OA17515A - Signaling of picture order count to timing information relations for video timing in video coding. - Google Patents

Abstract

In an example, the disclosure provides for receiving a coded video sequence comprising encoded pictures of a video sequence and receiving timing parameters for the coded video sequence that include an indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure referenced by the coded video sequence. Another example provides for encoding pictures of a video sequence to generate the coded video sequence comprising the encoded pictures and signaling timing parameters for the coded video sequence by signaling the indication in the VPS syntax structure referenced by the coded video sequence.

Description

DEMANDE DE BREVET D’INVENTION

PCT/US2013/077279 DU 20/12/2013

Nom du Déposant(s): QUALCOMM INCORPORATED

Titre d’invention: SIGNALING OF PICTURE ORDER COUNT TO TIMING

INFORMATION RELATIONS FOR VIDEO TIMING IN VIDEO CODING

Noms d’inventeur(s): WANG, Ye-Kui

Mandataire : SCP AKKUM, AKKUM & Associâtes

B.P 4966 Yaoundé - Cameroun.

I

SIGNALING OF PICTURE ORDER COUNT TO TIMING INFORMATION RELATIONS FOR VIDEO TIMING IN VIDEO CODING [0001] This application daims the benefit of U.S. Provisional Application No. 61/749,866, filed January 7, 2013, the entire content of which is incorporated herein by reference.

TECHNICAL F1ELD [0002] This disclosure relates to video coding and video processing, and more particularly to techniques for signaling timing information in video information.

BACKGROUND [0003] Digital video capabilities can be incorporated into a widc range of devices, including digital télévisions, digital direct broadcast Systems, wireless broadcast Systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital caméras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio téléphonés, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like. Digital video devices impleinent video compression techniques, such as those described in the standards defïned by MPEG-2, MPEG-4, 1TU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard, and extensions of such standards. The video devices may transmit, receive, encode, décodé, and/or store digital video information more efficienlly by implementing such video compression techniques.

[0004] Video compression techniques perform spatial (intra-picturc) prédiction and/or temporal (inter-picture) prédiction to reduce or remove redundancy inhérent in video sequences. For block-bascd video coding, a video slice (i.e., a video frame or a portion of a video frame) may be partitioned into video blocks, which may also be refened to as treeblocks, coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (l) slice of a picture are encoded using spatial prédiction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an intcr-coded (P or B) slice of a picture may use spatial prédiction with respect to reference samples in neighboring blocks in the same picture or temporal prédiction with respect to reference samples in otlier reference pictures. Pictures may be referred to as frames, and refcrence pictures may be referred to a reference frames.

[0005] Spatial or temporal prédiction utilizes a prédictive block. Residual data represents pixel différences between the original block to be coded and the prédictive block. An inter-coded block is encoded according to a motion vector that points to a block of reference samples forming the prédictive block, and the residual data indicating the différence between the coded block and die prédictive block. An inlra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain, resulting in residual transform coefficients, which then may be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned in order to produce a one-dimensional vector of transform coefficients, and entropy coding may be applied to achieve even more compression.

[0006] A given coded video sequence encoded to a bilstream includes an ordered sequence of coded pictures. In the H.264/AVC and HEVC standards, the decoding order of the coded pictures for a bitsüeani is équivalent to the ordered sequence. However, the standards also support an output order of decoded pictures that differs from Üie decoding order, and in such cases each of the coded pictures is associated with a picture order count (POC) value that spécifiés the output order for the picture in the video sequence.

[0007] Video timing information for a video sequence may be signaled in syntax éléments of one or more syntax structures (alternalively referred to as “parameter set structures” or simply “parameter sets”). The syntax structures may include a sequence parameter set (SPS) that includes coding information that applied to ail slices of a coded video sequence. The SPS may itself include parameters referred to as video usability information (VUl), which include hypothetical reference décoder (HRD) information as well as information For enhancing the use of the corresponding video sequence for various puiposes. The HRD information may itself be signaled using a HRD syntax structure includable within other syntax structures such as the VUl syntax structure. The syntax structures may also include a video parameter set (VPS) that describes characteristics of a corresponding video sequence, such as comnion syntax cléments shared by multiple layers or operation points as well as other operation point information that may be common to multiple sequence parameter sets, such as HRD information for various layers or sub-Iayers.

SUMMARY [0008] In general, this disclosure describes techniques for video coding, and more particularly to techniques for signaling timing information, e.g., to specify picture 5 output timing and/or to define a buffering model such as a hypolhetical reference décoder (HRD). In some examples, the techniques may include generating, for a coded video sequence, an encoded bitstream to signal, in a video parameter set (VPS) syntax structure, a flag indicating whether the picture order count (POC) value for each picture in the coded video sequence that is not the first picture in the coded video sequence, in 10 decoding order, is proportional to the output time of the picture relative to the output time of the first picture in the coded video sequence. In some instances, the techniques may include generating the encoded bitstream to signal the flag in the VPS syntax structure only if timing information in the form of the time scale and number of unils in a clock tick syntax éléments are also included in the VPS syntax structure.

[0009] In one example of the disclosure, a method of processing video data includes receiving a coded video sequence comprising encoded pictures of a video sequence; and receiving timing parameters for the coded video sequence that include an indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is 20 proportional to an output time of the picture relative to an output lime of the first picture in the coded video sequence in a video parameter set (VPS) syntax stmcture referenced by the coded video sequence.

[0010] In another example of the disclosure, a method of encoding video data includes encoding pictures of a video sequence to generate a coded video sequence comprising 25 the encoded pictures; and signaling timing parameters for the coded video sequence by signaling an indication of whether a picture order count (POC) value for each picture in the coded video sequence thaï is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output lime of the first picture in the coded video sequence in a video parameter set 30 (VPS) syntax stmcture referenced by the coded video sequence.

[0011] In another example of the disclosure, a device for processing video data includes a processor configured to receive a coded video sequence comprising encoded pictures of a video sequence and receive timing parameters Ibr the coded video sequence that

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include an indication of whether a piclure order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time of the first picture in the coded video sequence in a video parameter set 5 (VPS) syntax structure referenced by the coded video sequence.

[0012] In another example of the disclosure, a device for encoding video data includes a processor configured to encode pictmes of a video sequence to generate a coded video sequence comprising the encoded pictures and signal timing parameters for the coded video sequence by signaling an indication of whether a piclure order count (POC) value 10 for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure referenced by the coded video sequence.

[0013] In another example of the disclosure, a device for processing video data includes 15 means for receiving a coded video sequence comprising encoded pictures of a video sequence and means for receiving timing parameters for the coded video sequence that include an indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output lime of the piclure relative to 20 an output time of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure referenced by the coded video sequence.

[0014] In another example, the disclosure describes a computer-readable storage medium. The computer-readable storage medium having stored lhereon instructions that upon execution cause one or more processors to receive a coded video sequence 25 comprising encoded pictures of a video sequence and reçoive timing parameters for the coded video sequence that include ail indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time of the first picture in the coded video sequence in a 30 video parameter set (VPS) syntax structure referenced by the coded video sequence.

[0015] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from tire description and drawings, and from the claims.

BRIEF DESCRIPTION OFDRAWINGS [0016] FIG. 1 is a block diagram illustrating an example video encoding and decoding System thaï may utilize the techniques described in this disclosure.

[0017] FIG. 2 is a block diagram illustrating an example video encoder that may 5 implement the techniques described in this disclosure.

[0018] FIG. 3 ïs a block diagram illustrating an example video décoder that may implement tire techniques described in this disclosure.

[0019] FIG. 4 is a block diagram illustrating timing information for an example coding structure for a reference picture set according to techniques described herein.

[0020] FIG. 5 is a flowchart illustrating an example method of operation according to techniques described in this disclosure.

[0021] FIGS. 6A-6B are flowcharts illustrating example methods of operation according to techniques described in this disclosure.

[0022] FIG. 7 is a flowchart illustraLing an example method of operation according to 15 techniques described in this disclosure.

[0023] FIG. 8 is a flowchart illustrating an example method of operation according to techniques described in this disclosure.

[0024] FIGS. 9A-9B are flowcharts illustraLing example methods of operation according to techniques described in this disclosure.

[0025] FIG. 10 is a flowchart illustrating an example method of operation according to techniques described in this disclosure.

DETA1LED DESCRIPTION [0026] This disclosure describes various teelmiques for video coding, and more 25 particularly to techniques for signaling timing information, e.g., to specify picture output timing and/or to define a buffering or decoding mode! such as a hypothetical reference décoder (HRD). In general, the Lerm “signaling” is used in this disclosure to refer to signaling that takes place within a coded bitstream. An encoder may generale syntax éléments to signal information in a bitstream as part of a video encoding process.

A decoding device or other video processing device, may reçoive a coded bitstream, and interprel syntax éléments in the coded bitstream as part of a video decoding process or other video processing. For example, to indicate the output timing for switching from a given picture to the next picture in a coded video sequence according to the output

ordering, the timing information for the coded video sequence may in some cases signal a number of clock ticks that correspond to a différence of picture order count (POC) values equal to one. A différence of POC values equal to one may represent the différence between a POC value for a given picture and the POC value for the next 5 picture according to the output ordering, e.g. the POC value l'or the 2^nd picture and the

POC value for the 3^ld picture according to the output ordering. The video timing information may also include a condition that spécifiés whether the video timing information signais the number of clock ticks that correspond to a différence of picture order count values equal to one. In other words, only if tire condition holds does the 10 video timing information signal the number of clock ticks that correspond to a différence of picture order count values equal to one. In some cases, the condition does not hold and the video timing information does not signal the number of clock ticks that correspond to a différence of picture order count values equal to one. The number of clock ticks may dépend upon the time scale (corresponding, e.g., to an oscillator 15 frequency - such as 27 MHz - that defines a lime coordinate System for the signaled information) and the number of time units of a clock operating at the lime scale Üiat corresponds to one incrément of a clock tick counter, which is referred to as a clock tick.” [0027] In some examples, the techniques may include generating, for a coded video 20 sequence, an encoded bitstream to signal, in a video parameter sel (VPS) syntax structure, a flag indicating whether the picture order count (POC) value for each picture in the coded video sequence tirât is not the first picture in tire coded video sequence, in decoding order, is proportional to the output time of the picture relative to the output time of the first picture in the coded video sequence. in some instances, the techniques 25 may include generating the encoded bitstream to signal the flag in the VPS syntax stiucture only if timing information in the form of the time scale and number of units in a clock tick syntax éléments are also included in the VPS syntax structure.

[0028] Video coding standards include ITU-T H.261, ISO/lEC MPEG-1 Visual, 1TU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263,1SO/IEC MPEG-4 Visual and ITU-T 30 H.264 (also known as ISO/lEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions.

[0029] In addition, there is a new video coding standard, namely High Efficiency Video Coding (1-IEVC), being 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). The latest Working Draft (WD) of HEVC, and referred to as HEVC WD9 or simply WD9 hereinaftcr, is Bross et al., “Proposed éditorial hnproveinents for High Efficiency Video Coding (HEVC) text spécification draft 9 (SoDIS),” Joint Collaborative Team on Video Coding (JCT-VC) of ÎTU-T SG 16 WP 3 5 and ISO/IEC JTC l/SC 29/WG U, 12th Meeting: Geneva, CH, 14-23 Jan. 2013, available from http://phenix.intevi-y.fr/jct/doc_end_user/documents/12_Geneva/wgl l/JCTVC-L0030-vl.zip, as of January 7, 2013.

[0030] A recent draft of the HEVC standard, referred to as “HEVC Working Draft 10” 10 or “WD10,” is described in document JCTVC-L1003v34, Bross et al., “High efficiency video coding (HEVC) text spécification draft 10 (for FDIS & Last Call), Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP3 and 1SO/1EC JTC1/SC29/WG11, 12tli Meeting: Geneva, CH, 14-23 January, 2013, which is downloadable from: http://phenix.int15 evry. fr/jct/doc_end_user/documents/ 12_Geneva/wgl l /J CTVC-L1003-v34.zip.

[0031] Another draft of the HEVC standard, referred to herein as “WD 10 révisions,” is described in Bross et al., “Editors’ proposed corrections to HEVC version 1,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP3 and ISO/IEC JTC1/SC29/WG11, 13' Meeting, Incheon, KR, April 2013, which as of June7, 2013, is 20 available from:

http://phenix.int-evry.fi-/jct/doc_cnd_user/docunients/13_Incheon/wgl 1/JCTVCM0432-v3.zip [0032] HEVC standardization efforts are based on a model of a video coding device referred to as the HEVC Test Model (HM). The HM présumés iniprovemcnts in the 25 capabilities of current video coding devices with respect to video coding devices available during tlie development of other previous video coding standards, e.g., ITU-T H.264/AVC. For example, wliereas H.264 provides nine inlra-prediction encoding modes, HEVC provides as many as thirty-five intra-prediction encoding modes. The entire contents of HEVC WD9 and HEVC WD 10 are incorporaled herein by référencé.

[0033] Video coding standards typically include a spécification of a video buffering model. In AVC and HEVC, the buffering model is referred to as the hypothetical référencé décoder (1-IRD), which includes a buffering model of both the coded picture buffer (CPB) and the decoded picture buffer (DPB). As defined in HEVC WD9, aii HRD is a hypothetical décoder model that spécifiés constrains on the variability of

Network Abstraction Layer (NAL) unit streams or conforming byle slreams that an encoding process may produce. The CPB and DPB behaviors are matheraalically specified. The HRD directly imposes constraints on different timing, buffer sizes and bit rates, and indirectly imposes constraints on bitstream characteristics and statistics. A 5 complété set of HRD parameters include five basic parameters: initial CPB removal delay, CPB size, bit rate, initial DPB output delay, and DPB size.

[0034] In AVC and HEVC, bitslream conformance and décoder conformance are specified as parts of the HRD spécification. Although “Hypolhctical Reference Décoder” includes the tenu “décoder,” HRD is typically needed at the encoder side to 10 guarantee bitstream conformance and is typically not needed at the décoder side. Two types of bitstream or HRD conformance, namely Type I and Type II, are specified. Also, two types of décoder conformance, output timing décoder conformance and output order décoder conformance are specified.

[0035] In I-IEVC WD9, HRD operations require parameters signaled in the 15 hrd_parameters( ) syntax structures, buffering period supplémentai enhancement information (SE1) messages, picture timing SEI messages and sometimes also in decoding unit information SEI messages. The hrd_parameters( ) syntax structures may be signaled in the video parameter sel (VPS), the sequence parameter set (SPS), or any combination thereof.

[0036] In HEVC WD9, lhe hrd_parameters( ) syntax structure includes syntax éléments for signaling of video timing information, including time seule and the number of units in a clock tick. The video usability information (VU1) part of the SPS includes a flag indicating whether lhe picture order count (POC) value for each picture in the coded video sequence that is not the first picture in lhe codcd video sequence, in decoding 25 order, is proportional to the output time of die picture relative to lhe output time of the first picture in the coded video sequence; if yes, then the number of clock ticks corresponding to a différence of picture order count values equal to 1.

[0037] The related syntax and semantics in HEVC WD9 are as follows. Table 1 shows an example video parameter set raw byte sequence payload (RBSP) syntax structure 30 according to WD9.

video parameter set rbsp( ) {	Descriptor
...
vps num hrd parameters	ue(v)
for( i = 0; i < vps num hrd parameteis; i++ ) {
hrd op set idx[ i ]	ue(v)
if( i>0)
cprms present flag[ i ]	u(l)
hrd_parameters( cpnns_presenl_fiag[ i ], vps max sub layers minusl )
}
...
1

Table 1: Example video parameter set RBSP syntax structure [0038] In Table 1 above, the syntax element vps_num_hrd_parameters spécifiés the number of hrd_paranieters( ) syntax structures présent in the video parameter set Raw Byte Sequence Payload (RBSP). In bitstreams conforming to this version of this Spécification, the value of vps_num_hrd_paiameters shall be less than or equal to I. Although the value of vps_num_hrd_parameters is required to be less than or equal Ιο I in HEVC WD9, decoders shall allow other values of vps_num_hrd_parameters in the range of 0 to 1024, inclusive to appear in the syntax.

[0039] The syntax element hrd_op_set_idx[ i ] spécifiés the index, in the list of operation point sets specified by the video parameter set, of the operation point set to which the i-lh hrd_parameters( ) syntax structure in the video parameter set (VPS) applies. In bitstreams conforming to this version of this Spécification, the value of hrd_op_set_idx[ i ] shall be equal to 0. Although tlie value of hrd_op_set_idx[ i [ is required to be less than or equal to l in HEVC WD9, decoders shall allow other values of hrd_op_set_idx| i [ in the range of 0 to 1023 to appear in the syntax.

[0040] The syntax element cpims_present_flag[ i ] equal to 1 spécifiés that the HRD parameters that are common for ail sub-Iayers are présent in the i-lh hrd_parameters( ) syntax structure in the video parameter set. cprms_prcsent_flag[ i ] equal to 0 spécifiés that the HRD parameters that are common for ail sub-layers are not présent in the i-lh hid_parameters( ) syntax structure in the video parameter sel and are derived to be the same as the ( i - 1 )-th hrd„parameters( ) syntax structure in the video parameter set. cpnns_present_flagl 0 ] is inferred to be equal to 1.

[0041] Table 2 below shows a VUI parameters syntax structure according to WD9.

vui parameters( ) {	Descriptor
...
hrd parameters preseiit ilag	u(l)
if( hrd parameters present flag )
hrd parameters( 1, sps max sub layers minusl )
poc proportional to timing flag	u(I)
if(poc_piOportional_lo_timing_fiag && timingjnfo present flag )
num ticks poc diff one minusl	ue(v)
·»·
}

Table 2: VUl parameters syntax structure [0042] In Table 2 above, the syntax element hrd_parameters_present_nag equal to l 5 spécifiés that the syntax structure hrd_parameters( ) is présent in tire vui_parameters( ) syntax structure. The hrd_paraineters_prcsent_flag equal to 0 spécifiés that the syntax structure hrd_parameters( ) is not présent in the vui_parameters( ) syntax structure.

[0043] The syntax element poc_proportional_to_timing_flag equal to I indicates that the picture order count value for each picture in the coded video sequence that is not the 10 first picture in the coded video sequence, in decoding order, is proportional to the output lime of the picture relative to the output lime of the first picture in the coded video sequence. Tire poc_piOportional_to_timing_fIag equal to 0 indicates that the picture order count value for each picture in tire coded video sequence that is not the first picture in the coded video sequence, in decoding order, may or may not be proportional 15 to the output time of tire picture relative to the output time of tire first picture in the coded video sequence.

[0044] The syntax element num_ticks_poc_diff_one_minus 1 plus 1 spécifiés the number of clock ticks corresponding to a différence of picture order count values equal to 1.

[0045] Table 3 below shows an example HRD parameters syntax structure according to

WD9.

hrd_parameters( commonlnfPresentFlag, maxNumSubLayersMinusl ) {	Descriptor
if( commonlnfPresentFlag ) {
timing info present flag	u(l)
if( timing info present flag ) {
nuni units in tick	u(32)
time scale	u(32)
]
···
)

Table 3: Example HRD parameters syntax structure [0046] In Table 3 above, the syntax element timing_info_present_flag equal to 1 spécifiés that nuvn_units_in_tick and time_scale are présent in the hrd_parameters( ) syntax structure. If line timing_info_present_flag is equal to 0, the num_units_in_tick and time_scale are nol présent in the hrd_parameters( ) syntax structure. If not présent, tire value of timing_info_present_flag is inferred to be 0.

[0047] The syntax element num_units_in_tick is the number of time units of a clock operating at the frequency lime_scale Hz that corresponds to one incrément (called a io clock tick) of a clock tick counter. The value for syntax element num_units_in_tick shall be greater than 0. A clock tick is the minimum interval of time that can be represented in the coded data when sub_pic_cpb_params_present_flag is equal to 0. For example, when the picture rate of a video signal is 25 Hz, time_scale may be equal to 27,000,000 and num_units_in_tick may be equal to 1,080,000.

[0048] The syntax element time_scale is the number of time units that pass in one second. For example, a lime coordinate System that measures time using a 27 MHz clock has a lime_scale of 27,000,000. The value for syntax element lime_scale shall be greater than 0.

[0049] The timing signaling as specified in HEVC WD9 and as described above may 20 exhibit a number of problems. First, the condition for signaling of the syntax element num_licks_poc_diff_one_mmus 1 is “if( poc_proportional_to_timing_nag &&. liming_info_present_nag )”. This condition includes dependencies upon two signaled syntax éléments: poc_propoitionaLto_tiining_flag and limingjnfo_present_flag.

However, it is not clear from the HEVC WD9 spécification whether the 25 timing_info_present_flag for the- condition référencés the syntax element timing_info_present_flag of an hrd_parametcrs( ) syntax structure (if présent) in the

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VU1 part of the SPS or référencés référencés the syntax element timing_info_present_flag of an hrd_paramelers( ) syntax structure in the VPS.

[0050] In addition, multiple layers or multiple possible bitstream subsets of a scalable video bitstream may share the common values of time scale and the number of unils in a 5 clock tick, which are specified in HEVC WD9 in the syntax éléments time_scale and num_units_in_tick of an hrd_parameters( ) syntax structure, which may be repeatedly signaled in the VUI part of the SPS and in the VPS, for instance. Such réplication, if présent in the bitstream, may resuit in bit wastage.

[0051] Further, picture order count (POC) values arc typically proportional to output 10 times for ail layers of a scalable video bitstream if the POC values are proportional to output times for any of the layers of a scalable video bitstream. 1-Iowever, The HEVC WD9 spécification does not provide for signaling, in the scalable video bitstream, an indication that POC values are proportional to output times for ail layers or ail possible bitstream subsets of the scalable video bitstream. Référencé to a “layer” of a scalable 15 video bitstream may refer to a scalable layer, a texture view, and/or a deplh view, for instance. In addition, although HEVC WD9 spécifiés that the flag poc_proportional_to_timing_flag is always signaled in the VUI syntax is always signaled in the VUI syntax structure of the SPS, the flag poc_proportional_to_timing_flag has no utility if the syntax éléments time_scale and 20 num_units_in_tick are not also signaled in the bitstream.

[0052] The techniques of this disclosure may solve one or more of the above problème, as well as provide other improvements, to enable efficient signaling of parameters for HRD operations. Various examples of the techniques are described herein with référencé to HEVC WD9 and potential improvemenLs thereto. The solutions apply to 25 any video coding standards, including AVC and HEVC, for example, that include a spécification for a video buffering rnodel, though for purposes of illustration the description is spécifie to the HRD parameters signaling defîned in HEVC WD9 and modified in accordance with the techniques of this disclosure.

[0053] FIG. 1 is a block diagram illustrating an exaraple video encoding and decoding 30 System 10 that may ulilize the techniques described in this disclosure. As shown in

FIG. 1, System 10 includes a source device 12 that generates encoded video data to be decoded at a later time by a destination device 14. Source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, téléphoné handsets

such as so-called “smart” phones, so-called “smart” pads, télévisions, caméras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device 12 and destination device 14 may be equipped for wireless communication.

[0054] Destination device 14 may receive the encoded video data to be decoded via a link 16. Link 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. In one example, link 16 may comprise a communication medium to enable source device 12 to transmit encoded video data directly to destination device 14 in real-time. The encoded video data may be modulaled according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, swilches, base stations, or any other equipment that may be useful to facilitate communication from source device 12 to destination device 14.

[0055] Altematively, encoded data may be output from output interface 22 to a storage device 34. Similarly, encoded data may be accessed from storage device 34 by input interface. Storage device 34 may include any of a variety of dislributed or locally accessed data storage media such as a hard drive, Blu-ray dises, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, storage device 34 may correspond to a file server or another intermediate storage device that may hold the encoded video generated by source device 12. Destination device 14 may access stored video data from storage device 34 via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device 14. Example file servers include a web server (e.g., for a website), an FTP server, network attached storage (NAS) devices, or a local disk drive. Destination device 14 may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data sLored on a file

server. The transmission of encoded video data from storage device 34 may be a streaming transmission, a download transmission, or a combination of both.

[0056] The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of 5 any of a variety of multimedia applications, such as over-the-air télévision broadcasls, cable télévision transmissions, satellite télévision transmissions, streaming video transmissions, e.g., via the Internet, encoding of digital video for storage on a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, system 10 may be configured to support one-way or 10 two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

[0057] In the example of FIG. 1, source device 12 includes a video source 18, video encoder 20 and an output interface 22. In some cases, output interface 22 may include a modulator/demodulator (modem) and/or a transmitter. In source device 12, video 15 source 18 may include a source such as a video capture device, e.g., a video caméra, a video archive containing previously captured video, a video feed interface to receive video from a video content provider, and/or a computer graphies system for generating computer graphies data as the source video, or a combination of such sources. As one example, if video source 18 is a video caméra, source device 12 and destination device 20 14 may form so-callcd caméra phones or video phones. However, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications.

[0058] The captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video data may be uansmitted dircctly to destination 25 device 14 via output interface 22 of source device 12. The encoded video data may also (or altematively) be stored onto storage device 34 for later access by destination device 14 or other devices, for decoding and/or playback.

[0059] Destination device 14 includes an input interface 28, a video décoder 30, and a display device 32. In some cases, input interface 28 may include a receiver and/or a 30 modem. Input interface 28 of destination device 14 receives the encoded video data over link 16. The encoded video data communicated over link 16, or provided on storage device 34, may include a variety of syntax éléments generated by video encoder 20 for use by a video décoder, such as video décoder 30, in decoding the video data.

Such syntax éléments may be included with the encoded video data transmitted on a communication medium, stored on a storage medium, or stored a file server.

[0060] Display device 32 may be integrated with, or extemal to, destination device 14. In some examples, destination device 14 may include an integrated display device and also be configured to interface with an extemal display device. In other examples, destination device 14 may be a display device. In general, display device 32 displays the decoded video data to a user, and may comprise any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0061] Video encoder 20 and video décoder 30 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard presently under development, and may conform to the HEVC Test Model (HM). Altematively, video encoder 20 and video décoder 30 may operate according to other proprietary or industry standards, such as the ITU-T PI.264 standard, alternalively referred to as MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. The techniques of this disclosure, however, are not limited to any particular coding standard. Other examples of video compression standards include MPEG-2 and ITU-T H.263.

[0062] Although not shown in FIG. I, in some aspects, video encoder 20 and video 20 décoder 30 may each be integrated with an audio encoder and décoder, and may include appropriate MUX-DEMUX units, or other hardware and software, to handle encoding of bolh audio and video in a common data stream or separate data streams. If applicable, in some examples, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocole such as the user datagram protocol (UDP).

[0063] Video encoder 20 and video décoder 30 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application spécifie integrated circuits (ASICs), field programmable gâte arrays (FPGAs), discrète iogic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-lransitory coniputer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 20 and video décoder 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.

[0064] The JCT-VC is working on development of the HEVC standard. The HEVC standardization efforts are based on an evolving model of a video coding device referred to as the HEVC Test Model (HM). The HM présumés several additional capabilities of video coding devices relative to existing devices according to, e.g., ITU-T H.264/AVC.

For example, whereas H.264 provides nine intra-prediction encoding modes, the HM may provide as many as thirty-three intra-prediction encoding modes.

[0065] In general, the working model of tlie HM describes that a video frame or picture may be divided into a sequence of treeblocks or largest coding units (LCU) that include both luma and chroma samples. A treeblock has a similar puipose as a macroblock of to the H.264 standard. A slice includes a number of consecutive treeblocks in coding order. A video frame or picture may be partitioned into one or more slices. Each treeblock may be split into coding units (CUs) according to a quadtree. For example, a treeblock, as a root node of the quadtree, may be split into four child nodes, and each child node may in Lum be a parent node and be split into another four child nodes. A 15 final, unsplit child node, as a leaf node of the quadtree, comprises a coding node, i.e., a coded video biock. Syntax data associatcd with a coded Bitstream may define a maximum number of times a treeblock may be split, and may also define a minimum size of the coding nodes.

[0066] A CU includes a coding node and prédiction units (PUs) and transform units 20 (TUs) associated with the coding node. A size of the CU generally corresponds to a size of the coding node and must typically be square in shape. The size of the CU may range from 8x8 pixels up to the size of tlie treeblock with a maximum of 64x64 pixels or greater. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may dcscribe, for example, partitioning of tlie CU into one or 25 more PUs. Partitioning modes may differ between whether the CU is skip or direct mode encoded, intra-prediction mode encoded, or inter-prediction mode encoded. PUs may be partitioned to be non-square in shape. Syntax data associated with a CU may also describe, for example, partitioning of the CU into one or more TUs according to a quadtree. A TU can be square or non-square in shape.

[0067] Tlie HEVC standard allows for transformations according to TUs, which may be different for different CUs. Tlie TUs are typically sized based on the size of PUs within a given CU defined l'or a partitioned LCU, although this may not always be tlie case. The TUs are typically the same size or smaller than the PUs. In some examples, residual samples corresponding to a CU may be subdivided into smaller units using a

quadtree structure known as resïdual quad tree (RQT). The leaf nodes of the RQT may be referred to as transform units (TUs). Pixel différence values associated with the TUs may be transformed to produce transform coefficients, which may be quantized. [0068] In general, a PU includes data related to the prédiction process. For example, 5 when the PU is intra-mode encoded, the PU may include data describing an intraprediction mode for the PU. As another example, when the PU is inter-mode encoded, the PU may include data defining a motion vector for tlie PU. The data defining the motion vector for a PU may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a résolution for the motion 10 vector (e.g., one-quarter pixel précision or one-eighth pixel précision), a reference picture to which the motion vector points, and/or a reference picture list (e.g., List 0, List 1, or Lisl C) for the motion vector.

[0069] In general, a TU is used for the transform and quantization proccsses. A given CU having one or more PUs may also include one or more transform units (TUs).

Following prédiction, video encoder 20 may calculate residual values from the video block identified by the coding node in accordance with the PU. Tlie coding node is then updated to reference tlie residual values radier than the original video block. Tlie residual values comprise pixel différence values that may be transformed into transform coefficients, quantized, and scanned using the transforins and other transform 20 information specified in die TUs to produce serialized transform coefficients for entropy coding. The coding node may once again be updated to refer to these serialized transform coefficients. This disclosure typically uses the term “video block to refer to a coding node of a CU. In some spécifie cases, this disclosure may also use the terni “video block” to refer to a treeblock, i.e., LCU, or a CU, which includes a coding node 25 and PUs and TUs.

[0070] A video sequence typically includes a sériés of video fiâmes or pictures. A group of pictures (GOP) generally comprises a sériés of one or more of the video pictures. A GOP may include syntax data in a lieader of the GOP, a header of one or more of the pictures, or elsewhere, that describes a number of pictures included in tlie 30 GOP. Each slice of a picture may include slice syntax data that describes an encoding mode for tlie respective slice. Video encoder 20 typically opérâtes on video blocks within individual video slices in order to encode tlie video data. A video block may correspond to a coding node within a CU. Tlie video blocks may hâve fixed or varying sizes, and may differ in size according to a specified coding standard.

W [0071] As an example, the HM supports prédiction in various PU sizes. Assuming that the size of a particular CU is 2Nx2N, the HM supports intra-prediction in PU sizes of 2Nx2N or NxN, and inter-prediction in symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, or NxN. The HM also supports asymmetric partitioning for inter-prediction in PU sizes of 5 2NxnU, 2NxnD, nLx2N, and nRx2N. In asymmetric partitioning, one direction of a CU is not partitioned, while the other direction is partitioned into 25% and 75%. The portion of the CU corresponding to the 25% partition is indicated by an “n followed by an indication of “Up”, “Down,” “Left,” or “Right.” Thus, for example, “2NxnU” refers to a 2Nx2N CU that is partitioned horizonlally with a 2NxO.5N PU on top and a 1 o 2Nxl.5N PU on bottom.

[0072] In this disclosure, “NxN” and “N by N” may be used interchangeably to refer to the pixel dimensions of a video block in terms of vertical and horizontal dimensions, e.g., 16x16 pixels or 16 by 16 pixels. In general, a 16x16 block will hâve 16 pixels in a vertical direction (y = 16) and 16 pixels in a horizontal direction (x = 16). Likewise, an 15 NxN block generally has N pixels in a vertical direction and N pixels in a horizontal direction, where N represents a nonnegative integer value. The pixels in a block may be arranged in rows and columns. Moreover, blocks need not necessarily hâve the same number of pixels in the horizontal direction as in the vertical direction. For example, blocks may comprise NxM pixels, where M is not necessarily equal to N.

[0073] Following intra-predictive or inter-prediclive coding using the PUs of a CU, video encoder 20 may calculate residual data to which lhe transforme specified by TUs of the CU are applied. The residual data may correspond to pixel différences between pixels of the unencoded picture and prédiction values corresponding to lhe CUs. Video encoder 20 may form the residual data for llie CU, and then transfonn the residual data 25 to produce transform coefficients.

[0074] Following any transforms to produce transfonn coefficients, video encoder 20 may perform quantization of the transfonn coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the coefficients, providing further compression. The quantization 30 process may reduce the bit depth associated with some or ail of the coefficients. For example, an n-bit value may be rounded down to an /«-bit value during quantization, where n is greater than in.

[0075] In some examples, video encoder 20 may utilize a predefined scan order to scan the quantized transfonn coefficients to produce a serialized vector that can be entropy

encoded. In other examples, video encoder 20 may perform an adaptive scan. After scanning the quantized transform coefficients to form a one-dimensional vector, video encoder 20 may entropy encode the one-dimensional vector, e.g., according to context adaptive variable length coding (CAVLC), context adaptive binary arithnietic coding 5 (CABAC), syntax-based context-adaptive binary arithnietic coding (SBAC), Probability

Interval Partitioning Entropy (PIPE) coding or another entropy encoding methodology.

Video encoder 20 may also entropy encode syntax éléments associated with the encoded video data for use by video décoder 30 in decoding the video data.

[0076] To perform CABAC, video encoder 20 may assign a context within a context 10 model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are non-zero or not. To perform CAVLC, video encoder 20 may select a variable length code for a symbol to be transmitted. Codewords in VLC may be constructed such that relatively shorter codes correspond to more probable symbols, while longer codes correspond to less probable symbols. In 15 this way, the use of VLC may achieve a bit savings over, for example, using cquallenglli codewords for each symbol to be transmitted. The probability détermination may be based on a context assigned to the symbol.

[0077] Source device 12 may generate an encoded bitstream to include syntax éléments that conform to a syntax structure in accordance with techniques described in this 20 disclosure. In some examples, video encoder 20 may generale the encoded bitstream to directly signal, in the video parameter set (VPS) syntax structure or in the video usability information (VUI) part of the sequence parameter set (SPS) syntax structure for a coded video sequence, ail variables that definc the condition for signaling a number of clock ticks corresponding to a différence of picture order count (POC) values 25 equal to l. In other words, radier than signaling the syntax éléments for the condition for signaling a number of clock ticks corresponding to a différence of picture order count (POC) values equal to 1 in another syntax structure (such as the HRD parameters syntax structure) that is incorporated into a VPS syntax structure or VUI part of the SPS syntax structure, the video encoder 20 generates the encoded bitstream to signal the 30 syntax éléments that define the condition in the VPS and/or VUI syntax structure without reference to another syntax structure potentially incorporated within either/both of the VPS and VUI syntax structure. The syntax éléments may include the tiniing_info_present_flag syntax element that is specified in HEVC WD9 as a syntax element of the HRD parameters syntax structure. As a resuit, the techniques may

œtse»*’

reduce and potentially eliminate ambiguity within the HEVC WD9 spécification by clearly specifying in the syntax the source of syntax éléments that define the condition.

[0078] The video encoder 20 may test tire encoded bitstream for conformance to requirements specified as one or more bitstream conformance tests defined in a video 5 coding spécification, such as HEVC WD9 or a successor spécification such as HEVC

WD10. The video encoder 20 may include or otherwise use a hypolhetical reference décoder to test the encoded bitstream for conformance. According to techniques described herein, the video encoder 20 may test the encoded bitstream for conformance by decoding the encoded bitstream to détermine, from the VPS syntax structure or in the 10 VU1 part of the SPS syntax structure for a coded video sequence, the syntax éléments that define the condition for signaling tlie number of clock ticks corresponding to a différence of POC values equal to 1. If the condition holds according to the syntax element values, video encoder 20 may détermine the number of clock ticks corresponding to a différence of POC values equal to 1 and use the detennined number 15 of clock ticks as input for, e.g., determining CPB underflow or overflow during decoding of encoded pictures included in the encoded bitstream.

[0079] In some instances, al the destination device 14, a video décoder 30 under test (or VUT) may in some cases receive a représentation of the encoded bitstream generated by video encoder 20 to directly signal, in the VPS syntax stnicture or in the VU! part of the 20 SPS syntax structure for a coded video sequence, ail syntax éléments that define the condition for signaling a number of dock ticks corresponding to a différence of picture order count (POC) values equal to 1. Video décoder 30 may décodé the encoded bitstream to détermine, from the VPS syntax structure or in the VUI part of the SPS syntax structure for a coded video sequence, the syntax éléments that define the 25 condition for signaling the number of clock ticks corresponding to a différence of POC values equal to 1. If the condition holds according to the syntax element values, video décoder 30 may déterminé tlie number of clock ticks conesponding to a différence of POC values equal to 1 and use tlie detennined number of clock ticks as input for, e.g., determining CPB underflow or overflow during decoding of encoded pictures included 30 in the encoded bitstream.

[0080] In some examples, the video encoder 20 may generate the encoded bitstream to signal the time seule and the number of units in a clock tick at most once in each of the VPS and VUI syntax structures for a given coded video sequence. That is, in a given VPS syntax structure for tlie encoded bitstream, video encoder 20 may signal the lime

scale and number of units in a clock tick syntax éléments al most once. Likewise, in a given VUI syntax structure (e.g., the VUI part of an SPS syntax structure) for the encoded bitstream, video encoder 20 may signal the time scale and number of units in a clock tick syntax éléments at most once. As a result, the video encoder 20 operatîng 5 according to techniques described herein may reduce a number of instances of the time scale syntax element (time_scale per WD9) and (lie number of units in a clock tick (num_units_in_tick per WD9) syntax element in the encoded bitstream. In addition, the video encoder 20 may in some instances generate the encoded bitstream to directly signal the time scale and the number of units in a clock tick in each of the VPS and VUI 10 syntax structures for a given coded video sequence, radier than in an HRD parameters syntax structure incorporated within a VPS and/or VUI syntax structure.

[0081] According to techniques described herein, the video encoder 20 may test an encoded bitstream, generated by video encoder 20 to signal the time scale and the number of units in a clock tick at most once in each of the VPS and VUI syntax 15 structures for a given coded video sequence, for conformance by decoding the encoded bitstream to détermine die time scale and die number of units in a clock tick from a VPS syntax structure of the encoded bitstream diat encodes the time scale and die number of units in a clock tick syntax éléments at most once in the VPS syntax stmcture. In some instances, die video encoder 20 may test the encoded bitstream for conformance by 20 decoding the encoded bitstream to détermine die time scale and the number of units in a clock tick from a VUI syntax stmcture of die encoded bitstream diat encodes the lime scale and die number of units in a clock tick syntax éléments at most once in the VUI syntax structure. The time scale and number of units in a clock tick may be signaled other than in an HRD parameters syntax stmcture incorporated within the VPS and/or 25 VUI syntax structure. Video encoder 20 may use the determined time scale and the determined number of units in a clock tick as input for, e.g., detennining CPB underflow or overflow during decoding of encoded pictures included in die encoded bitstream.

[0082] In some instances, at the destination device 14, a video décoder 30 under test 30 may in some cases receive a représentation of the encoded bitstream generated by video encoder 20 to signal the lime scale and the number of units in a clock tick al most once in each of die VPS and VUI syntax structures for a given coded video sequence. The video décoder 30 may décodé the encoded bitstream to détermine the time scale and the number of units in a clock tick from a VPS syntax structure of die encoded bitstream

that encodes the lime scale and the number of units in a dock tick syntax éléments at most once in the VPS syntax structure. In some instances, the video décoder 30 may lest the encoded bitstream for conformance by decoding tire encoded bitstream to détermine the time scale and the number of units in a clock tick from a VUI syntax 5 structure of the encoded bitstream. that encodes the lime scale and the number of units in a clock tick syntax éléments at most once in tlie VUI syntax structure. The time scale and number of units in a clock tick may be signaled other than in an HRD parameters syntax structure incorporated williin the VPS and/or VUI syntax structure. Video décoder 30 may use the determined time scale and the delermined number of units in a to clock tick as input for, e.g., determining CPB underflow or overflow during decoding of encoded piclures included in the encoded bitstream.

[0083] In some examples, the video encoder 20 may generale the encoded bitstream to signal, in a VPS syntax structure for one or more coded video sequences, a flag indicating whether the POC value for each picture in a coded video sequence that is not 15 the first picture in the coded video sequence, in decoding order, is proportional to the output time of the picture relative to tlie output time of the first picture in the coded video sequence. This indication flag may altematively be referred to as the POC proportional to timing indication flag. As a resuit, tlie video encoder 20 may reduce a number of instances of the indication in the timing information signaled for multiple 20 layers of a coded video sequence and/or for a scalable video bitstream having multiple loyers. In some instances, the video encoder 20 may include this flag in tlie VPS syntax structure only if tlie time scale and number of units in a clock tick syntax éléments are also included. The video encoder 20 may in this way avoid signaling this particular timing information (i.e., whether the POC value for each picture in a coded video 25 sequence that is not the first picture in the coded video sequence, in decoding order, is proportional to the output time of the picture relative to the output time of the first picture in tlie coded video sequence) if the clock tick information needed for using the POC proportional to timing indication is not also présent.

[0084] According to techniques described herein, the video encoder 20 may lest for 30 conformance an encoded bitstream, generated by video encoder 20 to signal, in a VPS syntax structure for one or more coded video séquences, the POC proportional to timing indication flag. The video encoder 20 may test the encoded bitstream for conformance by decoding the encoded bitstream to détermine a value for tlie flag. The video encoder 20 may additionally, or altematively, test an encoded bitstream, generated by video

encoder 20 to signal the flag in the VPS synlax structure only if the time scale and number of units in a clock tick syntax éléments are also included. The video encoder 20 may use the determined value of the POC proportional to timing indication flag and the time scale and number of units in a clock tick syntax éléments as input for, e.g., 5 determining CPB underflow or overflow during decoding of encoded picturcs included in the encoded bitstream.

[0085] In some instances, at the destination device 14, a video décoder 30 under test may in some cases receive a représentation of the encoded bitstream generated by video encoder 20 to signal, in a VPS syntax structure for one or more coded video sequences, 10 a POC proportional to timing indication flag. The video décoder 30 may lest the encoded bitstream for conformance by decoding the encoded bitstream to détermine a value for the flag. The video décoder 30 may additionally, or allernatively, test an encoded bitstream, generated by video décoder 30 to signal the flag in the VPS syntax structure only if the time scale and number of units in a clock tick syntax éléments are 15 also included. The video décoder 30 may use the determined value of the POC proportional to timing indication flag and the time scale and number of units in a clock tick syntax éléments as input for, e.g., determining CPB underflow or overflow during decoding of encoded pictures included in the encoded bitstream.

[0086] FIG. 2 is a block diagram illuslrating an example video encoder 20 that may 20 implement the techniques described in this disclosure. Video encoder 20 may perform intra- and inter-coding of video blocks within video slices. Intra-coding relies on spatial prédiction to reduce or remove spatial rcdundancy in video within a given video frame or picture. Inter-coding relies on temporal prédiction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode 25 (I mode) may refer to any of several spatial based compression modes. Inter-modes, such as uni-directional prédiction (P mode) or bi-prediction (B mode), may refer to any of several temporal-based compression modes.

[0087] In the example of FIG. 2, video encoder 20 includes a partitioning unit 35, prédiction module 41, reference picture memory 64, summer 50, transform module 52, 30 quantization unit 54, and entropy encoding unit 56. Prédiction module 41 includes motion estimation unit 42, motion compensation unit 44, and intra prédiction module 46. For video block reconstruction, video encoder 20 also includes inverse quantization unit 58, inverse transform module 60, and summer 62. A deblocking filter (not shown in FIG. 2) may also be included to filter block boundarics to remove blockiness arlifacts

from reconstructed video. If desired, tlie deblocking filter would typically filter the output of summer 62. Additional loop filters (in loop or post loop) may also be used in addition to tlie deblocking filter.

[0088] As shown in FIG. 2, video encoder 20 receives video data, and partitioning unit 5 35 partitions the data into video blocks. This partitioning may also include partitioning into slices, liles, or otlier larger units, as wells as video block partitioning, e.g., according to a quadtree structure of LCUs and CUs. Video encoder 20 generally illustrâtes lhe components that encode video blocks within a video slice to be encoded. The slice may be divided into multiple video blocks (and possibly into sets of video 10 blocks referred to as liles). Prédiction module 41 may select one of a plurality of possible coding modes, such as one of a plurality of intra coding modes or one of a plurality of inter coding modes, for the current video block based on error results (e.g., coding rate and the level of distortion). Prédiction module 41 may provide the resulting intra- or inter-codcd block to summer 50 to generale residual block data and to summer 15 62 to reconstruct the encoded block for use as a reference picture.

[0089] Intra prédiction module 46 within prédiction module 41 may perform intrapredictive coding of the current video block relative to one or more neighboring blocks in die same frame or slice as the current block to be coded to provide spatial compression. Motion estimation unit 42 and motion compensation unit 44 within 20 prédiction module 41 perform inter-predictive coding of lhe current video block relative to one or more prédictive blocks in one or more reference pictures to provide temporal compression.

[0090] Motion estimation unit 42 may be configured to détermine the inter-prediction mode for a video slice according to a predetermined pattern for a video sequence. The 25 predetermined pattern may designate video slices in the sequence as P slices, B slices or

GPB slices. Motion estimation unit 42 and motion compensation unit 44 may be highly integraled, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation unit 42, is tlie process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate 30 tlie displacemenl of a PU of a video block within a current video frame or picture relative to a prédictive block within a reference picture.

[0091] A prédictive block is a block thaï is found to closely match lhe PU of tlie video block to be coded in ternis of pixel différence, which may be determined by sum of absolule différence (SAD), sum of square différence (SSD), or other différence metrics.

In some examples, video encoder 20 may calculate values for sub-integer pixel positions of reference pictures stored in reference picture memory 64. For example, video encoder 20 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion 5 estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel précision.

[0092] Motion estimation unit 42 calculâtes a motion vector for a PU of a video block in an inter-coded slice by comparing tire position of the PU to die position of a prédictive block of a reference picture. Tire reference picture may be selected from a 10 first reference picture list (List 0) or a second reFerence picture list (List 1), each of which identify one or more reference pictures stored in reference picture memory 64.

Motion estimation unit 42 sends the calculated motion vector to enlropy encoding unit 56 and motion compensation unit 44.

[0093] Motion compensation, performed by motion compensation unit 44, may involve 15 fetching or generating the prédictive block based on the motion vector determined by motion estimation, possibly performing interpolations to sub-pixel précision. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locale the prédictive block to which the motion vector points in one of the reference picture lisls. Video encoder 20 fonns a residual video block by subtract ing 20 pixel values of die prédictive block from the pixel values of the current video block being coded, forming pixel différence values. The pixel différence values form residual data for the block, and may include both luma and chroma différence components. Summer 50 represents the component or components that perform this subtraction operation. Motion compensation unit 44 may also generale syntax éléments 55 25 associated with the video blocks and the video slicc for use by video décoder 30 in decoding the video blocks of the video slice.

[0094] Motion compensation unit 44 may generale syntax éléments 55 that conform to a syntax structure in accordance willi techniques described in this disclosure. In some examples, video encoder 20 may generate syntax éléments 55 to directly signal, in die 30 video parameter set (VPS) syntax structure or in the video usability information (VUI) part of the sequence parameter set (SPS) syntax structure associated with (lie video blocks, ail syntax éléments that define the condition for signaling a number of clock ticks corresponding to a différence of picture order count (POC) values equal to 1. In other words, radier than signaling the syntax éléments for the condition for signaling a

number of clock ticks coiresponding to a différence of picture order count (POC) values equal to l in another syntax structure (such as the HRD paramelers syntax structure) tirât is incorporated into a VPS syntax structure or VUI part of the SPS syntax structure, the motion compensation unit 44 generates die encoded bitstream to signal the syntax 5 éléments for the syntax éléments that define the condition in the VPS and/or VUI syntax structure wiüiout reference to another syntax structure potcnlially incorporated within either/both of the VPS and VUI syntax structure.

[0095] In some examples, the motion compensation unit 44 may generate the syntax éléments 55 to signal the lime scale and the number of units in a clock tick at most once 10 in each of tire VPS and VUI syntax structures for a given coded video sequence. That is, in a given VPS syntax structure for the encoded bitstream, the motion compensation unit 44 may generate the syntax éléments 55 to signal the lime scale and number of units in a clock tick syntax éléments at most once. Likewise, in a given VUI syntax structure (e.g., the VUI part of an SPS syntax structure) for the encoded bitstream, the 15 motion compensation unit 44 may generate the syntax éléments 55 signal the time scale and number of units in a clock tick syntax éléments at most once. In addition, the motion compensation unit 44 may in some instances generate die syntax éléments 55 to directly signal the time scale and the number of units in a clock tick in each of die VPS and VUI syntax structures for a given coded video sequence, radier dian in an HRD 20 parameters syntax structure incorporated within a VPS and/or VUI syntax structure.

[0096] In some exaniples, the motion compensation unit 44 may generale the syntax éléments 55 to signal, in a VPS syntax structure for one or more coded video sequences, a flag indicating whether the POC value for each picture in a coded video sequence diat is not the first picture in die coded video sequence, in decoding order, is proportional to 25 the outpul lime of lhe picture relative to the output time of the first picture in the coded video sequence. This indication flag may altcnialively be referred to as lhe POC proportional to timing indication flag. As a resuit, lhe motion compensation unit 44 may reduce a number of instances of die indication in the timing information signaled for multiple layers of a coded video sequence and/or for a scalable video bitstream 30 having multiple layers. In some instances, lhe motion compensation unit 44 may include this flag in the VPS syntax structure only if the tinte scale and number of units in a clock tick syntax éléments are also included. The motion compensation unit 44 may in this way avoid signaling diis particular timing information (i.e., whether the POC value for each picture in a coded video sequence thaï is not the first picture in the

coded video sequence, in decoding order, is proportional to the output time of the picture relative to the output time of the first picture in the coded video sequence) if the clock tick information needed for using the POC proportional to timing indication is not also présent.

[0097] Example changes to the HEVC WD9 text to effectuate the above techniques for generating syntax éléments 55 are as follows (other parts not mentioned may unmodified vis-à-vis HEVC WD9):

[0098] Tire following is an example of a video parameter set RBSP syntax structure modified to solve one or more of the above problème (the underlined syntax is an 10 addition to the video parameters set RBSP syntax structure of HEVC WD9; other syntax may be unchanged relative to HEVC WD9):

video parameter set rbsp( ) {	Descri ptor
...
vus timing info présent flag	ufn
if( vos timing info présent fias ) 1
vos num units in tick	u(32)
vps time scale	q£32).
vps poc proportional to timing flag	u(l)
iff vps poc proportional to timing flag 1
vos num ticks poc diff one minusl	uefv)
1
vps num hrd parameters	ue(v)
for( i = 0; i < vps num hrd parameters·, i++ ) {
cprms present flag[ i ]	u(l)
hrd_paramelers( cprms_present_flag[ i ], vps nrax subjayers minusl )
1
...
}

Table 4: Example video parameter set RBSP syntax structure [0099] Table 4 defines newly-added syntax éléments according to the following video 15 parameter set (VPS) RBSP semantics:

[0100] vps_tiniing_info_present_flag equal to 1 spécifiés tirât vps_num_units_in_tick, vps_time_scale, and vps_poc_proportional_to_liming_flag are présent in lire video parameter set. vps_timing_inro_present_flag equal to 0 spécifiés that

vps_num_units_in_tick, vps_time_scale, and vps_poc_propoitional_to_timing_flag are not présent in the video parameter set.

[0101] vps_num_unitsjn_ticl< is tlie number of time unils of a clock operating at the frequency vps_time_scale Hz that corresponds to one incrément (called a clock tick) of 5 a clock tick counter. The value of vps_num_units_in_tick shall be greater than 0. A clock tick, in units of seconds, is equal to the quotient of vps_num_units_in_tick divided by vps_time_scale. For example, when the picture rate of a video signal is 25 Hz, vps_time_scale may be equal to 27,000,000 and vps_num_units_in_tick may be equal to 1,080,000, and consequently a clock tick may be 0.04 seconds.

[0102] vps_time_scale is the number of time units that pass in one second. For exaniple, a time coordinate System that measures time using a 27 MHz clock has a vps_time_scale of 27,000,000. The value of vps_lime_scale shall be greater than 0.

[0103] vps_poc_proportional_to_liming_flag equal Ιο I indicates that the picture order count value for each picture in the coded video sequence that is not the first 15 picture in the coded video sequence, in decoding order, is proportional to the output time of the picture relative to the output time of the first picture in the coded video sequence. vps_poc_proportional_to_timing_flag equal to 0 indicates that the picture order count value for each picture in the coded video sequence diat is not the first picture in the coded video sequence, in decoding order, may or may not be proportional 20 to tlie output lime of the picture relative to the output time of the first picture in the coded video sequence.

[0104] vps_num_tîcks_poc_dilT_one_minusl plus 1 spécifiés tlie number of clock ticks corresponding to a différence of picture order count values equal to 1. The value of vps_num_ticks_poc_diff_one_minusi shall be in the range ofO to 2^Λ32 - 1, inclusive.

[0105] The following is an example of a VUl parameters syntax structure modified to solve one or more of tlie above problems (tlie underlincd syntax is an addition to tlie VUl parameters syntax structure of HEVC WD9; tlie italicized syntax is removed from tlie VUl parameters syntax structure of HEVC WD9; other portions of the syntax table are unchanged relative to HEVC WD9):

vui parameters( ) {	Descriptor
...
sns timing info présent flag	uiD
ifC sns timins info présent fias ) 1
sps nuni units in tick	u(32)
sps time scale	u(32)
sns noc nronortional to timing flag	ufl)
iff sns noc nronortional to timing fias )
sps num ticks noc diff one minusl	ucfv)
1
hrd parameters presen t flag	u(l)
if( hrd parameters present flag )
hrd parameters( 1, sps max sub layers minusl )
poc proportional to timing fiag	i<(l)
if( poc_proportional_to_timing_Jlug &<i timingJnfo^present flag )
num ticks poc diff one minusl	ue(v)
...
}

Table 5: Example modified VUI parameters syntax structure [0106] Table 5 defines newly-added syntax éléments according to the following VUI parameters scmantics (semantics for the removed syntax cléments are likewise 5 removed):

[0107] sps_timing_info_present_nag equal lo 1 spécifiés Üiat sps_num_unils_in_tick, sps_time_scale, and sps_poc_proporlional_to_timing_flag are présent in the vui_paranieters( ) syntax structure, sps_timing_jnfo_present_flag equal to 0 spécifiés that sps_num_units_in_tick, sps_time_scale, and sps_poc_proporlional_to_timing_flag 10 are not présent in the vui_parameters( ) syntax structure.

[0108] sps_num_units_m_tick is the number of time units of a clock operating al the frequency sps_lime_scale Hz that con’csponds to one incrément (called a clock tick) of a dock tick counter. sps_num_units_in_tick shall be greater than 0. A dock tick, in units of seconds, is equal lo the quotient of sps_num_units_in_lick divided by 15 sps_time_scale. For example, when the picture rate of a video signal is 25 1-Iz, sps_time_scale may be equal to 27,000,000 and sps_num_units_in_tick may be equal to 1,080,000, and consequently a clock tick may be equal to 0.04 seconds (see Equation (1)). When vps_num_units_in_tick is présent in the video parameter set referred lo by

the sequence parameter set, sps_num_units_in_tick, when présent, shall be equal to vps_nurn_units_in_tick.

[0109] The formula for deriving tlie variable ClockTick (also referred to herein as a “clock tick”) is modified to be as follows:

„ . sps _iunn_itnils _in_tick .

ClockTick =------------------------ Equation (]) sps_tbne_scale [0110] sps_time_scale is the number of time units dial pass in one second. For example, a time coordinate System that measures time using a 27 MHz clock lias a sps_time_scale of 27,000,000. The value of sps_time_scale shall be greater than 0. When vps_lime_scale is présent in the video parameter set referred to by the sequence 10 parameter set, sps_time_scale, when présent, shall be equal to vps_tinie_scale.

[OUI] sps_poc_proportional_to_timing_flag equal to 1 indicates that the picture order count value for each picture in the coded video sequence that is not die first picture in the coded video sequence, in decoding order, is proportional to tlie output time of tlie picture relative to the output time of tlie first picture in Lhe coded video 15 sequence. The sps_poc_proportional_to_timing_flag equal to 0 indicates that lhe picture order count value for each picture in tlie coded video sequence lliat is not the first picture in tlie coded video sequence, in decoding order, may or may not be proportional to tlie output time of the picture relative to tlie output time of the first picture in tlie coded video sequence. When vps_poc_proportional_to_timing_flag is 20 présent in the video parameter set referred to by lhe sequence parameter set, sps_poc_proportional_lo_liming_flag, when présent, shall be equal to vps_poc_proportional_to_timiiig_flag.

[0112] sps_num_ticks_poc_diff_one_minusl plus 1 spécifiés the number of clock ticks corresponding to a différence of picture order count values equal to 1. The value of 25 sps_num_ticks_poc_diff_one_minusl shall be in lhe range of 0 to 2^Λ32 - 1, inclusive.

When vps_numj.icks_poc_diff_one_minusl is présent in tlie video parameter set referred to by tlie sequence parameter set, sps_nuni_ticks_poc_dtff_oiie_minusl, when présent, shall be equal to sps_num_ticks_poc_diff_one_niinusl.

[0113] The following is an example of an HRD parameters syntax structure modified to 30 solve one or more of tlie above problems (tlie italicized syntax is removed from the

1-IRD parameters syntax structure of HEVC WD9):

«esesm

3I

hrd_parameters( commonlnfPresenlFlag,	Descript
maxNumSubLayersMinusl ) {	or
if( commonlnfPresentFlag ) (
timing info present flag	u(D
if( timing info present flag ) (
num units in tick	432)
time_scale	u(32)
}
...
}

Table 6: Example modified HRD parameters syntax structure [0114] Semantics for syntax éléments removed according to the example modified HRD parameters syntax structure of Table 6 are likewise removed.

[0115] The intra-prediction module 46 may intra-predict a current block, as an alternative to the inter-prcdîction performed by motion estimation unit 42 and motion compensation unit 44, as described above. In particular, intra-prediction module 46 may détermine an intra-prediction mode to use to encode a current block. In some examples, intra-prediction module 46 may encode a current block using various intra10 prédiction modes, e.g., during separate encoding passes, and intra-prediction module 46 (or mode select unit 40, in some examples) may select an appropriate intra-prediction mode to use from the tcsted modes. For example, intra-prediction module 46 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rale15 distortion characteristics among the tested modes. Rate-distortion analysis generally détermines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bit rate (that is, a number of bits) used to produce the encoded block. Intra-prediction module 46 may calculate ratios from the distortions and rates for the various encoded blocks to détermine which intra-prediction mode cxhibits the best rate-distortion value for the block.

[0116] ln any case, after selecting an intra-prediction mode for a block, intra-prediction module 46 may provide information indicative of the selected intra-prediction mode for the block to enlropy encoding unit 56. Entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode in accordance with the techniques of this disclosure. Video encoder 20 may include in the transmilted bitstream configuration data, which may include a plurality of intra-prediction mode index tables and a plurality of modified intra-prediction mode index tables (also referred to as codeword mapping tables), définitions of encoding contexts for various blocks, and indications of a most probable intra-prediction mode, an intra-prediction mode 5 index table, and a modified intra-prediction mode index table to use for each of Üie contexts.

[0117] After prédiction module 41 générâtes the prédictive block for the current video block via either inter-prediction or intra-prediction, video encoder 20 forms a residual video block by subtracting the prédictive block from the current video block. The 10 residual video data in the residual block may be included in one or more TUs and applied to transform module 52. Transform module 52 transforms the residual video data into residual transform coefficients using a transform, such as a discrète cosine transform (DCT) or a conceptually similar transform. Transform module 52 may convert the residual video data from a pixel domain to a transform domain, such as a 15 frequency domain.

[0118] Transform module 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process may reduce the bit depth associated with some or ail of the coefficients. The degree of quantization may be modified by 20 adjusting a quantization parameter. In some examples, quantizalion unit 54 may then perform a scan of the matrix including the quantized transform coefficients. Alternat!vel y, entropy encoding unit 56 may perform the scan.

[0119] Following quantization, entropy encoding unit 56 entropy encodes the quantized transform coefficients. For example, entropy encoding unit 56 may perform context 25 adaptive variable length coding (CAVLC), context adaptive binary arilhmetic coding (CABAC), syntax-based context-adaplive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique. Following the entropy encoding by entropy encoding unit 56, the encodcd bitstream may be transmitted lo video décoder 30, or archived for later transmission or 30 retrieval by video décoder 30. Entropy encoding unit 56 may also entropy encode the motion vectors and the other syntax éléments for the current video slice being coded.

[0120] Inverse quantization unit 58 and inverse transform module 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain for later use as a reference block of a reference picture. Motion

compensation unit 44 may calculate a reference block by adding the residual block to a prédictive block of one of the reference pictures within one of the reference picture lists. Motion compensation unit 44 may also apply one or more interpolation filters to tlie reconstructed residual block to calculate sub-integer pixel values for use in motion 5 estimation. Summer 62 adds the reconstructed residual block to the motion compensated prédiction block produced by motion compensation unit 44 to produce a reference block for storage in reference picture memory 64 (sontelimes calted a decoded picture buffer (DPB)). The reference block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block to inter-predict a block in a 1 o subséquent video frame or picture.

[0121] The video encoder 20 may optionally include a hypothetical référencé décoder (HRD) 57 (illustrated as optional by use of dashed Iines) to clieck cncoded bitstreams generated by éléments of video encoder 20 for conformance to the buffer model defined for the HRD 57. The HRD 57 may check Type I and/or Type II bitstreams or bitstream 15 subsets for HRD conformance. Parameters sets needed for operation of the HRD 57 are signaled by one of two types of HRD parameter sets, NAL HRD parameters and VCL HRD parameters. As described above, the HRD parameter sets may be incorporated within the SPS syntax structure and/or the VPS syntax structure.

[0122] The HRD 57 may test the video blocks and associated syntax éléments 55 for 20 conformance to requirements specified as one or more bitstream conformance tests defined in a video coding spécification, such as HEVC WD9 or a successor spécification such as HEVC WD 10. For example, the HRD 57 may test the encoded bitstream for conformance by processing the syntax éléments 55 to détermine, front the VPS syntax structure or in tlie VUI part of the SPS syntax structure for a coded video 25 sequence, the syntax éléments that define the condition for signaling the number of clock ticks corresponding to a différence of POC values equal to l. If the condition holds according to tlie syntax element values, HRD 57 may détermine the number of clock ticks conesponding to a différence of POC values equal to 1 and use the determined number of clock ticks as input for, e.g., determining CPB underflow or 30 overflow during decoding of encoded pictures included in the cncoded bitstream. Use herein of the term “processing” with regard to a syntax éléments may refer to extracting, decoding and extracting, reading, parsing, and any other serviceable operation or combination of operations to obtain syntax cléments in a form usablc by a dccoder/HRD 57.

[0123] As another example, lhe HRD 57 may test the encoded bitstream for conformance by decoding die encoded bitstream to détermine lhe time scale and dre number of units in a clock tick from a VPS syntax structure of syntax éléments 55 diat encodes die time scale and the number of units in a clock tick syntax éléments at most 5 once in the VPS syntax structure. In some instances, lhe HRD 57 may test die encoded bitstream for conformance by decoding the syntax éléments 55 to détermine the time scale and the number of units in a clock tick from a VU1 syntax structure of the encoded bitstream that encodes the time scale and die number of units in a clock tick syntax éléments at most once in the VUI syntax structure. The time scale and number of units 10 in a clock tick may be signaled other than in an HRD parameters syntax structure incorporated within the VPS and/or VUI syntax structure. The HRD 57 may use the determined time scale and the determined number of units in a dock tick as input for, e.g., determining CPB underflow or overflow during decoding of encoded pictures included in die encoded bitstream.

[0124] According to techniques described herein, the HRD 57 may lest the encoded bitstream for conformance by decoding, from a VPS syntax structure of the syntax éléments 55 for one or inoie coded video sequences, the value for a POC proporlional to timing indication flag. Tlie HRD 57 may additionally, or allernatively, lest an encoded bitstream for conformance by decoding dre value for a POC proportional to timing 20 indication flag in the VPS syntax structure only if the time scale and number of units in a clock tick syntax éléments are also included. The HRD 57 may use lhe determined value of the POC proportional to timing indication flag and the time scale and number of units in a clock tick syntax éléments as input for, e.g., detennining CPB underflow or overflow during decoding of encoded pictures included in die encoded bitstream.

[0125] FIG. 3 is a block diagram illustrating an example video décoder 76 that may implenient die techniques described in this disclosure. In the example of FIG. 3, video décoder 76 includes coded picture buffer (CPB) 78, entropy decoding unit 80, prédiction module 81, inverse quantization unit 86, inverse transformation unit 88, summer 90, and decoded picture buffer (DPB) 92. Prédiction module 81 includes 30 motion compensation unit 82 and inlra prédiction module 84. Video décoder 76 may, in some examples, perforai a decoding pass generally reciprocal to tlie encoding pass described with respect to video encoder 20 from FIG. 2. Video décoder 76 may represent an exaniple instance of video décoder 30 of destination device 14 or of hypolhctical référencé décoder 57 of FIG. 2.

[0126] CPB 78 stores coded pictures from the encoded picture bitstream. In one example, CBP 78 is a first-in first-out buffer containing access units (AU) in decoding order. An AU is set of network abstraction layer (NAL) units that are associated with each otlier according to a specified classification rule, are consecutive in decoding 5 order, and each contain exactly one coded picture. Decoding order is the order in which pictures are decoded, and may differ from the order in which pictures are displayed (i.e., the display order). The operation of the CPB may be specified by a hypothetical référencé décoder (HRD).

[0127] During the decoding process, video décoder 76 receives an encoded video 10 bitstream that represents video blocks of an encoded video slice and associated syntax éléments from video encoder 20. Entropy decoding unit 80 of video décoder 76 décodés the bitstream to gencrate quantized coefficients, motion vectors, and other syntax éléments 55. Entropy decoding unit 80 forwards the motion vectors and other syntax éléments 55 to prédiction module 81. Video décoder 76 may receive the syntax 15 éléments 55 at the video slice level and/or the video block level. The encoded video bitstream may include timing information signaled according to techniques described below. For example, the encoded video bitstream may include a video parameler set (VPS), a sequence parameter set (SPS), or any combination thereof having syntax structures according to techniques described herein to signal parameters for HRD 20 operations.

[0128] When the video slice is coded as an intra-coded (1) slice, intra predicLion module 84 of prédiction module 81 may generate prédiction data for a video block of the current video slice based on a signaled intra prédiction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inler-coded 25 (i.e., B, P or GPB) slice, motion compensation unit 82 of prédiction module 81 produces prédictive blocks for a video block of the current video slice based on the motion vectors and other syntax éléments 55 received from entropy decoding unit 80. The prédictive blocks may be produced from one of the référencé pictures within one of the référencé picture lisls. Video décoder 76 may construct the référencé frame lists, List 0 30 and List 1, using default construction techniques based on référencé pictures stored in DPB 92.

[0129] Motion compensation unit 82 détermines prédiction information for a video block of the current video slice by parsing the motion vectors and other syntax éléments 55, and uses the prédiction information to produce the prédictive blocks for the current

video block being decoded. For example, motion compensation unit 82 uses some of the received syntax éléments 55 to détermine a prédiction mode (e.g., intra- or interprediction) used to code the video blocks of the video slice, an inter-prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of 5 the reference picture lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information to décodé the video blocks in the cun'ent video slice.

[0130] Motion compensation unit 82 may also perform interpolation based on interpolation filters. Motion compensation unit 82 may use interpolation filters as used 10 by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 82 may détermine the interpolation filters used by video encoder 20 from the received syntax éléments 55 and use the interpolation filters to praduce prédictive blocks.

[0131] Inverse quantization unit 86 inverse quantizes, i.e., dc-quanlizes, the quantized 15 transform coefficients provided in the bitstream and decoded by entropy decoding unit

80. The inverse quantization process may include use of a quantization parameter calculated by video encoder 20 for each video block in the video slice to détermine a degree of quantization and, likewïse, a degree of inverse quantization that should be applied. Inverse transform unit 88 applies an inverse transform, e.g., an inverse DCT, 20 an inverse integer transfonn, or a conceptually similar inverse transform process, to the transform coefficients in order to produce residual blocks in the pixel domain.

[0132] After motion compensation unit 82 generates the prédictive block for the current video block based on the motion vectors and other syntax éléments 55, video décoder 76 forms a decoded video block by summing the residual blocks from inverse transform 25 unit 88 with the corresponding prédictive blocks generated by motion compensation unit

82. Summer 90 represents the coniponent or components that perform this sommation operation. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. Other loop filters (either in the coding loop or after the coding loop) may also be used to smooth pixel transitions, or otherwise 30 improve the video quality. The decoded video blocks in a given frarne or picture are then stored in DPB 92, which stores reference pictures used for subséquent motion compensation. DPB 92 also stores decoded video for later présentation on a display device, such as display device 32 of FIG. 1. Like CPB 78, in one cxample, the operation of DPB 92 ntay be specified by the Hypolhetical Reference Décoder (HRD).

[0133] Encoder 20 and décoder 76, as described in this disclosuie, represent examples of devices configured to perform techniques for signaling timing in a video coding process as described in this disclosure. Accordingly, operations described in this disclosure for signaling time may be performed by encoder 20, décoder 76 or both. In some instances, encoder 20 may signal timing information and décoder 76 may receive such timing information, e.g., for using in defining one or more HRD features, characteristics, parameters, or conditions.

[0134] Video décoder 76 may in some instances be a video décoder 76 under test (or VUT). The video décoder 76 may reçoive a représentation of the encoded bitstream generaled by a video encoder 20 to directly signal, in the VPS syntax structure or in the VUI part of the SPS syntax structure of syntax éléments 55 for a coded video sequence, ail syntax éléments that define the condition for signaling a number of clock ticks corresponding to a différence of picture order cotint (POC) values equal to 1. Video décoder 76 may décodé the encodcd bitstream to détermine, from lhe VPS syntax structure or in the VUI part of the SPS syntax structure for a coded video sequence, the syntax éléments that define the condition for signaling tlie number of clock ticks corresponding to a différence of POC values equal to 1. If the condition holds according to the syntax element values, video décoder 76 may detennine the number of clock ticks corresponding to a différence of POC values equal to 1 and use the determined number of clock ticks as input for, e.g., delennining CPB 78 underflow or overflow during decoding of encoded pictures included in the encoded bitstream.

[0135] In another example, the video encoder 20 may receive a représentation of the encoded bitstream generaled by video encoder 20 to signal the time scale and the number of units in a clock tick at most once in each of the VPS and VUI syntax structures of syntax éléments 55 for a given coded video sequence. Tire video décoder 76 may décodé the encoded bitstream to detennine the time scale and the number of units in a clock tick from a VPS syntax structure of the encoded bitstream that encodes lhe time scale and the number of units in a clock tick syntax éléments at most once in the VPS syntax structure. In some instances, the video décoder 76 may test the encoded bitstream for conformance by decoding lhe encoded bitstream to detennine the time scale and the number of units in a clock tick from a VUI syntax structure of the encoded bitstream that encodes (lie time scale and lhe number of units in a clock tick syntax éléments at most once in (lie VUI syntax structure. The time scale and number of units in a clock tick may be signaled other than in an HRD parameters syntax structure φ

incorporated within tlie VPS and/or VUI syntax structure. Video décoder 76 may use tlie determined time scale and tire determined number of units in a clock tick as input for, e.g., determining CPB 78 underflow or overflow during decoding of encoded pictures included in die encoded bitstream.

[0136] In another example, the video décoder 76 may receive a représentation of tlie encoded bitstream generated by video encoder 20 to signai, in a VPS syntax structure of syntax éléments 55 for one or more coded video sequences, a POC proportional to timing indication flag. The video décoder 76 may test the encoded bitstream for conformance by decoding the encoded bitstream to détermine a value for the flag. The video décoder 76 may additionally, or altematively, test an encoded bitstream, generated by video décoder 76 to signal the flag in tlie VPS syntax structure only if tlie lime scale and number of units in a clock tick syntax éléments are also included. Tlie video décoder 76 may use the determined value of the POC proportional to timing indication flag and the time scale and number of units in a clock tick syntax éléments as input for, e.g., determining CPB 78 underflow or overflow during decoding of encoded pictures included in the encoded bitstream.

[0137] FrG. 4 is a block diagram illustrating an exaniple coding structure 100 for a reference picture set. Tlie coding structure 100 includes slices 102A-102E (collectively, “slices 102”). Picture order count 108 associated with the coding structure

100 dénotés the output order of the corresponding slice in the reference picture set. For example, I-slice 102A is to be output first (POC value 0) while b-slice 102B is to be output second (POC value 1). Decoding order 110 associated with the coding structure 100 dénotés die decoding order for tlie corresponding slice in tlie reference picture set. For example, I-slice 102 A is to be output first (decoding order 1) while b-slice 102B is to be output second (decoding order 2).

[0138] Arrow 104 indicates an output time for the pictures along a time continuum t. Time interval 106 represents a time interval corresponding to a différence of picture order count (POC) values equal to 1. The time interval 106 may include a number of clock licks, which may dépend upon the time scale (corresponding, e.g., to an oscillator 30 frequency - such as 27 MHz - that defines a time coordinale system for the signaled information) and the number of time units of a clock operating at the time scale that corresponds to one incrément of a clock tick counter, which is referred to as a “clock tick.” In accordance with techniques described herein, a video encoder 20 may generate a bitstream to directly signal, in the video parameter set (VPS) syntax structure or in the

video usabilily information (VUI) part of tlie sequence parameter set (SPS) syntax structure for a coded video sequence, syntax éléments that define a condition for signaling a number of clock ticks corresponding to a différence of picture order count (POC) values equal to 1.

[0139] FIG. 5 is a flowchart illustrating an example method of operation according to techniques described in this disclosure. A video encoder 20 encodes pictures of a video sequence to generate a coded video sequence (200). The video encoder 20 addilionally generales parameter sets for the coded video sequence. The parameter sets may include parameters encoded according to a sequence parameter set (SPS) syntax structure and/or 10 according to a video parameter set (VPS) syntax structure. According to techniques described herein, tlie video encoder 20 encodes syntax éléments for tlie number of units in a clock tick and tlie time scale directly to the VPS syntax structure and/or directly to tlie SPS syntax structure for the coded video sequence (202). The term “directly indicates üiat such encoding may be generated without incorporating, in tlie VPS syntax 15 structure or SPS syntax structure (as applicable), the syntax cléments for the number of units in a clock tick and the lime scale defined for a separate parameter set syntax structure, such as that corresponding to the hypothelical reference décoder (HRD) parameler set as defined in HEVC WD9.

[0140] In addition, tlie video encoder 20 encodes, directly to the VPS syntax structure and/or SPS syntax structure of tlie coded video sequence, a condition for signaling a number of clock ticks corresponding to a différence of picture order count (POC) values equal to one (204). The condition may include one or more syntax éléments Üiat represent variables for a Boolean formula, in which case video encoder 20 may encode each such syntax element directly to tlie VPS syntax structure and/or SPS syntax 25 structure of the coded video sequence. The video encoder 20 oulpuls tlie coded video sequence and tlie VPS syntax structure and/or the SPS syntax structure for the coded video sequence (206). In some cases, the video encoder 20 outputs these structures lo a HRD of tlie video encoder 20.

[0141] FIGS. 6A-6B aie flowcharts illustrating cxample methods of operation 30 according to techniques described in tliis disclosure. In FIG. 6A, a video encoder 20 encodes pictures of a video sequence to generate a coded video sequence (300). The video encoder 20 additionally generales parameter sets for the coded video sequence. The parameter sets may include parameters encoded according to a video parameler set (VPS) syntax structure. According to techniques described herein, tlie video encoder 20

encodes syntax éléments for the number of units in a clock tick and the time scale directly, and at most once, to a VPS syntax structure for the coded video sequence (302). In some instances, even in cases in which tire VPS syntax structure includes multiple instances of HRD parameters, by encoding the syntax éléments directly to the 5 VPS syntax structure (at most once) and not to the HRD parameter sets (or any other incorporated parameter set syntax structure), tlie VPS syntax structure may include a single syntax element for each of the number of units in a clock tick and the time scale.

The video encoder 20 outputs the coded video sequence and the VPS syntax structure for the coded video sequence (304). In some cases, the video encoder 20 outputs these 10 structures to a HRD of tlie video encoder 20.

[0142] In FIG. 6B, a video encoder 20 encodes pictures of a video sequence to generate a coded video sequence (310). The video encoder 20 additionally generates parameter sets for the coded video sequence. The parameter sets may include parameters encoded according to a video parameter sel (SPS) syntax structure. According to techniques 15 described herein, the video encoder 20 encodes syntax éléments for the number of units in a clock tick and the lime scale directly, and at most once, to a SPS syntax structure for tlie coded video sequence (312). In some instances, even in cases in which the SPS syntax structure includes multiple instances of HRD parameters, by encoding tlie syntax éléments directly to the SPS syntax structure (at most once) and not to the HRD 20 parameter sels (or any other incorporated parameter set syntax structure), the SPS syntax structure may include a single syntax element for each of the number of units in a clock tick and the time scale. The video encoder 20 outputs the coded video sequence and lhe SPS syntax structure for the coded video sequence (314). In some cases, the video encoder 20 outputs these structures to a HRD of the video encoder 20. In some 25 instances, video encoder 20 may encode lhe syntax éléments for lhe number of units in a clock tick and the time scale to both a VPS syntax structure and an SPS syntax structure for the coded video sequence.

[0143] FIG. 7 is a flowehart illustrating an example method of operation according to techniques described in this disclosure. A video encoder 20 encodes pictures of a video 30 sequence to generate a coded video sequence (400). The video encoder 20 additionally generates parameter sets for the coded video sequence. The parameter sets may include parameters encoded according to a video parameter set (VPS) syntax structure. If timing information is to be included, e.g., for defining a HRD buffering model (YES branch of 402), tlie video encoder 20 encodes·, directly to A VPS syntax structure for lhe

coded video sequence, a syntax element having a value that spécifiés whether the picture order count (POC) value for each picture in the coded video sequence that is not the first picture in die coded video sequence, in decoding order, is proportional to the output time of the picture relative to the output time of the first picture in the coded 5 video sequence (404). The syntax element may be seniantically similar to the poc_proportional_to_timing_flag defined by HEVC WD9. The timing information may represent the number of units in a clock tick and the time scale.

[0144] If the value of the syntax element is true (YES branch of 406), the video encoder 20 also encodes a syntax element for the number of clock ticks corresponding to a 10 différence of picture order count values equal to one (408). Because the video encoder encodes the syntax éléments to the VPS, the values of the syntax éléments may appiy to ail layers or ali possible bitstream subsets of a scalable video bitstream, for the VPS represents the highest layer parameter set and describes the overall characteristics of coded picture sequences.

[0145] If the timing information is not to be included in the VPS syntax structure (NO branch of 402), the video encoder 20 encodes neither the syntax element for indicating the POC is proportional to the timing information nor the syntax element for the number of clock. ticks conesponding to a différence of picture order count values equal to one. If the POC is not proportional to the timing information (i.e., the value is false) (NO branch of 406), the video encoder 20 does not encode the syntax element for the number of clock ticks corresponding to a différence of picture order count values equal to one.

[0146] The video encoder 20 outputs the coded video sequence and the VPS syntax structure for the coded video sequence (410). In some cases, the video encoder 20 outputs these structures to a HRD of the video encoder 20.

[0147] FIG. 8 is a flowehart illustrating an example method of operation according to techniques described in this disclosure. A video décoder device 30 or hypothetical reference décoder 57 of a video encoder device 20 (hereinafter, “the décoder”) receives a coded video sequence and a video parameter set (VPS) syntax structure and/or a sequence parameter set (SPS) syntax structure for the coded video sequence (500). The coded video sequence and/or the syntax structure(s) may bc encoded to a bitstream that includes one or more encoded pictures.

[0148] The décoder processes Lhe VPS syntax structure and/or the SPS syntax structure to extract a syntax element that spécifiés, direclly in the VPS syntax structure and/or tlie SPS syntax structure, a condition for signaling a number of clock ticks corresponding to

a différence of picture order count (POC) values equal to one (502). The condition may include one or more syntax éléments Lhat represent variables for a Boolean formula, in which case the décoder may process each such syntax element directly from the VPS syntax structure and/or SPS syntax structure of the coded video sequence.

[0149] The décoder additionally processes the VPS syntax structure and/or the SPS syntax structure to extract syntax éléments for the number of units in a clock tick and the time scale directly from the VPS syntax structure and/or directly from the SPS syntax structure for the coded video sequence (504). The décoder may then verify conformance of the coded video sequence to a video buffering model Üiat is defined, at 10 least in part, by the values for the condition, the number of units in a clock tick, and the time scale as extracted from the VPS syntax structure and/or the SPS syntax structure and as read from the corresponding syntax éléments (506).

[0150] FIGS. 9A-9B are floweharts illustrating example methods of operation according to techniques described in this disclosure. In FIG. 9A, a video décoder device 15 30 or hypolhetical reference décoder 57 of a video encoder device 20 (hereinafter, “tire décoder”) receives a coded video sequence and a video parameter set (VPS) syntax structure for the coded video sequence (600). The coded video sequence and/or the VPS syntax structure maÿ be encoded to a bitstream that includes one or more encoded pictures.

[0151] According to techniques described herein, the décoder processcs the VPS syntax structure to extract syntax éléments for the number of units in a clock tick and tire time scale that aie occur directly, and at most once, in the VPS syntax structure For the coded video sequence (602). The décoder may then verify conformance of the coded video sequence to a video buffering model that is defined, at least in part, by the values for the number of units in a clock tick and the lime scale as extracted from the VPS syntax structure and as read from the corresponding syntax éléments (604).

[0152] In FIG. 9B, the décoder receives a coded video sequence and a video parameter set (SPS) syntax structure for the coded video sequence (610). The coded video sequence and/or the SPS syntax structures may be encoded to a bitstream diat includes 30 one or more encoded pictures.

[0153] According to techniques described herein, the décoder processes the SPS syntax structure to extract syntax éléments For the number of units in a clock tick and the time scale tliaL are occur directly, and at most once, in the SPS syntax structure for the coded video sequence (612). The décoder may then verify conformance of Üie coded video

sequence to a video buffering model that is defined, at least in part, by tlie values for the number of unils in a clock tick and die lime scale as extracted from tlie SPS syntax structure and as read from the corresponding syntax éléments (614).

[0154] FIG. 10 is a flowchart illustrating an example method of operation according to 5 techniques described in tliis disclosure. In FIG. 10, a video décoder device 30 or hypothetical reference décoder 57 of a video encoder device 20 (hereinafter, “the décoder”) receives a coded video sequence and a video parameter set (VPS) syntax structure for the coded video sequence (700). The coded video sequence and/or tlie VPS syntax structure may be encoded to a bitstream that includes one or more encoded 10 picluies.

[0155] The décoder processes tlie VPS syntax structure to extract a syntax élément that spécifiés whether tlie picture order count value for each picture in tlie coded video sequence that is not the first picture in tlie coded video sequence, in decoding order, is proportional to lhe output Lime of the picture relative to the output time of tlie first 15 picture in tlie coded video sequence (702). If die value for the syntax element is true, then die décoder further processes the VPS syntax structure to extract a syntax element for tlie number of clock ticks corresponding to a différence of picture order count values equal to one (706). The décoder may then verify conformance of the coded video sequence to a video buffering model that is defined, at least in part, by the value for tlie 20 number of clock ticks corresponding to a différence of picture order count values equal to one extracted from the VPS syntax structure and as read from the corresponding syntax element (708).

[0156] In one or more examples, lhe fonctions described may be implemented in hardware, software, firmwarc, or any combination thereof. If implemented in software, 25 the fonctions may be stored on or transmilted over, as one or niotc 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 média, or communication media including any medium that facilitâtes transfer of a computer program from one place to 30 another, e.g., according to a communication protocol. In tliis manner, computerreadable media generally may correspond to (I) tangible compuler-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 thaï can be accessed by one or more computers or one or more processors to relrieve instructions, code and/or

data structures for implémentation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0157] 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 s disk storage, or other magnetic storage devices, Flash memory, or any other medium that can be used to store desired program code in tire 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 10 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 définition of medium. It shouid be understood, however, thaï computer-readable storage media and data storage media do not include connections, carrier waves, signais, or other transient 15 media, but are inslead directed to non-transienl, tangible storage media. Disk and dise, as used herein, includes compact dise (CD), laser dise, optical dise, digital versatile dise (DVD), floppy disk and Blu-ray dise, where disks usually reproduce data magnetically, while dises reproduce data optically with lasers. Combinations of the above shouid also be included within the scope of computer-readable media.

[0158] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application spécifie integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other équivalent integrated or discrète logic circuitry. Accordingly, the term “processor, as used herein may refer to any of the foregoing structure or any other structure suitable for 25 implémentation of the techniques described herein. In addition, in some aspects, die functionality described herein may be provided within dedicaled hardware and/or software modules confîgured for encoding and decoding, or incorporated in a combined codée. Also, die techniques could be fully implemented in one or more circuits or logic éléments.

[0159] 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 sel). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices confîgured 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 codée 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 linnware.

[0160] Various examples hâve been described. These and other examples are within the 5 scope of the following daims.

receiving a coded video sequence comprising encoded pictures of a video sequence; and receiving timing parameters for the coded video sequence that include an indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in tire coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time 10 of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure referenced by the coded video sequence.

Claims (47)

1. 2. The method of claim 1, wherein the indication comprises a vps_poc_propoitional_to_timing_flag syntax element.
2. 3. The method of claim 1, wherein receiving timing parameters for the coded video sequence further comprises:

   only if the indication indicates the POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to the

   20 decoding order is proportional to the output time of the picture relative to the output time of the first picture in the coded video sequence, receiving a number of clock ticks that correspond to a différence of POC values equal to one in the VPS syntax structure.
3. 4. The method of claim 1,

   25 wherein receiving the indication comprises receiving the indication only if syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax structure.
4. 5. The method of claim 1, wherein receiving the timing parameters for the coded

   30 video sequence further comprises:

   receiving an indication in the VPS syntax structure of whether syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax structure.
5. 6. The method of claim 5, wherein the indication in tlie VPS syntax structure of whether syntax éléments for the time scale and the number of units in a clock tick are présent in the VPS syntax structure comprises a vps_timing_info_present_flag syntax element.
6. 7. The method of claim l, wherein receiving the timing parameters for the coded video sequence further comprises:

   only if tlie POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to the decoding order is proportional 10 to Üie output time of the picture relative to the output time of the first picture in the coded video sequence, receiving a number of clock ticks that correspond to a différence of POC values equal to one in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by the coded video sequence.

   15
7. 8. The method of claim 1, wherein tlie indication comprises a first indication, and wherein receiving the timing parameters for üie coded video sequence further comprises:

   only if syntax éléments for a time scale and a number of units in a clock tick are présent in a video usability information (VUI) part of a sequence parameter set (SPS) 20 syntax structure referenced by the coded video sequence, receiving a second indication of whether the POC value for each picture in tlie coded video sequence that is not tlie first picture in the coded video sequence according to the decoding order is proportional to the output time of the picture relative to the output time of tlie first picture in the coded video sequence in the VUI part of the SPS syntax structure.
8. 9. The method of claim 8, wherein the second indication comprises a sps_poc_proportionaLto_timing_flag syntax element.
9. 10. Tlie method of claim 1, wherein receiving the timing parameters for tlie coded

   30 video sequence further comprises:

   receiving an indication in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by the coded video sequence of whether syntax éléments for a time scale and a number of units in a clock tick are présent in the VUI part of tlie SPS syntax structure.

   1L The method of claim 10, wherein the indication in the VUI part of SPS syntax structure referenced by the coded video sequence of wheüier syntax éléments for lire time scale and the number of units in a clock tick are présent in the VUI part of the SPS syntax structure comprises a sps_timing_info_present_flag syntax element.
10. 12. The method of claim 1, wherein receiving tire coded video sequence comprises receiving a coded bitstream comprising a sequence of bits that forms a représentation of the encoded pictures, the method further comprising:

    verifying conformance of the bitstream to a video buffering model of a coded picture buffer and a decoded picture buffer defïned, at least in part, by tire indication.
11. 13. The method of claim 1, wherein the timing paramelers comprise timing parameters for hypothetical reference decoding operations.
12. 14. A method of encoding video data, the method comprising:

    encoding pictures of a video sequence to generate a coded video sequence comprising the encoded pictures; and signaling timing parameters for the coded video sequence by signaling an indication of whether a picture order count (POC) value for each picture in the coded video sequence thaï is not a first picture in tire coded video sequence according to a decoding order is proportional lo an output time of the picture relative to an output time of lhe first picture in the coded video sequence in a video parameter set (VPS) syntax structure referenced by lhe coded video sequence.
13. 15. The method of claim 14, wherein the indication comprises a vps_poc_proportional_to_timing_flag syntax element.
14. 16. The method of claim 14, wherein signaling the timing parameters for the coded video sequence further comprises:

    only if the POC value for each picture in the coded video sequence diat is not the first picture in tire coded video sequence according to the decoding order is proportional lo lhe oulput time of the picture relative to lhe oulpul time of the first picture in the coded video sequence, signaling a number of clock ticks thaL correspond to a différence of POC values equal lo one in the VPS syntax structure.
15. 17. The method of claim 14, wherein signaling the indication comprises signaling the indication only if syntax éléments for a time scale and a number of units in a clock tick aie présent in tlie VPS syntax structure.
16. 18. The method of claim 14, wherein signaling tlie timing parameters for the coded video sequence further comprises:

    signaling an indication in the VPS syntax structure of whetlier syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax 10 structure.
17. 19. The method of claim 18, wherein tlie indication in the VPS syntax structure of whether syntax éléments for the time scale and the number of units in a clock tick are présent in the VPS syntax structure comprises a vps_timingjnfo_present_flag syntax

    15 element.
18. 20. The method of claim 14, wherein signaling tlie timing parameters for tlie coded video sequence furdier comprises:

    only if the POC value for each picture in the coded video sequence that is not the

    20 first picture in the coded video sequence according to tlie decoding order is proportional to tlie output time of the picture relative to the output lime of the first picture in the coded video sequence, signaling a number of clock licks that correspond to a différence of POC values equal to one in a video usability information (VUl) part of a sequence parameter set (SPS) syntax structure referenced by the coded video sequence.
19. 21. Tlie method of claim 14, wherein the indication comprises a first indication, and wherein signaling the timing parameters for the coded video sequence further comprises:

    only if syntax éléments for a time scale and a number of units in a clock tick are

    5 présent in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by tlie coded video sequence, signaling a second indication of whether lhe POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to tlie decoding order is proportional to the output time of the picture relative to tlie output time of the first picture in the

    10 coded video sequence in the VUI part of the SPS syntax structure.
20. 22. Tlie method of claim 21, wherein the second indication comprises a sps_poc_proportional_to_timing_flag syntax element.

    15
21. 23. The method of claim 14, wherein signaling the timing parameters for the coded video sequence further comprises:

    signaling an indication in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by lhe coded video sequence of whether syntax éléments for a lime scale and a number of units in a clock tick are présent in the 20 VUI part of the SPS syntax structure.
22. 24. Tlie method of claim 23, wherein tlie indication in the VUI part of SPS syntax structure referenced by the coded video sequence of whether syntax éléments for the time scale and tlie number of units in a clock tick are présent in tlie VUI part of lhe SPS 25 syntax structure comprises a sps_timing_mfo_present_flag syntax element.
23. 25. A device for processing video data, the device comprising:

    a processor configured to:

    receive a coded video sequence comprising encoded pictures of a video sequence; and

    5 receive timing parameters for the coded video sequence tliaL include an indication of whether a picture order count (POC) value for each picture in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to an output time of the picture relative to an output time of the first picture in the coded video sequence in a video parameter set (VPS) syntax

    10 structure referenced by the coded video sequence.
24. 26. The device of claim 25, wherein the indication comprises a vps_poc_proportional_to_timing_flag syntax element.

    15
25. 27. The device of claim 25, wherein to receive timing parameters for the coded video sequence the processor is further configured to:

    only if tlie indication indicatcs tlie POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to the decoding order is proportional to the output time of the picture relative to tlie output

    20 time of the first picture in the coded video sequence, receive a number of clock ticks that correspond to a différence of POC values equal to one in tlie VPS syntax structure.
26. 28. Tlie device of claim 25, wherein to receive tlie indication the processor is further configured to receive

    25 the indication only if syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax structure.
27. 29. Tlie device of claim 25, wherein lo receive the timing parameters for the coded video sequence the processor is further configured to receive an indication in tlie VPS
28. 30 syntax structure of whether syntax éléments for a lime scale and a number of units in a clock tick are présent in the VPS syntax structure.

    30. Tlie device of claim 29, wherein the indication in tlie VPS syntax structure of whether syntax éléments for the time scale and the number of units in a clock tick are présent in the VPS syntax structure comprises a vps_timing_info_present_flag syntax element.
29. 31. The device of claim 25, wherein to receive the timing parameters for the coded video sequence the processor is further configured to:

    only if the POC value for each picture in the coded video sequence that is not the first picture in tlie coded video sequence according to tlie decoding order is proportional 10 to the output time of lhe picture relative to the output time of tlie first picture in the coded video sequence, receive, in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by tlie coded video sequence, a number of clock ticks that correspond to a différence of POC values equal to one.

    15
30. 32. The device of claim 25, wherein tlie indication comprises a first indication, and wherein to receive the timing parameters for the coded video sequence tlie processor is further configured to:

    only if syntax éléments for the time scale and the number of units in a clock tick are présent in a video usability information (VUI) part of a sequence parameter set 20 (SPS) syntax structure referenced by the coded video sequence, receive a second indication of whether tlie POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to lhe decoding order is proportional to the output time of tlie picture relative to the output time of the first picture in the coded video sequence in the VUI part of the SPS syntax structure.
31. 33. The device of claim 32, wherein the second indication comprises a sps_poc_piOportional_to_timing_flag syntax element.
32. 34. The device of claim 25, wherein to receive the timing parameters for tlie coded

    30 video sequence the processor is further configured to:

    receive an indication in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by lhe coded video sequence of whether syntax éléments for a time scale and a number of units in a clock tick are présent in tlie VUI part of tlie SPS syntax structure.

    3û. The device of claim 34, wherein tlie indication in the VUI part of SPS syntax structure referenced by die coded video sequence of whether syntax éléments for lhe time scale and the number of units in a clock tick are présent in the VUI part of the SPS syntax structure comprises a sps_timing_infb_present_flag syntax element.
33. 36. The device of claim 25, wherein to receive the coded video sequence tlie processor is further configured to:

    receive a coded bitstream comprising a sequence of bits thaï forms a représentation of the encoded pictures; and verify conformance of the bitstream to a video buffering model of a coded picture buffer and a decoded picture buffer defined, at least in part, by the indication.
34. 37. Tlie device of claim 25, wherein the timing parameters comprise timing parameters for hypothetical reference decoding operations.
35. 38. A device for encoding video data, the device comprising:

    a processor configured to:

    encode pictures of a video sequence to generale a coded video sequence comprising the encoded pictures; and signal timing parameters for the coded video sequence by signaling an indication of whether a picture order count (POC) value l'or each picture in lhe coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportional to ail output time of tlie picture relative to ail output lime of the first picture in tlie coded video sequence in a video parameter set (VPS) syntax structure referenced by the coded video sequence.
36. 39. The device of claim 38, wherein lhe indication comprises a vps_poc_piOportional_to_timing_flag syntax element.
37. 40. Tlie device of claim 38, wherein to signal tlie timing parameters for the coded video sequence the processor is further configured to:

    only if the POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to the decoding order is proportional 5 to the output time of tlie picture relative to the output lime of tlie first picture in tlie coded video sequence, signal a number of clock ticks tliat correspond to a différence of POC values equal to one in the VPS syntax structure.
38. 41. The device of claim 38,

    10 wherein to signal the indication the processor is further configured to signal the indication only if syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax structure.
39. 42. The device of claim 38, wherein to signal tlie timing parameters for the coded

    15 video sequence further tlie processor is further configured to:

    signal an indication in the VPS syntax structure of whether syntax éléments for a time scale and a number of units in a clock tick are présent in the VPS syntax structure.
40. 43. The device of claim 42, wherein tlie indication in the VPS syntax structure of

    20 whether syntax éléments for the lime scale and the number of units in a clock tick are présent in tlie VPS syntax structure comprises a vps_timing_info_present_flag syntax element.
41. 44. The device of claim 38, wherein to signal the timing parameters for tlie coded

    25 video sequence the processor is further configured to:

    only if the POC value for each picture in the coded video sequence lliat is not the first picture in tlie coded video sequence according to the decoding order is proportional to the output time of tlie picture relative lo the output time of tlie first picture in the coded video sequence, signal a number of clock ticks tliat correspond to a différence of 30 POC values equal to one in a video usabilily information (VUI) part of a sequence parameter set (SPS) syntax structure reterenced by the coded video sequence.
42. 45. The device of claim 38, wherein the indication comprises a first indication, and wherein to signal the timing parameters for the coded video sequence the processor is further configured to:

    only if syntax éléments for a time scale and a number of units in a clock tick are

    5 présent in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by the coded video sequence, signal a second indication of whelher the POC value for each picture in the coded video sequence that is not the first picture in the coded video sequence according to the decoding order is proportional to the output time of the picture relative to the output time of the first picture in die coded 10 video sequence in the VUI part of the SPS syntax structure.
43. 46. The device of claim 45, wherein the second indication comprises a sps_poc_proportional_to_timing_flag syntax element.

    15
44. 47. The device of claim 38, wherein to signal the timing parameters for the coded video sequence the processor is further configured to:

    signal an indication in a video usability information (VUI) part of a sequence parameter set (SPS) syntax structure referenced by die coded video sequence of whelher syntax éléments for a time scale and a number of units in a clock tick are présent in the 20 VUI part of the SPS syntax structure.
45. 48. The device of claim 47, wherein the indication in the VUI part of SPS syntax structure referenced by the coded video sequence of whether syntax éléments for the time scale and the number of units in a clock tick are présent in the VUI part of the SPS 25 syntax structure comprises a sps_timing_info_present_flag syntax element.
46. 49. A device for processing video data comprising:

    means for receiving a coded video sequence comprising encoded pictures of a video sequence; and means for receiving timing parameters for the coded video sequence that include

    5 an indication of whether a picture order count (POC) value for each piclure in the coded video sequence that is not a first picture in the coded video sequence according to a decoding order is proportionaî to an output time of the picture relative to an output time of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure refevenced by the coded video sequence.
47. 50. A non-transitory computer readable storage medium sioring instructions for processing video data that upon execution by one or more processors cause the one or more processors to:

    receive a coded video sequence comprising encoded pictures of a video

    15 sequence; and receive timing parameters for the coded video sequence that include an indication of whether a piclure order count (POC) value for each picture in the coded video sequence that is not a first picture in lhe coded video sequence according to a decoding order is proportionaî to an output lime of tire picture relative to an output time 20 of the first picture in the coded video sequence in a video parameter set (VPS) syntax structure refevenced by lhe coded video sequence.