more
representation format syntax structures is associated with
respective layer of the plurality of layers. The first flag may
indicate that color components of chroma format should be coded of
a layer separately when the value of the first flag is equal to 1,
and the first variable may indicate that color components of chroma
format of a layer should be coded separately when the value of the
first variable is equal to 1. The first flag may indicate that
color components of chroma format of a layer should not be coded
separately when the value of the first flag is equal to 0, and the
first variable may indicate that color components of chroma format
of a layer should not be coded separately when the value of the
first variable is equal to 0. In one embodiment, the first flag
comprises separate_colour_plane_vps_flag, and the first variable
comprises separate_colour_plane_flag. In another embodiment, the
reference to the second representation format syntax structure
comprises sps_rep_format_idx. The VPS can apply to all of the
plurality of layers, and the SPS can apply to a particular layer
among the plurality of layers. In one embodiment, the encoder 23
encodes the video information.
[0205] In certain embodiments, the encoder 23 is a wireless
communication device, further comprising a transmitter configured
to transmit video data according to at least one radio access
technology (RAT); and a receiver configured to operate in
accordance with the at least one RAT. The wireless communication
device may be a cellular telephone, and the transmitted video data
may be transmitted by the transmitter and may be modulated
according to cellular communication standard.
[0206] In some embodiments, the process 700 may be executable on a
wireless communication device comprising: a transmitter configured
to transmit video data according to at least one radio access
technology (RAT); a receiver configured to operate in accordance
with the at least one RAT; a memory configured to store the video
data; and a processor configured to execute instructions to process
the video data stored in the memory. The wireless communication
device may be a cellular telephone, and the transmitted video data
may be transmitted by the transmitter and may be modulated
according to cellular communication standard.
[0207] The process 700 ends at block 704. Blocks may be added
and/or omitted in the process 700, depending on the embodiment, and
blocks of the process 700 may be performed in different orders,
depending on the embodiment.
[0208] Any features and/or embodiments described with respect to
updating the representation format in this disclosure may be
implemented separately or in any combination thereof. For example,
any features and/or embodiments described in connection with FIGS.
1-7 and other parts of the disclosure may be implemented in any
combination with any features and/or embodiments described in
connection with FIG. 7, and vice versa.
[0209] Information and signals disclosed herein may be represented
using any of a variety of different technologies and techniques.
For example, data, instructions, commands, information, signals,
bits, symbols, and chips that may be referenced throughout the
above description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof.
[0210] The various illustrative logical blocks, circuits, and
algorithm steps described in connection with the embodiments
disclosed herein may be implemented as electronic hardware,
computer software, or combinations of both. To clearly illustrate
this interchangeability of hardware and software, various
illustrative components, blocks, modules, circuits, and steps have
been described above generally in terms of their functionality.
Whether such functionality is implemented as hardware or software
depends upon the particular application and design constraints
imposed on the overall system. Skilled artisans may implement the
described functionality in varying ways for each particular
application, but such implementation decisions should not be
interpreted as causing a departure from the scope of the present
invention.
[0211] The techniques described herein may be implemented in
hardware (e.g., computer hardware), software, firmware, or any
combination thereof. Such techniques may be implemented in any of a
variety of devices such as general purposes computers, wireless
communication device handsets, or integrated circuit devices having
multiple uses including application in wireless communication
device handsets and other devices. Any features described as
modules or components may be implemented together in an integrated
logic device or separately as discrete but interoperable logic
devices. If implemented in software, the techniques may be realized
at least in part by a computer readable medium (e.g., a
computer-readable data storage medium) comprising program code
including instructions that, when executed, performs one or more of
the methods described above. The computer readable medium may be a
non-transitory computer readable medium. The computer-readable
medium may form part of a computer program product, which may
include packaging materials. The computer-readable medium may
comprise memory or data storage media, such as random access memory
(RAM) such as synchronous dynamic random access memory (SDRAM),
read-only memory (ROM), non-volatile random access memory (NVRAM),
electrically erasable programmable read-only memory (EEPROM), FLASH
memory, magnetic or optical data storage media, and the like. The
techniques additionally, or alternatively, may be realized at least
in part by a computer-readable communication medium that carries or
communicates program code in the form of instructions or data
structures and that can be accessed, read, and/or executed by a
computer, such as propagated signals or waves.
[0212] The program code may be executed by a processor, which may
include one or more processors, such as one or more digital signal
processors (DSPs), general purpose microprocessors, an application
specific integrated circuits (ASICs), field programmable logic
arrays (FPGAs), or other equivalent integrated or discrete logic
circuitry. Such a processor may be configured to perform any of the
techniques described in this disclosure. A general purpose
processor may be a microprocessor; but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration. Accordingly, the term
"processor," as used herein may refer to any of the foregoing
structure, any combination of the foregoing structure, or any other
structure or apparatus suitable for implementation of the
techniques described herein. In addition, in some aspects, the
functionality described herein may be provided within dedicated
software modules or hardware modules configured for encoding and
decoding, or incorporated in a combined video encoder-decoder
(CODEC). Also, the techniques could be fully implemented in one or
more circuits or logic elements.
[0213] The techniques of this disclosure may be implemented in a
wide variety of devices or apparatuses, including a wireless
handset, an integrated circuit (IC) or a set of ICs (e.g., a chip
set). Various components, modules, or units are described in this
disclosure to emphasize functional aspects of devices configured to
perform the disclosed techniques, but do not necessarily require
realization by different hardware units. Rather, as described
above, various units may be combined in a codec hardware unit or
provided by a collection of inter-operative hardware units,
including one or more processors as described above, in conjunction
with suitable software and/or firmware.
[0214] Various embodiments of the disclosure have been described.
These and other embodiments are within the scope of the following
claims.
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