U.S. patent application number 14/043335 was filed with the patent office on 2014-04-10 for file format for video data.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Ye-Kui Wang.
Application Number | 20140098868 14/043335 |
Document ID | / |
Family ID | 50432651 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140098868 |
Kind Code |
A1 |
Wang; Ye-Kui |
April 10, 2014 |
FILE FORMAT FOR VIDEO DATA
Abstract
A device generates a file that comprises a plurality of samples
that contain coded pictures. In addition, the file contains a box
that identifies a sample group that contains one or more samples
from among the plurality of samples, wherein the box further
indicates that each sample in the sample group is a step-wise
temporal sub-layer access (STSA) sample. The same or different
device identifies, based on data in the box that identifies the
sample group, STSA samples from among the samples in the file that
contains the box.
Inventors: |
Wang; Ye-Kui; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
50432651 |
Appl. No.: |
14/043335 |
Filed: |
October 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61709748 |
Oct 4, 2012 |
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Current U.S.
Class: |
375/240.13 |
Current CPC
Class: |
H04N 19/31 20141101;
H04N 19/70 20141101 |
Class at
Publication: |
375/240.13 |
International
Class: |
H04N 7/36 20060101
H04N007/36; H04N 7/50 20060101 H04N007/50; H04N 7/34 20060101
H04N007/34 |
Claims
1. A method of processing video data, the method comprising:
identifying, based on data in a box that identifies a sample group,
step-wise temporal sub-layer access (STSA) samples of the video
data from among samples in a file that contains the box.
2. The method of claim 1, wherein the box is a SampleToGroup
box.
3. The method of claim 1, wherein the box includes a grouping type
element with a value of "stsa".
4. The method of claim 1, wherein the file includes a sample group
description box that includes an entry that indicates that the
sample group is used to mark STSA samples.
5. The method of claim 1, wherein: the box is a first box, the
sample group is a first sample group, the file contains a second
box that identifies a second sample group, and the method further
comprises identifying, based on data in the second box, intra
samples from among the samples in the file.
6. The method of claim 5, wherein: the second box is a
SampleToGroup box, and the second box includes a grouping type
element with a value of "ipsg".
7. The method of claim 5, wherein the file includes a sample group
description box that includes an entry that indicates that the
second sample group is used to mark samples that contain intra
coded pictures.
8. The method of claim 1, further comprising performing temporal
up-switching at one of the STSA samples in the sample group.
9. A method of storing video data, the method comprising generating
a file that comprises: a plurality of samples that contain coded
pictures of the video data; and a box that identifies a sample
group that contains one or more samples from among the plurality of
samples, wherein the box further indicates that each sample in the
sample group is a step-wise temporal sub-layer access (STSA)
sample.
10. The method of claim 9, wherein the box is a SampleToGroup
box.
11. The method of claim 9, wherein the box includes a grouping type
element with a value of "stsa".
12. The method of claim 9, wherein generating the file comprises
generating a sample group description box that indicates that the
sample group is used to mark STSA samples.
13. The method of claim 9, wherein: the box is a first box, the
sample group is a first sample group, and generating the file
comprises generating a second box in the file, the second box
identifying a second sample group that contains one or more samples
from among the plurality of samples, wherein the second box further
indicates that each sample in the second sample group is an intra
sample.
14. The method of claim 13, wherein: the second box is a
SampleToGroup box, and the second box includes a grouping type
element with a value of "ipsg".
15. The method of claim 13, wherein generating the file comprises
including, in the file, a sample group description box that
includes an entry that indicates that the second sample group is
used to mark samples that contain intra coded pictures.
16. A device comprising one or more processors configured to
identify, based on data in a box that identifies a sample group,
step-wise temporal sub-layer access (STSA) samples from among
samples of video data in a file that contains the box.
17. The device of claim 16, wherein the box is a SampleToGroup
box.
18. The device of claim 16, wherein the box includes a grouping
type element with a value of "stsa".
19. The device of claim 16, wherein the file includes a sample
group description box that includes an entry that indicates that
the sample group is used to mark STSA samples.
20. The device of claim 16, wherein: the box is a first box, the
sample group is a first sample group, the file contains a second
box that identifies a second sample group, and the one or more
processors are further configured to identify, based on data in the
second box, intra samples from among the samples in the file.
21. The device of claim 20, wherein: the second box is a
SampleToGroup box, and the second box includes a grouping type
element with a value of "ipsg".
22. The device of claim 20, wherein the file includes a sample
group description box that includes an entry that indicates that
the second sample group is used to mark samples that contain intra
coded pictures.
23. The device of claim 16, wherein the one or more processors are
further configured to perform temporal up-switching at one of the
STSA samples in the sample group.
24. A device comprising one or more processors configured to
generate a file that comprises: a plurality of samples that contain
coded pictures of video data; and a box that identifies a sample
group that contains one or more samples from among the plurality of
samples, wherein the box further indicates that each sample in the
sample group is a step-wise temporal sub-layer access (STSA)
sample.
25. The device of claim 24, wherein the box is a SampleToGroup
box.
26. The device of claim 24, wherein the box includes a grouping
type element with a value of "stsa".
27. The device of claim 24, wherein the one or more processors are
configured to generate, in the file, a sample group description box
that indicates that the sample group is used to mark STSA
samples.
28. The device of claim 24, wherein: the box is a first box, the
sample group is a first sample group, and the one or more
processors are configured to generate a second box in the file, the
second box identifying a second sample group that contains one or
more samples from among the plurality of samples, wherein the
second box further indicates that each sample in the second sample
group is an intra sample.
29. The device of claim 28, wherein: the second box is a
SampleToGroup box, and the second box includes a grouping type
element with a value of "ipsg".
30. The device of claim 28, wherein the one or more processors are
configured to generate the file such that the file includes a
sample group description box that includes an entry that indicates
that the second sample group is used to mark samples that contain
intra coded pictures.
31. A device comprising: means for receiving a file that contains a
box that identifies a sample group; and means for identifying,
based on data in the box, step-wise temporal sub-layer access
(STSA) samples of video data from among samples in the file.
32. A device comprising: means for generating a file that
comprises: a plurality of samples that contain coded pictures of
video data; and a box that identifies a sample group that contains
one or more samples from among the plurality of samples, wherein
the box further indicates that each sample in the sample group is a
step-wise temporal sub-layer access (STSA) sample; and means for
outputting the file.
33. A non-transitory computer-readable storage medium having
instructions stored thereon that, when executed, cause one or more
processors to identify, based on data in a box that identifies a
sample group, step-wise temporal sub-layer access (STSA) samples
from among samples in a file that contains the box.
34. A non-transitory computer-readable storage medium having
instructions stored thereon that, when executed, cause one or more
processors to generate a file that comprises: a plurality of
samples that contain coded pictures; and a box that identifies a
sample group that contains one or more samples from among the
plurality of samples, wherein the box further indicates that each
sample in the sample group is a step-wise temporal sub-layer access
(STSA) sample.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/709,748, filed Oct. 4, 2012, the entire
content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] This disclosure relates to video encoding and decoding.
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, tablet computers,
e-book readers, digital cameras, digital recording devices, digital
media players, video gaming devices, video game consoles, cellular
or satellite radio telephones, so-called "smart phones," video
teleconferencing devices, video streaming 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 presently
under development, 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
compression 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 (i.e., a video frame or a portion of a
video frame) may be partitioned into video blocks. 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 indicates 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
coefficients, which then may be quantized. The quantized
coefficients, initially arranged in a two-dimensional array, may be
scanned in order to produce a one-dimensional vector of
coefficients, and entropy coding may be applied to achieve even
more compression.
[0006] A multiview coding bitstream may be generated by encoding
views, e.g., from multiple perspectives. Some three-dimensional
(3D) video standards have been developed that make use of multiview
coding aspects. For example, different views may transmit left and
right eye views to support 3D video. Alternatively, some 3D video
coding processes may apply so-called multiview plus depth coding.
In multiview plus depth coding, a 3D video bitstream may contain
not only texture view components, but also depth view components.
For example, each view may comprise one texture view component and
one depth view component.
SUMMARY
[0007] In general, this disclosure describes techniques for storage
of video content. In some examples, the techniques provide for
storage of High Efficiency Video Coding (HEVC) content in a file
based on an International Organization for Standardization (ISO)
base media file format (ISOBMFF). For instance, a device may
generate a file that comprises a plurality of samples that contain
coded pictures. In addition, the file may contain a box that
identifies a sample group that contains one or more samples from
among the plurality of samples. The box may further indicate that
each sample in the sample group is a step-wise temporal sub-layer
access (STSA) sample. The same or different device may identify,
based on data in the box that identifies the sample group, STSA
samples from among the samples in the file that contains the
box.
[0008] In one example, this disclosure describes a method of
processing video data, the method comprising: identifying, based on
data in a box that identifies a sample group, STSA samples of the
video data from among samples in a file that contains the box.
[0009] In another example, this disclosure describes a method of
storing video data, the method comprising generating a file that
comprises: a plurality of samples that contain coded pictures of
the video data; and a box that identifies a sample group that
contains one or more samples from among the plurality of samples,
wherein the box further indicates that each sample in the sample
group is a STSA sample.
[0010] In another example, this disclosure describes a device
comprising one or more processors configured to identify, based on
data in a box that identifies a sample group, STSA samples from
among samples of video data in a file that contains the box.
[0011] In another example, this disclosure describes a device
comprising one or more processors configured to generate a file
that comprises: a plurality of samples that contain coded pictures
of video data; and a box that identifies a sample group that
contains one or more samples from among the plurality of samples,
wherein the box further indicates that each sample in the sample
group is a STSA sample.
[0012] In another example, this disclosure describes a device
comprising: means for receiving a file that contains a box that
identifies a sample group; and means for identifying, based on data
in the box, STSA samples of video data from among samples in the
file.
[0013] In another example, this disclosure describes a device
comprising: means for generating a file that comprises: a plurality
of samples that contain coded pictures of video data; and a box
that identifies a sample group that contains one or more samples
from among the plurality of samples, wherein the box further
indicates that each sample in the sample group is a STSA sample;
and means for outputting the file.
[0014] In another example, this disclosure describes a
non-transitory computer-readable storage medium having instructions
stored thereon that, when executed, cause one or more processors to
identify, based on data in a box that identifies a sample group,
STSA samples from among samples in a file that contains the
box.
[0015] In another example, this disclosure describes a
non-transitory computer-readable storage medium having instructions
stored thereon that, when executed, cause one or more processors to
generate a file that comprises: a plurality of samples that contain
coded pictures; and a box that identifies a sample group that
contains one or more samples from among the plurality of samples,
wherein the box further indicates that each sample in the sample
group is a STSA sample.
[0016] The details of one or more examples of the disclosure are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages will be apparent from the
description, drawings, and claims.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a block diagram illustrating an example video
coding system that may utilize the techniques described in this
disclosure.
[0018] FIG. 2 is a block diagram illustrating an example video
encoder that may implement the techniques described in this
disclosure.
[0019] FIG. 3 is a block diagram illustrating an example video
decoder that may implement the techniques described in this
disclosure.
[0020] FIG. 4 is a flowchart illustrating an example operation in
accordance with one or more techniques of this disclosure.
[0021] FIG. 5 is a flowchart illustrating an example operation in
accordance with one or more additional techniques of this
disclosure.
[0022] FIG. 6 is a conceptual diagram illustrating an example
structure of a file, in accordance with one or more techniques of
this disclosure.
DETAILED DESCRIPTION
[0023] A bitstream, such as a High Efficiency Video Coding (HEVC)
bitstream, may comprise a sequence of bits that forms a
representation of coded pictures and associated data forming one or
more coded video sequences (CVSs). A coded picture may comprise a
coded representation of a picture containing all coding tree units
of the picture. A coding tree unit (CTU) may comprise a coding tree
block (CTB) of luma samples and two corresponding CTBs of chroma
samples and syntax structures used to code the samples. A CVS may
comprise a sequence of access units. Each of the access units may
comprise a set of coded pictures associated with the same time
instance.
[0024] A media aware network element (MANE) or other type of device
may apply bitstream thinning to a HEVC bitstream that is encoded
with multiple sub-layers. A subset of pictures within a layer that
may be decoded without reference to other pictures within the layer
may be referred to herein as a "sub-layer" or a "temporal
sub-layer." The temporal identifier of a Network Abstraction Layer
(NAL) unit identifies a sub-layer with which the NAL unit is
associated. Thus, each sub-layer of a bitstream may be associated
with a different temporal identifier. If the temporal identifier of
a first NAL unit is less than the temporal identifier of a second
NAL unit, the data encapsulated by the first NAL unit may be
decoded without reference to the data encapsulated by the second
NAL unit.
[0025] At any point in the bitstream, a MANE can start removing
Network Abstraction Layer (NAL) units of higher sub-layers on the
basis that the pictures in the lower sub-layers are still decodable
since the decoding process for the pictures in the lower sub-layers
does not depend on the NAL units of the higher sub-layers. The
action of removing all NAL units with temporal identifiers higher
than a certain value can be referred to as temporal down-switching.
Temporal down-switching may always be possible.
[0026] The action of starting to forward NAL units of a certain
sub-layer that has not been forwarded up until that point can be
referred to as temporal up-switching. In some examples, temporal
up-switching is only possible if none of the pictures in the layer
that is switched to depend on any picture in the same sub-layer
prior to the point in the bitstream at which the switch was
performed. Points in a bitstream at which temporal up-switching is
possible may be referred to as sub-layer switching points.
[0027] In HEVC, there are two picture types associated with
sub-layer switching points, namely the temporal sub-layer access
(TSA) picture type and the step-wise temporal sub-layer access
(STSA) picture type. The TSA and STSA picture types can be used to
indicate temporal sub-layer switching points. A TSA picture enables
up-switching, at the TSA picture, to the sub-layer containing the
TSA picture or any higher sub-layer, from the immediately lower
sub-layer. An STSA picture enables up-switching, at the STSA
picture, to the sub-layer containing the STSA picture, from the
immediately lower sub-layer. Thus, in contrast to a TSA picture, an
STSA does not necessarily enable up-switching to any higher
sub-layer, just the sub-layer containing the STSA picture.
[0028] In accordance with a file format for storage of HEVC content
(i.e., an HEVC file format), a file may comprise a plurality of
"boxes." Thus, files conforming to the HEVC file format may
comprise a series of objects, called boxes. A "box" may be an
object-oriented building block defined by a unique type identifier
and a length. In some instances, all data in a file conforming to
the HEVC file format may be contained within boxes and there may be
no data in the file that is not in a box.
[0029] Furthermore, a file conforming to the HEVC file format may
include a plurality of tracks. Each track may be a timed sequence
of related samples. In the context of the HEVC file format, a
"sample" may comprise data associated with a single timestamp.
Examples of a sample include: an individual frame of video, a
series of video frames in decoding order, or a compressed section
of audio in decoding order.
[0030] Furthermore, in the HEVC file format, a sample grouping is
an assignment of each of the samples in a track to be a member of
one sample group. Samples in a sample group are not required to be
contiguous. Sample groups may be represented by two data
structures: a SampleToGroup box and a SampleGroupDescription box.
The SampleToGroup box represents the assignment of samples to
sample groups. There may be one instance of the
SampleGroupDescription box for each sample group entry. A
SampleGroupDescription box describes the properties of the
corresponding sample group.
[0031] There are several problems or shortcomings with existing
designs of the file format for storage of HEVC content. For
example, there is no compact way for signaling samples that contain
STSA pictures (also referred to as STSA samples). In another
example, there is no efficient way for signaling whether temporal
sub-layer up-switching to any higher temporal layer can be
performed at any sample.
[0032] The techniques of this disclosure may solve one or more of
the previously-mentioned problems or shortcomings. In accordance
with an example technique of this disclosure, a device (e.g., a
video encoder or another device) may generate a file that comprises
a plurality of samples that contain coded pictures. The file may
also include a box (e.g., a SampleToGroupBox) that identifies a
sample group that contains one or more samples from among the
plurality of samples. The box further indicates that each sample in
the sample group is a STSA sample. Accordingly, a device (e.g., a
video decoder or another device) may identify, based on data in a
box that identifies a sample group, STSA samples from among samples
in a file that contains the box.
[0033] In accordance with another example technique of this
disclosure, a video encoder or another device may generate a file
that stores coded samples that contain coded pictures of the video
data. The file may also include a box that includes a record that
includes an element that indicates whether all sequence parameter
sets (SPSs) that are activated when a stream to which the record
applies is decoded have syntax elements that indicate that temporal
sub-layer up-switching to any higher temporal sub-layer can be
performed at any sample associated with the SPSs. Accordingly, a
video decoder or other device may determine, based on an element in
a record in a box of a file that contains samples that contain
coded pictures of the video data, that all SPSs that are activated
when a stream to which the record applies is decoded have syntax
elements that indicate that temporal sub-layer up-switching to any
higher temporal sub-layer can be performed at any sample associated
with the SPSs.
[0034] For instance, a video encoder may generate an HEVC decoder
configuration record. The HEVC decoder configuration record may
include a temporalIdNested element. The temporalIDNested element
may indicate whether temporal sub-layer up-switching to any higher
temporal layer can be performed at any sample of a stream to which
the HEVC decoder configuration record applies.
[0035] FIG. 1 is a block diagram illustrating an example video
coding system 10 that may utilize the techniques of this
disclosure. As used 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 or video decoding.
[0036] As shown in FIG. 1, video coding system 10 includes a source
device 12 and a destination device 14. Source device 12 generates
encoded video data. Accordingly, source device 12 may be referred
to as a video encoding device or a video encoding apparatus.
Destination device 14 may decode the encoded video data generated
by source device 12. Accordingly, destination device 14 may be
referred to as a video decoding device or a video decoding
apparatus. Source device 12 and destination device 14 may be
examples of video coding devices or video coding apparatuses.
[0037] Source device 12 and destination device 14 may comprise a
wide range of devices, including desktop computers, mobile
computing devices, notebook (e.g., laptop) computers, tablet
computers, set-top boxes, telephone handsets such as so-called
"smart" phones, televisions, cameras, display devices, digital
media players, video gaming consoles, in-car computers, or the
like.
[0038] Destination device 14 may receive encoded video data from
source device 12 via a channel 16. Channel 16 may comprise one or
more media or devices capable of moving the encoded video data from
source device 12 to destination device 14. In one example, channel
16 may comprise one or more communication media that enable source
device 12 to transmit encoded video data directly to destination
device 14 in real-time. In this example, source device 12 may
modulate the encoded video data according to a communication
standard, such as a wireless communication protocol, and may
transmit the modulated video data to destination device 14. The one
or more communication media may include wireless and/or wired
communication media, such as a radio frequency (RF) spectrum or one
or more physical transmission lines. The one or more communication
media may form part of a packet-based network, such as a local area
network, a wide-area network, or a global network (e.g., the
Internet). The one or more communication media may include routers,
switches, base stations, or other equipment that facilitate
communication from source device 12 to destination device 14.
[0039] In another example, channel 16 may include a storage medium
that stores encoded video data generated by source device 12. In
this example, destination device 14 may access the storage medium,
e.g., via disk access or card access. The storage medium may
include a variety of locally-accessed data storage media such as
Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable
digital storage media for storing encoded video data.
[0040] In a further example, channel 16 may include a file server
or another intermediate storage device that stores encoded video
data generated by source device 12. In this example, destination
device 14 may access encoded video data stored at the file server
or other intermediate storage device via streaming or download. The
file server may be a type of server capable of storing encoded
video data and transmitting the encoded video data to destination
device 14. Example file servers include web servers (e.g., for a
website), file transfer protocol (FTP) servers, network attached
storage (NAS) devices, and local disk drives.
[0041] Destination device 14 may access the encoded video data
through a standard data connection, such as an Internet connection.
Example types of data connections may include wireless channels
(e.g., Wi-Fi connections), wired connections (e.g., digital
subscriber line (DSL), cable modem, etc.), or combinations of both
that are suitable for accessing encoded video data stored on a file
server. The transmission of encoded video data from the file server
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 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, encoding of video data for
storage on a data storage medium, decoding of video data 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] FIG. 1 is merely an example and the techniques of this
disclosure may apply to video coding settings (e.g., video encoding
or video decoding) that do not necessarily include any data
communication between the encoding and decoding devices. In other
examples, data is retrieved from a local memory, streamed over a
network, or the like. A video encoding device may encode and store
data to memory, and/or a video decoding device may retrieve and
decode data from memory. In many examples, the encoding and
decoding is performed by devices that do not communicate with one
another, but simply encode data to memory and/or retrieve and
decode data from memory.
[0044] In the example of FIG. 1, source device 12 includes a video
source 18, a video encoder 20, and an output interface 22. In some
examples, output interface 22 may include a modulator/demodulator
(modem) and/or a transmitter. Video source 18 may include a video
capture device, e.g., a video camera, a video archive containing
previously-captured video data, a video feed interface to receive
video data from a video content provider, and/or a computer
graphics system for generating video data, or a combination of such
sources of video data.
[0045] Video encoder 20 may encode video data from video source 18.
In some examples, source device 12 directly transmits the encoded
video data to destination device 14 via output interface 22. In
other examples, the encoded video data may also be stored onto a
storage medium or a file server for later access by destination
device 14 for decoding and/or playback.
[0046] In the example of FIG. 1, destination device 14 includes an
input interface 28, a video decoder 30, and a display device 32. In
some examples, input interface 28 includes a receiver and/or a
modem. Input interface 28 may receive encoded video data over
channel 16. Video decoder 30 may decode encoded video data. Display
device 32 may display the decoded video data. Display device 32 may
be integrated with or may be external to destination device 14.
Display device 32 may comprise 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] Video encoder 20 and video decoder 30 each may be
implemented as any of a variety of suitable circuitry, such as one
or more microprocessors, digital signal processors (DSPs),
application-specific integrated circuits (ASICs),
field-programmable gate arrays (FPGAs), discrete logic, hardware,
or any combinations thereof. If the techniques are implemented
partially in software, a device may store instructions for the
software in a suitable, non-transitory computer-readable storage
medium and may execute the instructions in hardware using one or
more processors to perform the techniques of this disclosure. Any
of the foregoing (including hardware, software, a combination of
hardware and software, etc.) may be considered to be one or more
processors. Each of video encoder 20 and 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.
[0048] This disclosure may generally refer to video encoder 20
"signaling" certain information to another device, such as video
decoder 30. The term "signaling" may generally refer to the
communication of syntax elements and/or other data used to decode
the compressed video data. Such communication may occur in real- or
near-real-time. Alternately, such communication may occur over a
span of time, such as might occur when storing syntax elements to a
computer-readable storage medium in an encoded bitstream at the
time of encoding, which then may be retrieved by a decoding device
at any time after being stored to this medium.
[0049] In some examples, video encoder 20 and video decoder 30
operate according to a video compression standard, such as
International Organization for Standardization (ISO)/IEC MPEG-4
Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),
including its Scalable Video Coding (SVC) extension, Multiview
Video Coding (MVC) extension, and MVC-based three-dimensional video
(3DV) extension. In some instances, any bitstream conforming to the
MVC-based 3DV extension of H.264/AVC always contains a
sub-bitstream that is compliant to the MVC extension of H.264/AVC.
Furthermore, video encoder 20 and video decoder 30 may operate
according to a 3DV coding extension to H.264/AVC (i.e., AVC-based
3DV) that is currently under development. In other examples, video
encoder 20 and video decoder 30 may operate according to
International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) H.261, International Organization
for Standardization (ISO)/International Electrotechnical Commission
(IEC) Moving Picture Experts Group (MPEG)-1 Visual, ITU-T H.262 or
ISO/IEC MPEG-2 Visual, and ITU-T H.264, ISO/IEC Visual.
[0050] In other examples, video encoder 20 and video decoder 30 may
operate according to the High Efficiency Video Coding (HEVC)
developed by the Joint Collaboration Team on Video Coding (JCT-VC)
of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion
Picture Experts Group (MPEG). A draft of the HEVC standard,
referred to as "HEVC Working Draft 8" is described in Bross et al.,
"High Efficiency Video Coding (HEVC) text specification draft 8,"
Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3
and ISO/IEC JTC1/SC29/WG11, 10.sup.th Meeting, Stockholm, Sweden,
July 2012, which as of Sep. 17, 2013, is available from
http://phenix.int-evry.fr/jct/doc_end
user/documents/10_Stockholm/wg11/JCTVC-J1003-v8.zip. Furthermore,
video encoder 20 and video decoder 30 may operate according to
scalable video coding, multi-view coding, and 3DV extensions for
HEVC that are currently under development. The scalable video
coding extension of HEVC may be referred to as SHEVC. The 3DV
extension of HEVC may be referred to as HEVC-based 3DV or
3D-HEVC.
[0051] In HEVC and other video coding specifications, a video
sequence typically includes a series of pictures. Pictures may also
be referred to as "frames." A picture may include three sample
arrays, denoted S.sub.L, S.sub.Cb, and S.sub.Cr. S.sub.L is a
two-dimensional array (i.e., a block) of luma samples. S.sub.Cb is
a two-dimensional array of Cb chrominance samples. S.sub.Cr is a
two-dimensional array of Cr chrominance samples. Chrominance
samples may also be referred to herein as "chroma" samples. In
other instances, a picture may be monochrome and may only include
an array of luma samples.
[0052] To generate an encoded representation of a picture, video
encoder 20 may generate a set of coding tree units (CTUs). Each of
the CTUs may comprise a coding tree block of luma samples, two
corresponding coding tree blocks of chroma samples, and syntax
structures used to code the samples of the coding tree blocks. In
monochrome pictures or pictures having three separate color planes,
a CTU may comprise a single coding tree block and syntax structures
used to code the samples of the coding tree block. A coding tree
block may be an N.times.N block of samples. A CTU may also be
referred to as a "tree block" or a "largest coding unit" (LCU). The
CTUs of HEVC may be broadly analogous to the macroblocks of other
standards, such as H.264/AVC. However, a CTU is not necessarily
limited to a particular size and may include one or more coding
units (CUs). A slice may include an integer number of CTUs ordered
consecutively in a raster scan order.
[0053] To generate a coded CTU, video encoder 20 may recursively
perform quad-tree partitioning on the coding tree blocks of a CTU
to divide the coding tree blocks into coding blocks, hence the name
"coding tree units." A coding block is an N.times.N block of
samples. A CU may comprise a coding block of luma samples and two
corresponding coding blocks of chroma samples of a picture that has
a luma sample array, a Cb sample array, and a Cr sample array, and
syntax structures used to code the samples of the coding blocks. In
monochrome pictures or pictures having three separate color planes,
a CU may comprise a single coding block and syntax structures used
to code the samples of the coding block.
[0054] Video encoder 20 may partition a coding block of a CU into
one or more prediction blocks. A prediction block is a rectangular
(i.e., square or non-square) block of samples on which the same
prediction is applied. A prediction unit (PU) of a CU may comprise
a prediction block of luma samples, two corresponding prediction
blocks of chroma samples, and syntax structures used to predict the
prediction blocks. In monochrome pictures or pictures having three
separate color planes, a PU may comprise a single prediction block
and syntax structures used to predict the prediction block. Video
encoder 20 may generate predictive luma, Cb, and Cr blocks for
luma, Cb, and Cr prediction blocks of each PU of the CU.
[0055] Video encoder 20 may use intra prediction or inter
prediction to generate the predictive blocks for a PU. If video
encoder 20 uses intra prediction to generate the predictive blocks
of a PU, video encoder 20 may generate the predictive blocks of the
PU based on decoded samples of the picture associated with the PU.
In this disclosure, the phrase "based on" may indicate "based at
least in part on." If video encoder 20 uses inter prediction to
generate the predictive blocks of a PU, video encoder 20 may
generate the predictive blocks of the PU based on decoded samples
of one or more pictures other than the picture associated with the
PU.
[0056] To support inter prediction, video encoder 20 may generate
one or more reference picture lists. These reference picture lists
may be referred to as RefPicList0 and RefPicList1. In some
examples, video encoder 20 may generate different reference picture
lists for different pictures or different slices of pictures.
Hence, different PUs of different pictures and/or slices may be
associated with different versions of RefPicList0 and
RefPicList1.
[0057] Furthermore, when video encoder 20 uses inter prediction to
generate a predictive block of a PU, video encoder 20 may signal
motion information for the PU. The motion information may include a
reference index for the PU and a motion vector for the PU. The
reference index for the PU may indicate a position, within one of
the reference picture lists associated with the PU, of a reference
picture. The motion vector for the PU may indicate a spatial
displacement between a prediction block of the PU and a reference
location in the reference picture. Video encoder 20 may use samples
of the reference picture associated with the reference location to
generate a predictive block for the PU. Because a PU may be
associated with two reference pictures, the PU may have two
reference indexes and two motion vectors. Hence, a PU may have a
RefPicList0 reference index and a RefPicList1 reference index. The
PU's RefPicList0 reference index indicates a reference picture in
the PU's version of RefPicList0. The PU's RefPicList1 reference
index indicates a reference picture in the PU's version of
RefPicList1. Similarly, the PU may have a RefPicList0 motion vector
and a RefPicList1 motion vector. The PU's RefPicList0 motion vector
may indicate a reference location in a reference picture in the
PU's version of RefPicList0. The PU's RefPicList1 motion vector may
indicate a reference location in a reference picture in the PU's
version of RefPicList1.
[0058] Video encoder 20 may signal a PU's reference indexes and
motion vectors in a bitstream. In other words, video encoder 20 may
include, in the bitstream, data that indicate the PU's reference
indexes and motion vectors. Video decoder 30 may reconstruct the
PU's versions of RefPicList0 and/or RefPicList1 and may use the
PU's reference indexes and motion vectors to determine one or more
predictive blocks for the PU. Video decoder 30 may use the
predictive blocks for the PU, along with residual data, to decode
samples.
[0059] After video encoder 20 generates predictive luma blocks for
one or more PUs of a CU, video encoder 20 may generate a luma
residual block for the CU. Each sample in the CU's luma residual
block indicates a difference between a luma sample in one of the
CU's predictive luma blocks and a corresponding sample in the CU's
original luma coding block. In addition, video encoder 20 may
generate a Cb residual block for the CU. Each sample in the CU's Cb
residual block may indicate a difference between a Cb sample in one
of the CU's predictive Cb blocks and a corresponding sample in the
CU's original Cb coding block. Video encoder 20 may also generate a
Cr residual block for the CU. Each sample in the CU's Cr residual
block may indicate a difference between a Cr sample in one of the
CU's predictive Cr blocks and a corresponding sample in the CU's
original Cr coding block.
[0060] Furthermore, video encoder 20 may use quad-tree partitioning
to decompose the luma, Cb, and Cr residual blocks of a CU into one
or more luma, Cb, and Cr transform blocks. A transform block may be
a rectangular (e.g., square or non-square) block of samples on
which the same transform is applied. A transform unit (TU) of a CU
may comprise a transform block of luma samples, two corresponding
transform blocks of chroma samples, and syntax structures used to
transform the transform block samples. Thus, each TU of a CU may be
associated with a luma transform block, a Cb transform block, and a
Cr transform block. The luma transform block associated with the TU
may be a sub-block of the CU's luma residual block. The Cb
transform block may be a sub-block of the CU's Cb residual block.
The Cr transform block may be a sub-block of the CU's Cr residual
block. In monochrome pictures or pictures having three separate
color planes, a TU may comprise a single transform block and syntax
structures used to transform the samples of the transform
block.
[0061] Video encoder 20 may apply one or more transforms to a luma
transform block of a TU to generate a luma coefficient block for
the TU. A coefficient block may be a two-dimensional array of
transform coefficients. A transform coefficient may be a scalar
quantity. Video encoder 20 may apply one or more transforms to a Cb
transform block of a TU to generate a Cb coefficient block for the
TU. Video encoder 20 may apply one or more transforms to a Cr
transform block of a TU to generate a Cr coefficient block for the
TU.
[0062] After generating a coefficient block (e.g., a luma
coefficient block, a Cb coefficient block or a Cr coefficient
block), video encoder 20 may quantize the 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. After video encoder 20 quantizes a coefficient block,
video encoder 20 may entropy encode syntax elements indicating the
quantized transform coefficients. For example, video encoder 20 may
perform Context-Adaptive Binary Arithmetic Coding (CABAC) on the
syntax elements indicating the quantized transform
coefficients.
[0063] Video encoder 20 may output a bitstream that includes a
sequence of bits that forms a representation of coded pictures and
associated data. The term "bitstream" may be a collective term used
to refer to either a Network Abstraction Layer (NAL) unit stream
(e.g., a sequence of NAL units) or a byte stream (e.g., an
encapsulation of a NAL unit stream containing start code prefixes
and NAL units as specified by Annex B of the HEVC standard). A NAL
unit is a syntax structure containing an indication of the type of
data in the NAL unit and bytes containing that data in the form of
a raw byte sequence payload (RBSP) interspersed as necessary with
emulation prevention bits. Each of the NAL units may include a NAL
unit header and may encapsulate an RBSP. The NAL unit header may
include a syntax element that indicates a NAL_unit_type code. The
NAL_unit_type code specified by the NAL unit header of a NAL unit
indicates the type of the NAL unit. A RBSP may be a syntax
structure containing an integer number of bytes that is
encapsulated within a NAL unit. In some instances, an RBSP includes
zero bits.
[0064] Different types of NAL units may encapsulate different types
of RBSPs. For example, a first type of NAL unit may encapsulate an
RBSP for a picture parameter set (PPS), a second type of NAL unit
may encapsulate an RBSP for a coded slice, a third type of NAL unit
may encapsulate an RBSP for SEI, and so on. NAL units that
encapsulate RBSPs for video coding data (as opposed to RBSPs for
parameter sets and SEI messages) may be referred to as video coding
layer (VCL) NAL units. NAL units that contain parameter sets (e.g.,
video parameter sets (VPSs), sequence parameter sets (SPSs), PPSs,
etc.) may be referred to as parameter set NAL units.
[0065] Video decoder 30 may receive a bitstream generated by video
encoder 20. In addition, video decoder 30 may parse the bitstream
to obtain syntax elements from the bitstream. Video decoder 30 may
reconstruct the pictures of the video data based at least in part
on the syntax elements obtained from the bitstream. The process to
reconstruct the video data may be generally reciprocal to the
process performed by video encoder 20. For instance, video decoder
30 may use motion vectors of PUs to determine predictive blocks for
the PUs of a current CU. In addition, video decoder 30 may inverse
quantize coefficient blocks associated with TUs of the current CU.
Video decoder 30 may perform inverse transforms on the coefficient
blocks to reconstruct transform blocks associated with the TUs of
the current CU. Video decoder 30 may reconstruct the coding blocks
of the current CU by adding the samples of the predictive blocks
for PUs of the current CU to corresponding samples of the transform
blocks of the TUs of the current CU. By reconstructing the coding
blocks for each CU of a picture, video decoder 30 may reconstruct
the picture.
[0066] In multi-view coding, there may be multiple views of the
same scene from different viewpoints. In the context of multi-view
coding, the term "access unit" may be used to refer to the set of
pictures that correspond to the same time instance. Thus, video
data may be conceptualized as a series of access units occurring
over time. A "view component" may be a coded representation of a
view in a single access unit. In this disclosure, a "view" may
refer to a sequence of view components associated with the same
view identifier. In some examples, a view component may be a
texture view component (i.e., a texture picture) or a depth view
component (i.e., a depth picture).
[0067] Multi-view coding supports inter-view prediction. Inter-view
prediction is similar to the inter prediction used in HEVC and may
use the same syntax elements. However, when a video coder performs
inter-view prediction on a current video unit (such as a PU), the
video coder may use, as a reference picture, a picture that is in
the same access unit as the current video unit, but in a different
view. In contrast, conventional inter prediction only uses pictures
in different access units as reference pictures.
[0068] In multi-view coding, a view may be referred to as a "base
view" if a video decoder (e.g., video decoder 30) can decode
pictures in the view without reference to pictures in any other
view. When coding a picture in a non-base view, a video coder (such
as video encoder 20 or video decoder 30) may add a picture into a
reference picture list if the picture is in a different view but
within a same time instance (i.e., access unit) as the picture that
the video coder is currently coding. Like other inter prediction
reference pictures, the video coder may insert an inter-view
prediction reference picture at any position of a reference picture
list.
[0069] For instance, NAL units may include headers (i.e., NAL unit
headers) and payloads (e.g., RBSPs). The NAL unit headers may
include nuh_reserved_zero.sub.--6bits syntax elements. NAL units
that have nuh_reserved_zero.sub.--6bit syntax elements that specify
different values belong to different "layers" of a bitstream. Thus,
in multi-view coding, 3DV, or SVC, the
nuh_reserved_zero.sub.--6bits syntax element of a NAL unit
specifies a layer identifier (i.e., a layer ID) of the NAL unit. In
some examples, the nuh_reserved_zero.sub.--6bits syntax element of
a NAL unit is equal to 0 if the NAL unit relates to a base layer in
multi-view coding, 3DV coding, or SVC. Data in a base layer of a
bitstream may be decoded without reference to data in any other
layer of the bitstream. If the NAL unit does not relate to a base
layer in multi-view coding, 3DV, or SVC, the
nuh_reserved_zero.sub.--6bits syntax element may have a non-zero
value. In multi-view coding and 3DV coding, different layers of a
bitstream may correspond to different views. In SVC, layers other
than the base layer may be referred to as "enhancement layers" and
may provide information that enhances the visual quality of video
data decoded from the bitstream.
[0070] Furthermore, some pictures within a layer may be decoded
without reference to other pictures within the same layer. Thus,
NAL units encapsulating data of certain pictures of a layer may be
removed from the bitstream without affecting the decodability of
other pictures in the layer. Removing NAL units encapsulating data
of such pictures may reduce the frame rate of the bitstream. A
subset of pictures within a layer that may be decoded without
reference to other pictures within the layer may be referred to
herein as a "sub-layer" or a "temporal sub-layer."
[0071] NAL units may include temporal_id syntax elements. The
temporal_id syntax element of a NAL unit specifies a temporal
identifier of the NAL unit. The temporal identifier of a NAL unit
identifies a sub-layer with which the NAL unit is associated. Thus,
each sub-layer of a bitstream may be associated with a different
temporal identifier. If the temporal identifier of a first NAL unit
is less than the temporal identifier of a second NAL unit, the data
encapsulated by the first NAL unit may be decoded without reference
to the data encapsulated by the second NAL unit.
[0072] In H.264/AVC and HEVC, SPSs may contain information that
applies to all slices of a CVS. In HEVC, a CVS may start from an
instantaneous decoding refresh (IDR) picture, or a broken link
access (BLA) picture, or a clean random access (CRA) picture that
is the first picture in the bitstream, including all subsequent
pictures that are not an IDR or BLA picture. That is, in HEVC, a
CVS may comprise a sequence of access units that may consist, in
decoding order, of a CRA access unit that is the first access unit
in the bitstream, an IDR access unit or a BLA access unit, followed
by zero or more non-IDR and non-BLA access units including all
subsequent access units up to but not including any subsequent IDR
or BLA access unit.
[0073] HEVC and other video coding standards provide mechanisms for
enabling random access into bitstreams. Random access refers to a
decoding of a bitstream starting from a coded picture that is not
the first coded picture in the bitstream. Random access to a
bitstream may be needed in various video applications, such as
broadcasting and streaming. Random access to a bitstream may enable
users to tune in to a program at any time, to switch between
different channels, to jump to specific parts of a video, or to
switch to a different bitstream for stream adaptation (e.g.,
adaption of a bit rate, adaptation of a frame rate, adaptation of a
spatial resolution, etc.). The insertion of random access point
(RAP) pictures into a bitstream at regular intervals may enable
random access. Example types of RAP pictures include IDR pictures,
CRA pictures, and BLA pictures. Hence, IDR pictures, CRA pictures
and BLA pictures are collectively referred to as random access
point (RAP) pictures.
[0074] An IDR picture contains only I slices (i.e., slices in which
only intra prediction is used). An IDR picture may be the first
picture in the bitstream in decoding order, or may appear later in
the bitstream. Each IDR picture is the first picture of a CVS in
decoding order. IDR pictures, as specified in HEVC and H.264/AVC,
may be used for random access. However, pictures following an IDR
picture in decoding order cannot use pictures decoded prior to the
IDR picture as reference. Accordingly, bitstreams relying on IDR
pictures for random access can have significantly lower coding
efficiency than bitstreams that use additional types of random
access pictures. An IDR access unit is an access unit that contains
an IDR picture.
[0075] The concept of CRA pictures was introduced in HEVC to allow
pictures that follow a CRA picture in decoding order, but precede
the CRA picture in output order, to use pictures decoded before the
CRA picture for reference. Pictures that follow a CRA picture in
decoding order, but precede the CRA picture in output order, are
referred to as leading pictures associated with the CRA picture (or
leading pictures of the CRA picture). That is, to improve coding
efficiency, the concept of CRA pictures was introduced in HEVC to
allow pictures that follow a CRA picture in decoding order but
precede the CRA picture in output order to use pictures decoded
before the CRA picture as reference. A CRA access unit is an access
unit in which the coded picture is a CRA picture.
[0076] The leading pictures of a CRA picture are correctly
decodable if the decoding starts from an IDR picture or CRA picture
occurring before the CRA picture in decoding order. However, the
leading pictures of a CRA picture may be non-decodable when random
access from the CRA picture occurs. Hence, a video decoder
typically decodes the leading pictures of a CRA picture during
random access decoding. To prevent error propagation from reference
pictures that may not be available depending on where the decoding
starts, no picture that follows a CRA picture both in decoding
order and output order may use any picture that precedes the CRA
picture either in decoding order or output order (which includes
the leading pictures) as reference.
[0077] The concept of a broken link access (BLA) picture was
introduced in HEVC after the introduction of CRA pictures and is
based on the concept of CRA pictures. A BLA picture typically
originates from bitstream splicing at the position of a CRA
picture, and in the spliced bitstream the splicing point CRA
picture is changed to a BLA picture. An access unit that contains a
RAP picture may be referred to herein as a RAP access unit. A BLA
access unit is an access unit that contains a BLA picture.
[0078] One difference between BLA pictures and CRA pictures is as
follows. For a CRA picture, the associated leading pictures are
correctly decodable if the decoding starts from a RAP picture
before the CRA picture in decoding order. However, the leading
pictures associated with a CRA picture may not be correctly
decodable when random access from the CRA picture occurs (i.e.,
when decoding starts from the CRA picture, or in other words, when
the CRA picture is the first picture in the bitstream). In
contrast, there may be no scenario where the leading pictures
associated with a BLA picture are decodable, even when decoding
starts from a RAP picture before the BLA picture in decoding
order.
[0079] Some of the leading pictures associated with a particular
CRA picture or a particular BLA picture may be correctly decodable
even when the particular CRA picture or the particular BLA picture
is the first picture in a bitstream. These leading pictures may be
referred to as decodable leading pictures (DLPs). Other leading
pictures may be referred to as non-decodable leading pictures
(NLPs). HEVC Working Draft 8 may also refer to NLPs as tagged for
discard (TFD) pictures.
[0080] A VPS is a syntax structure comprising syntax elements that
apply to zero or more entire CVSs. An SPS is a syntax structure
containing syntax elements that apply to zero or more entire CVSs.
An SPS may include a syntax element that identifies a VPS that is
active when the SPS is active. Thus, the syntax elements of a VPS
may be more generally applicable than the syntax elements of a
SPS.
[0081] A parameter set (e.g., a VPS, SPS, PPS, etc.) may contain an
identification that is referenced, directly or indirectly, from a
slice header of a slice. The referencing process is known as
"activation." Thus, when video decoder 30 is decoding a particular
slice, a parameter set referenced, directly or indirectly, by a
syntax element in a slice header of the particular slice is said to
be "activated." Depending on the parameter set type, the activation
may occur on a per picture basis or a per sequence basis. For
example, a slice header of a slice may include a syntax element
that identifies a PPS. Thus, when a video coder codes the slice,
the PPS may be activated. Furthermore, the PPS may include a syntax
element that identifies a SPS. Thus, when a PPS that identifies the
SPS is activated, the SPS may be activated. The SPS may include a
syntax element that identifies a VPS. Thus, when a SPS that
identifies the VPS is activated, the VPS is activated.
[0082] HEVC and other video coding standards specify profiles,
tiers, and levels. Profiles, tiers, and levels specify restrictions
on bitstreams and hence limits on the capabilities needed to decode
the bitstreams. Profiles, tiers, and levels may also be used to
indicate interoperability points between individual decoder
implementations. Each profile may specify a subset of algorithmic
features and limits that is supported by all video decoders
conforming to that profile. Video encoders are not required to make
use of all features supported in a profile. Each level of a tier
may specify a set of limits on the values that syntax elements may
have. The same set of tier and level definitions may be used with
all profiles, but individual implementations may support different
tiers and, within a tier, different levels for each supported
profile. For any given profile, a level of a tier may generally
correspond to a particular decoder processing load and memory
capability. Capabilities of video decoders may be specified in
terms of the ability to decode video streams conforming to the
constraints of particular profiles, tiers, and levels. For each
such profile, the tier and level supported for that profile may
also be expressed. Some video decoders may not be able to decode
particular profiles, tiers, or levels.
[0083] In HEVC, profiles, tiers, and levels may be signaled by the
syntax structure profile_tier_level( ) syntax structure. The
profile_tier_level( ) syntax structure may be included in a VPS
and/or a SPS. The profile_tier_level( ) syntax structure may
include a general_profile_idc syntax element, a general_tier_flag
syntax element, and a general_level_idc syntax element. The
general_profile_idc syntax element may indicate a profile to which
a CVS conforms. The general_tier_flag syntax element may indicate a
tier context for interpretation of the general_level_idc syntax
element. The general_level_idc syntax element may indicate a level
to which a CVS conforms. Other values for these syntax elements may
be reserved.
[0084] Capabilities of video decoders may be specified in terms of
the ability to decode video streams conforming to the constraints
of profiles, tiers, and levels. For each such profile, the tier and
level supported for that profile may also be expressed. In some
examples, video decoders do not infer that a reserved value of the
general_profile_idc syntax element between the values specified in
HEVC indicates intermediate capabilities between the specified
profiles. However, video decoders may infer that a reserved value
of the general_level_idc syntax element associated with a
particular value of the general_tier_flag syntax element between
the values specified in HEVC indicates intermediate capabilities
between the specified levels of the tier.
[0085] One or more HEVC bitstreams may be stored in a file that
conforms to a particular file format. In some examples, one or more
video data bitstreams (e.g., HEVC bitstreams) may be stored in a
file that conforms to an ISO base media file format (ISOBMFF).
ISOBMFF may also be referred to as ISO/IEC 14496-12. Other example
file formats for storage of video data bitstreams include file
formats derived from ISOBMFF, including the MPEG-4 file format
(ISO/IEC 14496-14), the Third Generation Partnership Project (3GPP)
file format (3GPP TS 26.244), and the AVC file format (ISO/IEC
14496-15). An amendment to the AVC file format for storage of HEVC
video content is under development by MPEG. This AVC file format
amendment may be referred to as the HEVC file format. That is, the
HEVC file format is being developed by MPEG, which is becoming a
part of ISO/IEC 14496-15.
[0086] A file conforming to the HEVC file format may have a logical
structure, a time structure, and a physical structure. The logical
structure of the file may be that of a movie that contains a set of
time parallel tracks. The time structure of the file is that the
tracks contain sequences of samples in time. The sequences of
samples may be mapped into a timeline of the movie by edit lists.
In the context of the HEVC file format, a "sample" may comprise
data associated with a single timestamp. Examples of a sample
include: an individual frame of video, a series of video frames in
decoding order, or a compressed section of audio in decoding
order.
[0087] Physically, a file conforming to the HEVC file format may
comprise a series of objects, called boxes. A box may be an
object-oriented building block defined by a unique type identifier
and length. In some instances, all data in a file conforming to the
HEVC file format may be contained within boxes and there may be no
data in the file that is not in a box. A file conforming to the
HEVC file format may include various types of boxes.
[0088] For example, a file conforming to the HEVC file format may
include a file type box, a media data box, a movie box, a movie
fragment box, and so on. In this example, a file type box includes
file type and compatibility information. A media data box may
contain samples (e.g., coded pictures). A movie box may contain
metadata regarding a movie (e.g., logical and timing relationships
between samples, and also pointers to locations of samples). Movie
boxes may include several types of sub-boxes. The sub-boxes in
movie boxes may include one or more track boxes. A track box may
include information about an individual track of a movie. A track
box may include a track header box that specifies overall
information of a single track. In addition, a track box may include
a media box that contains a media information box. The media
information box may include a sample table box that contains data
indexing of media samples in the track. Information in the sample
table box may be used to locate samples in time and, for each of
the samples of the track, a type, size, container, and offset into
that container of the sample.
[0089] Furthermore, a sample table box may include one or more
SampleToGroup boxes and one or more sample group description boxes
(i.e., SampleGroupDescription boxes). A SampleToGroup box may be
used to determine a sample group to which a sample belongs, along
with an associated description of the sample group. In other words,
a SampleToGroup box may indicate a group to which a sample belongs.
A SampleToGroup box may have a box type of "sbgp." A SampleToGroup
box may include a grouping type element (e.g., grouping_type). The
grouping type element may be an integer that identifies a type
(i.e., a criterion used to form the sample groups) of a sample
grouping. Furthermore, a SampleToGroup box may include one or more
entries. Each entry in a SampleToGroup box may be associated with a
different, non-overlapping series of consecutive samples in the
track. Each entry may indicate a sample count element (e.g.,
sample_count) and a group description index element (e.g., group
description index). The sample count element of an entry may
indicate a number of samples associated with the entry. In other
words, the sample count element of the entry may be an integer that
gives the number of consecutive samples with the same sample group
descriptor. The group description index element may identify a
SampleGroupDescription box that contains a description of the
samples associated with the entry. The group description index
elements of multiple entries may identify the same
SampleGroupDescription box.
[0090] In some examples, the following pseudo-code describes a
SampleToGroup box.
TABLE-US-00001 aligned(8) class SampleToGroupBox extends
FullBox(`sbgp`, version = 0, 0) { unsigned int(32) grouping_type;
unsigned int(32) entry_count; for (i=1; i <= entry_count; i++) {
unsigned int(32) sample_count; unsigned int(32)
group_description_index; } }
[0091] As indicated above, a sample table box may include zero or
more SampleGroupDescription boxes. A SampleGroupDescription box may
include a description of a sample group. There may be multiple
instances of the SampleGroupDescription box if there is more than
one sample grouping for the samples in a track. A
SampleGroupDescription box may have a box type of "sgpd."
[0092] In some examples, the following pseudo-code describes a
SampleGroupDescription box.
TABLE-US-00002 aligned(8) class SampleGroupDescriptionBox (unsigned
int(32) handler_type) extends FullBox(`sgpd`, 0, 0){ unsigned
int(32) grouping_type; unsigned int(32) entry_count; int i; for (i
= 1 ; i <= entry_count ; i++){ switch (handler_type){ case
`vide`: // for video tracks VisualSampleGroupEntry ( ); break; case
`soun`: // for audio tracks AudioSampleGroupEntry( ); break; case
`hint`: // for hint tracks HintSampleGroupEntry( ); break; } }
}
[0093] As shown in the pseudo-code above, a SampleGroupDescription
box may include a grouping_type element, an entry_count element,
and one or more entries. The grouping_type element of a
SampleGroupDescriptionBox may be an integer that identifies a
SampleToGroup box that is associated with the
SampleGroupDescription box. The entry_count element may indicate a
number of entries in the SampleGroupDescription box. Each entry in
the SampleGroupDescription box may include a VisualSampleGroupEntry
object, an AudioSampleGroupEntry object, or a HintSampleGroupEntry
object. A VisualSampleGroupEntry object may provide a description
about a group of visual (e.g., video) samples. An
AudioSampleGroupEntry object may provide a description about a
group of audio samples. A HintSampleGroupEntry object may provide a
description about a group of hint samples. VisualSampleGroupEntry
objects and AudioSampleGroupEntry objects may belong to an abstract
class that extends an abstract SampleGroupDescriptionEntry
class.
[0094] Furthermore, a sample table box may include a sample
description box that comprises a format description for a stream.
In particular, the sample description box may include a list of one
or more sample entries. Each of the sample entries may contain a
name of a media type (e.g., a type of decoder needed to decode the
stream) and any parameterization of that decoder needed. For
instance, in the context of HEVC, a sample entry may include an
HEVC decoder configuration record. Thus, an HEVC decoder
configuration record may be a sub-box of a sample table box. An
HEVC decoder configuration record may include decoder configuration
information for ISO/IEC 23008-2 (i.e., HEVC) video content. For
example, a HEVC decoder configuration record may include one or
more NAL units that contain parameter sets (e.g., VPSs, SPS, PPSs,
etc.)
[0095] As indicated above, a file conforming to the HEVC file
format may include a movie fragment box. A movie fragment box may
contain metadata regarding a movie fragment (i.e., a fragment of a
movie). A movie fragment box may include a track fragment box that
includes information about a fragment of a track of a movie
fragment. Furthermore, a track fragment box may include one or more
SampleToGroup boxes that may indicate sample groups to which
samples of a movie fragment belong.
[0096] In the example of FIG. 1, video coding system 10 includes a
media aware network element (MANE) 27. MANE 27 may receive video
data generated by source device 12 and may forward video data to
destination device 14. MANE 27 (or other type of device) may apply
bitstream thinning to an HEVC bitstream that is encoded with
multiple sub-layers. At any point in the bitstream, MANE 27 can
start removing NAL units of higher sub-layers (i.e., sub-layers
associated with higher temporal identifiers) based on the fact that
the pictures in the lower sub-layers (i.e., sub-layers associated
with lower temporal identifiers) are still decodable because the
decoding process for the pictures in the lower sub-layers does not
depend on the NAL units of the higher sub-layers. The action of
removing all NAL units with temporal identifiers higher than a
certain value can be referred to as temporal down-switching.
Temporal down-switching may always be possible. Thus, the term
temporal sub-layer switching point may refer to a picture that has
no dependency on any other picture that is in the same sub-layer as
the picture and that precedes the picture in decoding order.
[0097] The term "temporal up-switching" may refer to the action of
starting to forward NAL units of a certain sub-layer that has not
been forwarded up until that point. Temporal up-switching may only
be possible if none of the pictures in the layer that is switched
to depend on any picture in the same sub-layer prior to the point
in the bitstream at which the switch was performed.
[0098] In the scalable video coding extension of the H.264/AVC
video coding standard (i.e., H.264/SVC), temporal sub-layer
switching points can be indicated through temporal_id_nesting_flag
syntax elements in SPSs. For instance, if a
temporal_id_nesting_flag syntax element in a SPS applicable to a
particular CVS is equal to 1, all pictures in the CVS with temporal
identifiers greater than 0 may be temporal layer switching points.
Furthermore, in H.264/SVC, temporal level switching point SEI
messages may indicate temporal sub-layer switching points. In some
examples where temporal level switching point SEI messages indicate
temporal sub-layer switching points, a temporal level switching
point SEI message may contain information about how long a period
temporal layer M should have been decoded prior to a switch point
in order to switch up to temporal layer M+1 at the switch
point.
[0099] In HEVC, as in H.264/SVC, a SPS may include a
sps_temporal_id_nesting_flag syntax element. When the
sps_temporal_id_nesting_flag syntax element has a value equal to 1,
all pictures with temporal identifiers greater than 0 are sub-layer
switching points. In HEVC, there may be two picture types
associated with sub-layer switching points, namely the temporal
sub-layer access (TSA) picture type and the step-wise temporal
sub-layer access (STSA) picture type. The TSA and STSA picture
types can be used to indicate temporal sub-layer switching
points.
[0100] A TSA picture and pictures following the TSA picture in
decoding order do not use pictures with temporal identifiers equal
to or greater than that of the TSA picture for inter prediction
reference. A TSA picture enables up-switching, at the TSA picture,
to the sub-layer containing the TSA picture or any higher
sub-layer, from the immediately lower sub-layer. In some examples,
all TSA pictures have temporal identifiers greater than 0.
[0101] An STSA picture does not use pictures with the same
TemporalId as the STSA picture for inter prediction reference.
Pictures following an STSA picture in decoding order with the same
temporal identifier as the STSA picture do not use pictures prior
to the STSA picture in decoding order with the same temporal
identifier as the STSA picture for inter prediction reference. An
STSA picture enables up-switching, at the STSA picture, to the
sub-layer containing the STSA picture, from the immediately lower
sub-layer. In some examples, all STSA pictures have temporal
identifiers greater than 0. Thus, in contrast to a TSA picture, an
STSA picture does not necessarily enable up-switching to any higher
sub-layer. Rather, an STSA picture may only enable up-switching to
the sub-layer containing the STSA picture.
[0102] There are several problems or shortcomings with existing
designs of the file format for storage of HEVC content. For
example, there is no compact way for signaling of samples that
contain STSA pictures (also referred to as STSA samples). In
another example, there may be no efficient way for signaling of
samples that contain intra pictures. Signaling of samples that
contain intra pictures may enable certain types of trick mode play
that only use intra pictures. In another example, there may be no
efficient way to signal whether temporal sub-layer up-switching to
any higher temporal layer can be performed at any sample.
[0103] In accordance with one example technique of this disclosure,
a sample group, named a step-wise temporal sub-layer access sample
group, for which the sample grouping type may be `stsa`, marks STSA
samples. With this mechanism, a video coder or other device may
easily identify STSA samples.
[0104] In accordance with this example technique, a device (e.g.,
video encoder 20 or another device) may generate a file that
comprises a plurality of samples that contain coded pictures. The
file may also include a box (e.g., a SampleToGroupBox) that
identifies a sample group that contains one or more samples from
among the plurality of samples. The box further indicates that each
sample in the sample group is a STSA sample. In some examples, the
device may output the file. In such examples, an output interface
(e.g., a network interface, a disk or drive interface, a memory
access system, etc.) of the device may output the file.
[0105] Similarly, a device (e.g., video decoder 30 or another
device) may identify, based on data in a box that identifies a
sample group, STSA samples from among samples in a file that
contains the box. In some examples, an input interface (e.g., a
network interface, a disk or drive interface, a memory access
system, etc.) of the device may receive the file that contains the
box that identifies the sample group. Furthermore, in some
examples, the device may perform temporal up-switching at one of
the STSA samples in the sample group. Furthermore, in some
examples, video decoder 30 may decode one or more of the STSA
samples.
[0106] Furthermore, in accordance with some example techniques of
this disclosure, a sample group, named an intra picture sample
group (i.e., an intra picture sample grouping entry), for which the
sample grouping type may be `ipsg`, is designed to mark samples
that contain intra coded pictures (also referred to intra samples).
Thus, an HEVC video track may contain zero instances or one
instance of a SampleToGroupBox with a grouping_type element of
"ipsg." With this mechanism, samples containing intra coded
pictures can be easily identified, through the intra picture sample
group only. Video decoder 30 may decode one or more of the intra
coded pictures.
[0107] Alternatively, the intra picture sample group only marks
samples that contain non-RAP intra coded pictures, i.e. intra
pictures that are not RAP pictures as defined in HEVC Working Draft
8. With this mechanism, samples containing intra coded pictures can
be easily identified, through both the sync sample table, which
marks all the samples that contain RAP pictures, and the intra
picture sample group. In this way, a device (e.g., video encoder 20
or another device) may generate a file that comprises non-random
access point (non-RAP) intra coded pictures, wherein a sample group
marks the non-RAP intra coded pictures in the file.
[0108] Furthermore, in accordance with some example techniques of
this disclosure, whether temporal sub-layer up-switching to any
higher temporal layer can be performed at any sample is signaled in
a sample entry, e.g., using a flag. In some examples, video encoder
20 or another device may generate a record (e.g., an HEVC decoder
configuration record) that includes an element. The element having
a first value indicates that temporal sub-layer up-switching to any
higher temporal layer can be performed at any sample. The element
having a second value indicates that it is not guaranteed that
temporal sub-layer up-switching to any higher temporal layer can be
performed at any sample. Furthermore, in some examples, when the
element has the first value, all SPSs that are activated when a
stream to which the record applies is decoded have syntax elements
that indicate whether temporal sub-layer up-switching to any higher
temporal layer can be performed at any sample.
[0109] In this way, a device (e.g., video encoder 20 or other
device) may generate a file that stores coded samples that contain
coded pictures of the video data. The file may also include a box
that includes a record (e.g., a decoder configuration record such
as an HEVC decoder configuration record) that includes an element
that indicates whether all SPSs that are activated when a stream to
which the record applies is decoded have syntax elements that
indicate that temporal sub-layer up-switching to any higher
temporal sub-layer can be performed at any sample associated with
the SPSs. In some examples, an output interface (e.g., a network
interface, a disk or drive interface, a memory access system, etc.)
of the device may output the file. Accordingly, a device (e.g.,
video decoder 30 or another device) may determine, based on an
element in a record (e.g., a decoder configuration record such as
an HEVC decoder configuration record) in a box of a file that
contains samples that contain coded pictures of the video data,
that all SPSs that are activated when a stream to which the record
applies is decoded have syntax elements that indicate that temporal
sub-layer up-switching to any higher temporal sub-layer can be
performed at any sample associated with the SPSs. In some examples,
an input interface (e.g., a network interface, a disk or drive
interface, a memory access system, etc.) of the device may receive
the file that contains the samples that contain the coded pictures
of video data. Furthermore, in some examples, the device may
perform temporal up-switching at a sample associated with one of
the SPSs.
[0110] The techniques of this disclosure may also apply to other
video content encoded using video codecs other than HEVC.
[0111] FIG. 2 is a block diagram illustrating an example video
encoder 20 that may implement the techniques of this disclosure.
FIG. 2 is provided for purposes of explanation and should not be
considered limiting of the techniques as broadly exemplified and
described in this disclosure. For purposes of explanation, this
disclosure describes video encoder 20 in the context of HEVC
coding. However, the techniques of this disclosure may be
applicable to other coding standards or methods.
[0112] In the example of FIG. 2, video encoder 20 includes 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 processing unit 110, a
reconstruction unit 112, a filter unit 114, a decoded picture
buffer 116, and an entropy encoding unit 118. Prediction processing
unit 100 includes an inter-prediction processing unit 120 and an
intra-prediction processing unit 126. Inter-prediction processing
unit 120 includes a motion estimation unit 122 and a motion
compensation unit 124. In other examples, video encoder 20 may
include more, fewer, or different functional components.
[0113] Video encoder 20 may receive video data. Video encoder 20
may encode each CTU in a slice of a picture of the video data.
Video encoder 20 may encode CUs of a CTU to generate encoded
representations of the CUs (i.e., coded CUs). As part of encoding a
CU, prediction processing unit 100 may partition the coding blocks
associated with the CU among one or more PUs of the CU. Thus, each
PU may be associated with a luma prediction block and corresponding
chroma prediction blocks. Video encoder 20 and video decoder 30 may
support PUs having various sizes. The size of a CU may refer to the
size of the luma coding block of the CU and the size of a PU may
refer to the size of a luma prediction block of the PU. Assuming
that the size of a particular CU is 2N.times.2N, video encoder 20
and video decoder 30 may support PU sizes of 2N.times.2N or
N.times.N for intra prediction, and symmetric PU sizes of
2N.times.2N, 2N.times.N, N.times.2N, N.times.N, or similar for
inter prediction. Video encoder 20 and video decoder 30 may also
support asymmetric partitioning for PU sizes of 2N.times.nU,
2.times.nD, nL.times.2N, and nR.times.2N for inter prediction.
[0114] Inter-prediction processing unit 120 may generate predictive
data for a PU by performing inter prediction on each PU of a CU.
The predictive data for the PU may include predictive blocks of the
PU and motion information for the PU. Inter-prediction processing
unit 120 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, inter-prediction processing unit 120 does not
perform inter prediction on the PU.
[0115] If a PU is in a P slice, motion estimation unit 122 may
search the reference pictures in a list of reference pictures
(e.g., "RefPicList0") for a reference region for the PU. The
reference region for the PU may be a region, within a reference
picture, that contains samples that most closely correspond to the
prediction blocks of the PU. Motion estimation unit 122 may
generate a reference index that indicates a position in RefPicList0
of the reference picture containing the reference region for the
PU. In addition, motion estimation unit 122 may generate a motion
vector that indicates a spatial displacement between a coding block
of the PU and a reference location associated with the reference
region. For instance, the motion vector may be a two-dimensional
vector that provides an offset from the coordinates in the current
picture to coordinates in a 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 the predictive blocks of the PU based on actual or
interpolated samples at the reference location indicated by the
motion vector of the PU.
[0116] If a PU is in a B slice, motion estimation unit 122 may
perform uni-prediction or bi-prediction for the PU. To perform
uni-prediction for the PU, motion estimation unit 122 may search
the reference pictures of RefPicList0 or a second reference picture
list ("RefPicList1") for a reference region for the PU. Motion
estimation unit 122 may output, as the motion information of the
PU, a reference index that indicates a position in RefPicList0 or
RefPicList1 of the reference picture that contains the reference
region, a motion vector that indicates a spatial displacement
between a prediction block of the PU and a reference location
associated with the reference region, and one or more prediction
direction indicators that indicate whether the reference picture is
in RefPicList0 or RefPicList1. Motion compensation unit 124 may
generate the predictive blocks of the PU based at least in part on
actual or interpolated samples at the reference location indicated
by the motion vector of the PU.
[0117] To perform bi-directional inter prediction for a PU, motion
estimation unit 122 may search the reference pictures in
RefPicList0 for a reference region for the PU and may also search
the reference pictures in RefPicList1 for another reference region
for the PU. Motion estimation unit 122 may generate reference
indexes that indicate positions in RefPicList0 and RefPicList1 of
the reference pictures that contain the reference regions. In
addition, motion estimation unit 122 may generate motion vectors
that indicate spatial displacements between the reference locations
associated with the reference regions and a prediction block of the
PU. The motion information of the PU may include the reference
indexes and the motion vectors of the PU. Motion compensation unit
124 may generate the predictive blocks of the PU based at least in
part on actual or interpolated samples at the reference locations
indicated by the motion vectors of the PU.
[0118] Intra-prediction processing unit 126 may generate predictive
data for a PU by performing intra prediction on the PU. The
predictive data for the PU may include predictive blocks for the PU
and various syntax elements. Intra-prediction processing unit 126
may perform intra prediction on PUs in I slices, P slices, and B
slices.
[0119] To perform intra prediction on a PU, intra-prediction
processing unit 126 may use multiple intra prediction modes to
generate multiple sets of predictive blocks for the PU. When
performing intra prediction using a particular intra prediction
mode, intra-prediction processing unit 126 may generate predictive
blocks for the PU using a particular set of samples from
neighboring blocks. The neighboring blocks may be above, above and
to the right, above and to the left, or to the left of the
prediction blocks of the PU, assuming a left-to-right,
top-to-bottom encoding order for PUs, CUs, and CTUs.
Intra-prediction processing unit 126 may use various numbers of
intra prediction modes, e.g., 33 directional intra prediction
modes. In some examples, the number of intra prediction modes may
depend on the size of the prediction blocks of the PU.
[0120] Prediction processing unit 100 may select the predictive
data for PUs of a CU from among the predictive data generated by
inter-prediction processing unit 120 for the PUs or the predictive
data generated by intra-prediction processing unit 126 for the PUs.
In some examples, prediction processing unit 100 selects the
predictive data for the PUs of the CU based on rate/distortion
metrics of the sets of predictive data. The predictive blocks of
the selected predictive data may be referred to herein as the
selected predictive blocks.
[0121] Residual generation unit 102 may generate, based on the
luma, Cb, and Cr coding blocks of a CU and the selected predictive
luma, Cb, and Cr blocks of the PUs of the CU, luma, Cb, and Cr
residual blocks of the CU. For instance, residual generation unit
102 may generate the residual blocks of the CU such that each
sample in the residual blocks has a value equal to a difference
between a sample in a coding block of the CU and a corresponding
sample in a corresponding selected predictive block of a PU of the
CU.
[0122] Transform processing unit 104 may perform quad-tree
partitioning to partition the residual blocks of a CU into
transform blocks associated with TUs of the CU. Thus, a TU may be
associated with a luma transform block and two corresponding chroma
transform blocks. The sizes and positions of the luma and chroma
transform blocks of TUs of a CU may or may not be based on the
sizes and positions of prediction blocks of the PUs of the CU.
[0123] Transform processing unit 104 may generate transform
coefficient blocks for each TU of a CU by applying one or more
transforms to the transform blocks of the TU. Transform processing
unit 104 may apply various transforms to a transform 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 a transform
block. In some examples, transform processing unit 104 does not
apply transforms to a transform block. In such examples, the
transform block may be treated as a transform coefficient
block.
[0124] Quantization unit 106 may quantize the transform
coefficients in a coefficient block. 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. Quantization unit 106 may quantize a
coefficient block associated with a TU of a CU based on a
quantization parameter (QP) value associated with the CU. Video
encoder 20 may adjust the degree of quantization applied to the
coefficient blocks associated with a CU by adjusting the QP value
associated with the CU. Quantization may introduce loss of
information, thus quantized transform coefficients may have lower
precision than the original ones.
[0125] Inverse quantization unit 108 and inverse transform
processing unit 110 may apply inverse quantization and inverse
transforms to a coefficient block, respectively, to reconstruct a
residual block from the coefficient block. Reconstruction unit 112
may add the reconstructed residual block to corresponding samples
from one or more predictive blocks generated by prediction
processing unit 100 to produce a reconstructed transform block
associated with a TU. By reconstructing transform blocks for each
TU of a CU in this way, video encoder 20 may reconstruct the coding
blocks of the CU.
[0126] Filter unit 114 may perform one or more deblocking
operations to reduce blocking artifacts in the coding blocks
associated with a CU. Decoded picture buffer 116 may store the
reconstructed coding blocks after filter unit 114 performs the one
or more deblocking operations on the reconstructed coding blocks.
Inter-prediction processing unit 120 may use a reference picture
that contains the reconstructed coding blocks to perform inter
prediction on PUs of other pictures. In addition, intra-prediction
processing unit 126 may use reconstructed coding blocks in decoded
picture buffer 116 to perform intra prediction on other PUs in the
same picture as the CU.
[0127] Entropy encoding unit 118 may receive data from other
functional components of video encoder 20. For example, entropy
encoding unit 118 may receive coefficient blocks from quantization
unit 106 and may receive syntax elements from prediction processing
unit 100. Entropy encoding unit 118 may perform one or more entropy
encoding operations on the data to generate entropy-encoded data.
For example, entropy encoding unit 118 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, an Exponential-Golomb encoding operation, or
another type of entropy encoding operation on the data. Video
encoder 20 may output a bitstream that includes entropy-encoded
data generated by entropy encoding unit 118.
[0128] In some examples, video encoder 20 may generate a file that
includes the bitstream. In accordance with one or more techniques
of this disclosure, the file may comprise a plurality of samples
that contain coded pictures. The file may also comprise a box that
identifies a sample group that contains one or more samples from
among the plurality of samples. The box may further indicate that
each sample in the sample group is a STSA sample. Furthermore, in
accordance with one or more techniques of this disclosure, the file
may store coded samples that contain coded pictures of video data.
The file may also include a box that includes a record that
includes an element that indicates whether all SPSs that are
activated when a stream to which the record applies is decoded have
syntax elements that indicate that temporal sub-layer up-switching
to any higher temporal sub-layer can be performed at any sample
associated with the SPSs.
[0129] FIG. 3 is a block diagram illustrating an example video
decoder 30 that is configured to implement the techniques of this
disclosure. FIG. 3 is provided for purposes of explanation and is
not limiting on the techniques as broadly exemplified and described
in this disclosure. For purposes of explanation, this disclosure
describes video decoder 30 in the context of HEVC coding. However,
the techniques of this disclosure may be applicable to other coding
standards or methods.
[0130] In the example of FIG. 3, video decoder 30 includes an
entropy decoding unit 150, a prediction processing unit 152, an
inverse quantization unit 154, an inverse transform processing unit
156, a reconstruction unit 158, a filter unit 160, and a decoded
picture buffer 162. Prediction processing unit 152 includes a
motion compensation unit 164 and an intra-prediction processing
unit 166. In other examples, video decoder 30 may include more,
fewer, or different functional components.
[0131] A coded picture buffer (CPB) 151 may receive and store
encoded video data (e.g., NAL units) of a bitstream. Entropy
decoding unit 150 may receive NAL units from CPB 151 and parse the
NAL units to obtain syntax elements from the bitstream. Entropy
decoding unit 150 may entropy decode entropy-encoded syntax
elements in the NAL units. Prediction processing unit 152, inverse
quantization unit 154, inverse transform processing unit 156,
reconstruction unit 158, and filter unit 160 may generate decoded
video data based on the syntax elements obtained from the
bitstream.
[0132] The NAL units of the bitstream may include coded slice NAL
units. As part of decoding the bitstream, entropy decoding unit 150
may parse and entropy decode syntax elements 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.
[0133] In addition to decoding syntax elements from the bitstream,
video decoder 30 may perform a decoding operation on a CU. By
performing the decoding operation on a CU, video decoder 30 may
reconstruct coding blocks of the CU.
[0134] As part of performing a decoding operation on a CU, inverse
quantization unit 154 may inverse quantize, i.e., de-quantize,
coefficient blocks associated with TUs of the CU. Inverse
quantization unit 154 may use a QP value associated with the CU of
the TU to determine a degree of quantization and, likewise, a
degree of inverse quantization for inverse quantization unit 154 to
apply. That is, the compression ratio, i.e., the ratio of the
number of bits used to represent original sequence and the
compressed one, may be controlled by adjusting the value of the QP
used when quantizing transform coefficients. The compression ratio
may also depend on the method of entropy coding employed.
[0135] After inverse quantization unit 154 inverse quantizes a
coefficient block, inverse transform processing unit 156 may apply
one or more inverse transforms to the coefficient block in order to
generate a residual block associated with the TU. For example,
inverse transform processing 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 coefficient
block.
[0136] If a PU is encoded using intra prediction, intra-prediction
processing unit 166 may perform intra prediction to generate
predictive blocks for the PU. Intra-prediction processing unit 166
may use an intra prediction mode to generate the predictive luma,
Cb, and Cr blocks for the PU based on the prediction blocks of
spatially-neighboring PUs. Intra-prediction processing unit 166 may
determine the intra prediction mode for the PU based on one or more
syntax elements decoded from the bitstream.
[0137] Prediction processing unit 152 may construct a first
reference picture list (RefPicList0) and a second reference picture
list (RefPicList1) based on syntax elements extracted from the
bitstream. Furthermore, if a PU is encoded using inter prediction,
entropy decoding unit 150 may obtain motion information for the PU.
Motion compensation unit 164 may determine, based on the motion
information of the PU, one or more reference regions for the PU.
Motion compensation unit 164 may generate, based on samples at the
one or more reference blocks for the PU, predictive luma, Cb, and
Cr blocks for the PU.
[0138] Reconstruction unit 158 may use the residual values from the
luma, Cb, and Cr transform blocks associated with TUs of a CU and
the predictive luma, Cb, and Cr blocks of the PUs of the CU, i.e.,
either intra-prediction data or inter-prediction data, as
applicable, to reconstruct the luma, Cb, and Cr coding blocks of
the CU. For example, reconstruction unit 158 may add samples of the
luma, Cb, and Cr transform blocks to corresponding samples of the
predictive luma, Cb, and Cr blocks to reconstruct the luma, Cb, and
Cr coding blocks of the CU.
[0139] Filter unit 160 may perform a deblocking operation to reduce
blocking artifacts associated with the luma, Cb, and Cr coding
blocks of the CU. Video decoder 30 may store the luma, Cb, and Cr
coding blocks of the CU in decoded picture buffer 162. Decoded
picture buffer 162 may provide reference pictures for subsequent
motion compensation, intra prediction, and presentation on a
display device, such as display device 32 of FIG. 1. For instance,
video decoder 30 may perform, based on the luma, Cb, and Cr blocks
in decoded picture buffer 162, intra prediction or inter prediction
operations on PUs of other CUs. In this way, video decoder 30 may
extract, from the bitstream, transform coefficient levels of the
significant luma coefficient block, inverse quantize the transform
coefficient levels, apply a transform to the transform coefficient
levels to generate a transform block, generate, based at least in
part on the transform block, a coding block, and output the coding
block for display.
[0140] As indicated above, a file that conforms to a HEVC file
format may include zero or more instances of a SampleToGroup box.
Furthermore, as indicated above, each SampleToGroup box may include
a grouping type element that identifies a type of a sample
grouping. In accordance with one or more techniques of this
disclosure, a SampleToGroup box may include a grouping type element
with a value (e.g., "stsa") that indicates that samples belonging
to a sample group associated with the SampleToGroup box are STSAs.
For example, an HEVC video track may contain zero instances or one
instance of a SampleToGroupBox with a grouping_type of "stsa."
Instances of SampleToGroup boxes with grouping type elements with
values that indicate that samples belonging to sample groups
associated with the SampleToGroup boxes are STSAs (e.g.,
SampleToGroup boxes with grouping_type "stsa") may be referred to
as step-wise temporal sub-layer sample group entries. A step-wise
temporal sub-layer sample group entry may represent a marking of
samples as step-wise temporal sub-layer access points (i.e.,
STSAs). In other words, the step-wise temporal sub-layer sample
group entry may be a sample group used to mark STSA samples. The
grouping types of a step-wise temporal sub-layer sample group entry
may have a group type of "stsa."
[0141] Thus, a video encoder or another device may generate a box
(e.g., a SampleToGroup box) identifying a sample group that
contains one or more samples from among a plurality of samples in a
file. The box may further indicate (e.g., by specifying the
grouping type of "stsa") that each sample in the sample group is an
STSA sample. Accordingly, a video decoder or another device may
identify, based on data in the box, STSA samples from among the
samples in the file.
[0142] As indicated above, a SampleGroupDescription box may include
a description of a sample group. Furthermore, as indicated above, a
SampleGroupDescription box may include zero or more entries. The
entries in a SampleGroupDescription box may include one or more
VisualSampleGroupEntry objects. A VisualSampleGroupEntry object may
provide a description about a group of visual (e.g., video)
samples. A VisualSampleGroupEntry object may belong to a
VisualSampleGroupEntry class. In accordance with one or more
techniques of this disclosure, a StepWiseTemporalSubLayerEntry
class may extend the VisualSampleGroupEntry class. Thus, an entry
in a SampleGroupDescription box may include an object belonging to
the StepWiseTemporalSubLayerEntry class (i.e., a
StepWiseTemporalSubLayerEntry object). Hence, a
SampleGroupDescription box may be a container of a
StepWiseTemporalSubLayerEntry object. It may not be mandatory for a
file to contain a StepWiseTemporalSubLayerEntry object and the file
may contain zero or more StepWiseTemporalSubLayerEntry objects.
[0143] Thus, the following description may apply to step-wise
temporal sub-layer sample group entries: [0144] Group Types: `stsa`
[0145] Container: Sample Group Description Box (`sgpd`) [0146]
Mandatory: No [0147] Quantity: Zero or more [0148] This sample
group is used to mark step-wise temporal sub-layer access (STSA)
samples.
[0149] The following is an example syntax for a step-wise temporal
sub-layer sample group entry.
TABLE-US-00003 class StepWiseTemporalSubLayerEntry( ) extends
VisualSampleGroupEntry (`stsa`) { }
[0150] In some examples, an instance of a SampleGroupDescription
box that includes a StepWiseTemporalSubLayerEntry object may
accompany a step-wise temporal sub-layer sample group entry (e.g.,
an instance of a SampleToGroup box with a grouping type element of
"stsa"). Hence, in some examples, when a SampleToGroup box has a
grouping type of "stsa," an accompanying instance of the
SampleGroupDescription box with the same grouping type shall be
present.
[0151] In accordance with one or more techniques of this
disclosure, an HEVC video track may contain zero instances or one
instance of a SampleToGroup box with a grouping_type element of
"ipsg." Instances of SampleToGroup boxes with grouping_type element
of "ipsg" may be referred to as intra picture sample groupings. A
SampleToGroup box instance with a grouping type of "ipsg" (i.e., an
intra picture sample grouping) may represent a marking of samples
as step-wise temporal sub-layer access points. Thus, a video
encoder or another device may generate a box (e.g., a SampleToGroup
box) identifying a sample group that contains one or more samples
from among a plurality of samples in a file. The box may further
indicate (e.g., by specifying the grouping type of "ipsg") that
each sample in the sample group is an intra sample. Accordingly, a
video decoder or another device may identify, based on data in the
box, intra samples from among the samples in the file.
[0152] In some examples, an accompanying instance of the
SampleGroupDescription box with the same grouping type is present
in the HEVC video track. As indicated above, a
SampleGroupDescription box may include zero or more entries. The
entries in a SampleGroupDescription box may include one or more
VisualSampleGroupEntry objects. A VisualSampleGroupEntry object may
belong to a VisualSampleGroupEntry class. Furthermore, in
accordance with one or more techniques of this disclosure, an
IntraPictureEntry class may extend the VisualSampleGroupEntry
class. Thus, an entry in a SampleGroupDescription box may include
an object belonging to the IntraPictureEntry class (i.e., an
IntraPictureEntry object or an intra picture sample grouping
entry). Hence, a SampleGroupDescription box may be a container of
an IntraPictureEntry object. It may not be mandatory for a file to
contain an IntraPictureEntry object and the file may contain zero
or more IntraPictureEntry objects. In this way, a file may include
a sample group description box (e.g., a SampleGroupDescription box)
that includes an entry (e.g., an IntraPictureEntry object) that
indicates that a sample group is used to mark samples that contain
intra coded pictures.
[0153] Thus, the following description may apply to
IntraPictureEntry entries: [0154] Group Types: `ipsg` [0155]
Container: Sample Group Description Box (`sgpd`) [0156] Mandatory:
No [0157] Quantity: Zero or more [0158] This sample group is used
to mark samples that contain intra coded pictures, i.e. samples for
which all slices are intra slices.
[0159] The following is an example syntax for an intra picture
sample grouping entry.
TABLE-US-00004 class IntraPictureEntry( ) extends
VisualSampleGroupEntry (`ipsg`) { }
[0160] As indicated above, the HEVC file format provides for an
HEVC decoder configuration record. For instance, a sample table box
within a track box of a file that conforms to the HEVC file format
may include an HEVC decoder configuration record. The HEVC decoder
configuration record contains configuration information for HEVC
video content. For instance, the HEVC decoder record may include
zero or more NAL units. The NAL units contained in an HEVC decoder
record may include NAL units that contain parameter sets, such as
VPSs, SPSs, PPSs, etc.
[0161] The following provides an example syntax for a HEVC decoder
configuration record. Portions of the following syntax shown in
bold may indicate modified portions of the HEVC decoder
configuration record specified in MPEG output document W12846,
"Study of ISO/IEC 14496-15:2010/PDAM 2 Carriage of HEVC", the 101th
meeting of MPEG, Stockholm, Sweden, 2012-07-16 to 2012-07-20.
TABLE-US-00005 aligned(8) class HEVCDecoderConfigurationRecord {
unsigned int(8) configurationVersion = 1; unsigned int(2)
profile_space; unsigned int(1) tier_flag; unsigned int(5)
profile_idc; unsigned int(32) profile_compatibility_indications;
unsigned int(16) constraint_indicator_flags; unsigned int(8)
level_idc; bit(6) reserved = `111111`b; unsigned int(2)
chromaFormat; bit(5) reserved = `11111`b; unsigned int(3)
bitDepthLumaMinus8; bit(5) reserved = `11111`b; unsigned int(3)
bitDepthChromaMinus8; bit(16) avgFrameRate; bit(2)
constantFrameRate; bit(3) numTemporalLayers; bit(1)
temporalIdNested; unsigned int(2) lengthSizeMinusOne; unsigned
int(8) numOfArrays; for (j=0; j < numOfArrays; j++) { bit(1)
array_completeness; unsigned int(1) reserved = 0; unsigned int(6)
NAL_unit_type; unsigned int(16) numNalus; for (i=0; i< numNalus;
i++) { unsigned int(16) nalUnitLength; bit(8*nalUnitLength)
nalUnit; } } }
[0162] The HEVC decoder configuration record contains a size of a
length field (e.g., lengthSizeMinusOne) used in each sample to
indicate the length of NAL units contained by the HEVC decoder
configuration record, as well as the parameter sets, if stored in a
sample entry. The HEVC decoder configuration record may be
externally framed. In other words, the size of the HEVC decoder
configuration record may be supplied by the structure that contains
the HEVC decoder configuration record.
[0163] Furthermore, the HEVC decoder configuration record may
contain a version field. In the example syntax provided above, this
version field is named configurationVersion. Incompatible changes
to the record may be indicated by a change of version number. In
some examples, a device or other reader must not attempt to decode
a HEVC decoder configuration record or streams to which the HEVC
decoder configuration record applies if the device or other reader
does not recognize the version number specified by the version
field of the HEVC decoder configuration record. In some examples,
compatible extensions to the HEVC decoder configuration record do
not extend the HEVC decoder configuration record and do not change
the configuration version code specified by the version field of
the HEVC decoder configuration record. A device or other reader
may, in some examples, be prepared to ignore unrecognized data
beyond the definition of the data that the device or other reader
understands.
[0164] A VPS may include, among other syntax elements, a
general_profile_space syntax element, a general_profile_idc syntax
element, a general_profile_compatibility_flag[i] syntax element,
and a general_reserved_zero.sub.--16bits syntax element. The
general_profile_space syntax element specifies a context for the
interpretation of the general_profile_idc syntax element and the
general_profile_compatibility_flag[i] syntax element for all values
of i in the range of 0 to 31, inclusive. When the
general_profile_space syntax element is equal to 0, the
general_profile_idc syntax element indicates the profile to which a
CVS conforms. Annex A of HEVC Working Draft 8 describes an example
set of profiles. When the general_profile_space syntax element is
equal to 0 and the general_profile_compatibility_flag[i] syntax
element is equal to 1, the general_profile_compatibility_flag[i]
syntax element indicates that a CVS conforms to a profile indicated
by the general_profile_idc syntax element equal to i. When the
general_profile_space syntax element is equal to 0, the
general_profile_idc[general_profile_idc] is equal to 1.
"general_profile_idc[general_profile_idc]" denotes the
general_profile_idc syntax element associated with an index value
specified by the general_profile_idc syntax element. In some
examples, the general_profile_compatibility_flag[i] syntax element
is equal to 0 for any value of i that is not specified as an
allowed value of general_profile_idc Annex A of HEVC Working Draft
8 specifies an example set of allowed values of the
general_profile_idc syntax element. The
general_reserved_zero.sub.--16bits syntax element is equal to 0 in
bitstreams. Certain values of the
general_reserved_zero.sub.--16bits syntax elements may be used for
extensions of HEVC.
[0165] Furthermore, a VPS may include a profile_tier_level syntax
structure that includes a general_tier_flag syntax element and a
general_level_idc syntax element. The general_tier_flag syntax
element specifies a tier context for the interpretation of the
general_level_idc syntax element. The general_level_idc syntax
element indicates a level to which a CVS conforms Annex A of HEVC
Working Draft 8 specifies an example interpretation of the
general_level_idc syntax element based on the tier context
specified by the general_tier_flag syntax element.
[0166] In the example syntax of HEVC decoder configuration records
provided above, the profile_space, tier_flag, profile_idc,
profile_compatibility_indications, constraint_indicator_flags, and
level_idc elements contain matching values for the syntax elements
general_profile_space, general_tier_flag, general_profile_idc,
general_profile_compatibility_flag[i] for i ranging from 0 to 31,
inclusive, general_reserved_zero.sub.--16bits, and
general_level_idc, respectively, as defined in ISO/IEC 23008-2, for
the stream to which this HEVC decoder configuration record
applies.
[0167] In one example, the values for the profile_space, tier_flag,
profile_idc, profile_compatibility_indications,
constraint_indicator_flags, and level_idc elements of a HEVC
decoder configuration record must be valid for all parameter sets
that are activated when the stream described by the HEVC decoder
configuration record is decoded (referred to as all parameter sets
of the stream or all the parameter sets). In other words, in this
example, the values of the profile_space, tier_flag, profile_idc,
profile_compatibility_indications, constraint_indicator_flags, and
level_idc elements of a HEVC decoder configuration record must
correctly describe the values of a corresponding syntax elements in
the parameter sets that are activated when the stream described by
the HEVC decoder configuration record is decoded.
[0168] For instance, the general_profile_space syntax elements in
each of the VPSs activated when the stream is decoded may have
values identical to a value of the profile_space element. In other
words, the value of the profile_space element in all the parameter
sets must be identical. Hence, the HEVC decoder configuration
record may include a profile_space element (e.g., a profile_space
element). All general profile space flag syntax elements (e.g.,
general_profile_space syntax elements) in parameter sets that are
activated when a stream to which the HEVC decoder configuration
record applies is decoded may have values matching values of the
profile_space element.
[0169] Furthermore, in this example, the tier indication (e.g.,
tier_flag) must indicate a tier equal to or greater than the
highest tier indicated in all the parameter sets activated when the
stream described by the HEVC decoder configuration record is
decoded. Hence, the HEVC decoder configuration record may include a
tier_flag element (e.g., a tier_flag element). A device may
determine that all general_tier_flag syntax elements (e.g.,
general_tier_flag syntax elements) in parameter sets that are
activated when a stream to which the HEVC decoder configuration
record applies is decoded have values matching a value of the
tier_flag element. Each of the general_tier_flag syntax elements
may indicate a tier context for interpretation of general level
indicator syntax elements that indicate levels to which coded video
sequences conform.
[0170] In this example, the level indication element (e.g.,
level_idc) must indicate a level of capability equal to or greater
than the highest level indicated for the highest tier in all the
parameter sets. Hence, the HEVC decoder configuration record may
include a level indicator element (e.g., a level_idc element). A
device may determine that all general level indication syntax
elements (e.g., general_level_idc syntax elements) in parameter
sets that are activated when a stream to which the HEVC decoder
configuration record applies is decoded have values matching a
value of the level element. Each of the general level indication
syntax elements may indicate a level to which a coded video
sequence conforms.
[0171] In this example, the profile indication element (e.g.,
profile_idc) must indicate a profile to which the stream associated
with the HEVC decoder configuration record conforms. Hence, the
HEVC decoder configuration record may include a profile indicator
element (e.g., a profile_idc element). A device may determine that
all profile indication syntax elements (e.g., profile_idc syntax
elements) in parameter sets that are activated when a stream to
which the HEVC decoder configuration record applies is decoded have
values matching a value of the profile indication element. Each of
the profile indication syntax elements may indicate a profile to
which a coded video sequence conforms.
[0172] Each bit in profile_compatibility_indications element may
only be set if all the parameter sets set that bit. Hence, the HEVC
decoder configuration record may include a
profile_compatibility_indications element (e.g., a
profile_compatibility_indications element). A device may determine
that all general profile compatibility flag syntax elements (e.g.,
general_profile_compatibility_flag syntax elements) in parameter
sets that are activated, when a stream to which the HEVC decoder
configuration record is applicable is decoded, have values that
match values of the profile compatibility indications element.
[0173] In addition, the HEVC decoder configuration record may
include a constraint indicator flags element (e.g., a
constraint_indicator_flags element). A device may determine that
all general_reserved_zero.sub.--16bits syntax elements (e.g.,
general_reserved_zero.sub.--16bits syntax elements) in parameter
sets that are activated when a stream to which the HEVC decoder
configuration record applies is decoded have values that match
values of the profile_compatibility_indications element.
[0174] Because HEVC decoder configuration records specify the
profile_space, tier_flag, profile_idc,
profile_compatibility_indications, constraint_indicator_flags, and
level_idc elements, a device (e.g., video decoder 30) may be able
to determine the corresponding properties of the stream without
parsing the stream. Rather, the device may determine the
corresponding properties of the stream by inspecting a HEVC decoder
configuration record that applies to the stream.
[0175] If the SPSs of the stream are marked with different
profiles, then the stream may need examination to determine the
profile, if any, to which the entire stream conforms. If the entire
stream is not examined, or the examination reveals that there is no
profile to which the entire stream conforms, then, in this example,
the entire stream must be split into two or more sub-streams with
separate configuration records (e.g., HEVC decoder configuration
records) in which these rules can be met.
[0176] An HEVC decoder configuration record may provide explicit
indication about the chroma_format and bit depth as well as other
format information used by a HEVC video elementary stream. An
elementary stream may comprise a sequence of one or more
bitstreams. If an elementary stream contains multiple bitstreams,
each of the bitstreams except for the last bitstream terminates
with an end of bitstream (EOS) NAL unit.
[0177] In some examples, each type of such information must be
identical in all parameter sets, if present, in a single HEVC
decoder configuration record. If two sequences differ in any type
of such information, a video processor may be required to generate
two different HEVC decoder configuration records. If the two
sequences differ in color space indications in their video
usability information (VUI), a video processor (e.g., video encoder
20 or another device) may be required to generate two different
HEVC decoder configuration records. In HEVC, a SPS may include a
VUI syntax structure that contains VUI syntax elements.
[0178] In the example syntax for HEVC decoder configuration records
described above, the chromaFormat element contains a chroma_format
indicator as defined by the chroma_format idc syntax element in
ISO/IEC 23008-2 (i.e., HEVC), for the stream to which this HEVC
decoder configuration record applies. The chroma_format idc syntax
element of an SPS may specify a chroma sampling. In HEVC Working
Draft 8, the chroma_format idc syntax element specifies the chroma
sampling relative to a luma sampling specified in subclause 6.2 of
HEVC Working Draft 8. If the chroma_format idc syntax element of a
SPS activated for a current picture is equal to 0, the current
picture may consist of one sample array (e.g., S.sub.L). Otherwise,
if the chroma_format idc syntax element is not equal to 0, the
current picture may comprise three sample arrays (e.g., S.sub.L,
S.sub.Cb, and S.sub.Cr).
[0179] In the example syntax for the HEVC decoder configuration
record provided above, the bitDepthLumaMinus8 element contains a
luma bit depth indicator as defined by the bit_depth_luma_minus8
syntax element in ISO/IEC 23008-2, for the stream to which this
HEVC decoder configuration record applies. The bitDepthChromaMinus8
element may contain a chroma bit depth indicator as defined by the
bit_depth_chroma_minus8 syntax element in ISO/IEC 23008-2, for the
stream to which this configuration record applies. The bit depth
for a sample value (e.g., a luma sample or a chroma sample) may
indicate how many bits are used to represent the sample value.
[0180] In addition, in the example syntax for HEVC decoder
configuration record provided above, the avgFrameRate element gives
an average frame rate in units of frames/(256 seconds), for the
stream to which the HEVC decoder configuration record applies. An
avgFramRate element having a value equal to 0 may indicate an
unspecified average frame rate.
[0181] In the example syntax for the HEVC decoder configuration
record provided above, the constantFrameRate element equal to 1 may
indicate that the stream to which this HEVC decoder configuration
record applies is of constant frame rate. The constantFrameRate
element equal to 2 may indicate that the representation of each
temporal layer in the stream is of constant frame rate. The
constantFrameRate element equal to 0 indicates that the stream may
or may not be of constant frame rate.
[0182] Furthermore, in the example syntax for the HEVC decoder
configuration record provided above, the numTemporalLayers element
may indicate whether the stream to which the HEVC decoder
configuration record applies is temporally scalable and whether the
contained number of temporal layers (also referred to as temporal
sub-layer or sub-layer in ISO/IEC 23008-2) is equal to
numTemporalLayers. For example, the numTemporalLayers syntax
element greater than 1 may indicate that the stream to which this
HEVC decoder configuration record applies is temporally scalable
and that the contained number of temporal layers is equal to
numTemporalLayers. In this example, the numTemporalLayers element
equal to 1 may indicate that the stream is not temporally scalable.
Furthermore, in this example, the numTemporalLayers element equal
to 0 may indicate that it is unknown whether the stream is
temporally scalable.
[0183] In the example syntax for the HEVC decoder configuration
record provided above, the temporalIdNested element may indicate
whether all SPSs that are activated when the stream to which the
HEVC decoder configuration record applies have
sps_temporal_id_nesting_flag syntax elements equal to 0. For
example, the temporalIdNested element equal to 1 may indicate that
all SPSs that are activated when the stream to which the HEVC
decoder configuration record applies is decoded have
sps_temporal_id_nesting_flag syntax elements as defined in ISO/IEC
23008-2 equal to 1 and temporal sub-layer up-switching to any
higher temporal layer can be performed at any sample. In this
example, the temporalIdNested element equal to 0 may indicate that
at least one of the SPSs that are activated when the stream to
which the HEVC decoder configuration record applies is decoded has
a sps_temporal_id_nesting_flag syntax element equal to 0.
[0184] In this way, a device may generate a file that stores coded
samples that contain coded pictures of the video data. The file
also including a box that includes a record that includes an
element that indicates whether all SPSs that are activated when a
stream to which the record applies is decoded have
sps_temporal_id_nesting_flag syntax elements that indicate that
temporal sub-layer up-switching to any higher temporal sub-layer
can be performed at any sample associated with the SPSs.
[0185] In the example syntax for the HEVC decoder configuration
record provided above, the lengthSizeMinusOne element plus 1
indicates the length in bytes of the NALUnitLength field in an HEVC
video sample in the stream to which the HEVC decoder configuration
record applies. For example, a size of one byte is indicated with a
value of 0. The value of this field shall be one of 0, 1, or 3
corresponding to a length encoded with 1, 2, or 4 bytes,
respectively.
[0186] Furthermore, a HEVC decoder configuration may contain a set
of arrays that carry initialization NAL units. In other words, in a
HEVC decoder configuration record there is a set of arrays to carry
initialization NAL units. The NAL_unit_types in a HEVC decoder
configuration record may be restricted to NAL units that contain
VPSs, SPSs, PPSs, and SEI messages. HEVC Working Draft 8 and the
present disclosure provide for several reserved NAL_unit_types. In
the future, such reserved NAL_unit_types may be defined to
implement extensions to HEVC. In other words, NAL_unit_types that
are reserved in ISO/IEC 23008-2 and in this specification may
acquire a definition in future. In some examples, readers (e.g.,
devices that receive and process an HEVC decoder configuration
record) should ignore arrays of NAL units with reserved or
unpermitted NAL_unit_type values. This `tolerant` behavior of
ignoring arrays of NAL units with reserved or unpermitted
NAL_unit_type values is designed so that errors are not raised,
thereby allowing the possibility of backwards-compatible extensions
to these arrays in future specifications. In some examples, the
arrays may be in the order of VPS, SPS, PPS, and SEI. In other
examples, the arrays may be ordered within a HEVC decoder
configuration record by size. For instance, the arrays may be
ordered within a HEVC decoder configuration record such that
smaller arrays occur before larger arrays.
[0187] Furthermore, in the example syntax for HEVC decoder
configuration records provided above, the numArrays element
indicates the number of arrays of NAL units of the indicated
type(s). The array_completeness elements of HEVC decoder
configuration records may indicate whether the stream may include
NAL units of a given type in addition to those NAL units of the
given type that are in an array in the HEVC decoder configuration
record. For example, an array_completeness element equal to 1 may
indicate that all NAL units of the given type are in the array of
NAL units in the HEVC decoder configuration record and none are in
the stream. An array_completeness element equal to 0 indicates that
additional NAL units of the indicated type may be in the stream.
The default and permitted values of the array_completeness element
may be constrained by the sample entry code.
[0188] Furthermore, in the example syntax of HEVC decoder
configuration records provided above, the NAL_unit_type element
indicates the type of the NAL units in the array of NAL units. In
this example, all of the NAL units in the array must belong to the
type specified by the NAL_unit_type element. The NAL_unit_type
element may take a value as defined in ISO/IEC 23008-2. In some
examples, the NAL_unit_type element is restricted to take one of
the values indicating a VPS, SPS, PPS, or SEI NAL unit.
[0189] In the example HEVC decoder configuration record syntax
provided above, the numNalus element indicates the number of NAL
units of the indicated type included in the HEVC decoder
configuration record for the stream to which this HEVC decoder
configuration record applies. In some examples, the NAL_unit_type
element of the HEVC decoder configuration record may indicate that
the HEVC decoder configuration record includes a SEI array (i.e.,
an array of SEI NAL units). For instance, in such examples, if the
numNalus is equal to four, the SEI array may consist of four SEI
NAL units. Furthermore, in some such examples, the SEI array must
only contain SEI messages of a `declarative` nature. That is, the
SEI array may only contain SEI messages that provide information
about the stream as a whole. An example of an SEI message of a
`declarative` nature is a user-data SEI message.
[0190] Furthermore, in the example syntax of HEVC decoder
configuration records provided above, the nalUnitLength element of
the HEVC decoder configuration record indicates the length in bytes
of a NAL unit. The nalUnit element of the HEVC decoder
configuration record may contain a VPS, a SPS, a PPS, or a
declarative SEI NAL unit, as specified in ISO/IEC 23008-2.
[0191] FIG. 4 is a flowchart illustrating an example operation 200
in accordance with one or more techniques of this disclosure. In
the example of FIG. 4, a first device (e.g., video encoder 20 or
another device) generates a file (202). The file comprises a
plurality of samples that contain coded pictures a box that
identifies a sample group that contains one or more samples from
among the plurality of samples. The box further indicates that each
sample in the sample group is a STSA sample.
[0192] Furthermore, in the example of FIG. 4, a second device
(e.g., video decoder 30 or another device) identifies, based on
data in the box that identifies the sample group, STSA samples from
among samples in the file that contains the box (204).
[0193] FIG. 5 is a flowchart illustrating an example operation 250
in accordance with one or more additional techniques of this
disclosure. In the example of FIG. 5, a first device (e.g., video
encoder 20 or another device) may generate a file that stores coded
samples that contain coded pictures of the video data (252). The
file also may include a sample entry that includes an element that
indicates whether all SPSs, that are activated when a stream to
which the sample entry applies is decoded, have syntax elements
that indicate that temporal sub-layer up-switching to any higher
temporal sub-layer can be performed at any sample associated with
the SPSs.
[0194] Furthermore, in the example of FIG. 5, a second device
(e.g., video decoder 30 or another device) may determine, based on
the element in the sample entry of the file that contains samples
that contain coded pictures of the video data, that all SPSs that
are activated when the stream to which the record applies is
decoded have syntax elements that indicate that temporal sub-layer
up-switching to any higher temporal sub-layer can be performed at
any sample associated with the SPSs (254).
[0195] FIG. 6 is a conceptual diagram illustrating an example
structure of a file 300, in accordance with one or more techniques
of this disclosure. In the example of FIG. 6, file 300 includes a
movie box 302 and a plurality of media data boxes 304. Each of
media data boxes 304 may include one or more samples 305.
Furthermore, in the example of FIG. 6, movie box 302 includes a
track box 306. In other examples, movie box 302 may include
multiple track boxes for different tracks. Track box 306 includes a
sample table box 308. Sample table box 308 includes a SampleToGroup
box 310, a SampleGroupDescription box 312, and an HEVC decoder
configuration record 314. In other examples, sample table box 308
may include other boxes in addition to SampleToGroup box 310 and
SampleGroupDescription box 312, and/or may include multiple
SampleToGroup boxes and SampleGroupDescription boxes.
[0196] In accordance with one or more example techniques of this
disclosure, SampleToGroup box 310 may identify a sample group that
contains one or more samples from among samples 305. SampleToGroup
box 310 may further indicate that each sample in the sample group
is a STSA sample. Hence, a device may identify, based on data in
SampleToGroup box 310, STSA samples from among samples 305 in file
300. In accordance with one or more additional example techniques
of this disclosure, SampleToGroup box 310 may indicate that each
sample in the sample group is an intra samples. Hence, a device may
identify, based on data in SampleToGroup box 310, intra samples
from among samples 305 in file 300.
[0197] In accordance with one or more additional example techniques
of this disclosure, HEVC decoder configuration record 314 may
include an element that indicates whether all SPSs, that are
activated when a stream to which HEVC decoder configuration record
314 applies is decoded, have syntax elements that indicate that
temporal sub-layer up-switching to any higher temporal sub-layer
can be performed at any sample associated with the SPSs. Hence, a
device may determine, based on an element in HEVC decoder
configuration record 314 in sample table box 308 of file 300 that
contains samples 305 that contain coded pictures of video data,
that all SPSs that are activated when a stream to which HEVC
decoder configuration record 314 applies is decoded have syntax
elements that indicate that temporal sub-layer up-switching to any
higher temporal sub-layer can be performed at any sample associated
with the SPSs.
[0198] In one or more examples, the functions described may be
implemented in hardware, software, firmware, or any combination
thereof. If implemented in software, the functions may be stored on
or transmitted over, as one or more instructions or code, a
computer-readable medium and executed by a hardware-based
processing unit. Computer-readable media may include
computer-readable storage media, which corresponds to a tangible
medium such as data storage media, or communication media including
any medium that facilitates transfer of a computer program from one
place to another, e.g., according to a communication protocol. In
this manner, computer-readable media generally may correspond to
(1) tangible computer-readable storage media which is
non-transitory or (2) a communication medium such as a signal or
carrier wave. Data storage media may be any available media that
can be accessed by one or more computers or one or more processors
to retrieve instructions, code and/or data structures for
implementation of the techniques described in this disclosure. A
computer program product may include a computer-readable
medium.
[0199] By way of example, and not limitation, such
computer-readable storage media can comprise RAM, ROM, EEPROM,
CD-ROM or other optical disk storage, magnetic disk storage, or
other magnetic storage devices, flash memory, or any other medium
that can be used to store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Also, any connection is properly termed a
computer-readable medium. For example, if instructions are
transmitted from a website, server, or other remote source using a
coaxial cable, fiber optic cable, twisted pair, digital subscriber
line (DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of medium. It should be
understood, however, that computer-readable storage media and data
storage media do not include connections, carrier waves, signals,
or other transient media, but are instead directed to
non-transient, tangible storage media. Disk and disc, as used
herein, includes compact disc (CD), laser disc, optical disc,
digital versatile disc (DVD), floppy disk and Blu-ray disc, where
disks usually reproduce data magnetically, while discs reproduce
data optically with lasers. Combinations of the above should also
be included within the scope of computer-readable media.
[0200] Instructions may be executed by one or more processors, such
as one or more digital signal processors (DSPs), general purpose
microprocessors, application specific integrated circuits (ASICs),
field programmable logic arrays (FPGAs), or other equivalent
integrated or discrete logic circuitry. Accordingly, the term
"processor," as used herein may refer to any of the foregoing
structure or any other structure suitable for implementation of the
techniques described herein. In addition, in some aspects, the
functionality described herein may be provided within dedicated
hardware and/or software modules configured for encoding and
decoding, or incorporated in a combined codec. Also, the techniques
could be fully implemented in one or more circuits or logic
elements.
[0201] 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 interoperative hardware units,
including one or more processors as described above, in conjunction
with suitable software and/or firmware.
[0202] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *
References