idnits 2.17.1 draft-ietf-payload-rtp-ancillary-14.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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 11, 2018) is 2296 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) -- Possible downref: Non-RFC (?) normative reference: ref. 'RP168' -- Possible downref: Non-RFC (?) normative reference: ref. 'ST291' -- Possible downref: Non-RFC (?) normative reference: ref. 'ST352' -- Possible downref: Non-RFC (?) normative reference: ref. 'ST424' Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 A/V Transport Payloads Working Group T. Edwards 3 Internet-Draft FOX 4 Intended status: Standards Track January 11, 2018 5 Expires: July 15, 2018 7 RTP Payload for SMPTE ST 291-1 Ancillary Data 8 draft-ietf-payload-rtp-ancillary-14 10 Abstract 12 This memo describes a real-time transport protocol (RTP) payload 13 format for the Society of Motion Picture and Television Engineers 14 (SMPTE) Ancillary data, as defined by SMPTE ST 291-1. SMPTE 15 Ancillary data is generally used along with professional video 16 formats to carry a range of ancillary data types, including time 17 code, Closed Captioning, and the Active Format Description (AFD). 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on July 15, 2018. 36 Copyright Notice 38 Copyright (c) 2018 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 2. RTP Payload Format for SMPTE ST 291 Ancillary Data . . . . . 3 56 2.1. Payload Header Definitions . . . . . . . . . . . . . . . 5 57 3. Payload Format Parameters . . . . . . . . . . . . . . . . . . 11 58 3.1. Media Type Definition . . . . . . . . . . . . . . . . . . 11 59 4. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 13 60 4.1. Grouping ANC Streams with other Media Streams . . . . . . 14 61 5. Offer/Answer Model and Declarative Considerations . . . . . . 15 62 5.1. Offer/Answer Model . . . . . . . . . . . . . . . . . . . 15 63 5.2. Declarative SDP Considerations . . . . . . . . . . . . . 15 64 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 66 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 67 8.1. Normative References . . . . . . . . . . . . . . . . . . 16 68 8.2. Informative References . . . . . . . . . . . . . . . . . 18 69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19 71 1. Introduction 73 This memo describes a real-time transport protocol (RTP) payload 74 format for the Society of Motion Picture and Television Engineers 75 (SMPTE) Ancillary data (ANC), as defined by SMPTE ST 291-1 [ST291]. 76 ANC data is transmitted in the ancillary space of serial digital 77 video interfaces, the space outside of the active video region of 78 images intended for users to view. Ancillary space roughly 79 corresponds to vertical and horizontal blanking periods of cathode 80 ray tube type displays. ANC can carry a range of data types, 81 including time code, Closed Captioning, and the Active Format 82 Description (AFD). 84 ANC is generally associated with the carriage of metadata within the 85 bit stream of a Serial Digital Interface (SDI), such as the standard 86 definition (SD) Serial Digital Interface, the 1.5 Gb/s Serial Digital 87 Interface for high definition (HD) television applications, or the 3 88 Gb/s Signal/Data Serial Interface (SMPTE ST 259 [ST259], SMPTE ST 89 292-1 [ST292], SMPTE ST 424 [ST424]). 91 ANC data packet payload definitions for a specific application are 92 specified by a SMPTE Standard, Recommended Practice, Registered 93 Disclosure Document, or by a document generated by another 94 organization, a company, or an individual (an Entity). When a 95 payload format is registered with SMPTE, it is identified by a 96 registered data identification word. 98 This memo describes an RTP payload that supports carriage of ANC data 99 packets with origin from any location within any SMPTE defined SDI 100 signal, or even if the ANC packets did not originate in an SDI 101 signal. Sufficient information is provided to enable the ANC data 102 packets at the output of the decoder to be restored to their original 103 locations in the serial digital video signal raster (if that is 104 desired). An optional Media Type parameter allows for signaling of 105 carriage of one or more types of ANC data as specified by Data 106 Identification (DID) and Secondary Data Identification (SDID) words. 107 Another optional Media Type parameter allows for the identification 108 of the Video Payload ID (VPID) Code of the source interface of ANC 109 data packets. 111 Note that the ancillary data flag (ADF) word is not specifically 112 carried in this RTP payload. The ADF might be specified in a 113 document defining an interconnecting digital video interface, 114 otherwise a default ADF is specified by SMPTE ST 291-1 [ST291]. 116 This ANC payload can be used by itself, or used along with a range of 117 RTP video formats. In particular, it has been designed so that it 118 could be used along with RFC 4175 [RFC4175] "RTP Payload Format for 119 Uncompressed Video" or RFC 5371 [RFC5371] "RTP Payload Format for 120 JPEG 2000 Video Streams." 122 The data model in this document for the ANC data RTP payload is based 123 on the data model of SMPTE ST 2038 [ST2038], which standardizes the 124 carriage of ANC data packets in an MPEG-2 Transport Stream. 126 1.1. Requirements Language 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in RFC 2119 [RFC2119]. 132 2. RTP Payload Format for SMPTE ST 291 Ancillary Data 134 An example of the format of an RTP packet containing SMPTE ST 291 135 Ancillary Data is shown below: 137 0 1 2 3 138 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 1 139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 140 |V=2|P|X| CC |M| PT | sequence number | 141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 142 | timestamp | 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 | synchronization source (SSRC) identifier | 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 | Extended Sequence Number | Length=32 | 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | ANC_Count=2 | F | reserved | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 |C| Line_Number=9 | Horizontal_Offset |S| StreamNum=0 | 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 152 | DID | SDID | Data_Count=0x84 | 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 154 User_Data_Words... 155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 156 | Checksum_Word | word_align | 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 |C| Line_Number=10 | Horizontal_Offset |S| StreamNum=0 | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | DID | SDID | Data_Count=0x105 | 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 User_Data_Words... 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 | Checksum_Word |word_align | 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 Figure 1: SMPTE Ancillary Data RTP Packet Format 169 In this example, two ANC data packets are present. The first has 170 four 10-bit User Data Words, and the second has five 10-bit User Data 171 Words (note that few ANC data packets are this small, thus this 172 example does not reflect actual defined ANC data packets, and does 173 not specifically call out the DIDs and SDIDs). The ANC data packets 174 are located on lines 9 and 10 of the SDI raster. 176 The term "network byte order" in the payload format SHALL refer to 177 the Data Transmission Order as defined in Appendix B of RFC 791 178 [RFC0791]. 180 RTP packet header fields SHALL be interpreted as per RFC 3550 181 [RFC3550], with the following specifics: 183 Timestamp: 32 bits 184 The timestamp field is interpreted in a similar fashion to 185 RFC 4175 [RFC4175]: 187 For progressive scan video, the timestamp denotes the 188 sampling instant of the frame to which the ancillary data in 189 the RTP packet belongs. RTP packets MUST NOT include ANC 190 data from multiple frames, and all RTP packets with ANC data 191 belonging to the same frame MUST have the same timestamp. 193 For interlaced video, the timestamp denotes the sampling 194 instant of the field to which the ancillary data in the RTP 195 packet belongs. RTP packets MUST NOT include ANC data from 196 multiple fields, and all RTP packets belonging to the same 197 field MUST have the same timestamp. 199 If the sampling instant does not correspond to an integer 200 value of the clock, the value SHALL be truncated to the next 201 lowest integer, with no ambiguity. Section 3.1 describes 202 timestamp clock rates. 204 Marker bit (M): 1 bit 205 The marker bit set to "1" indicates the last ANC RTP packet 206 for a frame (for progressive scan video) or the last ANC RTP 207 packet for a field (for interlaced video). 209 2.1. Payload Header Definitions 211 The ANC RTP payload header fields are defined as: 213 Extended Sequence Number: 16 bits 214 The high order bits of the extended 32-bit sequence number, 215 in network byte order. This is the same as the Extended 216 Sequence Number field in RFC 4175 [RFC4175]. 218 Length: 16 bits 219 Number of octets of the ANC RTP payload, beginning with the 220 "C" bit of the first ANC packet data, as an unsigned integer 221 in network byte order. Note that all word_align fields 222 contribute to the calculation of the length field. 224 ANC_Count: 8 bits 225 This field is the count of the total number of ANC data 226 packets carried in the RTP payload, as an unsigned integer. 227 A single ANC RTP packet payload cannot carry more than 255 228 ANC data packets. 230 If more than 255 ANC data packets need to be carried in a 231 field or frame, additional RTP packets carrying ANC data MAY 232 be sent with the same RTP timestamp but with different 233 sequence numbers. ANC_Count of 0 indicates that there are no 234 ANC data packets in the payload (for example, for an RTP 235 packet with the marker bit set indicating the last ANC RTP 236 packet in a field/frame, even if that RTP packet carries no 237 actual ANC data packets.) If ANC_Count is 0, Length will 238 also be 0. 240 F: 2 bits 241 These two bits relate to signaling the field specified by the 242 RTP timestamp in an interlaced SDI raster. A value of 0b00 243 indicates that either the video format is progressive or that 244 no field is specified. A value of 0b10 indicates that the 245 timestamp refers to the first field of an interlaced video 246 signal. A value of 0b11 indicates that the timestamp refers 247 to the second field of an interlaced video signal. The value 248 0b01 is not valid. Receivers SHOULD ignore an ANC data 249 packet with an F field value of 0b01, and SHOULD process any 250 other ANC data packets with valid F field values that are 251 present in the RTP payload. 253 Note that some multi-stream SDI interfaces might use multiple 254 interlaced signal streams to transmit progressive images, in 255 which case the "F" bits would refer to the field of the 256 interlaced stream used for transport of the ANC data packet. 258 reserved: 22 bits 259 The 22 reserved bits of value "0" follow the F field to 260 ensure that the first ANC data packet header field in the 261 payload begins 32-bit word-aligned to ease implementation. 263 For each ANC data packet in the payload, the following ANC data 264 packet header fields MUST be present: 266 C: 1 bit 267 This flag, when set to "1", indicates that the ANC data 268 corresponds to the color-difference data channel (C). When 269 set to "0", this flag indicates either that the ANC data 270 corresponds to the luma (Y) data channel, that the ANC data 271 source is from an SD signal, or that the ANC data source has 272 no specific luma or color-difference data channels. For ANC 273 data from a multi-stream interface source, the C flag SHALL 274 refer to the channel of the stream used to transport the ANC 275 packet. For situations where there is no SDI source, if the 276 ANC data type definition specifically requires the use of the 277 C or Y data channel, the C flag SHALL reflect that 278 requirement. 280 Line_Number: 11 bits 281 This field contains the digital interface line number that 282 corresponds to the location of the ANC data packet as an 283 unsigned integer in network byte order. 285 The following special Line_Number values code for the 286 location of the ANC data packet to be in certain generic 287 vertical regions of the SDI raster: 289 +-------------+--------------------------------------------------------+ 290 | Line_Number | ANC data packet generic vertical location | 291 +-------------+--------------------------------------------------------+ 292 | 0x7FF | Without specific line location within the field or | 293 | | frame | 294 | | | 295 | 0x7FE | On any line in the range from the second line after | 296 | | the line specified for switching, as defined in SMPTE | 297 | | RP 168 [RP168], to the last line before active video, | 298 | | inclusive | 299 | | | 300 | 0x7FD | On a line number larger than can be represented in 11 | 301 | | bits of this field (if needed for future formats) | 302 +-------------+--------------------------------------------------------+ 304 Note that the lines that are available to convey ANC data are 305 as defined in the applicable sample structure specification 306 (e.g., SMPTE ST 274 [ST274], SMPTE ST 296 [ST296], ITU-R 307 BT.656 [BT656]) and possibly further restricted per SMPTE RP 308 168 [RP168]. 310 In multi-stream interfaces, this field refers to the line 311 number that an ANC packet is carried on within a particular 312 data stream in the interface. 314 Horizontal_Offset: 12 bits 315 This field defines the location of the ANC data packet in an 316 SDI raster relative to the start of active video (SAV, a 317 digital synchronizing signal present in SDI interfaces) as an 318 unsigned integer in network byte order. A value of 0 means 319 that the Ancillary Data Flag (ADF) of the ANC data packet 320 begins immediately following SAV. The horizontal offset from 321 SAV is measured in terms of 10-bit words of the indicated 322 data stream and data channel. 324 The following special Horizontal_Offset values code for the 325 location of the ANC data packet to be in certain generic 326 horizontal regions of the SDI raster: 328 +-------------+--------------------------------------------------------+ 329 | Horizontal_ | ANC data packet generic horizontal location | 330 | Offset | | 331 +-------------+--------------------------------------------------------+ 332 | 0xFFF | Without specific horizontal location | 333 | | | 334 | 0xFFE | Within horizontal ancillary data space (HANC) as | 335 | | defined in SMPTE ST 291-1 [ST291] | 336 | | | 337 | 0xFFD | Within the ancillary data space located between SAV | 338 | | (Start of Active Video) and EAV (End of Active Video) | 339 | | markers of the serial digital interface | 340 | | | 341 | 0xFFC | Horizontal offset is larger than can be represented in | 342 | | the 12 bits of this field (if needed for future | 343 | | formats, or for certain low frame rate 720p formats) | 344 +-------------+--------------------------------------------------------+ 346 In multi-stream interfaces, this field refers to the 347 horizontal location where an ANC packet is placed on a line 348 carried within a particular data stream in the interface. 350 Note that HANC data space will generally have higher luma 351 sample numbers than any samples in the active digital line. 352 Also note that SMPTE ST 296 [ST296] (1280 x 720 progressive 353 active images) image sampling systems 7 and 8 (1280 x 720 354 progressive @ 24 fps and 1280 x 720 progressive @ 23.98 fps 355 respectively) have a luma sample number maximum of 4124. It 356 is unlikely that an actual implementation would have an ANC 357 packet begin at a Horizontal_Offset beyond 4091 (0xFFB) in 358 these formats, but should that occur, the Horizontal_Offset 359 value 0xFFC can be used to signal a horizontal offset larger 360 than can be represented in the field. Further note that the 361 12-bit field of Horizontal_Offset is kept that size in this 362 memo to maintain easy conversion to/from SMPTE ST 2038 363 [ST2038] which also has a 12-bit Horizontal_Offset field. 365 S (Data Stream Flag): 1 bit 366 This field indicates whether the data stream number of a 367 multi-stream data mapping used to transport the ANC data 368 packet is specified. If the S bit is '0', then the StreamNum 369 field provides no guidance regarding the source data stream 370 number of the ANC data packet. If the S bit is '1', then the 371 StreamNum field carries information regarding the source data 372 stream number of the ANC data packet. 374 StreamNum: 7 bits 375 If the S (Data Stream Flag) bit is '1', then the StreamNum 376 field MUST carry identification of the source data stream 377 number of the ANC data packet. If the data stream is 378 numbered, then the StreamNum field SHALL carry the number of 379 the source data stream minus one. If the source multi-stream 380 interface does not have numbered data streams, the following 381 numbers SHALL be used in this field: '0' for link A data 382 stream, '1' for link B data stream. For stereoscopic multi- 383 stream interface formats that do not have numbered streams, 384 the following numbers SHALL be used in this field: '0' for 385 left eye stream, '1' for right eye stream. 387 Note that in multi-link SDI connections, the physical link 388 that a particular stream utilizes is typically specified by 389 the interface standard. Also note that numbering of data 390 streams is across the interface as a whole. For example, in 391 the SMPTE ST 425-3 dual-link 3 Gb/s interface, the data 392 streams are numbered 1-4 with data streams 1 and 2 on link 1 393 and data streams 3 and 4 on link 2. 395 An ANC data packet with the header fields Line_Number of 0x7FF and 396 Horizontal_Offset of 0xFFF SHALL be considered to be carried without 397 any specific location within the field or frame. 399 For each ANC data packet in the payload, immediately after the ANC 400 data packet header fields, the following data fields MUST be present, 401 with the fields DID, SDID, Data_Count, User_Data_Words, and 402 Checksum_Word representing the 10-bit words carried in the ANC data 403 packet, as per SMPTE ST 291-1 [ST291]: 405 DID: 10 bits 406 Data Identification Word 408 SDID: 10 bits 409 Secondary Data Identification Word. Used only for a "Type 2" 410 ANC data packet. Note that in a "Type 1" ANC data packet, 411 this word will actually carry the Data Block Number (DBN). 413 Data_Count: 10 bits 414 The lower 8 bits of Data_Count, corresponding to bits b7 415 (MSB) through b0 (LSB) of the 10-bit Data_Count word, contain 416 the actual count of 10-bit words in User_Data_Words. Bit b8 417 is the even parity for bits b7 through b0, and bit b9 is the 418 inverse (logical NOT) of bit b8. 420 User_Data_Words: integer number of 10 bit words 421 User_Data_Words (UDW) are used to convey information of a 422 type as identified by the DID word or the DID and SDID words. 424 The number of 10-bit words in the UDW is defined by the 425 Data_Count field. The 10-bit words are carried in order 426 starting with the most significant bit and ending with the 427 least significant bit. 429 Checksum_Word: 10 bits 430 The Checksum_Word can be used to determine the validity of 431 the ANC data packet from the DID word through the UDW. It 432 consists of 10 bits, where bits b8 (MSB) through b0 (LSB) 433 define the checksum value and bit b9 is the inverse (logical 434 NOT) of bit b8. The checksum value is equal to the nine 435 least significant bits of the sum of the nine least 436 significant bits of the DID word, the SDID word, the 437 Data_Count word, and all User_Data_Words in the ANC data 438 packet. The checksum is initialized to zero before 439 calculation, and any end carry resulting from the checksum 440 calculation is ignored. 442 At the end of each ANC data packet in the payload: 444 word_align: bits as needed to complete 32-bit word 445 Word align contains enough "0" bits as needed to complete the 446 last 32-bit word of the ANC packet's data in the RTP payload. 447 If an ANC data packet in the RTP payload ends aligned with a 448 word boundary, there is no need to add any word alignment 449 bits. Word align SHALL be used even for the last ANC data 450 packet in an RTP packet. Word align SHALL NOT be used if 451 there are zero ANC data packets being carried in the RTP 452 packet. 454 When reconstructing an SDI signal based on this payload, it is 455 important to place ANC data packets into the locations indicated by 456 the ANC payload header fields C, Line_Number and Horizontal_Offset, 457 and also to follow the requirements of SMPTE ST 291-1 [ST291] 458 Section 7 "Ancillary Data Space Formatting (Component or Composite 459 Interface)", which include rules on the placement of initial ANC data 460 into allowed spaces as well as the contiguity of ANC data packet 461 sequences within those spaces in order to assure that the resulting 462 ANC data packets in the SDI signal are valid. The optional Media 463 Type parameter VPID_Code can inform receivers of the type of 464 originating SDI interface. For multi-stream originating interfaces, 465 the StreamNum field can provide information regarding which stream an 466 ANC data packet can be placed in to match the ANC data location in 467 the originating SDI interface. 469 Senders of this payload SHOULD transmit available ANC data packets as 470 soon as practical to reduce end-to-end latency, especially if 471 receivers will be embedding the received ANC data packet into an SDI 472 signal emission. One millisecond is a reasonable upper bound for the 473 amount of time between when an ANC data packet becomes available to a 474 sender and the emission of an RTP payload containing that ANC data 475 packet. 477 ANC data packets with headers that specify specific location within a 478 field or frame SHOULD be sent in raster scan order, both in terms of 479 packing position within an RTP packet and in terms of transmission 480 time of RTP packets. 482 3. Payload Format Parameters 484 This RTP payload format is identified using the video/smpte291 media 485 type, which is registered in accordance with RFC 4855 [RFC4855], and 486 using the template of RFC 6838 [RFC6838]. 488 Note that the Media Type Definition is in the "video" tree due to the 489 expected use of SMPTE ST 291 Ancillary Data along with video formats. 491 3.1. Media Type Definition 493 Type name: video 495 Subtype name: smpte291 497 Required parameters: 499 Rate: 500 RTP timestamp clock rate. 502 When an ANC RTP stream is to be associated with an RTP video 503 stream, the RTP timestamp rates SHOULD be the same to ensure 504 that ANC data packets can be associated with the appropriate 505 frame or field. Otherwise, a 90 kHz rate SHOULD be used. 507 Note that techniques described in RFC 7273 [RFC7273] can 508 provide a common reference clock for multiple RTP streams 509 intended for synchronized presentation. 511 Optional parameters: 513 DID_SDID: 514 Data identification and Secondary data identification words. 516 The presence of the DID_SDID parameters signals that all 517 ancillary data packets of this stream are of a particular type 518 or types, i.e., labeled with a particular DIDs and SDIDs. DID 519 and SDID values of SMPTE Registered ANC packet types can be 520 found on the at the SMPTE Registry for Data Identification Word 521 Assignments [SMPTE-RA] web site. 523 "Type 1" ANC packets (which do not have SDIDs defined) SHALL be 524 labeled with SDID=0x00. 526 DID and SDID values can be registered with SMPTE as per SMPTE 527 ST 291-1 [ST291]. 529 The absence of the DID_SDID parameter signals that 530 determination of the DID and SDID of ANC packets in the payload 531 can only be achieved through direct inspection of the ANC data 532 packet fields. 534 The ABNF description of the DID_SDID parameter is described in 535 Section 4 of [this RFC]. 537 VPID_Code: 538 This integer parameter specifies the Video Payload ID (VPID) 539 Code of the source interface of ANC data packets using the 540 value from byte 1 of the VPID as defined in SMPTE ST 352 541 [ST352]. The integer SHALL be made with bit 7 of VPID byte 1 542 being the most significant bit, and bit 0 of VPID byte 1 being 543 the least significant bit. For example, 132 refers to SMPTE ST 544 292-1, 720-line video payloads on a 1.5 Gbps (nominal) serial 545 digital interface. 547 Encoding considerations: This media type is framed and binary; see 548 Section 4.8 of RFC 6838 [RFC6838]. 550 Security considerations: See Section 7 of [this RFC] 552 Interoperability considerations: Data items in smpte291 can be very 553 diverse. Receivers might only be capable of interpreting a subset of 554 the possible data items. Some implementations might care about the 555 location of the ANC data packets in the SDI raster, but other 556 implementations might not care. 558 Published specification: [this RFC] 560 Applications that use this media type: Devices that stream real-time 561 professional video, especially those that interoperate with legacy 562 serial digital interfaces (SDI). 564 Additional Information: 566 Deprecated alias names for this type: N/A 567 Magic number(s): N/A 569 File extension(s): N/A 571 Macintosh file type code(s): N/A 573 Person & email address to contact for further information: T. 574 Edwards , IETF Payload Working Group 575 577 Intended usage: COMMON 579 Restrictions on usage: This media type depends on RTP framing, and 580 hence is only defined for transfer via RTP RFC 3550 [RFC3550]. 581 Transport within other framing protocols is not defined at this time. 583 Author: T. Edwards 585 Change controller: The IETF PAYLOAD working group, or other party as 586 designated by the IESG. 588 4. SDP Considerations 590 The mapping of the above defined payload format media type and its 591 parameters SHALL be done according to Section 3 of RFC 4855 592 [RFC4855]. 594 o The type name ("video") goes in SDP "m=" as the media name. 596 o The subtype name ("smpte291") goes in SDP "a=rtpmap" as the 597 encoding name, followed by a slash ("/") and the rate parameter. 599 o The optional parameters VPID_Code and DID_SDID, when present, are 600 included in the "a=fmtp" attribute line of SDP as a semicolon- 601 separated list of parameter=value pairs. 603 DID and SDID values SHALL be specified in hexadecimal with a "0x" 604 prefix (such as "0x61"). The ABNF as per RFC 5234 [RFC5234] of the 605 DID_SDID optional parameter SHALL be: 607 TwoHex = "0x" 1*2(HEXDIG) 608 DidSdid = "DID_SDID={" TwoHex "," TwoHex "}" 610 For example, EIA 608 Closed Caption data would be signalled with the 611 parameter DID_SDID={0x61,0x02}. If a DID_SDID parameter is not 612 specified, then the ancillary data stream might potentially contain 613 ancillary data packets of any type. 615 Multiple DID_SDID parameters can be specified (separated by 616 semicolons) to signal the presence of multiple types of ANC data in 617 the stream. DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}, for example, 618 signals the presence of EIA 608 Closed Captions as well as AFD/Bar 619 Data. Multiple DID_SDID parameters do not imply any particular 620 ordering of the different types of ANC packets in the stream. 622 If the optional parameter VPID_Code is present, it SHALL be present 623 only once in the semicolon-separated list, taking a single integer 624 value. 626 A sample SDP mapping for ancillary data is as follows: 628 m=video 30000 RTP/AVP 112 629 a=rtpmap:112 smpte291/90000 630 a=fmtp:112 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05};VPID_Code=132 632 In this example, a dynamic payload type 112 is used for ancillary 633 data. The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" 634 line after the subtype. In the "a=fmtp:" line, DID 0x61 and SDID 635 0x02 are specified (registered to EIA 608 Closed Caption Data by 636 SMPTE), and also DID 0x41 and SDID 0x05 (registered to AFD/Bar Data). 637 The VPID_Code is 132 (referring to SMPTE ST 292-1, 720-line video 638 payloads on a 1.5 Gbps serial digital interface). 640 4.1. Grouping ANC Streams with other Media Streams 642 To indicate the association of an ancillary data stream with a 643 particular video stream, implementers MAY group the "m" lines 644 together using Flow Identificaiton ("FID") semantics as defined in 645 RFC 5888 [RFC5888]. 647 A sample SDP mapping for grouping ANC data with RFC 4175 video is as 648 follows: 650 v=0 651 o=Al 123456 11 IN IP4 host.example.com 652 s=Professional Networked Media Test 653 i=A test of synchronized video and ANC data 654 t=0 0 655 a=group:FID V1 M1 656 m=video 50000 RTP/AVP 96 657 c=IN IP4 233.252.0.1/255 658 a=rtpmap:96 raw/90000 659 a=fmtp:96 sampling=YCbCr-4:2:2; width=1280; height=720; depth=10 660 a=mid:V1 661 m=video 50010 RTP/AVP 97 662 c=IN IP4 233.252.0.2/255 663 a=rtpmap:97 smpte291/90000 664 a=fmtp:97 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05} 665 a=mid:M1 667 5. Offer/Answer Model and Declarative Considerations 669 5.1. Offer/Answer Model 671 Receivers might wish to receive ANC data streams with specific 672 DID_SDID parameters. Thus when offering ANC data streams using the 673 Session Description Protocol (SDP) in an Offer/Answer model 674 [RFC3264], the offeror MAY provide a list of ANC streams available 675 with specific DID_SDID parameters in the fmtp line. The answerer MAY 676 respond with all or a subset of the streams offered along with fmtp 677 lines with all or a subset of the DID_SDID parameters offered. Or 678 the answerer MAY set the corresponding port number to 0 to decline 679 the smpte291 stream if not in the same media section as a 680 corresponding video stream, or MAY remove the corresponding payload 681 type if the smpte291 stream is in the same media section as a 682 corresponding video stream. There are no restrictions on updating 683 DID_SDID parameters in a subsequent offer. 685 5.2. Declarative SDP Considerations 687 For declarative use of SDP, nothing specific is defined for this 688 payload format. The configuration given by the SDP MUST be used when 689 sending and/or receiving media in the session. 691 6. IANA Considerations 693 One media type (video/smpte291) has been defined and needs 694 registration in the media types registry. See Section 3.1 696 7. Security Considerations 698 RTP packets using the payload format defined in this specification 699 are subject to the security considerations discussed in the RTP 700 specification [RFC3550], and in any applicable RTP profile such as 701 RTP/AVP [RFC3551], RTP/AVPF [RFC4585] RTP/SAVP [RFC3711] or RTP/SAVPF 702 [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP 703 Does Not Mandate a Single Media Security Solution" [RFC7202] 704 discusses, it is not an RTP payload format's responsibility to 705 discuss or mandate what solutions are used to meet the basic security 706 goals like confidentiality, integrity and source authenticity for RTP 707 in general. This responsibility lays on anyone using RTP in an 708 application. They can find guidance on available security mechanisms 709 and important considerations in Options for Securing RTP Sessions 710 [RFC7201]. Applications SHOULD use one or more appropriate strong 711 security mechanisms. The rest of this security consideration section 712 discusses the security impacting properties of the payload format 713 itself. 715 To avoid potential buffer overflow attacks, receivers SHOULD validate 716 that the ANC data packets in the RTP payload are of the appropriate 717 length (using the Data_Count field) for the ANC data type specified 718 by DID & SDID. Also the Checksum_Word SHOULD be checked against the 719 ANC data packet to ensure that its data has not been damaged in 720 transit, but the Checksum_Word is unlikely to provide a payload 721 integrity check in case of a directed attack. 723 Some receivers will simply move the ANC data packet bits from the RTP 724 payload into a serial digital interface (SDI). It might still be a 725 good idea for these "re-embedders" to perform the above mentioned 726 validity tests to avoid downstream SDI systems from becoming confused 727 by bad ANC data packets, which could be used for a denial of service 728 attack. 730 "Re-embedders" into SDI SHOULD also double check that the Line_Number 731 and Horizontal_Offset leads to the ANC data packet being inserted 732 into a legal area to carry ancillary data in the SDI video bit stream 733 of the output video format. 735 8. References 737 8.1. Normative References 739 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 740 DOI 10.17487/RFC0791, September 1981, 741 . 743 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 744 Requirement Levels", BCP 14, RFC 2119, 745 DOI 10.17487/RFC2119, March 1997, 746 . 748 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 749 with Session Description Protocol (SDP)", RFC 3264, 750 DOI 10.17487/RFC3264, June 2002, 751 . 753 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 754 Jacobson, "RTP: A Transport Protocol for Real-Time 755 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 756 July 2003, . 758 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 759 Video Conferences with Minimal Control", STD 65, RFC 3551, 760 DOI 10.17487/RFC3551, July 2003, 761 . 763 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 764 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 765 RFC 3711, DOI 10.17487/RFC3711, March 2004, 766 . 768 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 769 "Extended RTP Profile for Real-time Transport Control 770 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 771 DOI 10.17487/RFC4585, July 2006, 772 . 774 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 775 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 776 . 778 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 779 Real-time Transport Control Protocol (RTCP)-Based Feedback 780 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 781 2008, . 783 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 784 Specifications: ABNF", STD 68, RFC 5234, 785 DOI 10.17487/RFC5234, January 2008, 786 . 788 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 789 Protocol (SDP) Grouping Framework", RFC 5888, 790 DOI 10.17487/RFC5888, June 2010, 791 . 793 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 794 Specifications and Registration Procedures", BCP 13, 795 RFC 6838, DOI 10.17487/RFC6838, January 2013, 796 . 798 [RP168] SMPTE, "RP 168:2009, Definition of Vertical Interval 799 Switching Point for Synchronous Video Switching", 2009. 801 [ST291] SMPTE, "ST 291-1:2011, Ancillary Data Packet and Space 802 Formatting", 2011. 804 [ST352] SMPTE, "ST 352:2013, Payload Identification Codes for 805 Serial Digital Interfaces", 2013. 807 [ST424] SMPTE, "ST 424:2012, 3 Gb/s Signal/Data Serial Interface", 808 2012. 810 8.2. Informative References 812 [BT656] ITU-R, "BT.656-5, Interfaces for Digital Component Video 813 Signals in 525-Line and 625-Line Television Systems 814 Operating at the 4:2:2 Level of Recommendation ITU-R 815 BT.601", December 2007. 817 [RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for 818 Uncompressed Video", RFC 4175, DOI 10.17487/RFC4175, 819 September 2005, . 821 [RFC5371] Futemma, S., Itakura, E., and A. Leung, "RTP Payload 822 Format for JPEG 2000 Video Streams", RFC 5371, 823 DOI 10.17487/RFC5371, October 2008, 824 . 826 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 827 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 828 . 830 [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP 831 Framework: Why RTP Does Not Mandate a Single Media 832 Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 833 2014, . 835 [RFC7273] Williams, A., Gross, K., van Brandenburg, R., and H. 836 Stokking, "RTP Clock Source Signalling", RFC 7273, 837 DOI 10.17487/RFC7273, June 2014, 838 . 840 [SMPTE-RA] 841 SMPTE Registration Authority, LLC, "SMPTE ST 291 Ancillary 842 Data Identification Word Assignments for Registered DIDs", 843 2011, . 846 [ST2038] SMPTE, "ST 2038:2008, Carriage of Ancillary Data Packets 847 in an MPEG-2 Transport Stream", 2008. 849 [ST259] SMPTE, "ST 259:2008, SDTV Digital Signal/Data - Serial 850 Digital Interface", 2008. 852 [ST274] SMPTE, "ST 274:2008, 1920 x 1080 Image Sample Structure, 853 Digital Representation and Digital Timing Reference 854 Sequences for Multiple Picture Rates", 2008. 856 [ST292] SMPTE, "ST 292-1:2012, 1.5 Gb/s Signal/Data Serial 857 Interface", 2012. 859 [ST296] SMPTE, "ST 296:2012, 1280 x 720 Progressive Image 4:2:2 860 and 4:4:4 Sample Structure - Analog and Digital 861 Representation and Analog Interface", 2012. 863 Author's Address 865 Thomas G. Edwards 866 FOX 867 10201 W. Pico Blvd. 868 Los Angeles, CA 90035 869 USA 871 Phone: +1 310 369 6696 872 Email: thomas.edwards@fox.com