idnits 2.17.1 draft-ietf-payload-rtp-h265-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 2 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (April 14, 2015) is 3297 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '0' on line 1744 == Unused Reference: 'RFC6190' is defined on line 3845, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-mmusic-sdp-bundle-negotiation' is defined on line 3876, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. 'HEVC' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) == Outdated reference: A later version (-11) exists of draft-ietf-avtcore-rtp-multi-stream-05 == Outdated reference: A later version (-54) exists of draft-ietf-mmusic-sdp-bundle-negotiation-02 == Outdated reference: A later version (-08) exists of draft-ietf-avtext-rtp-grouping-taxonomy-02 -- Obsolete informational reference (is this intentional?): RFC 2326 (Obsoleted by RFC 7826) -- Obsolete informational reference (is this intentional?): RFC 5117 (Obsoleted by RFC 7667) Summary: 1 error (**), 0 flaws (~~), 7 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Y.-K. Wang 2 Internet Draft Qualcomm 3 Intended status: Standards track Y. Sanchez 4 Expires: October 2015 T. Schierl 5 Fraunhofer HHI 6 S. Wenger 7 Vidyo 8 M. M. Hannuksela 9 Nokia 10 April 14, 2015 12 RTP Payload Format for High Efficiency Video Coding 13 draft-ietf-payload-rtp-h265-09.txt 15 Abstract 17 This memo describes an RTP payload format for the video coding 18 standard ITU-T Recommendation H.265 and ISO/IEC International 19 Standard 23008-2, both also known as High Efficiency Video Coding 20 (HEVC) and developed by the Joint Collaborative Team on Video 21 Coding (JCT-VC). The RTP payload format allows for packetization 22 of one or more Network Abstraction Layer (NAL) units in each RTP 23 packet payload, as well as fragmentation of a NAL unit into 24 multiple RTP packets. Furthermore, it supports transmission of 25 an HEVC bitstream over a single as well as multiple RTP streams. 26 When multiple RTP streams are used, a single or multiple 27 transports may be utilized. The payload format has wide 28 applicability in videoconferencing, Internet video streaming, and 29 high bit-rate entertainment-quality video, among others. 31 Status of this Memo 33 This Internet-Draft is submitted to IETF in full conformance with 34 the provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF), its areas, and its working groups. Note that 38 other groups may also distribute working documents as Internet- 39 Drafts. 41 Internet-Drafts are draft documents valid for a maximum of six 42 months and may be updated, replaced, or obsoleted by other 43 documents at any time. It is inappropriate to use Internet- 44 Drafts as reference material or to cite them other than as "work 45 in progress." 47 The list of current Internet-Drafts can be accessed at 48 http://www.ietf.org/ietf/1id-abstracts.txt. 50 The list of Internet-Draft Shadow Directories can be accessed at 51 http://www.ietf.org/shadow.html. 53 This Internet-Draft will expire on October 14, 2015. 55 Copyright and License Notice 57 Copyright (c) 2015 IETF Trust and the persons identified as the 58 document authors. All rights reserved. 60 This document is subject to BCP 78 and the IETF Trust's Legal 61 Provisions Relating to IETF Documents 62 (http://trustee.ietf.org/license-info) in effect on the date of 63 publication of this document. Please review these documents 64 carefully, as they describe your rights and restrictions with 65 respect to this document. Code Components extracted from this 66 document must include Simplified BSD License text as described in 67 Section 4.e of the Trust Legal Provisions and are provided 68 without warranty as described in the Simplified BSD License. 70 Table of Contents 72 Abstract.........................................................1 73 Status of this Memo..............................................1 74 Table of Contents................................................3 75 1 Introduction...................................................5 76 1.1 Overview of the HEVC Codec................................5 77 1.1.1 Coding-Tool Features.................................5 78 1.1.2 Systems and Transport Interfaces.....................7 79 1.1.3 Parallel Processing Support.........................14 80 1.1.4 NAL Unit Header.....................................16 81 1.2 Overview of the Payload Format...........................18 82 2 Conventions...................................................18 83 3 Definitions and Abbreviations.................................19 84 3.1 Definitions..............................................19 85 3.1.1 Definitions from the HEVC Specification.............19 86 3.1.2 Definitions Specific to This Memo...................21 87 3.2 Abbreviations............................................23 88 4 RTP Payload Format............................................24 89 4.1 RTP Header Usage.........................................24 90 4.2 Payload Header Usage.....................................27 91 4.3 Transmission Modes.......................................27 92 4.4 Payload Structures.......................................29 93 4.4.1 Single NAL Unit Packets.............................29 94 4.4.2 Aggregation Packets (APs)...........................30 95 4.4.3 Fragmentation Units (FUs)...........................35 96 4.4.4 PACI packets........................................38 97 4.4.4.1 Reasons for the PACI rules (informative).......41 98 4.4.4.2 PACI extensions (Informative)..................42 99 4.5 Temporal Scalability Control Information.................43 100 4.6 Decoding Order Number....................................45 101 5 Packetization Rules...........................................47 102 6 De-packetization Process......................................48 103 7 Payload Format Parameters.....................................51 104 7.1 Media Type Registration..................................51 105 7.2 SDP Parameters...........................................77 106 7.2.1 Mapping of Payload Type Parameters to SDP...........77 107 7.2.2 Usage with SDP Offer/Answer Model...................78 108 7.2.3 Usage in Declarative Session Descriptions...........87 109 7.2.4 Parameter Sets Considerations.......................89 110 7.2.5 Dependency Signaling in Multi-Stream Mode...........89 111 8 Use with Feedback Messages....................................89 112 8.1 Picture Loss Indication (PLI)............................90 113 8.2 Slice Loss Indication (SLI)..............................90 114 8.3 Reference Picture Selection Indication (RPSI)............91 115 8.4 Full Intra Request (FIR).................................92 116 9 Security Considerations.......................................93 117 10 Congestion Control...........................................94 118 11 IANA Consideration...........................................95 119 12 Acknowledgements.............................................95 120 13 References...................................................96 121 13.1 Normative References....................................96 122 13.2 Informative References..................................97 123 14 Authors' Addresses...........................................99 125 1 Introduction 127 1.1 Overview of the HEVC Codec 129 High Efficiency Video Coding [HEVC], formally known as ITU-T 130 Recommendation H.265 and ISO/IEC International Standard 23008-2 131 was ratified by ITU-T in April 2013 and reportedly provides 132 significant coding efficiency gains over H.264 [H.264]. 134 As both H.264 [H.264] and its RTP payload format [RFC6184] are 135 widely deployed and generally known in the relevant implementer 136 communities, frequently only the differences between those two 137 specifications are highlighted in non-normative, explanatory 138 parts of this memo. Basic familiarity with both specifications 139 is assumed for those parts. However, the normative parts of this 140 memo do not require study of H.264 or its RTP payload format. 142 H.264 and HEVC share a similar hybrid video codec design. 143 Conceptually, both technologies include a video coding layer 144 (VCL), which is often used to refer to the coding-tool features, 145 and a network abstraction layer (NAL), which is often used to 146 refer to the systems and transport interface aspects of the 147 codecs. 149 1.1.1 Coding-Tool Features 151 Similarly to earlier hybrid-video-coding-based standards, 152 including H.264, the following basic video coding design is 153 employed by HEVC. A prediction signal is first formed either by 154 intra or motion compensated prediction, and the residual (the 155 difference between the original and the prediction) is then 156 coded. The gains in coding efficiency are achieved by 157 redesigning and improving almost all parts of the codec over 158 earlier designs. In addition, HEVC includes several tools to 159 make the implementation on parallel architectures easier. Below 160 is a summary of HEVC coding-tool features. 162 Quad-tree block and transform structure 164 One of the major tools that contribute significantly to the 165 coding efficiency of HEVC is the usage of flexible coding blocks 166 and transforms, which are defined in a hierarchical quad-tree 167 manner. Unlike H.264, where the basic coding block is a 168 macroblock of fixed size 16x16, HEVC defines a Coding Tree Unit 169 (CTU) of a maximum size of 64x64. Each CTU can be divided into 170 smaller units in a hierarchical quad-tree manner and can 171 represent smaller blocks down to size 4x4. Similarly, the 172 transforms used in HEVC can have different sizes, starting from 173 4x4 and going up to 32x32. Utilizing large blocks and transforms 174 contribute to the major gain of HEVC, especially at high 175 resolutions. 177 Entropy coding 179 HEVC uses a single entropy coding engine, which is based on 180 Context Adaptive Binary Arithmetic Coding (CABAC), whereas H.264 181 uses two distinct entropy coding engines. CABAC in HEVC shares 182 many similarities with CABAC of H.264, but contains several 183 improvements. Those include improvements in coding efficiency 184 and lowered implementation complexity, especially for parallel 185 architectures. 187 In-loop filtering 189 H.264 includes an in-loop adaptive deblocking filter, where the 190 blocking artifacts around the transform edges in the 191 reconstructed picture are smoothed to improve the picture quality 192 and compression efficiency. In HEVC, a similar deblocking filter 193 is employed but with somewhat lower complexity. In addition, 194 pictures undergo a subsequent filtering operation called Sample 195 Adaptive Offset (SAO), which is a new design element in HEVC. 196 SAO basically adds a pixel-level offset in an adaptive manner and 197 usually acts as a de-ringing filter. It is observed that SAO 198 improves the picture quality, especially around sharp edges 199 contributing substantially to visual quality improvements of 200 HEVC. 202 Motion prediction and coding 204 There have been a number of improvements in this area that are 205 summarized as follows. The first category is motion merge and 206 advanced motion vector prediction (AMVP) modes. The motion 207 information of a prediction block can be inferred from the 208 spatially or temporally neighboring blocks. This is similar to 209 the DIRECT mode in H.264 but includes new aspects to incorporate 210 the flexible quad-tree structure and methods to improve the 211 parallel implementations. In addition, the motion vector 212 predictor can be signaled for improved efficiency. The second 213 category is high-precision interpolation. The interpolation 214 filter length is increased to 8-tap from 6-tap, which improves 215 the coding efficiency but also comes with increased complexity. 216 In addition, the interpolation filter is defined with higher 217 precision without any intermediate rounding operations to further 218 improve the coding efficiency. 220 Intra prediction and intra coding 222 Compared to 8 intra prediction modes in H.264, HEVC supports 223 angular intra prediction with 33 directions. This increased 224 flexibility improves both objective coding efficiency and visual 225 quality as the edges can be better predicted and ringing 226 artifacts around the edges can be reduced. In addition, the 227 reference samples are adaptively smoothed based on the prediction 228 direction. To avoid contouring artifacts a new interpolative 229 prediction generation is included to improve the visual quality. 230 Furthermore, discrete sine transform (DST) is utilized instead of 231 traditional discrete cosine transform (DCT) for 4x4 intra 232 transform blocks. 234 Other coding-tool features 236 HEVC includes some tools for lossless coding and efficient screen 237 content coding, such as skipping the transform for certain 238 blocks. These tools are particularly useful for example when 239 streaming the user-interface of a mobile device to a large 240 display. 242 1.1.2 Systems and Transport Interfaces 244 HEVC inherited the basic systems and transport interfaces 245 designs, such as the NAL-unit-based syntax structure, the 246 hierarchical syntax and data unit structure from sequence-level 247 parameter sets, multi-picture-level or picture-level parameter 248 sets, slice-level header parameters, lower-level parameters, the 249 supplemental enhancement information (SEI) message mechanism, the 250 hypothetical reference decoder (HRD) based video buffering model, 251 and so on. In the following, a list of differences in these 252 aspects compared to H.264 is summarized. 254 Video parameter set 256 A new type of parameter set, called video parameter set (VPS), 257 was introduced. For the first (2013) version of [HEVC], the 258 video parameter set NAL unit is required to be available prior to 259 its activation, while the information contained in the video 260 parameter set is not necessary for operation of the decoding 261 process. For future HEVC extensions, such as the 3D or scalable 262 extensions, the video parameter set is expected to include 263 information necessary for operation of the decoding process, e.g. 264 decoding dependency or information for reference picture set 265 construction of enhancement layers. The VPS provides a "big 266 picture" of a bitstream, including what types of operation points 267 are provided, the profile, tier, and level of the operation 268 points, and some other high-level properties of the bitstream 269 that can be used as the basis for session negotiation and content 270 selection, etc. (see Section 7.1). 272 Profile, tier and level 274 The profile, tier and level syntax structure that can be included 275 in both VPS and sequence parameter set (SPS) includes 12 bytes of 276 data to describe the entire bitstream (including all temporally 277 scalable layers, which are referred to as sub-layers in the HEVC 278 specification), and can optionally include more profile, tier and 279 level information pertaining to individual temporally scalable 280 layers. The profile indicator indicates the "best viewed as" 281 profile when the bitstream conforms to multiple profiles, similar 282 to the major brand concept in the ISO base media file format 283 (ISOBMFF) [ISOBMFF] and file formats derived based on ISOBMFF, 284 such as the 3GPP file format [3GPPFF]. The profile, tier and 285 level syntax structure also includes the indications of whether 286 the bitstream is free of frame-packed content, whether the 287 bitstream is free of interlaced source content and free of field 288 pictures, i.e. contains only frame pictures of progressive 289 source, such that clients/players with no support of post- 290 processing functionalities for handling of frame-packed or 291 interlaced source content or field pictures can reject those 292 bitstreams. 294 Bitstream and elementary stream 296 HEVC includes a definition of an elementary stream, which is new 297 compared to H.264. An elementary stream consists of a sequence 298 of one or more bitstreams. An elementary stream that consists of 299 two or more bitstreams has typically been formed by splicing 300 together two or more bitstreams (or parts thereof). When an 301 elementary stream contains more than one bitstream, the last NAL 302 unit of the last access unit of a bitstream (except the last 303 bitstream in the elementary stream) must contain an end of 304 bitstream NAL unit and the first access unit of the subsequent 305 bitstream must be an intra random access point (IRAP) access 306 unit. This IRAP access unit may be a clean random access (CRA), 307 broken link access (BLA), or instantaneous decoding refresh (IDR) 308 access unit. 310 Random access support 312 HEVC includes signaling in NAL unit header, through NAL unit 313 types, of IRAP pictures beyond IDR pictures. Three types of IRAP 314 pictures, namely IDR, CRA and BLA pictures are supported, wherein 315 IDR pictures are conventionally referred to as closed group-of- 316 pictures (closed-GOP) random access points, and CRA and BLA 317 pictures are those conventionally referred to as open-GOP random 318 access points. BLA pictures usually originate from splicing of 319 two bitstreams or part thereof at a CRA picture, e.g. during 320 stream switching. To enable better systems usage of IRAP 321 pictures, altogether six different NAL units are defined to 322 signal the properties of the IRAP pictures, which can be used to 323 better match the stream access point (SAP) types as defined in 324 the ISOBMFF [ISOBMFF], which are utilized for random access 325 support in both 3GP-DASH [3GPDASH] and MPEG DASH [MPEGDASH]. 326 Pictures following an IRAP picture in decoding order and 327 preceding the IRAP picture in output order are referred to as 328 leading pictures associated with the IRAP picture. There are two 329 types of leading pictures, namely random access decodable leading 330 (RADL) pictures and random access skipped leading (RASL) 331 pictures. RADL pictures are decodable when the decoding started 332 at the associated IRAP picture, and RASL pictures are not 333 decodable when the decoding started at the associated IRAP 334 picture and are usually discarded. HEVC provides mechanisms to 335 enable the specification of conformance of bitstreams with RASL 336 pictures being discarded, thus to provide a standard-compliant 337 way to enable systems components to discard RASL pictures when 338 needed. 340 Temporal scalability support 342 HEVC includes an improved support of temporal scalability, by 343 inclusion of the signaling of TemporalId in the NAL unit header, 344 the restriction that pictures of a particular temporal sub-layer 345 cannot be used for inter prediction reference by pictures of a 346 lower temporal sub-layer, the sub-bitstream extraction process, 347 and the requirement that each sub-bitstream extraction output be 348 a conforming bitstream. Media-aware network elements (MANEs) can 349 utilize the TemporalId in the NAL unit header for stream 350 adaptation purposes based on temporal scalability. 352 Temporal sub-layer switching support 354 HEVC specifies, through NAL unit types present in the NAL unit 355 header, the signaling of temporal sub-layer access (TSA) and 356 stepwise temporal sub-layer access (STSA). A TSA picture and 357 pictures following the TSA picture in decoding order do not use 358 pictures prior to the TSA picture in decoding order with 359 TemporalId greater than or equal to that of the TSA picture for 360 inter prediction reference. A TSA picture enables up-switching, 361 at the TSA picture, to the sub-layer containing the TSA picture 362 or any higher sub-layer, from the immediately lower sub-layer. 363 An STSA picture does not use pictures with the same TemporalId as 364 the STSA picture for inter prediction reference. Pictures 365 following an STSA picture in decoding order with the same 366 TemporalId as the STSA picture do not use pictures prior to the 367 STSA picture in decoding order with the same TemporalId as the 368 STSA picture for inter prediction reference. An STSA picture 369 enables up-switching, at the STSA picture, to the sub-layer 370 containing the STSA picture, from the immediately lower sub- 371 layer. 373 Sub-layer reference or non-reference pictures 375 The concept and signaling of reference/non-reference pictures in 376 HEVC are different from H.264. In H.264, if a picture may be 377 used by any other picture for inter prediction reference, it is a 378 reference picture; otherwise it is a non-reference picture, and 379 this is signaled by two bits in the NAL unit header. In HEVC, a 380 picture is called a reference picture only when it is marked as 381 "used for reference". In addition, the concept of sub-layer 382 reference picture was introduced. If a picture may be used by 383 another other picture with the same TemporalId for inter 384 prediction reference, it is a sub-layer reference picture; 385 otherwise it is a sub-layer non-reference picture. Whether a 386 picture is a sub-layer reference picture or sub-layer non- 387 reference picture is signaled through NAL unit type values. 389 Extensibility 391 Besides the TemporalId in the NAL unit header, HEVC also includes 392 the signaling of a six-bit layer ID in the NAL unit header, which 393 must be equal to 0 for a single-layer bitstream. Extension 394 mechanisms have been included in VPS, SPS, PPS, SEI NAL unit, 395 slice headers, and so on. All these extension mechanisms enable 396 future extensions in a backward compatible manner, such that 397 bitstreams encoded according to potential future HEVC extensions 398 can be fed to then-legacy decoders (e.g. HEVC version 1 decoders) 399 and the then-legacy decoders can decode and output the base layer 400 bitstream. 402 Bitstream extraction 404 HEVC includes a bitstream extraction process as an integral part 405 of the overall decoding process, as well as specification of the 406 use of the bitstream extraction process in description of 407 bitstream conformance tests as part of the hypothetical reference 408 decoder (HRD) specification. 410 Reference picture management 412 The reference picture management of HEVC, including reference 413 picture marking and removal from the decoded picture buffer (DPB) 414 as well as reference picture list construction (RPLC), differs 415 from that of H.264. Instead of the sliding window plus adaptive 416 memory management control operation (MMCO) based reference 417 picture marking mechanism in H.264, HEVC specifies a reference 418 picture set (RPS) based reference picture management and marking 419 mechanism, and the RPLC is consequently based on the RPS 420 mechanism. A reference picture set consists of a set of 421 reference pictures associated with a picture, consisting of all 422 reference pictures that are prior to the associated picture in 423 decoding order, that may be used for inter prediction of the 424 associated picture or any picture following the associated 425 picture in decoding order. The reference picture set consists of 426 five lists of reference pictures; RefPicSetStCurrBefore, 427 RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and 428 RefPicSetLtFoll. RefPicSetStCurrBefore, RefPicSetStCurrAfter and 429 RefPicSetLtCurr contain all reference pictures that may be used 430 in inter prediction of the current picture and that may be used 431 in inter prediction of one or more of the pictures following the 432 current picture in decoding order. RefPicSetStFoll and 433 RefPicSetLtFoll consist of all reference pictures that are not 434 used in inter prediction of the current picture but may be used 435 in inter prediction of one or more of the pictures following the 436 current picture in decoding order. RPS provides an "intra-coded" 437 signaling of the DPB status, instead of an "inter-coded" 438 signaling, mainly for improved error resilience. The RPLC 439 process in HEVC is based on the RPS, by signaling an index to an 440 RPS subset for each reference index; this process is simpler than 441 the RPLC process in H.264. 443 Ultra low delay support 445 HEVC specifies a sub-picture-level HRD operation, for support of 446 the so-called ultra-low delay. The mechanism specifies a 447 standard-compliant way to enable delay reduction below one 448 picture interval. Sub-picture-level coded picture buffer (CPB) 449 and DPB parameters may be signaled, and utilization of these 450 information for the derivation of CPB timing (wherein the CPB 451 removal time corresponds to decoding time) and DPB output timing 452 (display time) is specified. Decoders are allowed to operate the 453 HRD at the conventional access-unit-level, even when the sub- 454 picture-level HRD parameters are present. 456 New SEI messages 458 HEVC inherits many H.264 SEI messages with changes in syntax 459 and/or semantics making them applicable to HEVC. Additionally, 460 there are a few new SEI messages reviewed briefly in the 461 following paragraphs. 463 The display orientation SEI message informs the decoder of a 464 transformation that is recommended to be applied to the cropped 465 decoded picture prior to display, such that the pictures can be 466 properly displayed, e.g. in an upside-up manner. 468 The structure of pictures SEI message provides information on the 469 NAL unit types, picture order count values, and prediction 470 dependencies of a sequence of pictures. The SEI message can be 471 used for example for concluding what impact a lost picture has on 472 other pictures. 474 The decoded picture hash SEI message provides a checksum derived 475 from the sample values of a decoded picture. It can be used for 476 detecting whether a picture was correctly received and decoded. 478 The active parameter sets SEI message includes the IDs of the 479 active video parameter set and the active sequence parameter set 480 and can be used to activate VPSs and SPSs. In addition, the SEI 481 message includes the following indications: 1) An indication of 482 whether "full random accessibility" is supported (when supported, 483 all parameter sets needed for decoding of the remaining of the 484 bitstream when random accessing from the beginning of the current 485 CVS by completely discarding all access units earlier in decoding 486 order are present in the remaining bitstream and all coded 487 pictures in the remaining bitstream can be correctly decoded); 2) 488 An indication of whether there is no parameter set within the 489 current CVS that updates another parameter set of the same type 490 preceding in decoding order. An update of a parameter set refers 491 to the use of the same parameter set ID but with some other 492 parameters changed. If this property is true for all CVSs in the 493 bitstream, then all parameter sets can be sent out-of-band before 494 session start. 496 The decoding unit information SEI message provides coded picture 497 buffer removal delay information for a decoding unit. The 498 message can be used in very-low-delay buffering operations. 500 The region refresh information SEI message can be used together 501 with the recovery point SEI message (present in both H.264 and 502 HEVC) for improved support of gradual decoding refresh. This 503 supports random access from inter-coded pictures, wherein 504 complete pictures can be correctly decoded or recovered after an 505 indicated number of pictures in output/display order. 507 1.1.3 Parallel Processing Support 509 The reportedly significantly higher encoding computational demand 510 of HEVC over H.264, in conjunction with the ever increasing video 511 resolution (both spatially and temporally) required by the 512 market, led to the adoption of VCL coding tools specifically 513 targeted to allow for parallelization on the sub-picture level. 514 That is, parallelization occurs, at the minimum, at the 515 granularity of an integer number of CTUs. The targets for this 516 type of high-level parallelization are multicore CPUs and DSPs as 517 well as multiprocessor systems. In a system design, to be 518 useful, these tools require signaling support, which is provided 519 in Section 7 of this memo. This section provides a brief 520 overview of the tools available in [HEVC]. 522 Many of the tools incorporated in HEVC were designed keeping in 523 mind the potential parallel implementations in multi-core/multi- 524 processor architectures. Specifically, for parallelization, four 525 picture partition strategies are available. 527 Slices are segments of the bitstream that can be reconstructed 528 independently from other slices within the same picture (though 529 there may still be interdependencies through loop filtering 530 operations). Slices are the only tool that can be used for 531 parallelization that is also available, in virtually identical 532 form, in H.264. Slices based parallelization does not require 533 much inter-processor or inter-core communication (except for 534 inter-processor or inter-core data sharing for motion 535 compensation when decoding a predictively coded picture, which is 536 typically much heavier than inter-processor or inter-core data 537 sharing due to in-picture prediction), as slices are designed to 538 be independently decodable. However, for the same reason, slices 539 can require some coding overhead. Further, slices (in contrast 540 to some of the other tools mentioned below) also serve as the key 541 mechanism for bitstream partitioning to match Maximum Transfer 542 Unit (MTU) size requirements, due to the in-picture independence 543 of slices and the fact that each regular slice is encapsulated in 544 its own NAL unit. In many cases, the goal of parallelization and 545 the goal of MTU size matching can place contradicting demands to 546 the slice layout in a picture. The realization of this situation 547 led to the development of the more advanced tools mentioned 548 below. 550 Dependent slice segments allow for fragmentation of a coded slice 551 into fragments at CTU boundaries without breaking any in-picture 552 prediction mechanism. They are complementary to the 553 fragmentation mechanism described in this memo in that they need 554 the cooperation of the encoder. As a dependent slice segment 555 necessarily contains an integer number of CTUs, a decoder using 556 multiple cores operating on CTUs can process a dependent slice 557 segment without communicating parts of the slice segment's 558 bitstream to other cores. Fragmentation, as specified in this 559 memo, in contrast, does not guarantee that a fragment contains an 560 integer number of CTUs. 562 In wavefront parallel processing (WPP), the picture is 563 partitioned into rows of CTUs. Entropy decoding and prediction 564 are allowed to use data from CTUs in other partitions. Parallel 565 processing is possible through parallel decoding of CTU rows, 566 where the start of the decoding of a row is delayed by two CTUs, 567 so to ensure that data related to a CTU above and to the right of 568 the subject CTU is available before the subject CTU is being 569 decoded. Using this staggered start (which appears like a 570 wavefront when represented graphically), parallelization is 571 possible with up to as many processors/cores as the picture 572 contains CTU rows. 574 Because in-picture prediction between neighboring CTU rows within 575 a picture is allowed, the required inter-processor/inter-core 576 communication to enable in-picture prediction can be substantial. 577 The WPP partitioning does not result in the creation of more NAL 578 units compared to when it is not applied, thus WPP cannot be used 579 for MTU size matching, though slices can be used in combination 580 for that purpose. 582 Tiles define horizontal and vertical boundaries that partition a 583 picture into tile columns and rows. The scan order of CTUs is 584 changed to be local within a tile (in the order of a CTU raster 585 scan of a tile), before decoding the top-left CTU of the next 586 tile in the order of tile raster scan of a picture. Similar to 587 slices, tiles break in-picture prediction dependencies (including 588 entropy decoding dependencies). However, they do not need to be 589 included into individual NAL units (same as WPP in this regard), 590 hence tiles cannot be used for MTU size matching, though slices 591 can be used in combination for that purpose. Each tile can be 592 processed by one processor/core, and the inter-processor/inter- 593 core communication required for in-picture prediction between 594 processing units decoding neighboring tiles is limited to 595 conveying the shared slice header in cases a slice is spanning 596 more than one tile, and loop filtering related sharing of 597 reconstructed samples and metadata. Insofar, tiles are less 598 demanding in terms of inter-processor communication bandwidth 599 compared to WPP due to the in-picture independence between two 600 neighboring partitions. 602 1.1.4 NAL Unit Header 604 HEVC maintains the NAL unit concept of H.264 with modifications. 605 HEVC uses a two-byte NAL unit header, as shown in Figure 1. The 606 payload of a NAL unit refers to the NAL unit excluding the NAL 607 unit header. 609 +---------------+---------------+ 610 |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 |F| Type | LayerId | TID | 613 +-------------+-----------------+ 615 Figure 1 The structure of HEVC NAL unit header 617 The semantics of the fields in the NAL unit header are as 618 specified in [HEVC] and described briefly below for convenience. 619 In addition to the name and size of each field, the corresponding 620 syntax element name in [HEVC] is also provided. 622 F: 1 bit 623 forbidden_zero_bit. Required to be zero in [HEVC]. HEVC 624 declares a value of 1 as a syntax violation. Note that the 625 inclusion of this bit in the NAL unit header is to enable 626 transport of HEVC video over MPEG-2 transport systems 627 (avoidance of start code emulations) [MPEG2S]. 629 Type: 6 bits 630 nal_unit_type. This field specifies the NAL unit type as 631 defined in Table 7-1 of [HEVC]. If the most significant bit 632 of this field of a NAL unit is equal to 0 (i.e. the value of 633 this field is less than 32), the NAL unit is a VCL NAL unit. 634 Otherwise, the NAL unit is a non-VCL NAL unit. For a 635 reference of all currently defined NAL unit types and their 636 semantics, please refer to Section 7.4.1 in [HEVC]. 638 LayerId: 6 bits 639 nuh_layer_id. Required to be equal to zero in [HEVC]. It is 640 anticipated that in future scalable or 3D video coding 641 extensions of this specification, this syntax element will be 642 used to identify additional layers that may be present in the 643 CVS, wherein a layer may be, e.g. a spatial scalable layer, a 644 quality scalable layer, a texture view, or a depth view. 646 TID: 3 bits 647 nuh_temporal_id_plus1. This field specifies the temporal 648 identifier of the NAL unit plus 1. The value of TemporalId is 649 equal to TID minus 1. A TID value of 0 is illegal to ensure 650 that there is at least one bit in the NAL unit header equal to 651 1, so to enable independent considerations of start code 652 emulations in the NAL unit header and in the NAL unit payload 653 data. 655 1.2 Overview of the Payload Format 657 This payload format defines the following processes required for 658 transport of HEVC coded data over RTP [RFC3550]: 660 o Usage of RTP header with this payload format 662 o Packetization of HEVC coded NAL units into RTP packets using 663 three types of payload structures, namely single NAL unit 664 packet, aggregation packet, and fragment unit 666 o Transmission of HEVC NAL units of the same bitstream within a 667 single RTP stream or multiple RTP streams (within one or more 668 RTP sessions), where within an RTP stream transmission of NAL 669 units may be either non-interleaved (i.e. the transmission 670 order of NAL units is the same as their decoding order) or 671 interleaved (i.e. the transmission order of NAL units is 672 different from their decoding order) 674 o Media type parameters to be used with the Session Description 675 Protocol (SDP) [RFC4566] 677 o A payload header extension mechanism and data structures for 678 enhanced support of temporal scalability based on that 679 extension mechanism. 681 2 Conventions 683 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 684 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and 685 "OPTIONAL" in this document are to be interpreted as described in 686 BCP 14, RFC 2119 [RFC2119]. 688 In this document, these key words will appear with that 689 interpretation only when in ALL CAPS. Lower case uses of these 690 words are not to be interpreted as carrying the RFC 2119 691 significance. 693 This specification uses the notion of setting and clearing a bit 694 when bit fields are handled. Setting a bit is the same as 695 assigning that bit the value of 1 (On). Clearing a bit is the 696 same as assigning that bit the value of 0 (Off). 698 3 Definitions and Abbreviations 700 3.1 Definitions 702 This document uses the terms and definitions of [HEVC]. Section 703 3.1.1 lists relevant definitions copied from [HEVC] for 704 convenience. Section 3.1.2 provides definitions specific to this 705 memo. 707 3.1.1 Definitions from the HEVC Specification 709 access unit: A set of NAL units that are associated with each 710 other according to a specified classification rule, are 711 consecutive in decoding order, and contain exactly one coded 712 picture. 714 BLA access unit: An access unit in which the coded picture is a 715 BLA picture. 717 BLA picture: An IRAP picture for which each VCL NAL unit has 718 nal_unit_type equal to BLA_W_LP, BLA_W_RADL, or BLA_N_LP. 720 coded video sequence (CVS): A sequence of access units that 721 consists, in decoding order, of an IRAP access unit with 722 NoRaslOutputFlag equal to 1, followed by zero or more access 723 units that are not IRAP access units with NoRaslOutputFlag equal 724 to 1, including all subsequent access units up to but not 725 including any subsequent access unit that is an IRAP access unit 726 with NoRaslOutputFlag equal to 1. 728 Informative note: An IRAP access unit may be an IDR access 729 unit, a BLA access unit, or a CRA access unit. The value of 730 NoRaslOutputFlag is equal to 1 for each IDR access unit, each 731 BLA access unit, and each CRA access unit that is the first 732 access unit in the bitstream in decoding order, is the first 733 access unit that follows an end of sequence NAL unit in 734 decoding order, or has HandleCraAsBlaFlag equal to 1. 736 CRA access unit: An access unit in which the coded picture is a 737 CRA picture. 739 CRA picture: A RAP picture for which each VCL NAL unit has 740 nal_unit_type equal to CRA_NUT. 742 IDR access unit: An access unit in which the coded picture is an 743 IDR picture. 745 IDR picture: A RAP picture for which each VCL NAL unit has 746 nal_unit_type equal to IDR_W_RADL or IDR_N_LP. 748 IRAP access unit: An access unit in which the coded picture is an 749 IRAP picture. 751 IRAP picture: A coded picture for which each VCL NAL unit has 752 nal_unit_type in the range of BLA_W_LP (16) to RSV_IRAP_VCL23 753 (23), inclusive. 755 layer: A set of VCL NAL units that all have a particular value of 756 nuh_layer_id and the associated non-VCL NAL units, or one of a 757 set of syntactical structures having a hierarchical relationship. 759 operation point: bitstream created from another bitstream by 760 operation of the sub-bitstream extraction process with the 761 another bitstream, a target highest TemporalId, and a target 762 layer identifier list as inputs. 764 random access: The act of starting the decoding process for a 765 bitstream at a point other than the beginning of the bitstream. 767 sub-layer: A temporal scalable layer of a temporal scalable 768 bitstream consisting of VCL NAL units with a particular value of 769 the TemporalId variable, and the associated non-VCL NAL units. 771 sub-layer representation: A subset of the bitstream consisting of 772 NAL units of a particular sub-layer and the lower sub-layers. 774 tile: A rectangular region of coding tree blocks within a 775 particular tile column and a particular tile row in a picture. 777 tile column: A rectangular region of coding tree blocks having a 778 height equal to the height of the picture and a width specified 779 by syntax elements in the picture parameter set. 781 tile row: A rectangular region of coding tree blocks having a 782 height specified by syntax elements in the picture parameter set 783 and a width equal to the width of the picture. 785 3.1.2 Definitions Specific to This Memo 787 dependee RTP stream: An RTP stream on which another RTP stream 788 depends. All RTP streams in an MRST or MRMT except for the 789 highest RTP stream are dependee RTP streams. 791 highest RTP stream: The RTP stream on which no other RTP stream 792 depends. The RTP stream in an SRST is the highest RTP stream. 794 media aware network element (MANE): A network element, such as a 795 middlebox, selective forwarding unit, or application layer 796 gateway that is capable of parsing certain aspects of the RTP 797 payload headers or the RTP payload and reacting to their 798 contents. 800 Informative note: The concept of a MANE goes beyond normal 801 routers or gateways in that a MANE has to be aware of the 802 signaling (e.g. to learn about the payload type mappings of 803 the media streams), and in that it has to be trusted when 804 working with SRTP. The advantage of using MANEs is that they 805 allow packets to be dropped according to the needs of the 806 media coding. For example, if a MANE has to drop packets due 807 to congestion on a certain link, it can identify and remove 808 those packets whose elimination produces the least adverse 809 effect on the user experience. After dropping packets, MANEs 810 must rewrite RTCP packets to match the changes to the RTP 811 stream as specified in Section 7 of [RFC3550]. 813 Media Transport: As used in the MRST, MRMT, and SRST definitions 814 below, Media Transport denotes the transport of packets over a 815 transport association identified by a 5-tuple (source address, 816 source port, destination address, destination port, transport 817 protocol). See also Section 2.1.13 of [I-D.ietf-avtext-rtp- 818 grouping-taxonomy]. 820 Multiple RTP streams on a Single Transport (MRST): Multiple RTP 821 streams carrying a single HEVC bitstream on a Single Transport. 822 See also Section 3.5 of [I-D.ietf-avtext-rtp-grouping-taxonomy]. 824 Multiple RTP streams on Multiple Transports (MRMT): Multiple RTP 825 streams carrying a single HEVC bitstream on Multiple Transports. 826 See also Section 3.5 of [I-D.ietf-avtext-rtp-grouping-taxonomy]. 828 NAL unit decoding order: A NAL unit order that conforms to the 829 constraints on NAL unit order given in Section 7.4.2.4 in [HEVC]. 831 NAL unit output order: A NAL unit order in which NAL units of 832 different access units are in the output order of the decoded 833 pictures corresponding to the access units, as specified in 834 [HEVC], and in which NAL units within an access unit are in their 835 decoding order. 837 NAL-unit-like structure: A data structure that is similar to NAL 838 units in the sense that it also has a NAL unit header and a 839 payload, with a difference that the payload does not follow the 840 start code emulation prevention mechanism required for the NAL 841 unit syntax as specified in Section 7.3.1.1 of [HEVC]. Examples 842 NAL-unit-like structures defined in this memo are packet payloads 843 of AP, PACI, and FU packets. 845 NALU-time: The value that the RTP timestamp would have if the NAL 846 unit would be transported in its own RTP packet. 848 RTP stream: See [I-D.ietf-avtext-rtp-grouping-taxonomy]. Within 849 the scope of this memo, one RTP stream is utilized to transport 850 one or more temporal sub-layers. 852 Single RTP stream on a Single Transport (SRST): Single RTP 853 stream carrying a single HEVC bitstream on a Single (Media) 854 Transport. See also Section 3.5 of [I-D.ietf-avtext-rtp- 855 grouping-taxonomy]. 857 transmission order: The order of packets in ascending RTP 858 sequence number order (in modulo arithmetic). Within an 859 aggregation packet, the NAL unit transmission order is the same 860 as the order of appearance of NAL units in the packet. 862 3.2 Abbreviations 864 AP Aggregation Packet 866 BLA Broken Link Access 868 CRA Clean Random Access 870 CTB Coding Tree Block 872 CTU Coding Tree Unit 874 CVS Coded Video Sequence 876 DPH Decoded Picture Hash 878 FU Fragmentation Unit 880 HRD Hypothetical Reference Decoder 882 IDR Instantaneous Decoding Refresh 884 IRAP Intra Random Access Point 886 MANE Media Aware Network Element 888 MRMT Multiple RTP streams on Multiple Transports 889 MRST Multiple RTP streams on a Single Transport 891 MTU Maximum Transfer Unit 893 NAL Network Abstraction Layer 895 NALU Network Abstraction Layer Unit 897 PACI PAyload Content Information 899 PHES Payload Header Extension Structure 901 PPS Picture Parameter Set 903 RADL Random Access Decodable Leading (Picture) 905 RASL Random Access Skipped Leading (Picture) 907 RPS Reference Picture Set 909 SEI Supplemental Enhancement Information 911 SPS Sequence Parameter Set 913 SRST Single RTP stream on a Single Transport 915 STSA Step-wise Temporal Sub-layer Access 917 TSA Temporal Sub-layer Access 919 TSCI Temporal Scalability Control Information 921 VCL Video Coding Layer 923 VPS Video Parameter Set 925 4 RTP Payload Format 927 4.1 RTP Header Usage 929 The format of the RTP header is specified in [RFC3550] and 930 reprinted in Figure 2 for convenience. This payload format uses 931 the fields of the header in a manner consistent with that 932 specification. 934 The RTP payload (and the settings for some RTP header bits) for 935 aggregation packets and fragmentation units are specified in 936 Sections 4.4.2 and 4.4.3, respectively. 938 0 1 2 3 939 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 941 |V=2|P|X| CC |M| PT | sequence number | 942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 943 | timestamp | 944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 945 | synchronization source (SSRC) identifier | 946 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 947 | contributing source (CSRC) identifiers | 948 | .... | 949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 951 Figure 2 RTP header according to [RFC3550] 953 The RTP header information to be set according to this RTP 954 payload format is set as follows: 956 Marker bit (M): 1 bit 958 Set for the last packet, carried in the current RTP stream, of 959 the access unit, in line with the normal use of the M bit in 960 video formats, to allow an efficient playout buffer handling. 961 When MRST or MRMT is in use, if an access unit appears in 962 multiple RTP streams, the marker bit is set on each RTP 963 stream's last packet of the access unit. 965 Informative note: The content of a NAL unit does not tell 966 whether or not the NAL unit is the last NAL unit, in 967 decoding order, of an access unit. An RTP sender 968 implementation may obtain this information from the video 969 encoder. If, however, the implementation cannot obtain 970 this information directly from the encoder, e.g. when the 971 bitstream was pre-encoded, and also there is no timestamp 972 allocated for each NAL unit, then the sender implementation 973 can inspect subsequent NAL units in decoding order to 974 determine whether or not the NAL unit is the last NAL unit 975 of an access unit as follows. A NAL unit naluX is the last 976 NAL unit of an access unit if it is the last NAL unit of 977 the bitstream or the next VCL NAL unit naluY in decoding 978 order has the high-order bit of the first byte after its 979 NAL unit header equal to 1, and all NAL units between naluX 980 and naluY, when present, have nal_unit_type in the range of 981 32 to 35, inclusive, equal to 39, or in the ranges of 41 to 982 44, inclusive, or 48 to 55, inclusive. 984 Payload type (PT): 7 bits 986 The assignment of an RTP payload type for this new packet 987 format is outside the scope of this document and will not be 988 specified here. The assignment of a payload type has to be 989 performed either through the profile used or in a dynamic way. 991 Informative note: It is not required to use different 992 payload type values for different RTP streams in MRST or 993 MRMT. 995 Sequence number (SN): 16 bits 997 Set and used in accordance with RFC 3550 [RFC3550]. 999 Timestamp: 32 bits 1001 The RTP timestamp is set to the sampling timestamp of the 1002 content. A 90 kHz clock rate MUST be used. 1004 If the NAL unit has no timing properties of its own (e.g. 1005 parameter set and SEI NAL units), the RTP timestamp MUST be 1006 set to the RTP timestamp of the coded picture of the access 1007 unit in which the NAL unit (according to Section 7.4.2.4.4 of 1008 [HEVC]) is included. 1010 Receivers MUST use the RTP timestamp for the display process, 1011 even when the bitstream contains picture timing SEI messages 1012 or decoding unit information SEI messages as specified in 1014 [HEVC]. However, this does not mean that picture timing SEI 1015 messages in the bitstream should be discarded, as picture 1016 timing SEI messages may contain frame-field information that 1017 is important in appropriately rendering interlaced video. 1019 Synchronization source (SSRC): 32-bits 1021 Used to identify the source of the RTP packets. When using 1022 SRST, by definition a single SSRC is used for all parts of a 1023 single bitstream. In MRST or MRMT, different SSRCs are used 1024 for each RTP stream containing a subset of the sub-layers of 1025 the single (temporally scalable) bitstream. A receiver is 1026 required to correctly associate the set of SSRCs that are 1027 included parts of the same bitstream. 1029 Informative note: The term "bitstream" in this document is 1030 equivalent to the term "encoded stream" in [I-D.ietf- 1031 avtext-rtp-grouping-taxonomy]. 1033 4.2 Payload Header Usage 1035 The first two bytes of the payload of an RTP packet are referred 1036 to as the payload header. The payload header consists of the 1037 same fields (F, Type, LayerId, and TID) as the NAL unit header as 1038 shown in Section 1.1.4, irrespective of the type of the payload 1039 structure. 1041 The TID value indicates (among other things) the relative 1042 importance of an RTP packet, for example because NAL units 1043 belonging to higher temporal sub-layers are not used for the 1044 decoding of lower temporal sub-layers. A lower value of TID 1045 indicates a higher importance. More important NAL units MAY be 1046 better protected against transmission losses than less important 1047 NAL units. 1049 4.3 Transmission Modes 1051 This memo enables transmission of an HEVC bitstream over 1053 . a single RTP stream on a single Media Transport (SRST), 1054 . multiple RTP streams over a single Media Transport (MRST), 1055 or 1056 . multiple RTP streams over multiple Media Transports (MRMT). 1058 Informative Note: While this specification enables the use of 1059 MRST within the H.265 RTP payload, the signaling of MRST within 1060 SDP Offer/Answer is not fully specified at the time of this 1061 writing. See [RFC5576] and [RFC5583] for what is supported 1062 today as well as [I-D.ietf-avtcore-rtp-multi-stream] and [I- 1063 D.ietf-mmusic-sdp-bundle-negotiation] for future directions. 1065 When in MRMT, the dependency of one RTP stream on another RTP 1066 stream is typically indicated as specified in [RFC5583]. 1067 [RFC5583] can also be utilized to specify dependencies within 1068 MRST, but only if the RTP streams utilize distinct payload types. 1069 When an RTP stream A depends on another RTP stream B, the RTP 1070 stream B is referred to as a dependee RTP stream of the RTP 1071 stream A. 1073 SRST or MRST SHOULD be used for point-to-point unicast scenarios, 1074 while MRMT SHOULD be used for point-to-multipoint multicast 1075 scenarios where different receivers require different operation 1076 points of the same HEVC bitstream, to improve bandwidth utilizing 1077 efficiency. 1079 Informative note: A multicast may degrade to a unicast after 1080 all but one receivers have left (this is a justification of 1081 the first "SHOULD" instead of "MUST"), and there might be 1082 scenarios where MRMT is desirable but not possible e.g. when 1083 IP multicast is not deployed in certain network (this is a 1084 justification of the second "SHOULD" instead of "MUST"). 1086 The transmission mode is indicated by the tx-mode media parameter 1087 (see Section 7.1). If tx-mode is equal to "SRST", SRST MUST be 1088 used. Otherwise, if tx-mode is equal to "MRST", MRST MUST be 1089 used. Otherwise (tx-mode is equal to "MRMT"), MRMT MUST be used. 1091 Informative note: When an RTP stream does not depend on other 1092 RTP streams, any of SRST, MRST and MRMT may be in use for the 1093 RTP stream. 1095 Receivers MUST support all of SRST, MRST, and MRMT. 1097 Informative note: The required support of MRMT by receivers 1098 does not imply that multicast must be supported by receivers. 1100 4.4 Payload Structures 1102 Four different types of RTP packet payload structures are 1103 specified. A receiver can identify the type of an RTP packet 1104 payload through the Type field in the payload header. 1106 The four different payload structures are as follows: 1108 o Single NAL unit packet: Contains a single NAL unit in the 1109 payload, and the NAL unit header of the NAL unit also serves 1110 as the payload header. This payload structure is specified in 1111 Section 4.4.1. 1113 o Aggregation packet (AP): Contains more than one NAL unit 1114 within one access unit. This payload structure is specified 1115 in Section 4.4.2. 1117 o Fragmentation unit (FU): Contains a subset of a single NAL 1118 unit. This payload structure is specified in Section 4.4.3. 1120 o PACI carrying RTP packet: Contains a payload header (that 1121 differs from other payload headers for efficiency), a Payload 1122 Header Extension Structure (PHES), and a PACI payload. This 1123 payload structure is specified in Section 4.4.4. 1125 4.4.1 Single NAL Unit Packets 1127 A single NAL unit packet contains exactly one NAL unit, and 1128 consists of a payload header (denoted as PayloadHdr), a 1129 conditional 16-bit DONL field (in network byte order), and the 1130 NAL unit payload data (the NAL unit excluding its NAL unit 1131 header) of the contained NAL unit, as shown in Figure 3. 1133 0 1 2 3 1134 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1136 | PayloadHdr | DONL (conditional) | 1137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1138 | | 1139 | NAL unit payload data | 1140 | | 1141 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1142 | :...OPTIONAL RTP padding | 1143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1145 Figure 3 The structure a single NAL unit packet 1147 The payload header SHOULD be an exact copy of the NAL unit header 1148 of the contained NAL unit. However, the Type (i.e. 1149 nal_unit_type) field MAY be changed, e.g. when it is desirable to 1150 handle a CRA picture to be a BLA picture [JCTVC-J0107]. 1152 The DONL field, when present, specifies the value of the 16 least 1153 significant bits of the decoding order number of the contained 1154 NAL unit. If sprop-max-don-diff is greater than 0 for any of the 1155 RTP streams, the DONL field MUST be present, and the variable DON 1156 for the contained NAL unit is derived as equal to the value of 1157 the DONL field. Otherwise (sprop-max-don-diff is equal to 0 for 1158 all the RTP streams), the DONL field MUST NOT be present. 1160 4.4.2 Aggregation Packets (APs) 1162 Aggregation packets (APs) are introduced to enable the reduction 1163 of packetization overhead for small NAL units, such as most of 1164 the non-VCL NAL units, which are often only a few octets in size. 1166 An AP aggregates NAL units within one access unit. Each NAL unit 1167 to be carried in an AP is encapsulated in an aggregation unit. 1168 NAL units aggregated in one AP are in NAL unit decoding order. 1170 An AP consists of a payload header (denoted as PayloadHdr) 1171 followed by two or more aggregation units, as shown in Figure 4. 1173 0 1 2 3 1174 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1176 | PayloadHdr (Type=48) | | 1177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1178 | | 1179 | two or more aggregation units | 1180 | | 1181 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1182 | :...OPTIONAL RTP padding | 1183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1185 Figure 4 The structure of an aggregation packet 1187 The fields in the payload header are set as follows. The F bit 1188 MUST be equal to 0 if the F bit of each aggregated NAL unit is 1189 equal to zero; otherwise, it MUST be equal to 1. The Type field 1190 MUST be equal to 48. The value of LayerId MUST be equal to the 1191 lowest value of LayerId of all the aggregated NAL units. The 1192 value of TID MUST be the lowest value of TID of all the 1193 aggregated NAL units. 1195 Informative Note: All VCL NAL units in an AP have the same TID 1196 value since they belong to the same access unit. However, an 1197 AP may contain non-VCL NAL units for which the TID value in 1198 the NAL unit header may be different than the TID value of the 1199 VCL NAL units in the same AP. 1201 An AP MUST carry at least two aggregation units and can carry as 1202 many aggregation units as necessary; however, the total amount of 1203 data in an AP obviously MUST fit into an IP packet, and the size 1204 SHOULD be chosen so that the resulting IP packet is smaller than 1205 the MTU size so to avoid IP layer fragmentation. An AP MUST NOT 1206 contain Fragmentation Units (FUs) specified in Section 4.4.3. 1207 APs MUST NOT be nested; i.e. an AP MUST NOT contain another AP. 1209 The first aggregation unit in an AP consists of a conditional 16- 1210 bit DONL field (in network byte order) followed by a 16-bit 1211 unsigned size information (in network byte order) that indicates 1212 the size of the NAL unit in bytes (excluding these two octets, 1213 but including the NAL unit header), followed by the NAL unit 1214 itself, including its NAL unit header, as shown in Figure 5. 1216 0 1 2 3 1217 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1219 : DONL (conditional) | NALU size | 1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 | NALU size | | 1222 +-+-+-+-+-+-+-+-+ NAL unit | 1223 | | 1224 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1225 | : 1226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1228 Figure 5 The structure of the first aggregation unit in an AP 1230 The DONL field, when present, specifies the value of the 16 least 1231 significant bits of the decoding order number of the aggregated 1232 NAL unit. 1234 If sprop-max-don-diff is greater than 0 for any of the RTP 1235 streams, the DONL field MUST be present in an aggregation unit 1236 that is the first aggregation unit in an AP, and the variable DON 1237 for the aggregated NAL unit is derived as equal to the value of 1238 the DONL field. Otherwise (sprop-max-don-diff is equal to 0 for 1239 all the RTP streams), the DONL field MUST NOT be present in an 1240 aggregation unit that is the first aggregation unit in an AP. 1242 An aggregation unit that is not the first aggregation unit in an 1243 AP consists of a conditional 8-bit DOND field followed by a 16- 1244 bit unsigned size information (in network byte order) that 1245 indicates the size of the NAL unit in bytes (excluding these two 1246 octets, but including the NAL unit header), followed by the NAL 1247 unit itself, including its NAL unit header, as shown in Figure 6. 1249 0 1 2 3 1250 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1252 : DOND (cond) | NALU size | 1253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1254 | | 1255 | NAL unit | 1256 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1257 | : 1258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1260 Figure 6 The structure of an aggregation unit that is not the 1261 first aggregation unit in an AP 1263 When present, the DOND field plus 1 specifies the difference 1264 between the decoding order number values of the current 1265 aggregated NAL unit and the preceding aggregated NAL unit in the 1266 same AP. 1268 If sprop-max-don-diff is greater than 0 for any of the RTP 1269 streams, the DOND field MUST be present in an aggregation unit 1270 that is not the first aggregation unit in an AP, and the variable 1271 DON for the aggregated NAL unit is derived as equal to the DON of 1272 the preceding aggregated NAL unit in the same AP plus the value 1273 of the DOND field plus 1 modulo 65536. Otherwise (sprop-max-don- 1274 diff is equal to 0 for all the RTP streams), the DOND field MUST 1275 NOT be present in an aggregation unit that is not the first 1276 aggregation unit in an AP, and in this case the transmission 1277 order and decoding order of NAL units carried in the AP are the 1278 same as the order the NAL units appear in the AP. 1280 Figure 7 presents an example of an AP that contains two 1281 aggregation units, labeled as 1 and 2 in the figure, without the 1282 DONL and DOND fields being present. 1284 0 1 2 3 1285 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1287 | RTP Header | 1288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1289 | PayloadHdr (Type=48) | NALU 1 Size | 1290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1291 | NALU 1 HDR | | 1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 1 Data | 1293 | . . . | 1294 | | 1295 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1296 | . . . | NALU 2 Size | NALU 2 HDR | 1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1298 | NALU 2 HDR | | 1299 +-+-+-+-+-+-+-+-+ NALU 2 Data | 1300 | . . . | 1301 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1302 | :...OPTIONAL RTP padding | 1303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1305 Figure 7 An example of an AP packet containing two aggregation 1306 units without the DONL and DOND fields 1308 Figure 8 presents an example of an AP that contains two 1309 aggregation units, labeled as 1 and 2 in the figure, with the 1310 DONL and DOND fields being present. 1312 0 1 2 3 1313 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1315 | RTP Header | 1316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1317 | PayloadHdr (Type=48) | NALU 1 DONL | 1318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1319 | NALU 1 Size | NALU 1 HDR | 1320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1321 | | 1322 | NALU 1 Data . . . | 1323 | | 1324 + . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1325 | | NALU 2 DOND | NALU 2 Size | 1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1327 | NALU 2 HDR | | 1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NALU 2 Data | 1329 | | 1330 | . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1331 | :...OPTIONAL RTP padding | 1332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1334 Figure 8 An example of an AP containing two aggregation units 1335 with the DONL and DOND fields 1337 4.4.3 Fragmentation Units (FUs) 1339 Fragmentation units (FUs) are introduced to enable fragmenting a 1340 single NAL unit into multiple RTP packets, possibly without 1341 cooperation or knowledge of the HEVC encoder. A fragment of a NAL 1342 unit consists of an integer number of consecutive octets of that 1343 NAL unit. Fragments of the same NAL unit MUST be sent in consecutive 1344 order with ascending RTP sequence numbers (with no other RTP packets 1345 within the same RTP stream being sent between the first and last 1346 fragment). 1348 When a NAL unit is fragmented and conveyed within FUs, it is 1349 referred to as a fragmented NAL unit. APs MUST NOT be 1350 fragmented. FUs MUST NOT be nested; i.e. an FU MUST NOT contain 1351 a subset of another FU. 1353 The RTP timestamp of an RTP packet carrying an FU is set to the 1354 NALU-time of the fragmented NAL unit. 1356 An FU consists of a payload header (denoted as PayloadHdr), an FU 1357 header of one octet, a conditional 16-bit DONL field (in network 1358 byte order), and an FU payload, as shown in Figure 9. 1360 0 1 2 3 1361 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1363 | PayloadHdr (Type=49) | FU header | DONL (cond) | 1364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 1365 | DONL (cond) | | 1366 |-+-+-+-+-+-+-+-+ | 1367 | FU payload | 1368 | | 1369 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1370 | :...OPTIONAL RTP padding | 1371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1373 Figure 9 The structure of an FU 1375 The fields in the payload header are set as follows. The Type 1376 field MUST be equal to 49. The fields F, LayerId, and TID MUST 1377 be equal to the fields F, LayerId, and TID, respectively, of the 1378 fragmented NAL unit. 1380 The FU header consists of an S bit, an E bit, and a 6-bit FuType 1381 field, as shown in Figure 10. 1383 +---------------+ 1384 |0|1|2|3|4|5|6|7| 1385 +-+-+-+-+-+-+-+-+ 1386 |S|E| FuType | 1387 +---------------+ 1389 Figure 10 The structure of FU header 1391 The semantics of the FU header fields are as follows: 1392 S: 1 bit 1393 When set to one, the S bit indicates the start of a fragmented 1394 NAL unit i.e. the first byte of the FU payload is also the 1395 first byte of the payload of the fragmented NAL unit. When 1396 the FU payload is not the start of the fragmented NAL unit 1397 payload, the S bit MUST be set to zero. 1399 E: 1 bit 1400 When set to one, the E bit indicates the end of a fragmented 1401 NAL unit, i.e. the last byte of the payload is also the last 1402 byte of the fragmented NAL unit. When the FU payload is not 1403 the last fragment of a fragmented NAL unit, the E bit MUST be 1404 set to zero. 1406 FuType: 6 bits 1407 The field FuType MUST be equal to the field Type of the 1408 fragmented NAL unit. 1410 The DONL field, when present, specifies the value of the 16 least 1411 significant bits of the decoding order number of the fragmented 1412 NAL unit. 1414 If sprop-max-don-diff is greater than 0 for any of the RTP 1415 streams, and the S bit is equal to 1, the DONL field MUST be 1416 present in the FU, and the variable DON for the fragmented NAL 1417 unit is derived as equal to the value of the DONL field. 1418 Otherwise (sprop-max-don-diff is equal to 0 for all the RTP 1419 streams, or the S bit is equal to 0), the DONL field MUST NOT be 1420 present in the FU. 1422 A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e. 1423 the Start bit and End bit MUST NOT both be set to one in the same 1424 FU header. 1426 The FU payload consists of fragments of the payload of the 1427 fragmented NAL unit so that if the FU payloads of consecutive 1428 FUs, starting with an FU with the S bit equal to 1 and ending 1429 with an FU with the E bit equal to 1, are sequentially 1430 concatenated, the payload of the fragmented NAL unit can be 1431 reconstructed. The NAL unit header of the fragmented NAL unit is 1432 not included as such in the FU payload, but rather the 1433 information of the NAL unit header of the fragmented NAL unit is 1434 conveyed in F, LayerId, and TID fields of the FU payload headers 1435 of the FUs and the FuType field of the FU header of the FUs. An 1436 FU payload MUST NOT be empty. 1438 If an FU is lost, the receiver SHOULD discard all following 1439 fragmentation units in transmission order corresponding to the 1440 same fragmented NAL unit, unless the decoder in the receiver is 1441 known to be prepared to gracefully handle incomplete NAL units. 1443 A receiver in an endpoint or in a MANE MAY aggregate the first n- 1444 1 fragments of a NAL unit to an (incomplete) NAL unit, even if 1445 fragment n of that NAL unit is not received. In this case, the 1446 forbidden_zero_bit of the NAL unit MUST be set to one to indicate 1447 a syntax violation. 1449 4.4.4 PACI packets 1451 This section specifies the PACI packet structure. The basic 1452 payload header specified in this memo is intentionally limited to 1453 the 16 bits of the NAL unit header so to keep the packetization 1454 overhead to a minimum. However, cases have been identified where 1455 it is advisable to include control information in an easily 1456 accessible position in the packet header, despite the additional 1457 overhead. One such control information is the Temporal 1458 Scalability Control Information as specified in Section 4.5 1459 below. PACI packets carry this and future, similar structures. 1461 The PACI packet structure is based on a payload header extension 1462 mechanism that is generic and extensible to carry payload header 1463 extensions. In this section, the focus lies on the use within 1464 this specification. Section 4.4.4.2 below provides guidance for 1465 the specification designers in how to employ the extension 1466 mechanism in future specifications. 1468 A PACI packet consists of a payload header (denoted as 1469 PayloadHdr), for which the structure follows what is described in 1470 Section 4.2 above. The payload header is followed by the fields 1471 A, cType, PHSsize, F[0..2] and Y. 1473 Figure 11 shows a PACI packet in compliance with this memo; that 1474 is, without any extensions. 1476 0 1 2 3 1477 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1478 1 1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1480 +-+ 1481 | PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y| 1482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1483 +-+ 1484 | Payload Header Extension Structure (PHES) | 1486 |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=| 1487 | | 1488 | PACI payload: NAL unit | 1489 | . . . | 1490 | | 1491 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1492 +-+ 1493 | :...OPTIONAL RTP padding | 1494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1495 +- 1497 Figure 11 The structure of a PACI 1499 The fields in the payload header are set as follows. The F bit 1500 MUST be equal to 0. The Type field MUST be equal to 50. The 1501 value of LayerId MUST be a copy of the LayerId field of the PACI 1502 payload NAL unit or NAL-unit-like structure. The value of TID 1503 MUST be a copy of the TID field of the PACI payload NAL unit or 1504 NAL-unit-like structure. 1506 The semantics of other fields are as follows: 1508 A: 1 bit 1509 Copy of the F bit of the PACI payload NAL unit or NAL-unit- 1510 like structure. 1512 cType: 6 bits 1513 Copy of the Type field of the PACI payload NAL unit or NAL- 1514 unit-like structure. 1516 PHSsize: 5 bits 1517 Indicates the length of the PHES field. The value is limited 1518 to be less than or equal to 32 octets, to simplify encoder 1519 design for MTU size matching. 1521 F0 1522 This field equal to 1 specifies the presence of a temporal 1523 scalability support extension in the PHES. 1525 F1, F2 1526 MUST be 0, available for future extensions, see Section 1527 4.4.4.2. 1529 Y: 1 bit 1530 MUST be 0, available for future extensions, see Section 1531 4.4.4.2. 1533 PHES: variable number of octets 1534 A variable number of octets as indicated by the value of 1535 PHSsize. 1537 PACI Payload 1538 The single NAL unit packet or NAL-unit-like structure (such 1539 as: FU or AP) to be carried, not including the first two 1540 octets. 1542 Informative note: The first two octets of the NAL unit or 1543 NAL-unit-like structure carried in the PACI payload are not 1544 included in the PACI payload. Rather, the respective values 1545 are copied in locations of the PayloadHdr of the RTP 1546 packet. This design offers two advantages: first, the 1547 overall structure of the payload header is preserved, i.e. 1548 there is no special case of payload header structure that 1549 needs to be implemented for PACI. Second, no additional 1550 overhead is introduced. 1552 A PACI payload MAY be a single NAL unit, an FU, or an AP. 1553 PACIs MUST NOT be fragmented or aggregated. The following 1554 subsection documents the reasons for these design choices. 1556 4.4.4.1 Reasons for the PACI rules (informative) 1558 A PACI cannot be fragmented. If a PACI could be fragmented, and 1559 a fragment other than the first fragment would get lost, access 1560 to the information in the PACI would not be possible. Therefore, 1561 a PACI must not be fragmented. In other words, an FU must not 1562 carry (fragments of) a PACI. 1564 A PACI cannot be aggregated. Aggregation of PACIs is inadvisable 1565 from a compression viewpoint, as, in many cases, several to be 1566 aggregated NAL units would share identical PACI fields and values 1567 which would be carried redundantly for no reason. Most, if not 1568 all the practical effects of PACI aggregation can be achieved by 1569 aggregating NAL units and bundling them with a PACI (see below). 1570 Therefore, a PACI must not be aggregated. In other words, an AP 1571 must not contain a PACI. 1573 The payload of a PACI can be a fragment. Both middleboxes and 1574 sending systems with inflexible (often hardware-based) encoders 1575 occasionally find themselves in situations where a PACI and its 1576 headers, combined, are larger than the MTU size. In such a 1577 scenario, the middlebox or sender can fragment the NAL unit and 1578 encapsulate the fragment in a PACI. Doing so preserves the 1579 payload header extension information for all fragments, allowing 1580 downstream middleboxes and the receiver to take advantage of that 1581 information. Therefore, a sender may place a fragment into a 1582 PACI, and a receiver must be able to handle such a PACI. 1584 The payload of a PACI can be an aggregation NAL unit. HEVC 1585 bitstreams can contain unevenly sized and/or small (when compared 1586 to the MTU size) NAL units. In order to efficiently packetize 1587 such small NAL units, AP were introduced. The benefits of APs 1588 are independent from the need for a payload header extension. 1589 Therefore, a sender may place an AP into a PACI, and a receiver 1590 must be able to handle such a PACI. 1592 4.4.4.2 PACI extensions (Informative) 1594 This section includes recommendations for future specification 1595 designers on how to extent the PACI syntax to accommodate future 1596 extensions. Obviously, designers are free to specify whatever 1597 appears to be appropriate to them at the time of their design. 1598 However, a lot of thought has been invested into the extension 1599 mechanism described below, and we suggest that deviations from it 1600 warrant a good explanation. 1602 This memo defines only a single payload header extension (Temporal 1603 Scalability Control Information, described below in Section 4.5), 1604 and, therefore, only the F0 bit carries semantics. F1 and F2 are 1605 already named (and not just marked as reserved, as a typical video 1606 spec designer would do). They are intended to signal two additional 1607 extensions. The Y bit allows to, recursively, add further F and Y 1608 bits to extend the mechanism beyond 3 possible payload header 1609 extensions. It is suggested to define a new packet type (using a 1610 different value for Type) when assigning the F1, F2, or Y bits 1611 different semantics than what is suggested below. 1613 When a Y bit is set, an 8 bit flag-extension is inserted after 1614 the Y bit. A flag-extension consists of 7 flags F[n..n+6], and 1615 another Y bit. 1617 The basic PACI header already includes F0, F1, and F2. 1618 Therefore, the Fx bits in the first flag-extensions are numbered 1619 F3, F4, ..., F9, the F bits in the second flag-extension are 1620 numbered F10, F11, ..., F16, and so forth. As a result, at least 1621 3 Fx bits are always in the PACI, but the number of Fx bits (and 1622 associated types of extensions), can be increased by setting the 1623 next Y bit and adding an octet of flag-extensions, carrying 7 1624 flags and another Y bit. The size of this list of flags is 1625 subject to the limits specified in Section 4.4.4 (32 octets for 1626 all flag-extensions and the PHES information combined). 1628 Each of the F bits can indicate either the presence of 1629 information in the Payload Header Extension Structure (PHES), 1630 described below, or a given F bit can indicate a certain 1631 condition, without including additional information in the PHES. 1633 When a spec developer devises a new syntax that takes advantage 1634 of the PACI extension mechanism, he/she must follow the 1635 constraints listed below; otherwise the extension mechanism may 1636 break. 1638 1) The fields added for a particular Fx bit MUST be fixed in 1639 length and not depend on what other Fx bits are set (no 1640 parsing dependency). 1641 2) The Fx bits must be assigned in order. 1642 3) An implementation that supports the n-th Fn bit for any 1643 value of n must understand the syntax (though not 1644 necessarily the semantics) of the fields Fk (with k < n), so 1645 to be able to either use those bits when present, or at 1646 least be able to skip over them. 1648 4.5 Temporal Scalability Control Information 1650 This section describes the single payload header extension 1651 defined in this specification, known as Temporal Scalability 1652 Control Information (TSCI). If, in the future, additional 1653 payload header extensions become necessary, they could be 1654 specified in this section of an updated version of this document, 1655 or in their own documents. 1657 When F0 is set to 1 in a PACI, this specifies that the PHES field 1658 includes the TSCI fields TL0PICIDX, IrapPicID, S, and E as 1659 follows: 1661 0 1 2 3 1662 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1663 1 1664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1665 +-+ 1666 | PayloadHdr (Type=50) |A| cType | PHSsize |F0..2|Y| 1667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1668 +-+ 1669 | TL0PICIDX | IrapPicID |S|E| RES | | 1670 |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1671 | .... | 1672 | PACI payload: NAL unit | 1673 | | 1674 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1675 +-+ 1676 | :...OPTIONAL RTP padding | 1677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1678 +-+ 1680 Figure 12 The structure of a PACI with a PHES containing a TSCI 1682 TL0PICIDX (8 bits) 1683 When present, the TL0PICIDX field MUST be set to equal to 1684 temporal_sub_layer_zero_idx as specified in Section D.3.22 of 1685 [H.265] for the access unit containing the NAL unit in the 1686 PACI. 1688 IrapPicID (8 bits) 1689 When present, the IrapPicID field MUST be set to equal to 1690 irap_pic_id as specified in Section D.3.22 of [H.265] for the 1691 access unit containing the NAL unit in the PACI. 1693 S (1 bit) 1694 The S bit MUST be set to 1 if any of the following conditions 1695 is true and MUST be set to 0 otherwise: 1696 o The NAL unit in the payload of the PACI is the first VCL NAL 1697 unit, in decoding order, of a picture. 1699 o The NAL unit in the payload of the PACI is an AP and the NAL 1700 unit in the first contained aggregation unit is the first 1701 VCL NAL unit, in decoding order, of a picture. 1702 o The NAL unit in the payload of the PACI is an FU with its S 1703 bit equal to 1 and the FU payload containing a fragment of 1704 the first VCL NAL unit, in decoding order of a picture. 1706 E (1 bit) 1707 The E bit MUST be set to 1 if any of the following conditions 1708 is true and MUST be set to 0 otherwise: 1709 o The NAL unit in the payload of the PACI is the last VCL NAL 1710 unit, in decoding order, of a picture. 1711 o The NAL unit in the payload of the PACI is an AP and the NAL 1712 unit in the last contained aggregation unit is the last VCL 1713 NAL unit, in decoding order, of a picture. 1714 o The NAL unit in the payload of the PACI is an FU with its E 1715 bit equal to 1 and the FU payload containing a fragment of 1716 the last VCL NAL unit, in decoding order of a picture. 1718 RES (6 bits) 1719 MUST be equal to 0. Reserved for future extensions. 1721 The value of PHSsize MUST be set to 3. Receivers MUST allow 1722 other values of the fields F0, F1, F2, Y, and PHSsize, and MUST 1723 ignore any additional fields, when present, than specified above 1724 in the PHES. 1726 4.6 Decoding Order Number 1728 For each NAL unit, the variable AbsDon is derived, representing 1729 the decoding order number that is indicative of the NAL unit 1730 decoding order. 1732 Let NAL unit n be the n-th NAL unit in transmission order within 1733 an RTP stream. 1735 If sprop-max-don-diff is equal to 0 for all the RTP streams 1736 carrying the HEVC bitstream, AbsDon[n], the value of AbsDon for 1737 NAL unit n, is derived as equal to n. 1739 Otherwise (sprop-max-don-diff is greater than 0 for any of the 1740 RTP streams), AbsDon[n] is derived as follows, where DON[n] is 1741 the value of the variable DON for NAL unit n: 1743 o If n is equal to 0 (i.e. NAL unit n is the very first NAL unit 1744 in transmission order), AbsDon[0] is set equal to DON[0]. 1746 o Otherwise (n is greater than 0), the following applies for 1747 derivation of AbsDon[n]: 1749 If DON[n] == DON[n-1], 1750 AbsDon[n] = AbsDon[n-1] 1752 If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768), 1753 AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1] 1755 If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768), 1756 AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n] 1758 If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768), 1759 AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 - 1760 DON[n]) 1762 If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768), 1763 AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n]) 1765 For any two NAL units m and n, the following applies: 1767 o AbsDon[n] greater than AbsDon[m] indicates that NAL unit n 1768 follows NAL unit m in NAL unit decoding order. 1770 o When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding 1771 order of the two NAL units can be in either order. 1773 o AbsDon[n] less than AbsDon[m] indicates that NAL unit n 1774 precedes NAL unit m in decoding order. 1776 Informative note: When two consecutive NAL units in the NAL 1777 unit decoding order have different values of AbsDon, the 1778 absolute difference between the two AbsDon values may be 1779 greater than or equal to 1. 1781 Informative note: There are multiple reasons to allow for the 1782 absolute difference of the values of AbsDon for two 1783 consecutive NAL units in the NAL unit decoding order to be 1784 greater than one. An increment by one is not required, as at 1785 the time of associating values of AbsDon to NAL units, it may 1786 not be known whether all NAL units are to be delivered to the 1787 receiver. For example, a gateway may not forward VCL NAL 1788 units of higher sub-layers or some SEI NAL units when there is 1789 congestion in the network. In another example, the first 1790 intra-coded picture of a pre-encoded clip is transmitted in 1791 advance to ensure that it is readily available in the 1792 receiver, and when transmitting the first intra-coded picture, 1793 the originator does not exactly know how many NAL units will 1794 be encoded before the first intra-coded picture of the pre- 1795 encoded clip follows in decoding order. Thus, the values of 1796 AbsDon for the NAL units of the first intra-coded picture of 1797 the pre-encoded clip have to be estimated when they are 1798 transmitted, and gaps in values of AbsDon may occur. Another 1799 example is MRST or MRMT with sprop-max-don-diff greater than 1800 0, where the AbsDon values must indicate cross-layer decoding 1801 order for NAL units conveyed in all the RTP streams. 1803 5 Packetization Rules 1805 The following packetization rules apply: 1807 o If sprop-max-don-diff is greater than 0 for any of the RTP 1808 streams, the transmission order of NAL units carried in the RTP 1809 stream MAY be different than the NAL unit decoding order and the 1810 NAL unit output order. Otherwise (sprop-max-don-diff is equal 1811 to 0 for all the RTP streams), the transmission order of NAL 1812 units carried in the RTP stream MUST be the same as the NAL unit 1813 decoding order, and, when tx-mode is equal to "MRST" or "MRMT", 1814 MUST also be the same as the NAL unit output order. 1816 o A NAL unit of a small size SHOULD be encapsulated in an 1817 aggregation packet together with one or more other NAL units 1818 in order to avoid the unnecessary packetization overhead for 1819 small NAL units. For example, non-VCL NAL units such as 1820 access unit delimiters, parameter sets, or SEI NAL units are 1821 typically small and can often be aggregated with VCL NAL units 1822 without violating MTU size constraints. 1824 o Each non-VCL NAL unit SHOULD, when possible from an MTU size 1825 match viewpoint, be encapsulated in an aggregation packet 1826 together with its associated VCL NAL unit, as typically a non- 1827 VCL NAL unit would be meaningless without the associated VCL 1828 NAL unit being available. 1830 o For carrying exactly one NAL unit in an RTP packet, a single 1831 NAL unit packet MUST be used. 1833 6 De-packetization Process 1835 The general concept behind de-packetization is to get the NAL 1836 units out of the RTP packets in an RTP stream and all RTP streams 1837 the RTP stream depends on, if any, and pass them to the decoder 1838 in the NAL unit decoding order. 1840 The de-packetization process is implementation dependent. 1841 Therefore, the following description should be seen as an example 1842 of a suitable implementation. Other schemes may be used as well 1843 as long as the output for the same input is the same as the 1844 process described below. The output is the same when the set of 1845 output NAL units and their order are both identical. 1846 Optimizations relative to the described algorithms are possible. 1848 All normal RTP mechanisms related to buffer management apply. In 1849 particular, duplicated or outdated RTP packets (as indicated by 1850 the RTP sequences number and the RTP timestamp) are removed. To 1851 determine the exact time for decoding, factors such as a possible 1852 intentional delay to allow for proper inter-stream 1853 synchronization must be factored in. 1855 NAL units with NAL unit type values in the range of 0 to 47, 1856 inclusive may be passed to the decoder. NAL-unit-like structures 1857 with NAL unit type values in the range of 48 to 63, inclusive, 1858 MUST NOT be passed to the decoder. 1860 The receiver includes a receiver buffer, which is used to 1861 compensate for transmission delay jitter within individual RTP 1862 streams and across RTP streams, to reorder NAL units from 1863 transmission order to the NAL unit decoding order, and to recover 1864 the NAL unit decoding order in MRST or MRMT, when applicable. In 1865 this section, the receiver operation is described under the 1866 assumption that there is no transmission delay jitter within an 1867 RTP stream and across RTP streams. To make a difference from a 1868 practical receiver buffer that is also used for compensation of 1869 transmission delay jitter, the receiver buffer is here after 1870 called the de-packetization buffer in this section. Receivers 1871 should also prepare for transmission delay jitter; i.e. either 1872 reserve separate buffers for transmission delay jitter buffering 1873 and de-packetization buffering or use a receiver buffer for both 1874 transmission delay jitter and de-packetization. Moreover, 1875 receivers should take transmission delay jitter into account in 1876 the buffering operation; e.g. by additional initial buffering 1877 before starting of decoding and playback. 1879 When sprop-max-don-diff is equal to 0 for all the received RTP 1880 streams, the de-packetization buffer size is zero bytes and the 1881 process described in the remainder of this paragraph applies. 1882 When there is only one RTP stream received, the NAL units carried 1883 in the single RTP stream are directly passed to the decoder in 1884 their transmission order, which is identical to their decoding 1885 order. When there is more than one RTP stream received, the NAL 1886 units carried in the multiple RTP streams are passed to the 1887 decoder in their NTP timestamp order. When there are several NAL 1888 units of different RTP streams with the same NTP timestamp, the 1889 order to pass them to the decoder is their dependency order, 1890 where NAL units of a dependee RTP stream are passed to the 1891 decoder prior to the NAL units of the dependent RTP stream. When 1892 there are several NAL units of the same RTP stream with the same 1893 NTP timestamp, the order to pass them to the decoder is their 1894 transmission order. 1896 Informative note: The mapping between RTP and NTP 1897 timestamps is conveyed in RTCP SR packets. In addition, 1898 the mechanisms for faster media timestamp synchronization 1899 discussed in [RFC6051] may be used to speed up the 1900 acquisition of the RTP-to-wall-clock mapping. 1902 When sprop-max-don-diff is greater than 0 for any the received 1903 RTP streams, the process described in the remainder of this 1904 section applies. 1906 There are two buffering states in the receiver: initial buffering 1907 and buffering while playing. Initial buffering starts when the 1908 reception is initialized. After initial buffering, decoding and 1909 playback are started, and the buffering-while-playing mode is 1910 used. 1912 Regardless of the buffering state, the receiver stores incoming 1913 NAL units, in reception order, into the de-packetization buffer. 1914 NAL units carried in RTP packets are stored in the de- 1915 packetization buffer individually, and the value of AbsDon is 1916 calculated and stored for each NAL unit. When MRST or MRMT is in 1917 use, NAL units of all RTP streams of a bitstream are stored in 1918 the same de-packetization buffer. When NAL units carried in any 1919 two RTP streams are available to be placed into the de- 1920 packetization buffer, those NAL units carried in the RTP stream 1921 that is lower in the dependency tree are placed into the buffer 1922 first. For example, if RTP stream A depends on RTP stream B, 1923 then NAL units carried in RTP stream B are placed into the buffer 1924 first. 1926 Initial buffering lasts until condition A (the difference between 1927 the greatest and smallest AbsDon values of the NAL units in the 1928 de-packetization buffer is greater than or equal to the value of 1929 sprop-max-don-diff of the highest RTP stream) or condition B (the 1930 number of NAL units in the de-packetization buffer is greater 1931 than the value of sprop-depack-buf-nalus) is true. 1933 After initial buffering, whenever condition A or condition B is 1934 true, the following operation is repeatedly applied until both 1935 condition A and condition B become false: 1937 o The NAL unit in the de-packetization buffer with the smallest 1938 value of AbsDon is removed from the de-packetization buffer 1939 and passed to the decoder. 1941 When no more NAL units are flowing into the de-packetization 1942 buffer, all NAL units remaining in the de-packetization buffer 1943 are removed from the buffer and passed to the decoder in the 1944 order of increasing AbsDon values. 1946 7 Payload Format Parameters 1948 This section specifies the parameters that MAY be used to select 1949 optional features of the payload format and certain features or 1950 properties of the bitstream or the RTP stream. The parameters 1951 are specified here as part of the media type registration for the 1952 HEVC codec. A mapping of the parameters into the Session 1953 Description Protocol (SDP) [RFC4566] is also provided for 1954 applications that use SDP. Equivalent parameters could be 1955 defined elsewhere for use with control protocols that do not use 1956 SDP. 1958 7.1 Media Type Registration 1960 The media subtype for the HEVC codec is allocated from the IETF 1961 tree. 1963 The receiver MUST ignore any unrecognized parameter. 1965 Media Type name: video 1967 Media subtype name: H265 1969 Required parameters: none 1971 OPTIONAL parameters: 1973 profile-space, tier-flag, profile-id, profile-compatibility- 1974 indicator, interop-constraints, and level-id: 1976 These parameters indicate the profile, tier, default level, 1977 and some constraints of the bitstream carried by the RTP 1978 stream and all RTP streams the RTP stream depends on, or a 1979 specific set of the profile, tier, default level, and some 1980 constraints the receiver supports. 1982 The profile and some constraints are indicated collectively 1983 by profile-space, profile-id, profile-compatibility- 1984 indicator, and interop-constraints. The profile specifies 1985 the subset of coding tools that may have been used to 1986 generate the bitstream or that the receiver supports. 1988 Informative note: There are 32 values of profile-id, and 1989 there are 32 flags in profile-compatibility-indicator, 1990 each flag corresponding to one value of profile-id. 1991 According to HEVC version 1 in [HEVC], when more than 1992 one of the 32 flags is set for a bitstream, the 1993 bitstream would comply with all the profiles 1994 corresponding to the set flags. However, in a draft of 1995 HEVC version 2 in [HEVC draft v2], subclause A.3.5, 19 1996 Format Range Extensions profiles have been specified, 1997 all using the same value of profile-id (4), 1998 differentiated by some of the 48 bits in interop- 1999 constraints - this (rather unexpected way of profile 2000 signalling) means that one of the 32 flags may 2001 correspond to multiple profiles. To be able to support 2002 whatever HEVC extension profile that might be specified 2003 and indicated using profile-space, profile-id, profile- 2004 compatibility-indicator, and interop-constraints in the 2005 future, it would be safe to require symmetric use of 2006 these parameters in SDP offer/answer unless recv-sub- 2007 layer-id is included in the SDP answer for choosing one 2008 of the sub-layers offered. 2010 The tier is indicated by tier-flag. The default level is 2011 indicated by level-id. The tier and the default level 2012 specify the limits on values of syntax elements or 2013 arithmetic combinations of values of syntax elements that 2014 are followed when generating the bitstream or that the 2015 receiver supports. 2017 A set of profile-space, tier-flag, profile-id, profile- 2018 compatibility-indicator, interop-constraints, and level-id 2019 parameters ptlA is said to be consistent with another set 2020 of these parameters ptlB if any decoder that conforms to 2021 the profile, tier, level, and constraints indicated by ptlB 2022 can decode any bitstream that conforms to the profile, 2023 tier, level, and constraints indicated by ptlA. 2025 In SDP offer/answer, when the SDP answer does not include 2026 the recv-sub-layer-id parameter that is less than the 2027 sprop-sub-layer-id parameter in the SDP offer, the 2028 following applies: 2030 o The profile-space, tier-flag, profile-id, profile- 2031 compatibility-indicator, and interop-constraints 2032 parameters MUST be used symmetrically, i.e. the value 2033 of each of these parameters in the offer MUST be the 2034 same as that in the answer, either explicitly 2035 signalled or implicitly inferred. 2036 o The level-id parameter is changeable as long as the 2037 highest level indicated by the answer is either equal 2038 to or lower than that in the offer. Note that the 2039 highest level is indicated by level-id and max-recv- 2040 level-id together. 2042 In SDP offer/answer, when the SDP answer does include the 2043 recv-sub-layer-id parameter that is less than the sprop- 2044 sub-layer-id parameter in the SDP offer, the set of 2045 profile-space, tier-flag, profile-id, profile- 2046 compatibility-indicator, interop-constraints, and level-id 2047 parameters included in the answer MUST be consistent with 2048 that for the chosen sub-layer representation as indicated 2049 in the SDP offer, with the exception that the level-id 2050 parameter in the SDP answer is changable as long as the 2051 highest level indicated by the answer is either lower than 2052 or equal to that in the offer. 2054 More specifications of these parameters, including how they 2055 relate to the values of the profile, tier, and level syntax 2056 elements specified in [HEVC] are provided below. 2058 profile-space, profile-id: 2060 The value of profile-space MUST be in the range of 0 to 3, 2061 inclusive. The value of profile-id MUST be in the range of 2062 0 to 31, inclusive. 2064 When profile-space is not present, a value of 0 MUST be 2065 inferred. When profile-id is not present, a value of 1 2066 (i.e. the Main profile) MUST be inferred. 2068 When used to indicate properties of a bitstream, profile- 2069 space and profile-id are derived from the profile, tier, 2070 and level syntax elements in SPS or VPS NAL units as 2071 follows, where general_profile_space, general_profile_idc, 2072 sub_layer_profile_space[j], and sub_layer_profile_idc[j] 2073 are specified in [HEVC]: 2075 If the RTP stream is the highest RTP stream, the 2076 following applies: 2078 o profile_space = general_profile_space 2079 o profile_id = general_profile_idc 2081 Otherwise (the RTP stream is a dependee RTP stream), the 2082 following applies, with j being the value of the sprop- 2083 sub-layer-id parameter: 2085 o profile_space = sub_layer_profile_space[j] 2086 o profile_id = sub_layer_profile_idc[j] 2088 tier-flag, level-id: 2090 The value of tier-flag MUST be in the range of 0 to 1, 2091 inclusive. The value of level-id MUST be in the range of 0 2092 to 255, inclusive. 2094 If the tier-flag and level-id parameters are used to 2095 indicate properties of a bitstream, they indicate the tier 2096 and the highest level the bitstream complies with. 2098 If the tier-flag and level-id parameters are used for 2099 capability exchange, the following applies. If max-recv- 2100 level-id is not present, the default level defined by 2101 level-id indicates the highest level the codec wishes to 2102 support. Otherwise, max-recv-level-id indicates the 2103 highest level the codec supports for receiving. For either 2104 receiving or sending, all levels that are lower than the 2105 highest level supported MUST also be supported. 2107 If no tier-flag is present, a value of 0 MUST be inferred 2108 and if no level-id is present, a value of 93 (i.e. level 2109 3.1) MUST be inferred. 2111 When used to indicate properties of a bitstream, the tier- 2112 flag and level-id parameters are derived from the profile, 2113 tier, and level syntax elements in SPS or VPS NAL units as 2114 follows, where general_tier_flag, general_level_idc, 2115 sub_layer_tier_flag[j], and sub_layer_level_idc[j] are 2116 specified in [HEVC]: 2118 If the RTP stream is the highest RTP stream, the 2119 following applies: 2121 o tier-flag = general_tier_flag 2122 o level-id = general_level_idc 2124 Otherwise (the RTP stream is a dependee RTP stream), the 2125 following applies, with j being the value of the sprop- 2126 sub-layer-id parameter: 2128 o tier-flag = sub_layer_tier_flag[j] 2129 o level-id = sub_layer_level_idc[j] 2131 interop-constraints: 2133 A base16 [RFC4648] (hexadecimal) representation of six 2134 bytes of data, consisting of progressive_source_flag, 2135 interlaced_source_flag, non_packed_constraint_flag, 2136 frame_only_constraint_flag, and reserved_zero_44bits. 2138 If the interop-constraints parameter is not present, the 2139 following MUST be inferred: 2141 o progressive_source_flag = 1 2142 o interlaced_source_flag = 0 2143 o non_packed_constraint_flag = 1 2144 o frame_only_constraint_flag = 1 2145 o reserved_zero_44bits = 0 2147 When the interop-constraints parameter is used to indicate 2148 properties of a bitstream, the following applies, where 2149 general_progressive_source_flag, 2150 general_interlaced_source_flag, 2151 general_non_packed_constraint_flag, 2152 general_non_packed_constraint_flag, 2153 general_frame_only_constraint_flag, 2154 general_reserved_zero_44bits, 2155 sub_layer_progressive_source_flag[j], 2156 sub_layer_interlaced_source_flag[j], 2157 sub_layer_non_packed_constraint_flag[j], 2158 sub_layer_frame_only_constraint_flag[j], and 2159 sub_layer_reserved_zero_44bits[j] are specified in [HEVC]: 2161 If the RTP stream is the highest RTP stream, the 2162 following applies: 2164 o progressive_source_flag = 2165 general_progressive_source_flag 2166 o interlaced_source_flag = 2167 general_interlaced_source_flag 2168 o non_packed_constraint_flag = 2169 general_non_packed_constraint_flag 2170 o frame_only_constraint_flag = 2171 general_frame_only_constraint_flag 2172 o reserved_zero_44bits = general_reserved_zero_44bits 2174 Otherwise (the RTP stream is a dependee RTP stream), the 2175 following applies, with j being the value of the sprop- 2176 sub-layer-id parameter: 2178 o progressive_source_flag = 2179 sub_layer_progressive_source_flag[j] 2180 o interlaced_source_flag = 2181 sub_layer_interlaced_source_flag[j] 2182 o non_packed_constraint_flag = 2184 sub_layer_non_packed_constraint_flag[j] 2186 o frame_only_constraint_flag = 2188 sub_layer_frame_only_constraint_flag[j] 2189 o reserved_zero_44bits = 2190 sub_layer_reserved_zero_44bits[j] 2192 Using interop-constraints for capability exchange results 2193 in a requirement on any bitstream to be compliant with the 2194 interop-constraints. 2196 profile-compatibility-indicator: 2198 A base16 [RFC4648] representation of four bytes of data. 2200 When profile-compatibility-indicator is used to indicate 2201 properties of a bitstream, the following applies, where 2202 general_profile_compatibility_flag[j] and 2203 sub_layer_profile_compatibility_flag[i][j] are specified in 2204 [HEVC]: 2206 The profile-compatibility-indicator in this case 2207 indicates additional profiles to the profile defined by 2208 profile_space, profile_id, and interop-constraints the 2209 bitstream conforms to. A decoder that conforms to any 2210 of all the profiles the bitstream conforms to would be 2211 capable of decoding the bitstream. These additional 2212 profiles are defined by profile-space, each set bit of 2213 profile-compatibility-indicator, and interop- 2214 constraints. 2216 If the RTP stream is the highest RTP stream, the 2217 following applies for each value of j in the range of 0 2218 to 31, inclusive: 2220 o bit j of profile-compatibility-indicator = 2221 general_profile_compatibility_flag[j] 2223 Otherwise (the RTP stream is a dependee RTP stream), the 2224 following applies for i equal to sprop-sub-layer-id and 2225 for each value of j in the range of 0 to 31, inclusive: 2227 o bit j of profile-compatibility-indicator = 2228 sub_layer_profile_compatibility_flag[i][j] 2230 Using profile-compatibility-indicator for capability 2231 exchange results in a requirement on any bitstream to be 2232 compliant with the profile-compatibility-indicator. This 2233 is intended to handle cases where any future HEVC profile 2234 is defined as an intersection of two or more profiles. 2236 If this parameter is not present, this parameter defaults 2237 to the following: bit j, with j equal to profile-id, of 2238 profile-compatibility-indicator is inferred to be equal to 2239 1, and all other bits are inferred to be equal to 0. 2241 sprop-sub-layer-id: 2243 This parameter MAY be used to indicate the highest allowed 2244 value of TID in the bitstream. When not present, the value 2245 of sprop-sub-layer-id is inferred to be equal to 6. 2247 The value of sprop-sub-layer-id MUST be in the range of 0 2248 to 6, inclusive. 2250 recv-sub-layer-id: 2252 This parameter MAY be used to signal a receiver's choice of 2253 the offered or declared sub-layer representations in the 2254 sprop-vps. The value of recv-sub-layer-id indicates the 2255 TID of the highest sub-layer of the bitstream that a 2256 receiver supports. When not present, the value of recv- 2257 sub-layer-id is inferred to be equal to the value of the 2258 sprop-sub-layer-id parameter in the SDP offer. 2260 The value of recv-sub-layer-id MUST be in the range of 0 to 2261 6, inclusive. 2263 max-recv-level-id: 2265 This parameter MAY be used to indicate the highest level a 2266 receiver supports. The highest level the receiver supports 2267 is equal to the value of max-recv-level-id divided by 30. 2269 The value of max-recv-level-id MUST be in the range of 0 2270 to 255, inclusive. 2272 When max-recv-level-id is not present, the value is 2273 inferred to be equal to level-id. 2275 max-recv-level-id MUST NOT be present when the highest 2276 level the receiver supports is not higher than the default 2277 level. 2279 tx-mode: 2281 This parameter indicates whether the transmission mode is 2282 SRST, MRST, or MRMT. 2284 The value of tx-mode MUST be equal to "SRST", "MRST" or 2285 "MRMT". When not present, the value of tx-mode is inferred 2286 to be equal to "SRST". 2288 If the value is equal to "MRST", MRST MUST be in use. 2289 Otherwise, if the value is equal to "MRMT", MRMT MUST be in 2290 use. Otherwise (the value is equal to "SRST"), SRST MUST be 2291 in use. 2293 The value of tx-mode MUST be equal to "MRST" for all RTP 2294 streams in an MRST. 2296 The value of tx-mode MUST be equal to "MRMT" for all RTP 2297 streams in an MRMT. 2299 sprop-vps: 2301 This parameter MAY be used to convey any video parameter 2302 set NAL unit of the bitstream for out-of-band transmission 2303 of video parameter sets. The parameter MAY also be used 2304 for capability exchange and to indicate sub-stream 2305 characteristics (i.e. properties of sub-layer 2306 representations as defined in [HEVC]). The value of the 2307 parameter is a comma-separated (',') list of base64 2308 [RFC4648] representations of the video parameter set NAL 2309 units as specified in Section 7.3.2.1 of [HEVC]. 2311 The sprop-vps parameter MAY contain one or more than one 2312 video parameter set NAL unit. However, all other video 2313 parameter sets contained in the sprop-vps parameter MUST be 2314 consistent with the first video parameter set in the sprop- 2315 vps parameter. A video parameter set vpsB is said to be 2316 consistent with another video parameter set vpsA if any 2317 decoder that conforms to the profile, tier, level, and 2318 constraints indicated by the 12 bytes of data starting from 2319 the syntax element general_profile_space to the syntax 2320 element general_level_id, inclusive, in the first 2321 profile_tier_level( ) syntax structure in vpsA can decode 2322 any bitstream that conforms to the profile, tier, level, 2323 and constraints indicated by the 12 bytes of data starting 2324 from the syntax element general_profile_space to the syntax 2325 element general_level_id, inclusive, in the first 2326 profile_tier_level( ) syntax structure in vpsB. 2328 sprop-sps: 2330 This parameter MAY be used to convey sequence parameter set 2331 NAL units of the bitstream for out-of-band transmission of 2332 sequence parameter sets. The value of the parameter is a 2333 comma-separated (',') list of base64 [RFC4648] 2334 representations of the sequence parameter set NAL units as 2335 specified in Section 7.3.2.2 of [HEVC]. 2337 sprop-pps: 2339 This parameter MAY be used to convey picture parameter set 2340 NAL units of the bitstream for out-of-band transmission of 2341 picture parameter sets. The value of the parameter is a 2342 comma-separated (',') list of base64 [RFC4648] 2343 representations of the picture parameter set NAL units as 2344 specified in Section 7.3.2.3 of [HEVC]. 2346 sprop-sei: 2348 This parameter MAY be used to convey one or more SEI 2349 messages that describe bitstream characteristics. When 2350 present, a decoder can rely on the bitstream 2351 characteristics that are described in the SEI messages for 2352 the entire duration of the session, independently from the 2353 persistence scopes of the SEI messages as specified in 2354 [HEVC]. 2356 The value of the parameter is a comma-separated (',') list 2357 of base64 [RFC4648] representations of SEI NAL units as 2358 specified in Section 7.3.2.4 of [HEVC]. 2360 Informative note: Intentionally, no list of applicable 2361 or inapplicable SEI messages is specified here. 2362 Conveying certain SEI messages in sprop-sei may be 2363 sensible in some application scenarios and meaningless 2364 in others. However, a few examples are described below: 2366 1) In an environment where the bitstream was created 2367 from film-based source material, and no splicing is 2368 going to occur during the lifetime of the session, 2369 the film grain characteristics SEI message or the 2370 tone mapping information SEI message are likely 2371 meaningful, and sending them in sprop-sei rather than 2372 in the bitstream at each entry point may help saving 2373 bits and allows to configure the renderer only once, 2374 avoiding unwanted artifacts. 2375 2) The structure of pictures information SEI message in 2376 sprop-sei can be used to inform a decoder of 2377 information on the NAL unit types, picture order 2378 count values, and prediction dependencies of a 2379 sequence of pictures. Having such knowledge can be 2380 helpful for error recovery. 2381 3) Examples for SEI messages that would be meaningless 2382 to be conveyed in sprop-sei include the decoded 2383 picture hash SEI message (it is close to impossible 2384 that all decoded pictures have the same hash-tag), 2385 the display orientation SEI message when the device 2386 is a handheld device (as the display orientation may 2387 change when the handheld device is turned around), or 2388 the filler payload SEI message (as there is no point 2389 in just having more bits in SDP). 2391 max-lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, max-tc: 2393 These parameters MAY be used to signal the capabilities of 2394 a receiver implementation. These parameters MUST NOT be 2395 used for any other purpose. The highest level (specified 2396 by max-recv-level-id) MUST be such that the receiver is 2397 fully capable of supporting. max-lsr, max-lps, max-cpb, 2398 max-dpb, max-br, max-tr, and max-tc MAY be used to indicate 2399 capabilities of the receiver that extend the required 2400 capabilities of the highest level, as specified below. 2402 When more than one parameter from the set (max-lsr, max- 2403 lps, max-cpb, max-dpb, max-br, max-tr, max-tc) is present, 2404 the receiver MUST support all signaled capabilities 2405 simultaneously. For example, if both max-lsr and max-br 2406 are present, the highest level with the extension of both 2407 the picture rate and bitrate is supported. That is, the 2408 receiver is able to decode bitstreams in which the luma 2409 sample rate is up to max-lsr (inclusive), the bitrate is up 2410 to max-br (inclusive), the coded picture buffer size is 2411 derived as specified in the semantics of the max-br 2412 parameter below, and the other properties comply with the 2413 highest level specified by max-recv-level-id. 2415 Informative note: When the OPTIONAL media type 2416 parameters are used to signal the properties of a 2417 bitstream, and max-lsr, max-lps, max-cpb, max-dpb, max- 2418 br, max-tr, and max-tc are not present, the values of 2419 profile-space, tier-flag, profile-id, profile- 2420 compatibility-indicator, interop-constraints, and level- 2421 id must always be such that the bitstream complies fully 2422 with the specified profile, tier, and level. 2424 max-lsr: 2425 The value of max-lsr is an integer indicating the maximum 2426 processing rate in units of luma samples per second. The 2427 max-lsr parameter signals that the receiver is capable of 2428 decoding video at a higher rate than is required by the 2429 highest level. 2431 When max-lsr is signaled, the receiver MUST be able to 2432 decode bitstreams that conform to the highest level, with 2433 the exception that the MaxLumaSR value in Table A-2 of 2434 [HEVC] for the highest level is replaced with the value of 2435 max-lsr. Senders MAY use this knowledge to send pictures 2436 of a given size at a higher picture rate than is indicated 2437 in the highest level. 2439 When not present, the value of max-lsr is inferred to be 2440 equal to the value of MaxLumaSR given in Table A-2 of 2441 [HEVC] for the highest level. 2443 The value of max-lsr MUST be in the range of MaxLumaSR to 2444 16 * MaxLumaSR, inclusive, where MaxLumaSR is given in 2445 Table A-2 of [HEVC] for the highest level. 2447 max-lps: 2448 The value of max-lps is an integer indicating the maximum 2449 picture size in units of luma samples. The max-lps 2450 parameter signals that the receiver is capable of decoding 2451 larger picture sizes than are required by the highest 2452 level. When max-lps is signaled, the receiver MUST be able 2453 to decode bitstreams that conform to the highest level, 2454 with the exception that the MaxLumaPS value in Table A-1 of 2455 [HEVC] for the highest level is replaced with the value of 2456 max-lps. Senders MAY use this knowledge to send larger 2457 pictures at a proportionally lower picture rate than is 2458 indicated in the highest level. 2460 When not present, the value of max-lps is inferred to be 2461 equal to the value of MaxLumaPS given in Table A-1 of 2462 [HEVC] for the highest level. 2464 The value of max-lps MUST be in the range of MaxLumaPS to 2465 16 * MaxLumaPS, inclusive, where MaxLumaPS is given in 2466 Table A-1 of [HEVC] for the highest level. 2468 max-cpb: 2469 The value of max-cpb is an integer indicating the maximum 2470 coded picture buffer size in units of CpbBrVclFactor bits 2471 for the VCL HRD parameters and in units of CpbBrNalFactor 2472 bits for the NAL HRD parameters, where CpbBrVclFactor and 2473 CpbBrNalFactor are defined in Section A.4 of [HEVC]. The 2474 max-cpb parameter signals that the receiver has more memory 2475 than the minimum amount of coded picture buffer memory 2476 required by the highest level. When max-cpb is signaled, 2477 the receiver MUST be able to decode bitstreams that conform 2478 to the highest level, with the exception that the MaxCPB 2479 value in Table A-1 of [HEVC] for the highest level is 2480 replaced with the value of max-cpb. Senders MAY use this 2481 knowledge to construct coded bitstreams with greater 2482 variation of bitrate than can be achieved with the MaxCPB 2483 value in Table A-1 of [HEVC]. 2485 When not present, the value of max-cpb is inferred to be 2486 equal to the value of MaxCPB given in Table A-1 of [HEVC] 2487 for the highest level. 2489 The value of max-cpb MUST be in the range of MaxCPB to 2490 16 * MaxCPB, inclusive, where MaxLumaCPB is given in Table 2491 A-1 of [HEVC] for the highest level. 2493 Informative note: The coded picture buffer is used in 2494 the hypothetical reference decoder (Annex C of HEVC). 2495 The use of the hypothetical reference decoder is 2496 recommended in HEVC encoders to verify that the produced 2497 bitstream conforms to the standard and to control the 2498 output bitrate. Thus, the coded picture buffer is 2499 conceptually independent of any other potential buffers 2500 in the receiver, including de-packetization and de- 2501 jitter buffers. The coded picture buffer need not be 2502 implemented in decoders as specified in Annex C of HEVC, 2503 but rather standard-compliant decoders can have any 2504 buffering arrangements provided that they can decode 2505 standard-compliant bitstreams. Thus, in practice, the 2506 input buffer for a video decoder can be integrated with 2507 de-packetization and de-jitter buffers of the receiver. 2509 max-dpb: 2510 The value of max-dpb is an integer indicating the maximum 2511 decoded picture buffer size in units decoded pictures at 2512 the MaxLumaPS for the highest level, i.e. the number of 2513 decoded pictures at the maximum picture size defined by the 2514 highest level. The value of max-dpb MUST be in the range 2515 of 1 to 16, respectively. The max-dpb parameter signals 2516 that the receiver has more memory than the minimum amount 2517 of decoded picture buffer memory required by default, which 2518 is MaxDpbPicBuf as defined in [HEVC] (equal to 6). When 2519 max-dpb is signaled, the receiver MUST be able to decode 2520 bitstreams that conform to the highest level, with the 2521 exception that the MaxDpbPicBuff value defined in [HEVC] as 2522 6 is replaced with the value of max-dpb. Consequently, a 2523 receiver that signals max-dpb MUST be capable of storing 2524 the following number of decoded pictures (MaxDpbSize) in 2525 its decoded picture buffer: 2527 if( PicSizeInSamplesY <= ( MaxLumaPS >> 2 ) ) 2528 MaxDpbSize = Min( 4 * max-dpb, 16 ) 2529 else if ( PicSizeInSamplesY <= ( MaxLumaPS >> 1 ) ) 2530 MaxDpbSize = Min( 2 * max-dpb, 16 ) 2531 else if ( PicSizeInSamplesY <= ( ( 3 * MaxLumaPS ) >> 2 2532 ) ) 2533 MaxDpbSize = Min( (4 * max-dpb) / 3, 16 ) 2534 else 2535 MaxDpbSize = max-dpb 2537 Wherein MaxLumaPS given in Table A-1 of [HEVC] for the 2538 highest level and PicSizeInSamplesY is the current size of 2539 each decoded picture in units of luma samples as defined in 2540 [HEVC]. 2542 The value of max-dpb MUST be greater than or equal to the 2543 value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC]. 2544 Senders MAY use this knowledge to construct coded 2545 bitstreams with improved compression. 2547 When not present, the value of max-dpb is inferred to be 2548 equal to the value of MaxDpbPicBuf (i.e. 6) as defined in 2549 [HEVC]. 2551 Informative note: This parameter was added primarily to 2552 complement a similar codepoint in the ITU-T 2553 Recommendation H.245, so as to facilitate signaling 2554 gateway designs. The decoded picture buffer stores 2555 reconstructed samples. There is no relationship between 2556 the size of the decoded picture buffer and the buffers 2557 used in RTP, especially de-packetization and de-jitter 2558 buffers. 2560 max-br: 2561 The value of max-br is an integer indicating the maximum 2562 video bitrate in units of CpbBrVclFactor bits per second 2563 for the VCL HRD parameters and in units of CpbBrNalFactor 2564 bits per second for the NAL HRD parameters, where 2565 CpbBrVclFactor and CpbBrNalFactor are defined in Section 2566 A.4 of [HEVC]. 2568 The max-br parameter signals that the video decoder of the 2569 receiver is capable of decoding video at a higher bitrate 2570 than is required by the highest level. 2572 When max-br is signaled, the video codec of the receiver 2573 MUST be able to decode bitstreams that conform to the 2574 highest level, with the following exceptions in the limits 2575 specified by the highest level: 2577 o The value of max-br replaces the MaxBR value in Table A- 2578 2 of [HEVC] for the highest level. 2579 o When the max-cpb parameter is not present, the result of 2580 the following formula replaces the value of MaxCPB in 2581 Table A-1 of [HEVC]: 2583 (MaxCPB of the highest level) * max-br / (MaxBR of 2584 the highest level) 2586 For example, if a receiver signals capability for Main 2587 profile Level 2 with max-br equal to 2000, this indicates a 2588 maximum video bitrate of 2000 kbits/sec for VCL HRD 2589 parameters, a maximum video bitrate of 2200 kbits/sec for 2590 NAL HRD parameters, and a CPB size of 2000000 bits (2000000 2591 / 1500000 * 1500000). 2593 Senders MAY use this knowledge to send higher bitrate video 2594 as allowed in the level definition of Annex A of HEVC to 2595 achieve improved video quality. 2597 When not present, the value of max-br is inferred to be 2598 equal to the value of MaxBR given in Table A-2 of [HEVC] 2599 for the highest level. 2601 The value of max-br MUST be in the range of MaxBR to 2602 16 * MaxBR, inclusive, where MaxBR is given in Table A-2 of 2603 [HEVC] for the highest level. 2605 Informative note: This parameter was added primarily to 2606 complement a similar codepoint in the ITU-T 2607 Recommendation H.245, so as to facilitate signaling 2608 gateway designs. The assumption that the network is 2609 capable of handling such bitrates at any given time 2610 cannot be made from the value of this parameter. In 2611 particular, no conclusion can be drawn that the signaled 2612 bitrate is possible under congestion control 2613 constraints. 2615 max-tr: 2616 The value of max-tr is an integer indication the maximum 2617 number of tile rows. The max-tr parameter signals that the 2618 receiver is capable of decoding video with a larger number 2619 of tile rows than the value allowed by the highest level. 2621 When max-tr is signaled, the receiver MUST be able to 2622 decode bitstreams that conform to the highest level, with 2623 the exception that the MaxTileRows value in Table A-1 of 2624 [HEVC] for the highest level is replaced with the value of 2625 max-tr. 2627 Senders MAY use this knowledge to send pictures utilizing a 2628 larger number of tile rows than the value allowed by the 2629 highest level. 2631 When not present, the value of max-tr is inferred to be 2632 equal to the value of MaxTileRows given in Table A-1 of 2633 [HEVC] for the highest level. 2635 The value of max-tr MUST be in the range of MaxTileRows to 2636 16 * MaxTileRows, inclusive, where MaxTileRows is given in 2637 Table A-1 of [HEVC] for the highest level. 2639 max-tc: 2640 The value of max-tc is an integer indication the maximum 2641 number of tile columns. The max-tc parameter signals that 2642 the receiver is capable of decoding video with a larger 2643 number of tile columns than the value allowed by the 2644 highest level. 2646 When max-tc is signaled, the receiver MUST be able to 2647 decode bitstreams that conform to the highest level, with 2648 the exception that the MaxTileCols value in Table A-1 of 2649 [HEVC] for the highest level is replaced with the value of 2650 max-tc. 2652 Senders MAY use this knowledge to send pictures utilizing a 2653 larger number of tile columns than the value allowed by the 2654 highest level. 2656 When not present, the value of max-tc is inferred to be 2657 equal to the value of MaxTileCols given in Table A-1 of 2658 [HEVC] for the highest level. 2660 The value of max-tc MUST be in the range of MaxTileCols to 2661 16 * MaxTileCols, inclusive, where MaxTileCols is given in 2662 Table A-1 of [HEVC] for the highest level. 2664 max-fps: 2666 The value of max-fps is an integer indicating the maximum 2667 picture rate in units of pictures per 100 seconds that can 2668 be effectively processed by the receiver. The max-fps 2669 parameter MAY be used to signal that the receiver has a 2670 constraint in that it is not capable of processing video 2671 effectively at the full picture rate that is implied by the 2672 highest level and, when present, one or more of the 2673 parameters max-lsr, max-lps, and max-br. 2675 The value of max-fps is not necessarily the picture rate at 2676 which the maximum picture size can be sent, it constitutes 2677 a constraint on maximum picture rate for all resolutions. 2679 Informative note: The max-fps parameter is semantically 2680 different from max-lsr, max-lps, max-cpb, max-dpb, max- 2681 br, max-tr, and max-tc in that max-fps is used to signal 2682 a constraint, lowering the maximum picture rate from 2683 what is implied by other parameters. 2685 The encoder MUST use a picture rate equal to or less than 2686 this value. In cases where the max-fps parameter is absent 2687 the encoder is free to choose any picture rate according to 2688 the highest level and any signaled optional parameters. 2690 The value of max-fps MUST be smaller than or equal to the 2691 full picture rate that is implied by the highest level and, 2692 when present, one or more of the parameters max-lsr, max- 2693 lps, and max-br. 2695 sprop-max-don-diff: 2697 If tx-mode is equal to "SRST" and there is no NAL unit 2698 naluA that is followed in transmission order by any NAL 2699 unit preceding naluA in decoding order (i.e. the 2700 transmission order of the NAL units is the same as the 2701 decoding order), the value of this parameter MUST be equal 2702 to 0. 2704 Otherwise, if tx-mode is equal to "MRST" or "MRMT", the 2705 decoding order of the NAL units of all the RTP streams is 2706 the same as the NAL unit transmission order and the NAL 2707 unit output order, the value of this parameter MUST be 2708 equal to either 0 or 1. 2710 Otherwise, if tx-mode is equal to "MRST" or "MRMT" and the 2711 decoding order of the NAL units of all the RTP streams is 2712 the same as the NAL unit transmission order but not the 2713 same as the NAL unit output order, the value of this 2714 parameter MUST be equal to 1. 2716 Otherwise, this parameter specifies the maximum absolute 2717 difference between the decoding order number (i.e., AbsDon) 2718 values of any two NAL units naluA and naluB, where naluA 2719 follows naluB in decoding order and precedes naluB in 2720 transmission order. 2722 The value of sprop-max-don-diff MUST be an integer in the 2723 range of 0 to 32767, inclusive. 2725 When not present, the value of sprop-max-don-diff is 2726 inferred to be equal to 0. 2728 sprop-depack-buf-nalus: 2730 This parameter specifies the maximum number of NAL units 2731 that precede a NAL unit in transmission order and follow 2732 the NAL unit in decoding order. 2734 The value of sprop-depack-buf-nalus MUST be an integer in 2735 the range of 0 to 32767, inclusive. 2737 When not present, the value of sprop-depack-buf-nalus is 2738 inferred to be equal to 0. 2740 When sprop-max-don-diff is present and greater than 0, this 2741 parameter MUST be present and the value MUST be greater 2742 than 0. 2744 sprop-depack-buf-bytes: 2746 This parameter signals the required size of the de- 2747 packetization buffer in units of bytes. The value of the 2748 parameter MUST be greater than or equal to the maximum 2749 buffer occupancy (in units of bytes) of the de- 2750 packetization buffer as specified in Section 6. 2752 The value of sprop-depack-buf-bytes MUST be an integer in 2753 the range of 0 to 4294967295, inclusive. 2755 When sprop-max-don-diff is present and greater than 0, this 2756 parameter MUST be present and the value MUST be greater 2757 than 0. When not present, the value of sprop-depack-buf- 2758 bytes is inferred to be equal to 0. 2760 Informative note: The value of sprop-depack-buf-bytes 2761 indicates the required size of the de-packetization 2762 buffer only. When network jitter can occur, an 2763 appropriately sized jitter buffer has to be available as 2764 well. 2766 depack-buf-cap: 2768 This parameter signals the capabilities of a receiver 2769 implementation and indicates the amount of de-packetization 2770 buffer space in units of bytes that the receiver has 2771 available for reconstructing the NAL unit decoding order 2772 from NAL units carried in one or more RTP streams. A 2773 receiver is able to handle any RTP stream, and all RTP 2774 streams the RTP stream depends on, when present, for which 2775 the value of the sprop-depack-buf-bytes parameter is 2776 smaller than or equal to this parameter. 2778 When not present, the value of depack-buf-cap is inferred 2779 to be equal to 4294967295. The value of depack-buf-cap 2780 MUST be an integer in the range of 1 to 4294967295, 2781 inclusive. 2783 Informative note: depack-buf-cap indicates the maximum 2784 possible size of the de-packetization buffer of the 2785 receiver only. When network jitter can occur, an 2786 appropriately sized jitter buffer has to be available as 2787 well. 2789 sprop-segmentation-id: 2791 This parameter MAY be used to signal the segmentation tools 2792 present in the bitstream and that can be used for 2793 parallelization. The value of sprop-segmentation-id MUST 2794 be an integer in the range of 0 to 3, inclusive. When not 2795 present, the value of sprop-segmentation-id is inferred to 2796 be equal to 0. 2798 When sprop-segmentation-id is equal to 0, no information 2799 about the segmentation tools is provided. When sprop- 2800 segmentation-id is equal to 1, it indicates that slices are 2801 present in the bitstream. When sprop-segmentation-id is 2802 equal to 2, it indicates that tiles are present in the 2803 bitstream. When sprop-segmentation-id is equal to 3, it 2804 indicates that WPP is used in the bitstream. 2806 sprop-spatial-segmentation-idc: 2808 A base16 [RFC4648] representation of the syntax element 2809 min_spatial_segmentation_idc as specified in [HEVC]. This 2810 parameter MAY be used to describe parallelization 2811 capabilities of the bitstream. 2813 dec-parallel-cap: 2815 This parameter MAY be used to indicate the decoder's 2816 additional decoding capabilities given the presence of 2817 tools enabling parallel decoding, such as slices, tiles, 2818 and WPP, in the bitstream. The decoding capability of the 2819 decoder may vary with the setting of the parallel decoding 2820 tools present in the bitstream, e.g. the size of the tiles 2821 that are present in a bitstream. Therefore, multiple 2822 capability points may be provided, each indicating the 2823 minimum required decoding capability that is associated 2824 with a parallelism requirement, which is a requirement on 2825 the bitstream that enables parallel decoding. 2827 Each capability point is defined as a combination of 1) a 2828 parallelism requirement, 2) a profile (determined by 2829 profile-space and profile-id), 3) a highest level, and 4) a 2830 maximum processing rate, a maximum picture size, and a 2831 maximum video bitrate that may be equal to or greater than 2832 that determined by the highest level. The parameter's 2833 syntax in ABNF [RFC5234] is as follows: 2835 dec-parallel-cap = "dec-parallel-cap={" cap-point *("," 2836 cap-point) "}" 2838 cap-point = ("w" / "t") ":" spatial-seg-idc 1*(";" 2839 cap-parameter) 2841 spatial-seg-idc = 1*4DIGIT ; (1-4095) 2843 cap-parameter = tier-flag / level-id / max-lsr 2844 / max-lps / max-br 2846 tier-flag = "tier-flag" EQ ("0" / "1") 2848 level-id = "level-id" EQ 1*3DIGIT ; (0-255) 2850 max-lsr = "max-lsr" EQ 1*20DIGIT ; (0- 2851 18,446,744,073,709,551,615) 2853 max-lps = "max-lps" EQ 1*10DIGIT ; (0-4,294,967,295) 2855 max-br = "max-br" EQ 1*20DIGIT ; (0- 2856 18,446,744,073,709,551,615) 2858 EQ = "=" 2860 The set of capability points expressed by the dec-parallel- 2861 cap parameter is enclosed in a pair of curly braces ("{}"). 2862 Each set of two consecutive capability points is separated 2863 by a comma (','). Within each capability point, each set 2864 of two consecutive parameters, and when present, their 2865 values, is separated by a semicolon (';'). 2867 The profile of all capability points is determined by 2868 profile-space and profile-id that are outside the dec- 2869 parallel-cap parameter. 2871 Each capability point starts with an indication of the 2872 parallelism requirement, which consists of a parallel tool 2873 type, which may be equal to 'w' or 't', and a decimal value 2874 of the spatial-seg-idc parameter. When the type is 'w', 2875 the capability point is valid only for H.265 bitstreams 2876 with WPP in use, i.e. entropy_coding_sync_enabled_flag 2877 equal to 1. When the type is 't', the capability point is 2878 valid only for H.265 bitstreams with WPP not in use (i.e. 2879 entropy_coding_sync_enabled_flag equal to 0). The 2880 capability-point is valid only for H.265 bitstreams with 2881 min_spatial_segmentation_idc equal to or greater than 2882 spatial-seg-idc. 2884 After the parallelism requirement indication, each 2885 capability point continues with one or more pairs of 2886 parameter and value in any order for any of the following 2887 parameters: 2889 o tier-flag 2890 o level-id 2891 o max-lsr 2892 o max-lps 2893 o max-br 2895 At most one occurrence of each of the above five parameters 2896 is allowed within each capability point. 2898 The values of dec-parallel-cap.tier-flag and dec-parallel- 2899 cap.level-id for a capability point indicate the highest 2900 level of the capability point. The values of dec-parallel- 2901 cap.max-lsr, dec-parallel-cap.max-lps, and dec-parallel- 2902 cap.max-br for a capability point indicate the maximum 2903 processing rate in units of luma samples per second, the 2904 maximum picture size in units of luma samples, and the 2905 maximum video bitrate (in units of CpbBrVclFactor bits per 2906 second for the VCL HRD parameters and in units of 2907 CpbBrNalFactor bits per second for the NAL HRD parameters 2908 where CpbBrVclFactor and CpbBrNalFactor are defined in 2909 Section A.4 of [HEVC]). 2911 When not present, the value of dec-parallel-cap.tier-flag 2912 is inferred to be equal to the value of tier-flag outside 2913 the dec-parallel-cap parameter. When not present, the 2914 value of dec-parallel-cap.level-id is inferred to be equal 2915 to the value of max-recv-level-id outside the dec-parallel- 2916 cap parameter. When not present, the value of dec- 2917 parallel-cap.max-lsr, dec-parallel-cap.max-lps, or dec- 2918 parallel-cap.max-br is inferred to be equal to the value of 2919 max-lsr, max-lps, or max-br, respectively, outside the dec- 2920 parallel-cap parameter. 2922 The general decoding capability, expressed by the set of 2923 parameters outside of dec-parallel-cap, is defined as the 2924 capability point that is determined by the following 2925 combination of parameters: 1) the parallelism requirement 2926 corresponding to the value of sprop-segmentation-id equal 2927 to 0 for a bitstream, 2) the profile determined by profile- 2928 space, profile-id, profile-compatibility-indicator, and 2929 interop-constraints, 3) the tier and the highest level 2930 determined by tier-flag and max-recv-level-id, and 4) the 2931 maximum processing rate, the maximum picture size, and the 2932 maximum video bitrate determined by the highest level. The 2933 general decoding capability MUST NOT be included as one of 2934 the set of capability points in the dec-parallel-cap 2935 parameter. 2937 For example, the following parameters express the general 2938 decoding capability of 720p30 (Level 3.1) plus an 2939 additional decoding capability of 1080p30 (Level 4) given 2940 that the spatially largest tile or slice used in the 2941 bitstream is equal to or less than 1/3 of the picture size: 2943 a=fmtp:98 level-id=93;dec-parallel-cap={t:8;level- 2944 id=120} 2946 For another example, the following parameters express an 2947 additional decoding capability of 1080p30, using dec- 2948 parallel-cap.max-lsr and dec-parallel-cap.max-lps, given 2949 that WPP is used in the bitstream: 2951 a=fmtp:98 level-id=93;dec-parallel-cap={w:8; 2952 max-lsr=62668800;max-lps=2088960} 2954 Informative note: When min_spatial_segmentation_idc is 2955 present in a bitstream and WPP is not used, [HEVC] 2956 specifies that there is no slice or no tile in the 2957 bitstream containing more than 4 * PicSizeInSamplesY / 2958 ( min_spatial_segmentation_idc + 4 ) luma samples. 2960 include-dph: 2962 This parameter is used to indicate the capability and 2963 preference to utilize or include decoded picture hash (DPH) 2964 SEI messages (See Section D.3.19 of [HEVC]) in the 2965 bitstream. DPH SEI messages can be used to detect picture 2966 corruption so the receiver can request picture repair, see 2967 Section 8. The value is a comma separated list of hash 2968 types that is supported or requested to be used, each hash 2969 type provided as an unsigned integer value (0-255), with 2970 the hash types listed from most preferred to the least 2971 preferred. Example: "include-dph=0,2", which indicates the 2972 capability for MD5 (most preferred) and Checksum (less 2973 preferred). If the parameter is not included or the value 2974 contains no hash types, then no capability to utilize DPH 2975 SEI messages is assumed. Note that DPH SEI messages MAY 2976 still be included in the bitstream even when there is no 2977 declaration of capability to use them, as in general SEI 2978 messages do not affect the normative decoding process and 2979 decoders are allowed to ignore SEI messages. 2981 Encoding considerations: 2983 This type is only defined for transfer via RTP (RFC 3550). 2985 Security considerations: 2987 See Section 9 of RFC XXXX. 2989 Public specification: 2991 Please refer to Section 13 of RFC XXXX. 2993 Additional information: None 2995 File extensions: none 2997 Macintosh file type code: none 2999 Object identifier or OID: none 3001 Person & email address to contact for further information: 3003 Ye-Kui Wang (yekuiw@qti.qualcomm.com). 3005 Intended usage: COMMON 3007 Author: See Section 14 of RFC XXXX. 3009 Change controller: 3011 IETF Audio/Video Transport Payloads working group delegated 3012 from the IESG. 3014 7.2 SDP Parameters 3016 The receiver MUST ignore any parameter unspecified in this memo. 3018 7.2.1 Mapping of Payload Type Parameters to SDP 3020 The media type video/H265 string is mapped to fields in the 3021 Session Description Protocol (SDP) [RFC4566] as follows: 3023 o The media name in the "m=" line of SDP MUST be video. 3025 o The encoding name in the "a=rtpmap" line of SDP MUST be H265 3026 (the media subtype). 3028 o The clock rate in the "a=rtpmap" line MUST be 90000. 3030 o The OPTIONAL parameters "profile-space", "profile-id", "tier- 3031 flag", "level-id", "interop-constraints", "profile- 3032 compatibility-indicator", "sprop-sub-layer-id", "recv-sub- 3033 layer-id", "max-recv-level-id", "tx-mode", "max-lsr", "max- 3034 lps", "max-cpb", "max-dpb", "max-br", "max-tr", "max-tc", 3035 "max-fps", "sprop-max-don-diff", "sprop-depack-buf-nalus", 3036 "sprop-depack-buf-bytes", "depack-buf-cap", "sprop- 3037 segmentation-id", "sprop-spatial-segmentation-idc", "dec- 3038 parallel-cap", and "include-dph", when present, MUST be 3039 included in the "a=fmtp" line of SDP. This parameter is 3040 expressed as a media type string, in the form of a semicolon 3041 separated list of parameter=value pairs. 3043 o The OPTIONAL parameters "sprop-vps", "sprop-sps", and "sprop- 3044 pps", when present, MUST be included in the "a=fmtp" line of 3045 SDP or conveyed using the "fmtp" source attribute as specified 3046 in Section 6.3 of [RFC5576]. For a particular media format 3047 (i.e. RTP payload type), "sprop-vps" "sprop-sps", or "sprop- 3048 pps" MUST NOT be both included in the "a=fmtp" line of SDP and 3049 conveyed using the "fmtp" source attribute. When included in 3050 the "a=fmtp" line of SDP, these parameters are expressed as a 3051 media type string, in the form of a semicolon separated list 3052 of parameter=value pairs. When conveyed in the "a=fmtp" line 3053 of SDP for a particular payload type, the parameters "sprop- 3054 vps", "sprop-sps", and "sprop-pps" MUST be applied to each 3055 SSRC with the payload type. When conveyed using the "fmtp" 3056 source attribute, these parameters are only associated with 3057 the given source and payload type as parts of the "fmtp" 3058 source attribute. 3060 Informative note: Conveyance of "sprop-vps", "sprop-sps", 3061 and "sprop-pps" using the "fmtp" source attribute allows 3062 for out-of-band transport of parameter sets in topologies 3063 like Topo-Video-switch-MCU as specified in [RFC5117]. 3065 An example of media representation in SDP is as follows: 3067 m=video 49170 RTP/AVP 98 3068 a=rtpmap:98 H265/90000 3069 a=fmtp:98 profile-id=1; 3070 sprop-vps=