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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' Summary: 1 error (**), 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 June 15, 2017 5 Expires: December 17, 2017 7 RTP Payload for SMPTE ST 291 Ancillary Data 8 draft-ietf-payload-rtp-ancillary-10 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 http://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 December 17, 2017. 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 (http://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 . . . . . . . . . . . . . . . . . . 10 59 4. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 12 60 4.1. Grouping ANC Streams with other Media Streams . . . . . . 13 61 5. Offer/Answer Model and Declarative Considerations . . . . . . 14 62 5.1. Offer/Answer Model . . . . . . . . . . . . . . . . . . . 14 63 5.2. Declarative SDP Considerations . . . . . . . . . . . . . 14 64 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 66 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 67 8.1. Normative References . . . . . . . . . . . . . . . . . . 15 68 8.2. Informative References . . . . . . . . . . . . . . . . . 17 69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18 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 SMPTE ST 259 86 [ST259], the standard definition (SD) Serial Digital Interface (with 87 ANC data inserted as per SMPTE ST 125 [ST125]), or SMPTE ST 292-1 88 [ST292], the 1.5 Gb/s Serial Digital Interface for high definition 89 (HD) television applications. 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) or 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 | 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | ANC_Count | F | reserved | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 |C| Line_Number | Horizontal_Offset |S| StreamNum | 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 152 | DID | SDID | Data_Count | 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 154 User_Data_Words... 155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 156 | Checksum_Word | word_align | 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 |C| Line_Number | Horizontal_Offset |S| StreamNum | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | DID | SDID | Data_Count | 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. 173 The term "network byte order" in the payload format SHALL refer to 174 the Data Transmission Order as defined in Appendix B of RFC 791 175 [RFC0791]. 177 RTP packet header fields SHALL be interpreted as per RFC 3550 178 [RFC3550], with the following specifics: 180 Timestamp: 32 bits 181 The timestamp field is interpreted in a similar fashion to 182 RFC 4175 [RFC4175]: 184 For progressive scan video, the timestamp denotes the 185 sampling instant of the frame to which the ancillary data in 186 the RTP packet belongs. RTP packets MUST NOT include ANC 187 data from multiple frames, and all RTP packets with ANC data 188 belonging to the same frame MUST have the same timestamp. 190 For interlaced video, the timestamp denotes the sampling 191 instant of the field to which the ancillary data in the RTP 192 packet belongs. RTP packets MUST NOT include ANC data from 193 multiple fields, and all RTP packets belonging to the same 194 field MUST have the same timestamp. 196 If the sampling instant does not correspond to an integer 197 value of the clock, the value SHALL be truncated to the next 198 lowest integer, with no ambiguity. Section 3.1 describes 199 timestamp clock rates. 201 Marker bit (M): 1 bit 202 The marker bit set to "1" indicates the last ANC RTP packet 203 for a frame (for progressive scan video) or the last ANC RTP 204 packet for a field (for interlaced video). 206 2.1. Payload Header Definitions 208 The ANC RTP payload header fields are defined as: 210 Extended Sequence Number: 16 bits 211 The high order bits of the extended 32-bit sequence number, 212 in network byte order. This is the same as the Extended 213 Sequence Number field in RFC 4175 [RFC4175]. 215 Length: 16 bits 216 Number of octets of the ANC RTP payload, beginning with the 217 "C" bit of the first ANC packet data, as an unsigned integer 218 in network byte order. Note that all word_align fields 219 contribute to the calculation of the length field. 221 ANC_Count: 8 bits 222 This field is the count of the total number of ANC data 223 packets carried in the RTP payload, as an unsigned integer. 224 A single ANC RTP packet payload cannot carry more than 255 225 ANC data packets. 227 If more than 255 ANC data packets need to be carried in a 228 field or frame, additional RTP packets carrying ANC data MAY 229 be sent with the same RTP timestamp but with different 230 sequence numbers. ANC_Count of 0 indicates that there are no 231 ANC data packets in the payload (for example, for an RTP 232 packet with the marker bit set indicating the last ANC RTP 233 packet in a field/frame, even if that RTP packet carries no 234 actual ANC data packets.) If ANC_Count is 0, Length will 235 also be 0. 237 F: 2 bits 238 These two bits relate to signaling the field specified by the 239 RTP timestamp in an interlaced SDI raster. A value of 0b00 240 indicates that either the video format is progressive or that 241 no field is specified. A value of 0b10 indicates that the 242 timestamp refers to the first field of an interlaced video 243 signal. A value of 0b11 indicates that the timestamp refers 244 to the second field of an interlaced video signal. The value 245 0b01 is not valid. 247 Note that some multi-stream SDI interfaces might use multiple 248 interlaced signal streams to transmit progressive images, in 249 which case the "F" bits would refer to the field of the 250 interlaced stream used for transport of the ANC data packet. 252 reserved: 22 bits 253 The 22 reserved bits of value "0" follow the F field to 254 ensure that the first ANC data packet header field in the 255 payload begins 32-bit word-aligned to ease implementation. 257 For each ANC data packet in the payload, the following ANC data 258 packet header fields MUST be present: 260 C: 1 bit 261 This flag, when set to "1", indicates that the ANC data 262 corresponds to the color-difference data channel (C). When 263 set to "0", this flag indicates either that the ANC data 264 corresponds to the luma (Y) data channel, that the ANC data 265 source is from an SD signal, or that the ANC data source has 266 no specific luma or color-difference data channels. For ANC 267 data from a multi-stream interface source, the C flag SHALL 268 refer to the channel of the stream used to transport the ANC 269 packet. For situations where there is no SDI source, if the 270 ANC data type definition specifically requires the use of the 271 C or Y data channel, the C flag SHALL reflect that 272 requirement. 274 Line_Number: 11 bits 275 This field contains the line number (as defined in ITU-R 276 BT.1700 [BT1700] for SD video or ITU-R BT.1120 [BT1120] for 277 HD video) that corresponds to the location of the ANC data 278 packet in an SDI raster as an unsigned integer in network 279 byte order. A value of 0x7FF (all bits in the field are '1') 280 indicates that the ANC data is carried without a specific 281 line location within the field or frame. A value of 0x7FE 282 indicates that the ANC data is intended to be placed into any 283 legal area of VANC, specifically. 285 Note that the lines that are available to convey ANC data are 286 as defined in the applicable sample structure specification 287 (e.g., SMPTE 274M [ST274], SMPTE ST 296 [ST296], ITU-R BT.656 288 [BT656]) and possibly further restricted per SMPTE RP 168 289 [RP168]. 291 In multi-stream interfaces, this field refers to the line 292 number that an ANC packet is carried on within a particular 293 data stream in the interface. 295 Horizontal_Offset: 12 bits 296 This field defines the location of the ANC data packet in an 297 SDI raster relative to the start of active video (SAV) as an 298 unsigned integer in network byte order. A value of 0 means 299 that the Ancillary Data Flag (ADF) of the ANC data packet 300 begins immediately following SAV. For HD, this is in units 301 of luma sample numbers as specified by the defining document 302 of the particular image (e.g., SMPTE 274M [ST274] for 1920 x 303 1080 active images, or SMPTE ST 296 [ST296] for 1280 x 720 304 progressive active images). For SD, this is in units of 305 (27MHz) multiplexed word numbers, as specified in SMPTE ST 306 125 [ST125]. A value of 0xFFF (all bits in the field are 307 '1') indicates that the ANC data is carried without any 308 specific location within the line. A value of 0xFFE 309 indicates that the ANC data is intended to be placed into any 310 legal area of HANC, specifically. 312 In multi-stream interfaces, this field refers to the 313 horizontal location where an ANC packet is placed on a line 314 carried within a particular data stream in the interface. 316 Note that HANC space in the digital blanking area will 317 generally have higher luma sample numbers than any samples in 318 the active digital line. 320 S (Data Stream Flag): 1 bit 321 This field indicates whether the data stream number of a 322 multi-stream data mapping used to transport the ANC data 323 packet is specified. If the S bit is '0', then the StreamNum 324 field provides no guidance regarding the source data stream 325 number of the ANC data packet. If the S bit is '1', then the 326 StreamNum field carries information regarding the source data 327 stream number of the ANC data packet. 329 StreamNum: 7 bits 330 If the S (Data Stream Flag) bit is '1', then the StreamNum 331 field MUST carry identification of the source data stream 332 number of the ANC data packet. If the data stream is 333 numbered, then the StreamNum field SHALL carry the number of 334 the source data stream minus one. If the source multi-stream 335 interface does not have numbered data streams, the following 336 numbers SHALL be used in this field: '0' for link A data 337 stream, '1' for link B data stream. For stereoscopic multi- 338 stream interface formats that do not have numbered streams, 339 the following numbers SHALL be used in this field: '0' for 340 left eye stream, '1' for right eye stream. 342 Note that in multi-link SDI connections, the physical link 343 that a particular stream utilizes is typically specified by 344 the interface standard. Also note that numbering of data 345 streams is across the interface as a whole. For example in 346 the SMPTE ST 425-3 dual-link 3 Gb/s interface, the data 347 streams are numbered 1-4 with data streams 1 and 2 on link 1 348 and data streams 3 and 4 on link 2. 350 An ANC data packet with the header fields Line_Number of 0x7FF and 351 Horizontal_Offset of 0xFFF SHALL be considered to be carried without 352 any specific location within the field or frame. 354 For each ANC data packet in the payload, immediately after the ANC 355 data packet header fields, the following data fields MUST be present, 356 with the fields DID, SDID, Data_Count, User_Data_Words, and 357 Checksum_Word representing the 10-bit words carried in the ANC data 358 packet, as per SMPTE ST 291-1 [ST291]: 360 DID: 10 bits 361 Data Identification Word 363 SDID: 10 bits 364 Secondary Data Identification Word. Used only for a "Type 2" 365 ANC data packet. Note that in a "Type 1" ANC data packet, 366 this word will actually carry the Data Block Number (DBN). 368 Data_Count: 10 bits 369 The lower 8 bits of Data_Count, corresponding to bits b7 370 (MSB) through b0 (LSB) of the 10-bit Data_Count word, contain 371 the actual count of 10-bit words in User_Data_Words. Bit b8 372 is the even parity for bits b7 through b0, and bit b9 is the 373 inverse (logical NOT) of bit b8. 375 User_Data_Words: integer number of 10 bit words 376 User_Data_Words (UDW) are used to convey information of a 377 type as identified by the DID word or the DID and SDID words. 378 The number of 10-bit words in the UDW is defined by the 379 Data_Count field. The 10-bit words are carried in order 380 starting with the most significant bit and ending with the 381 least significant bit. 383 Checksum_Word: 10 bits 384 The Checksum_Word can be used to determine the validity of 385 the ANC data packet from the DID word through the UDW. It 386 consists of 10 bits, where bits b8 (MSB) through b0 (LSB) 387 define the checksum value and bit b9 is the inverse (logical 388 NOT) of bit b8. The checksum value is equal to the nine 389 least significant bits of the sum of the nine least 390 significant bits of the DID word, the SDID word, the 391 Data_Count word, and all User_Data_Words in the ANC data 392 packet. The checksum is initialized to zero before 393 calculation, and any end carry resulting from the checksum 394 calculation is ignored. 396 At the end of each ANC data packet in the payload: 398 word_align: bits as needed to complete 32-bit word 399 Word align contains enough "0" bits as needed to complete the 400 last 32-bit word of ANC packet's data in the RTP payload. If 401 an ANC data packet in the RTP payload ends aligned with a 402 word boundary, there is no need to add any word alignment 403 bits. Word align SHALL be used even for the last ANC data 404 packet in an RTP packet. Word align SHALL NOT be used if 405 there are zero ANC data packets being carried in the RTP 406 packet. 408 When reconstructing an SDI signal based on this payload, it is 409 important to place ANC data packets into the locations indicated by 410 the ANC payload header fields C, Line_Number and Horizontal_Offset, 411 and also to follow the requirements of SMPTE ST 291-1 [ST291] 412 Section 7 "Ancillary Data Space Formatting (Component or Composite 413 Interface)", which include rules on the placement of initial ANC data 414 into allowed spaces as well as the contiguity of ANC data packet 415 sequences within those spaces in order to assure that the resulting 416 ANC data packets in the SDI signal are valid. The optional Media 417 Type parameter VPID_Code can inform receivers of the type of 418 originating SDI interface. For multi-stream originating interfaces, 419 the StreamNum field can provide information regarding which stream an 420 ANC data packet can be placed in to match the ANC data location in 421 the originating SDI interface. 423 Senders of this payload SHOULD transmit available ANC data packets as 424 soon as practical to reduce end-to-end latency, especially if 425 receivers will be embedding the received ANC data packet into an SDI 426 signal emission. One millisecond is a reasonable upper bound for the 427 amount of time between when an ANC data packet becomes available to a 428 sender and the emission of an RTP payload containing that ANC data 429 packet. 431 ANC data packets with headers that specify specific location within a 432 field or frame SHOULD be sent in raster scan order, both in terms of 433 packing position within an RTP packet and in terms of transmission 434 time of RTP packets. 436 3. Payload Format Parameters 438 This RTP payload format is identified using the video/smpte291 media 439 type, which is registered in accordance with RFC 4855 [RFC4855], and 440 using the template of RFC 6838 [RFC6838]. 442 Note that the Media Type Definition is in the "video" tree due to the 443 expected use of SMPTE ST 291 Ancillary Data along with video formats. 445 3.1. Media Type Definition 447 Type name: video 449 Subtype name: smpte291 451 Required parameters: 453 Rate: 454 RTP timestamp clock rate. 456 When an ANC RTP stream is to be associated with an RTP video 457 stream, the RTP timestamp rates SHOULD be the same to ensure 458 that ANC data packets can be associated with the appropriate 459 frame or field. Otherwise, a 90 kHz rate SHOULD be used. 461 Note that techniques described in RFC 7273 [RFC7273] can 462 provide a common reference clock for multiple RTP streams 463 intended for synchronized presentation. 465 Optional parameters: 467 DID_SDID: 468 Data identification and Secondary data identification words. 470 The presence of the DID_SDID parameters signals that all 471 ancillary data packets of this stream are of a particular type 472 or types, i.e., labeled with a particular DIDs and SDIDs. DID 473 and SDID values of SMPTE Registered ANC packet types can be 474 found on the at the SMPTE Registry for Data Identification Word 475 Assignments [SMPTE-RA] web site. 477 "Type 1" ANC packets (which do not have SDIDs defined) SHALL be 478 labeled with SDID=0x00. 480 DID and SDID values can be registered with SMPTE as per SMPTE 481 ST 291-1 [ST291]. 483 The absence of the DID_SDID parameter signals that 484 determination of the DID and SDID of ANC packets in the payload 485 can only be achieved through direct inspection of the ANC data 486 packet fields. 488 VPID_Code: 489 This integer parameter specifies the Video Payload ID (VPID) 490 Code of the source interface of ANC data packets using the 491 value from byte 1 of the VPID as defined in SMPTE ST 352 492 [ST352]. The integer SHALL be made with bit 7 of VPID byte 1 493 being the most significant bit, and bit 0 of VPID byte 1 being 494 the least significant bit. For example, 132 refers to SMPTE ST 495 292-1, 720-line video payloads on a 1.5 Gbps (nominal) serial 496 digital interface. 498 Encoding considerations: This media type is framed and binary; see 499 Section 4.8 of RFC 6838 [RFC6838]. 501 Security considerations: See Section 7 of [this RFC] 503 Interoperability considerations: Data items in smpte291 can be very 504 diverse. Receivers might only be capable of interpreting a subset of 505 the possible data items. Some implementations might care about the 506 location of the ANC data packets in the SDI raster, but other 507 implementations might not care. 509 Published specification: [this RFC] 511 Applications that use this media type: Devices that stream real-time 512 professional video, especially those that interoperate with legacy 513 serial digital interfaces (SDI). 515 Additional Information: 517 Deprecated alias names for this type: N/A 518 Magic number(s): N/A 520 File extension(s): N/A 522 Macintosh file type code(s): N/A 524 Person & email address to contact for further information: T. 525 Edwards , IETF Payload Working Group 526 528 Intended usage: COMMON 530 Restrictions on usage: This media type depends on RTP framing, and 531 hence is only defined for transfer via RTP RFC 3550 [RFC3550]. 532 Transport within other framing protocols is not defined at this time. 534 Author: T. Edwards 536 Change controller: The IETF PAYLOAD working group, or other party as 537 designated by the IESG. 539 4. SDP Considerations 541 The mapping of the above defined payload format media type and its 542 parameters SHALL be done according to Section 3 of RFC 4855 543 [RFC4855]. 545 o The type name ("video") goes in SDP "m=" as the media name. 547 o The subtype name ("smpte291") goes in SDP "a=rtpmap" as the 548 encoding name, followed by a slash ("/") and the rate parameter. 550 o The optional parameters VPID_Code and DID_SDID, when present, are 551 included in the "a=fmtp" attribute line of SDP as a semicolon- 552 separated list of parameter=value pairs. 554 DID and SDID values SHALL be specified in hexadecimal with a "0x" 555 prefix (such as "0x61"). The ABNF as per RFC 5234 [RFC5234] of the 556 DID_SDID optional parameter SHALL be: 558 TwoHex = "0x" 1*2(HEXDIG) 559 DidSdid = "DID_SDID={" TwoHex "," TwoHex "}" 561 For example, EIA 608 Closed Caption data would be signalled with the 562 parameter DID_SDID={0x61,0x02}. If a DID_SDID parameter is not 563 specified, then the ancillary data stream might potentially contain 564 ancillary data packets of any type. 566 Multiple DID_SDID parameters can be specified (separated by 567 semicolons) to signal the presence of multiple types of ANC data in 568 the stream. DID_SDID={0x61,0x02};DID_SDID={0x41,0x05}, for example, 569 signals the presence of EIA 608 Closed Captions as well as AFD/Bar 570 Data. Multiple DID_SDID parameters do not imply any particular 571 ordering of the different types of ANC packets in the stream. 573 If the optional parameter VPID_Code is present, it SHALL be present 574 only once in the semicolon-separated list, taking a single integer 575 value. 577 A sample SDP mapping for ancillary data is as follows: 579 m=video 30000 RTP/AVP 112 580 a=rtpmap:112 smpte291/90000 581 a=fmtp:112 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05};VPID_Code=132 583 In this example, a dynamic payload type 112 is used for ancillary 584 data. The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" 585 line after the subtype. In the "a=fmtp:" line, DID 0x61 and SDID 586 0x02 are specified (registered to EIA 608 Closed Caption Data by 587 SMPTE), and also DID 0x41 and SDID 0x05 (registered to AFD/Bar Data). 588 The VPID_Code is 132 (referring to SMPTE ST 292-1, 720-line video 589 payloads on a 1.5 Gbps serial digital interface). 591 4.1. Grouping ANC Streams with other Media Streams 593 To associate an ANC RTP stream with other media streams, implementers 594 can use the Lip Synchronization (LS) grouping defined in RFC 5888 595 [RFC5888], which states that media streams whose corresponding "m" 596 lines are grouped together using LS semantics are to be played back 597 in a synchronized manner. 599 A sample SDP mapping for grouping ANC data with RFC 4175 video using 600 LS semantics is as follows: 602 v=0 603 o=Al 123456 11 IN IP4 host.example.com 604 s=Professional Networked Media Test 605 i=A test of synchronized video and ANC data 606 t=0 0 607 a=group:LS V1 M1 608 m=video 50000 RTP/AVP 96 609 c=IN IP4 233.252.0.1/255 610 a=rtpmap:96 raw/90000 611 a=fmtp:96 sampling=YCbCr-4:2:2; width=1280; height=720; depth=10 612 a=mid:V1 613 m=video 50010 RTP/AVP 97 614 c=IN IP4 233.252.0.2/255 615 a=rtpmap:97 smpte291/90000 616 a=fmtp:97 DID_SDID={0x61,0x02};DID_SDID={0x41,0x05} 617 a=mid:M1 619 5. Offer/Answer Model and Declarative Considerations 621 5.1. Offer/Answer Model 623 Receivers might wish to receive ANC data streams with specific 624 DID_SDID parameters. Thus when offering ANC data streams using the 625 Session Description Protocol (SDP) in an Offer/Answer model 626 [RFC3264], the offeror MAY provide a list of ANC streams available 627 with specific DID_SDID parameters in the fmtp line. The answerer MAY 628 respond with all or a subset of the streams offered along with fmtp 629 lines with all or a subset of the DID_SDID parameters offered. Or 630 the answerer MAY reject the offer. There are no restrictions on 631 updating DID_SDID parameters in a subsequent offer. 633 5.2. Declarative SDP Considerations 635 For declarative use of SDP, nothing specific is defined for this 636 payload format. The configuration given by the SDP MUST be used when 637 sending and/or receiving media in the session. 639 6. IANA Considerations 641 One media type (video/smpte291) has been defined and needs 642 registration in the media types registry. See Section 3.1 644 7. Security Considerations 646 RTP packets using the payload format defined in this specification 647 are subject to the security considerations discussed in the RTP 648 specification [RFC3550], and in any applicable RTP profile such as 649 RTP/AVP [RFC3551], RTP/AVPF [RFC4585] RTP/SAVP [RFC3711] or RTP/SAVPF 651 [RFC5124]. However, as "Securing the RTP Protocol Framework: Why RTP 652 Does Not Mandate a Single Media Security Solution" [RFC7202] 653 discusses, it is not an RTP payload format's responsibility to 654 discuss or mandate what solutions are used to meet the basic security 655 goals like confidentiality, integrity and source authenticity for RTP 656 in general. This responsibility lays on anyone using RTP in an 657 application. They can find guidance on available security mechanisms 658 and important considerations in Options for Securing RTP Sessions 659 [RFC7201]. Applications SHOULD use one or more appropriate strong 660 security mechanisms. The rest of this security consideration section 661 discusses the security impacting properties of the payload format 662 itself. 664 To avoid potential buffer overflow attacks, receivers SHOULD validate 665 that the ANC data packets in the RTP payload are of the appropriate 666 length (using the Data_Count field) for the ANC data type specified 667 by DID & SDID. Also the Checksum_Word SHOULD be checked against the 668 ANC data packet to ensure that its data has not been damaged in 669 transit, but the Checksum_Word is unlikely to provide a payload 670 integrity check in case of a directed attack. 672 Some receivers will simply move the ANC data packet bits from the RTP 673 payload into a serial digital interface (SDI). It might still be a 674 good idea for these "re-embedders" to perform the above mentioned 675 validity tests to avoid downstream SDI systems from becoming confused 676 by bad ANC data packets, which could be used for a denial of service 677 attack. 679 "Re-embedders" into SDI SHOULD also double check that the Line_Number 680 and Horizontal_Offset leads to the ANC data packet being inserted 681 into a legal area to carry ancillary data in the SDI video bit stream 682 of the output video format. 684 8. References 686 8.1. Normative References 688 [BT1120] ITU-R, "BT.1120-8, Digital Interfaces for HDTV Studio 689 Signals", January 2012. 691 [BT1700] ITU-R, "BT.1700, Characteristics of Composite Video 692 Signals for Conventional Analogue Television Systems", 693 February 2005. 695 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 696 DOI 10.17487/RFC0791, September 1981, 697 . 699 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 700 Requirement Levels", BCP 14, RFC 2119, 701 DOI 10.17487/RFC2119, March 1997, 702 . 704 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 705 with Session Description Protocol (SDP)", RFC 3264, 706 DOI 10.17487/RFC3264, June 2002, 707 . 709 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 710 Jacobson, "RTP: A Transport Protocol for Real-Time 711 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 712 July 2003, . 714 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 715 Video Conferences with Minimal Control", STD 65, RFC 3551, 716 DOI 10.17487/RFC3551, July 2003, 717 . 719 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 720 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 721 RFC 3711, DOI 10.17487/RFC3711, March 2004, 722 . 724 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 725 "Extended RTP Profile for Real-time Transport Control 726 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 727 DOI 10.17487/RFC4585, July 2006, 728 . 730 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 731 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 732 . 734 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 735 Real-time Transport Control Protocol (RTCP)-Based Feedback 736 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 737 2008, . 739 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 740 Specifications: ABNF", STD 68, RFC 5234, 741 DOI 10.17487/RFC5234, January 2008, 742 . 744 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 745 Protocol (SDP) Grouping Framework", RFC 5888, 746 DOI 10.17487/RFC5888, June 2010, 747 . 749 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 750 Specifications and Registration Procedures", BCP 13, 751 RFC 6838, DOI 10.17487/RFC6838, January 2013, 752 . 754 [ST291] SMPTE, "ST 291-1:2011, Ancillary Data Packet and Space 755 Formatting", 2011. 757 [ST352] SMPTE, "ST 352:2013, Payload Identification Codes for 758 Serial Digital Interfaces", 2013. 760 8.2. Informative References 762 [BT656] ITU-R, "BT.656-5, Interfaces for Digital Component Video 763 Signals in 525-Line and 625-Line Television Systems 764 Operating at the 4:2:2 Level of Recommendation ITU-R 765 BT.601", December 2007. 767 [RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for 768 Uncompressed Video", RFC 4175, DOI 10.17487/RFC4175, 769 September 2005, . 771 [RFC5371] Futemma, S., Itakura, E., and A. Leung, "RTP Payload 772 Format for JPEG 2000 Video Streams", RFC 5371, 773 DOI 10.17487/RFC5371, October 2008, 774 . 776 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 777 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 778 . 780 [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP 781 Framework: Why RTP Does Not Mandate a Single Media 782 Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 783 2014, . 785 [RFC7273] Williams, A., Gross, K., van Brandenburg, R., and H. 786 Stokking, "RTP Clock Source Signalling", RFC 7273, 787 DOI 10.17487/RFC7273, June 2014, 788 . 790 [RP168] SMPTE, "RP 168:2009, Definition of Vertical Interval 791 Switching Point for Synchronous Video Switching", 2009. 793 [SMPTE-RA] 794 SMPTE Registration Authority, LLC, "SMPTE ST 291 Ancillary 795 Data Identification Word Assignments for Registered DIDs", 796 2011, . 799 [ST125] SMPTE, "ST 125:2013, SDTV Component Video Signal Coding 800 4:4:4 and 4:2:2 for 13.5 MHz and 18 MHz Systems", 2013. 802 [ST2038] SMPTE, "ST 2038:2008, Carriage of Ancillary Data Packets 803 in an MPEG-2 Transport Stream", 2008. 805 [ST259] SMPTE, "ST 259:2008, SDTV Digital Signal/Data - Serial 806 Digital Interface", 2008. 808 [ST274] SMPTE, "ST 274:2008, 1920 x 1080 Image Sample Structure, 809 Digital Representation and Digital Timing Reference 810 Sequences for Multiple Picture Rates", 2008. 812 [ST292] SMPTE, "ST 292-1:2012, 1.5 Gb/s Signal/Data Serial 813 Interface", 2012. 815 [ST296] SMPTE, "ST 296:2012, 1280 x 720 Progressive Image 4:2:2 816 and 4:4:4 Sample Structure - Analog and Digital 817 Representation and Analog Interface", 2012. 819 Author's Address 821 Thomas G. Edwards 822 FOX 823 10201 W. Pico Blvd. 824 Los Angeles, CA 90035 825 USA 827 Phone: +1 310 369 6696 828 Email: thomas.edwards@fox.com