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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. 'BT1120' -- Possible downref: Non-RFC (?) normative reference: ref. 'BT1700' -- 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 (==), 6 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 October 19, 2017 5 Expires: April 22, 2018 7 RTP Payload for SMPTE ST 291-1 Ancillary Data 8 draft-ietf-payload-rtp-ancillary-12 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 April 22, 2018. 36 Copyright Notice 38 Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . 10 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 . . . . . . 14 62 5.1. Offer/Answer Model . . . . . . . . . . . . . . . . . . . 14 63 5.2. Declarative SDP Considerations . . . . . . . . . . . . . 15 64 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 66 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 67 8.1. Normative References . . . . . . . . . . . . . . . . . . 16 68 8.2. Informative References . . . . . . . . . . . . . . . . . 17 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 line number (as defined in ITU-R 282 BT.1700 [BT1700] for SD video or ITU-R BT.1120 [BT1120] for 283 HD video) that corresponds to the location of the ANC data 284 packet in an SDI raster as an unsigned integer in network 285 byte order. A value of 0x7FF (all bits in the field are '1') 286 indicates that the ANC data is carried without a specific 287 line location within the field or frame. A value of 0x7FE 288 indicates that the ANC data is intended to be placed into any 289 legal area of the vertical blanking period ("VANC data 290 space"), specifically. A value of 0x7FD indicates that the 291 ANC data line number is larger than can be represented in 11 292 bits (if needed for future formats). 294 Note that the lines that are available to convey ANC data are 295 as defined in the applicable sample structure specification 296 (e.g., SMPTE 274M [ST274], SMPTE ST 296 [ST296], ITU-R BT.656 297 [BT656]) and possibly further restricted per SMPTE RP 168 298 [RP168]. 300 In multi-stream interfaces, this field refers to the line 301 number that an ANC packet is carried on within a particular 302 data stream in the interface. 304 Horizontal_Offset: 12 bits 305 This field defines the location of the ANC data packet in an 306 SDI raster relative to the start of active video (SAV, a 307 digital synchronizing signal present in SDI interfaces) as an 308 unsigned integer in network byte order. A value of 0 means 309 that the Ancillary Data Flag (ADF) of the ANC data packet 310 begins immediately following SAV. For HD, this is in units 311 of luma sample numbers as specified by the defining document 312 of the particular image (e.g., SMPTE 274M [ST274] for 1920 x 313 1080 active images, or SMPTE ST 296 [ST296] for 1280 x 720 314 progressive active images). For SD, this is in units of 315 (27MHz) multiplexed word numbers, as specified in SMPTE ST 316 125 [ST125]. A value of 0xFFF (all bits in the field are 317 '1') indicates that the ANC data is carried without any 318 specific location within the line. A value of 0xFFE 319 indicates that the ANC data is intended to be placed into any 320 legal area of horizontal blanking ("HANC data space"), 321 specifically. A value of 0xFFD indicates that the ANC data 322 horizontal offset is larger than can be represented in the 12 323 bits of this field (if needed for future formats, or for low 324 frame rate 720p formats mentioned below). 326 In multi-stream interfaces, this field refers to the 327 horizontal location where an ANC packet is placed on a line 328 carried within a particular data stream in the interface. 330 Note that HANC data space will generally have higher luma 331 sample numbers than any samples in the active digital line. 332 Also note that SMPTE ST 296 [ST296] (1280 x 720 progressive 333 active images) image sampling systems 7 and 8 (1280 x 720 334 progressive @ 24 fps and 1280 x 720 progressive @ 23.98 fps 335 respectively) have a luma sample number maximum of 4124. It 336 is unlikely that an actual implementation would have an ANC 337 packet begin at a Horizontal_Offset beyond 4092 (0xFFC) in 338 these formats, but should that occur, the Horizontal_Offset 339 value 0xFFD can be used to signal a horizontal offset larger 340 than can be represented in the field. Further note that the 341 12-bit field of Horizontal_Offset is kept that size in this 342 memo to maintain easy conversion to/from SMPTE ST 2038 343 [ST2038] which also has a 12-bit Horizontal_Offset field. 345 S (Data Stream Flag): 1 bit 346 This field indicates whether the data stream number of a 347 multi-stream data mapping used to transport the ANC data 348 packet is specified. If the S bit is '0', then the StreamNum 349 field provides no guidance regarding the source data stream 350 number of the ANC data packet. If the S bit is '1', then the 351 StreamNum field carries information regarding the source data 352 stream number of the ANC data packet. 354 StreamNum: 7 bits 355 If the S (Data Stream Flag) bit is '1', then the StreamNum 356 field MUST carry identification of the source data stream 357 number of the ANC data packet. If the data stream is 358 numbered, then the StreamNum field SHALL carry the number of 359 the source data stream minus one. If the source multi-stream 360 interface does not have numbered data streams, the following 361 numbers SHALL be used in this field: '0' for link A data 362 stream, '1' for link B data stream. For stereoscopic multi- 363 stream interface formats that do not have numbered streams, 364 the following numbers SHALL be used in this field: '0' for 365 left eye stream, '1' for right eye stream. 367 Note that in multi-link SDI connections, the physical link 368 that a particular stream utilizes is typically specified by 369 the interface standard. Also note that numbering of data 370 streams is across the interface as a whole. For example, in 371 the SMPTE ST 425-3 dual-link 3 Gb/s interface, the data 372 streams are numbered 1-4 with data streams 1 and 2 on link 1 373 and data streams 3 and 4 on link 2. 375 An ANC data packet with the header fields Line_Number of 0x7FF and 376 Horizontal_Offset of 0xFFF SHALL be considered to be carried without 377 any specific location within the field or frame. 379 For each ANC data packet in the payload, immediately after the ANC 380 data packet header fields, the following data fields MUST be present, 381 with the fields DID, SDID, Data_Count, User_Data_Words, and 382 Checksum_Word representing the 10-bit words carried in the ANC data 383 packet, as per SMPTE ST 291-1 [ST291]: 385 DID: 10 bits 386 Data Identification Word 388 SDID: 10 bits 389 Secondary Data Identification Word. Used only for a "Type 2" 390 ANC data packet. Note that in a "Type 1" ANC data packet, 391 this word will actually carry the Data Block Number (DBN). 393 Data_Count: 10 bits 394 The lower 8 bits of Data_Count, corresponding to bits b7 395 (MSB) through b0 (LSB) of the 10-bit Data_Count word, contain 396 the actual count of 10-bit words in User_Data_Words. Bit b8 397 is the even parity for bits b7 through b0, and bit b9 is the 398 inverse (logical NOT) of bit b8. 400 User_Data_Words: integer number of 10 bit words 401 User_Data_Words (UDW) are used to convey information of a 402 type as identified by the DID word or the DID and SDID words. 403 The number of 10-bit words in the UDW is defined by the 404 Data_Count field. The 10-bit words are carried in order 405 starting with the most significant bit and ending with the 406 least significant bit. 408 Checksum_Word: 10 bits 409 The Checksum_Word can be used to determine the validity of 410 the ANC data packet from the DID word through the UDW. It 411 consists of 10 bits, where bits b8 (MSB) through b0 (LSB) 412 define the checksum value and bit b9 is the inverse (logical 413 NOT) of bit b8. The checksum value is equal to the nine 414 least significant bits of the sum of the nine least 415 significant bits of the DID word, the SDID word, the 416 Data_Count word, and all User_Data_Words in the ANC data 417 packet. The checksum is initialized to zero before 418 calculation, and any end carry resulting from the checksum 419 calculation is ignored. 421 At the end of each ANC data packet in the payload: 423 word_align: bits as needed to complete 32-bit word 424 Word align contains enough "0" bits as needed to complete the 425 last 32-bit word of the ANC packet's data in the RTP payload. 426 If an ANC data packet in the RTP payload ends aligned with a 427 word boundary, there is no need to add any word alignment 428 bits. Word align SHALL be used even for the last ANC data 429 packet in an RTP packet. Word align SHALL NOT be used if 430 there are zero ANC data packets being carried in the RTP 431 packet. 433 When reconstructing an SDI signal based on this payload, it is 434 important to place ANC data packets into the locations indicated by 435 the ANC payload header fields C, Line_Number and Horizontal_Offset, 436 and also to follow the requirements of SMPTE ST 291-1 [ST291] 437 Section 7 "Ancillary Data Space Formatting (Component or Composite 438 Interface)", which include rules on the placement of initial ANC data 439 into allowed spaces as well as the contiguity of ANC data packet 440 sequences within those spaces in order to assure that the resulting 441 ANC data packets in the SDI signal are valid. The optional Media 442 Type parameter VPID_Code can inform receivers of the type of 443 originating SDI interface. For multi-stream originating interfaces, 444 the StreamNum field can provide information regarding which stream an 445 ANC data packet can be placed in to match the ANC data location in 446 the originating SDI interface. 448 Senders of this payload SHOULD transmit available ANC data packets as 449 soon as practical to reduce end-to-end latency, especially if 450 receivers will be embedding the received ANC data packet into an SDI 451 signal emission. One millisecond is a reasonable upper bound for the 452 amount of time between when an ANC data packet becomes available to a 453 sender and the emission of an RTP payload containing that ANC data 454 packet. 456 ANC data packets with headers that specify specific location within a 457 field or frame SHOULD be sent in raster scan order, both in terms of 458 packing position within an RTP packet and in terms of transmission 459 time of RTP packets. 461 3. Payload Format Parameters 463 This RTP payload format is identified using the video/smpte291 media 464 type, which is registered in accordance with RFC 4855 [RFC4855], and 465 using the template of RFC 6838 [RFC6838]. 467 Note that the Media Type Definition is in the "video" tree due to the 468 expected use of SMPTE ST 291 Ancillary Data along with video formats. 470 3.1. Media Type Definition 472 Type name: video 474 Subtype name: smpte291 476 Required parameters: 478 Rate: 479 RTP timestamp clock rate. 481 When an ANC RTP stream is to be associated with an RTP video 482 stream, the RTP timestamp rates SHOULD be the same to ensure 483 that ANC data packets can be associated with the appropriate 484 frame or field. Otherwise, a 90 kHz rate SHOULD be used. 486 Note that techniques described in RFC 7273 [RFC7273] can 487 provide a common reference clock for multiple RTP streams 488 intended for synchronized presentation. 490 Optional parameters: 492 DID_SDID: 493 Data identification and Secondary data identification words. 495 The presence of the DID_SDID parameters signals that all 496 ancillary data packets of this stream are of a particular type 497 or types, i.e., labeled with a particular DIDs and SDIDs. DID 498 and SDID values of SMPTE Registered ANC packet types can be 499 found on the at the SMPTE Registry for Data Identification Word 500 Assignments [SMPTE-RA] web site. 502 "Type 1" ANC packets (which do not have SDIDs defined) SHALL be 503 labeled with SDID=0x00. 505 DID and SDID values can be registered with SMPTE as per SMPTE 506 ST 291-1 [ST291]. 508 The absence of the DID_SDID parameter signals that 509 determination of the DID and SDID of ANC packets in the payload 510 can only be achieved through direct inspection of the ANC data 511 packet fields. 513 The ABNF description of the DID_SDID parameter is described in 514 Section 4 of [this RFC]. 516 VPID_Code: 518 This integer parameter specifies the Video Payload ID (VPID) 519 Code of the source interface of ANC data packets using the 520 value from byte 1 of the VPID as defined in SMPTE ST 352 521 [ST352]. The integer SHALL be made with bit 7 of VPID byte 1 522 being the most significant bit, and bit 0 of VPID byte 1 being 523 the least significant bit. For example, 132 refers to SMPTE ST 524 292-1, 720-line video payloads on a 1.5 Gbps (nominal) serial 525 digital interface. 527 Encoding considerations: This media type is framed and binary; see 528 Section 4.8 of RFC 6838 [RFC6838]. 530 Security considerations: See Section 7 of [this RFC] 532 Interoperability considerations: Data items in smpte291 can be very 533 diverse. Receivers might only be capable of interpreting a subset of 534 the possible data items. Some implementations might care about the 535 location of the ANC data packets in the SDI raster, but other 536 implementations might not care. 538 Published specification: [this RFC] 540 Applications that use this media type: Devices that stream real-time 541 professional video, especially those that interoperate with legacy 542 serial digital interfaces (SDI). 544 Additional Information: 546 Deprecated alias names for this type: N/A 548 Magic number(s): N/A 550 File extension(s): N/A 552 Macintosh file type code(s): N/A 554 Person & email address to contact for further information: T. 555 Edwards , IETF Payload Working Group 556 558 Intended usage: COMMON 560 Restrictions on usage: This media type depends on RTP framing, and 561 hence is only defined for transfer via RTP RFC 3550 [RFC3550]. 562 Transport within other framing protocols is not defined at this time. 564 Author: T. Edwards 565 Change controller: The IETF PAYLOAD working group, or other party as 566 designated by the IESG. 568 4. SDP Considerations 570 The mapping of the above defined payload format media type and its 571 parameters SHALL be done according to Section 3 of RFC 4855 572 [RFC4855]. 574 o The type name ("video") goes in SDP "m=" as the media name. 576 o The subtype name ("smpte291") goes in SDP "a=rtpmap" as the 577 encoding name, followed by a slash ("/") and the rate parameter. 579 o The optional parameters VPID_Code and DID_SDID, when present, are 580 included in the "a=fmtp" attribute line of SDP as a semicolon- 581 separated list of parameter=value pairs. 583 DID and SDID values SHALL be specified in hexadecimal with a "0x" 584 prefix (such as "0x61"). The ABNF as per RFC 5234 [RFC5234] of the 585 DID_SDID optional parameter SHALL be: 587 TwoHex = "0x" 1*2(HEXDIG) 588 DidSdid = "DID_SDID={" TwoHex "," TwoHex "}" 590 For example, EIA 608 Closed Caption data would be signalled with the 591 parameter DID_SDID={0x61,0x02}. If a DID_SDID parameter is not 592 specified, then the ancillary data stream might potentially contain 593 ancillary data packets of any type. 595 Multiple DID_SDID parameters can be specified (separated by 596 semicolons) to signal the presence of multiple types of ANC data in 597 the stream. DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}, for example, 598 signals the presence of EIA 608 Closed Captions as well as AFD/Bar 599 Data. Multiple DID_SDID parameters do not imply any particular 600 ordering of the different types of ANC packets in the stream. 602 If the optional parameter VPID_Code is present, it SHALL be present 603 only once in the semicolon-separated list, taking a single integer 604 value. 606 A sample SDP mapping for ancillary data is as follows: 608 m=video 30000 RTP/AVP 112 609 a=rtpmap:112 smpte291/90000 610 a=fmtp:112 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05};VPID_Code=132 612 In this example, a dynamic payload type 112 is used for ancillary 613 data. The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" 614 line after the subtype. In the "a=fmtp:" line, DID 0x61 and SDID 615 0x02 are specified (registered to EIA 608 Closed Caption Data by 616 SMPTE), and also DID 0x41 and SDID 0x05 (registered to AFD/Bar Data). 617 The VPID_Code is 132 (referring to SMPTE ST 292-1, 720-line video 618 payloads on a 1.5 Gbps serial digital interface). 620 4.1. Grouping ANC Streams with other Media Streams 622 To indicate the association of an ancillary data stream with a 623 particular video stream, implementers MAY group the "m" lines 624 together using Flow Identificaiton ("FID") semantics as defined in 625 RFC 5888 [RFC5888]. 627 A sample SDP mapping for grouping ANC data with RFC 4175 video is as 628 follows: 630 v=0 631 o=Al 123456 11 IN IP4 host.example.com 632 s=Professional Networked Media Test 633 i=A test of synchronized video and ANC data 634 t=0 0 635 a=group:FID V1 M1 636 m=video 50000 RTP/AVP 96 637 c=IN IP4 233.252.0.1/255 638 a=rtpmap:96 raw/90000 639 a=fmtp:96 sampling=YCbCr-4:2:2; width=1280; height=720; depth=10 640 a=mid:V1 641 m=video 50010 RTP/AVP 97 642 c=IN IP4 233.252.0.2/255 643 a=rtpmap:97 smpte291/90000 644 a=fmtp:97 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05} 645 a=mid:M1 647 5. Offer/Answer Model and Declarative Considerations 649 5.1. Offer/Answer Model 651 Receivers might wish to receive ANC data streams with specific 652 DID_SDID parameters. Thus when offering ANC data streams using the 653 Session Description Protocol (SDP) in an Offer/Answer model 654 [RFC3264], the offeror MAY provide a list of ANC streams available 655 with specific DID_SDID parameters in the fmtp line. The answerer MAY 656 respond with all or a subset of the streams offered along with fmtp 657 lines with all or a subset of the DID_SDID parameters offered. Or 658 the answerer MAY set the corresponding port number to 0 to decline 659 the smpte291 stream if not in the same media section as a 660 corresponding video stream, or MAY remove the corresponding payload 661 type if the smpte291 stream is in the same media section as a 662 corresponding video stream. There are no restrictions on updating 663 DID_SDID parameters in a subsequent offer. 665 5.2. Declarative SDP Considerations 667 For declarative use of SDP, nothing specific is defined for this 668 payload format. The configuration given by the SDP MUST be used when 669 sending and/or receiving media in the session. 671 6. IANA Considerations 673 One media type (video/smpte291) has been defined and needs 674 registration in the media types registry. See Section 3.1 676 7. Security Considerations 678 RTP packets using the payload format defined in this specification 679 are subject to the security considerations discussed in the RTP 680 specification [RFC3550], and in any applicable RTP profile such as 681 RTP/AVP [RFC3551], RTP/AVPF [RFC4585] RTP/SAVP [RFC3711] or RTP/SAVPF 682 [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP 683 Does Not Mandate a Single Media Security Solution" [RFC7202] 684 discusses, it is not an RTP payload format's responsibility to 685 discuss or mandate what solutions are used to meet the basic security 686 goals like confidentiality, integrity and source authenticity for RTP 687 in general. This responsibility lays on anyone using RTP in an 688 application. They can find guidance on available security mechanisms 689 and important considerations in Options for Securing RTP Sessions 690 [RFC7201]. Applications SHOULD use one or more appropriate strong 691 security mechanisms. The rest of this security consideration section 692 discusses the security impacting properties of the payload format 693 itself. 695 To avoid potential buffer overflow attacks, receivers SHOULD validate 696 that the ANC data packets in the RTP payload are of the appropriate 697 length (using the Data_Count field) for the ANC data type specified 698 by DID & SDID. Also the Checksum_Word SHOULD be checked against the 699 ANC data packet to ensure that its data has not been damaged in 700 transit, but the Checksum_Word is unlikely to provide a payload 701 integrity check in case of a directed attack. 703 Some receivers will simply move the ANC data packet bits from the RTP 704 payload into a serial digital interface (SDI). It might still be a 705 good idea for these "re-embedders" to perform the above mentioned 706 validity tests to avoid downstream SDI systems from becoming confused 707 by bad ANC data packets, which could be used for a denial of service 708 attack. 710 "Re-embedders" into SDI SHOULD also double check that the Line_Number 711 and Horizontal_Offset leads to the ANC data packet being inserted 712 into a legal area to carry ancillary data in the SDI video bit stream 713 of the output video format. 715 8. References 717 8.1. Normative References 719 [BT1120] ITU-R, "BT.1120-8, Digital Interfaces for HDTV Studio 720 Signals", January 2012. 722 [BT1700] ITU-R, "BT.1700, Characteristics of Composite Video 723 Signals for Conventional Analogue Television Systems", 724 February 2005. 726 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 727 DOI 10.17487/RFC0791, September 1981, 728 . 730 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 731 Requirement Levels", BCP 14, RFC 2119, 732 DOI 10.17487/RFC2119, March 1997, 733 . 735 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 736 with Session Description Protocol (SDP)", RFC 3264, 737 DOI 10.17487/RFC3264, June 2002, 738 . 740 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 741 Jacobson, "RTP: A Transport Protocol for Real-Time 742 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 743 July 2003, . 745 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 746 Video Conferences with Minimal Control", STD 65, RFC 3551, 747 DOI 10.17487/RFC3551, July 2003, 748 . 750 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 751 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 752 RFC 3711, DOI 10.17487/RFC3711, March 2004, 753 . 755 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 756 "Extended RTP Profile for Real-time Transport Control 757 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 758 DOI 10.17487/RFC4585, July 2006, 759 . 761 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 762 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 763 . 765 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 766 Real-time Transport Control Protocol (RTCP)-Based Feedback 767 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 768 2008, . 770 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 771 Specifications: ABNF", STD 68, RFC 5234, 772 DOI 10.17487/RFC5234, January 2008, 773 . 775 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 776 Protocol (SDP) Grouping Framework", RFC 5888, 777 DOI 10.17487/RFC5888, June 2010, 778 . 780 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 781 Specifications and Registration Procedures", BCP 13, 782 RFC 6838, DOI 10.17487/RFC6838, January 2013, 783 . 785 [ST291] SMPTE, "ST 291-1:2011, Ancillary Data Packet and Space 786 Formatting", 2011. 788 [ST352] SMPTE, "ST 352:2013, Payload Identification Codes for 789 Serial Digital Interfaces", 2013. 791 [ST424] SMPTE, "ST 424:2012, 3 Gb/s Signal/Data Serial Interface", 792 2012. 794 8.2. Informative References 796 [BT656] ITU-R, "BT.656-5, Interfaces for Digital Component Video 797 Signals in 525-Line and 625-Line Television Systems 798 Operating at the 4:2:2 Level of Recommendation ITU-R 799 BT.601", December 2007. 801 [RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for 802 Uncompressed Video", RFC 4175, DOI 10.17487/RFC4175, 803 September 2005, . 805 [RFC5371] Futemma, S., Itakura, E., and A. Leung, "RTP Payload 806 Format for JPEG 2000 Video Streams", RFC 5371, 807 DOI 10.17487/RFC5371, October 2008, 808 . 810 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 811 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 812 . 814 [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP 815 Framework: Why RTP Does Not Mandate a Single Media 816 Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 817 2014, . 819 [RFC7273] Williams, A., Gross, K., van Brandenburg, R., and H. 820 Stokking, "RTP Clock Source Signalling", RFC 7273, 821 DOI 10.17487/RFC7273, June 2014, 822 . 824 [RP168] SMPTE, "RP 168:2009, Definition of Vertical Interval 825 Switching Point for Synchronous Video Switching", 2009. 827 [SMPTE-RA] 828 SMPTE Registration Authority, LLC, "SMPTE ST 291 Ancillary 829 Data Identification Word Assignments for Registered DIDs", 830 2011, . 833 [ST125] SMPTE, "ST 125:2013, SDTV Component Video Signal Coding 834 4:4:4 and 4:2:2 for 13.5 MHz and 18 MHz Systems", 2013. 836 [ST2038] SMPTE, "ST 2038:2008, Carriage of Ancillary Data Packets 837 in an MPEG-2 Transport Stream", 2008. 839 [ST259] SMPTE, "ST 259:2008, SDTV Digital Signal/Data - Serial 840 Digital Interface", 2008. 842 [ST274] SMPTE, "ST 274:2008, 1920 x 1080 Image Sample Structure, 843 Digital Representation and Digital Timing Reference 844 Sequences for Multiple Picture Rates", 2008. 846 [ST292] SMPTE, "ST 292-1:2012, 1.5 Gb/s Signal/Data Serial 847 Interface", 2012. 849 [ST296] SMPTE, "ST 296:2012, 1280 x 720 Progressive Image 4:2:2 850 and 4:4:4 Sample Structure - Analog and Digital 851 Representation and Analog Interface", 2012. 853 Author's Address 855 Thomas G. Edwards 856 FOX 857 10201 W. Pico Blvd. 858 Los Angeles, CA 90035 859 USA 861 Phone: +1 310 369 6696 862 Email: thomas.edwards@fox.com