idnits 2.17.1 draft-ietf-avtext-splicing-notification-06.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 (April 6, 2016) is 2941 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) ** Obsolete normative reference: RFC 5285 (Obsoleted by RFC 8285) ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) -- Obsolete informational reference (is this intentional?): RFC 5226 (Obsoleted by RFC 8126) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVTEXT Working Group J. Xia 3 INTERNET-DRAFT R. Even 4 Intended Status: Standards Track R. Huang 5 Expires: October 8, 2016 Huawei 6 L. Deng 7 China Mobile 8 April 6, 2016 10 RTP/RTCP extension for RTP Splicing Notification 11 draft-ietf-avtext-splicing-notification-06 13 Abstract 15 Content splicing is a process that replaces the content of a main 16 multimedia stream with other multimedia content, and delivers the 17 substitutive multimedia content to the receivers for a period of 18 time. The splicer is designed to handle RTP splicing and needs to 19 know when to start and end the splicing. 21 This memo defines two RTP/RTCP extensions to indicate the splicing 22 related information to the splicer: an RTP header extension that 23 conveys the information in-band and an RTCP packet that conveys the 24 information out-of-band. 26 Status of this Memo 28 This Internet-Draft is submitted to IETF in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF), its areas, and its working groups. Note that 33 other groups may also distribute working documents as 34 Internet-Drafts. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 The list of current Internet-Drafts can be accessed at 42 http://www.ietf.org/1id-abstracts.html 44 The list of Internet-Draft Shadow Directories can be accessed at 45 http://www.ietf.org/shadow.html 47 Copyright and License Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 65 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2 Overview of RTP Splicing Notification . . . . . . . . . . . . . 4 67 3 Conveying Splicing Interval in RTP/RTCP extensions . . . . . . 5 68 3.1 RTP Header Extension . . . . . . . . . . . . . . . . . . . . 5 69 3.2 RTCP Splicing Notification Message . . . . . . . . . . . . . 6 70 4 Reducing Splicing Latency . . . . . . . . . . . . . . . . . . . 7 71 5 Failure Cases . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 6 SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 8 73 6.1 Declarative SDP . . . . . . . . . . . . . . . . . . . . . . 9 74 6.2 Offer/Answer without BUNDLE . . . . . . . . . . . . . . . . 9 75 6.3 Offer/Answer with BUNDLE: All Media are spliced . . . . . . 10 76 6.4 Offer/Answer with BUNDLE: a Subset of Media are Spliced . . 12 77 7 Security Considerations . . . . . . . . . . . . . . . . . . . . 13 78 8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14 79 8.1 RTCP Control Packet Types . . . . . . . . . . . . . . . . . 14 80 8.2 RTP Compact Header Extensions . . . . . . . . . . . . . . . 14 81 8.3 SDP Grouping Semantic Extension . . . . . . . . . . . . . . 14 82 9 Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . . 15 83 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 84 10.1 Normative References . . . . . . . . . . . . . . . . . . . 15 85 10.2 Informative References . . . . . . . . . . . . . . . . . . 15 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 88 1 Introduction 90 Splicing is a process that replaces some multimedia content with 91 other multimedia content and delivers the substitutive multimedia 92 content to the receivers for a period of time. In some predictable 93 splicing cases, e.g., advertisement insertion, the splicing duration 94 needs to be inside of the specific, pre-designated time slot. 95 Certain timing information about when to start and end the splicing 96 must be first acquired by the splicer in order to start the splicing. 97 This document refers to this information as the Splicing Interval. 99 [SCTE35] provides a method that encapsulates the Splicing Interval 100 inside the MPEG2-TS layer in cable TV systems. When transported in 101 RTP, an middle box designed as the splicer to decode the RTP packets 102 and search for the Splicing Interval inside the payloads is required. 103 The middle box is either a translator or a mixer as described in 104 [RFC6828]. The need for such processing increases the workload of the 105 middle box and limits the number of RTP sessions the middle box can 106 support. 108 The document defines an RTP header extension [RFC5285] used by the 109 main RTP sender to provide the Splicing Interval by including it in 110 the RTP packets. 112 However, the Splicing Interval conveyed in the RTP header extension 113 might not reach the splicer successfully. Any splicing un-aware 114 middlebox on the path between the RTP sender might strip this RTP 115 header extension. 117 To increase robustness against such case, the document also defines a 118 complementary RTCP packet type to carry the same Splicing Interval to 119 the splicer. 121 1.1 Terminology 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 124 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 125 document are to be interpreted as described in RFC 2119 [RFC2119]. 127 In addition, we define following terminologies: 129 Main RTP sender: 131 The sender of RTP packets carrying the main RTP stream. 133 Splicer: 135 An intermediary node that inserts substitutive content into a main 136 RTP stream. The splicer sends substitutive content to the RTP 137 receiver instead of the main content during splicing. It is also 138 responsible for processing RTCP traffic between the RTP sender and 139 the RTP receiver. 141 Splicing-In Point 143 A virtual point in the RTP stream, suitable for substitutive 144 content entry, typically in the boundary between two independently 145 decodable frames. 147 Splicing-Out Point 149 A virtual point in the RTP stream, suitable for substitutive 150 content exit, typically in the boundary between two independently 151 decodable frames. 153 Splicing Interval: 155 The NTP-format timestamps, representing the main RTP sender 156 wallclock time, for the Splicing-In point and Splicing-Out point 157 per [RFC6828] allowing the splicer to know when to start and end 158 the RTP splicing. 160 Substitutive RTP Sender: 162 The sender of RTP packets carrying the RTP stream that will 163 replace the content in the main RTP stream. 165 2 Overview of RTP Splicing Notification 167 A splicer is designed to handle splicing on the RTP layer at the 168 reserved time slots set by the main RTP sender. This implies that the 169 splicer must first know the Splicing Interval from the main RTP 170 sender before it can start splicing. The splicer can be a mixer as 171 described in [RFC6828]. 173 When a new splicing is forthcoming, the main RTP sender needs to send 174 the Splicing Interval to the splicer. The Splicing Interval SHOULD be 175 sent more than once to mitigate the possible packet loss. To enable 176 the splicer to get the substitutive content before the splicing 177 starts, the main RTP sender MUST send the Splicing Interval far 178 ahead. For example, the main RTP sender can estimate when to send the 179 Splicing Interval based on the round-trip time (RTT) following the 180 mechanisms in section 6.4.1 of [RFC3550] when the splicer sends RTCP 181 RR to the main sender. 183 The substitutive sender also needs to learn the Splicing Interval 184 from the main RTP sender in advance, and thus estimates when to 185 transfer the substitutive content to the splicer. The Splicing 186 Interval could be transmitted from the main RTP sender to the 187 substitutive content using some out-of-band mechanisms, for example, 188 a proprietary mechanism to exchange the Splicing Interval, or the 189 substitutive sender is implemented together with the main RTP sender 190 inside a single device. To ensure the Splicing Interval is valid for 191 both the main RTP sender and the substitutive RTP sender, the two 192 senders MUST share a common reference clock so that the splicer can 193 achieve accurate splicing. The requirements for the common reference 194 clock (e.g. resolution, skew) depend on the codec used by the media 195 content. 197 In this document, the main RTP sender uses a pair of NTP-format 198 timestamps, to indicate when to start and end the splicing to the 199 splicer: the timestamp of the first substitutive RTP packet at the 200 splicing in point, and the timestamp of the first main RTP packet at 201 the splicing out point. 203 When the substitutive RTP sender gets the Splicing Interval, it must 204 prepare the substitutive stream. The main and the substitutive 205 content providers MUST ensure that the RTP timestamp of the first 206 substitutive RTP packet that would be presented to the receivers 207 corresponds to the same time instant as the former NTP-format 208 timestamp in the Splicing Interval. To enable the splicer to know the 209 first substitutive RTP packet it needs to send, the substitutive RTP 210 sender MUST send the substitutive RTP packet ahead of the Splicing In 211 point, allowing the splicer to find out the timestamp of this first 212 RTP packet in the substitutive RTP stream, e.g., using a prior RTCP 213 SR (Sender Report) message. 215 When the splicing will end, the main content provider and the 216 substitutive content provider MUST ensure the RTP timestamp of the 217 first main RTP packet that would be presented on the receivers 218 corresponds to the same time instant as the latter NTP-format 219 timestamp in the Splicing Interval. 221 3 Conveying Splicing Interval in RTP/RTCP extensions 223 This memo defines two backwards compatible RTP extensions to convey 224 the Splicing Interval to the splicer: an RTP header extension and an 225 RTCP splicing notification message. 227 3.1 RTP Header Extension 228 The RTP header extension mechanism defined in [RFC5285] can be 229 adapted to carry the Splicing Interval consisting of a pair of NTP- 230 format timestamps. 232 This RTP header extension carries the 6 octets splicing-out NTP- 233 format timestamp (lower 16-bit part of the Seconds of a NTP-format 234 timestamp and the 32 bits of the Fraction of a NTP-format timestamp 235 as defined in [RFC5905]), followed by the 8 octets splicing-in NTP- 236 format timestamp (64-bit NTP-format timestamp as defined in 237 [RFC5905]). The top 16 bits of the splicing-out NTP timestamp are 238 inferred from the top 16 bits of the splicing-in NTP timestamp, under 239 the assumption that the splicing-out time is after the splicing-in 240 time, and the splicing interval is less than 2^16 seconds. Therefore, 241 if the value of 6 octets splicing-out NTP-format timestamp is smaller 242 than the value of 6 lower octets splicing-in NTP-format, it implies a 243 wrap of the 48-bit splicing-out NTP-format timestamp which means the 244 top 16-bit value of the 64-bit splicing-out is equal to the top 16- 245 bit value of splicing-in NTP Timestamp plus 0x0001. Otherwise, the 246 top 16 bits of splicing-out NTP timestamp is equal to the top 16 bits 247 of splicing-in NTP Timestamp. 249 This RTP header extension can be encoded using either the one-byte or 250 two-byte header defined in [RFC5285]. Figure 1 and 2 show the 251 splicing interval header extension with each of the two header 252 formats. 254 0 1 2 3 255 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 1 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+E 257 | ID | L=13 |OUT NTP timestamp-Seconds(0-16)| Out |x 258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+t 259 | NTP timestamp format - Fraction (bit 0-31) | In |e 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n 261 | NTP timestamp format - Seconds (bit 0-31) | In |s 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+i 263 | NTP timestamp format - Fraction (bit 0-31) | 0 (pad) |o 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n 266 Figure 1: Splicing Interval 267 Using the One-Byte Header Format 269 0 1 2 3 270 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 1 271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+E 272 | ID | L=14 | OUT NTP timestamp - Seconds |x 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+t 274 | OUT NTP timestamp format - Fraction (bit 0-31) |e 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n 276 | IN NTP timestamp format - Seconds (bit 0-31) |s 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+i 278 | IN NTP timestamp format - Fraction (bit 0-31) |o 279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n 281 Figure 2: Splicing Interval 282 Using the Two-Byte Header Format 284 Since the inclusion of an RTP header extension will reduce the 285 efficiency of RTP header compression, it is RECOMMENDED that the main 286 sender inserts the RTP header extensions into only a number of RTP 287 packets, instead of all the RTP packets, prior to the splicing in. 289 After the splicer intercepts the RTP header extension and derives the 290 Splicing Interval, it will generate its own stream and SHOULD NOT 291 include the RTP header extension in outgoing packets to reduce header 292 overhead. 294 3.2 RTCP Splicing Notification Message 296 In addition to the RTP header extension, the main RTP sender includes 297 the Splicing Interval in an RTCP splicing notification message. 298 Whether or not the timestamps are included in the RTP header 299 extension, the main RTP sender MUST send the RTCP splicing 300 notification message. This provide robustness in the case where a 301 middlebox strips RTP header extensions. The main RTP sender MUST make 302 sure the splicing information contained in the RTCP splicing 303 notification message consistent with the information included in the 304 RTP header extensions. 306 The RTCP splicing notification message is a new RTCP packet type. It 307 has a fixed header followed by a pair of NTP-format timestamps: 309 0 1 2 3 310 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 1 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 |V=2|P|reserved | PT=TBA | length | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | SSRC | 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 | IN NTP Timestamp (most significant word) | 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 318 | IN NTP Timestamp (least significant word) | 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 | OUT NTP Timestamp (most significant word) | 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | OUT NTP Timestamp (least significant word) | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 Figure 2: RTCP Splicing Notification Message 327 The RSI packet includes the following fields: 329 Length: 16 bits 331 As defined in [RFC3550], the length of the RTCP packet in 32-bit 332 words minus one, including the header and any padding. 334 SSRC: 32 bits 336 The SSRC of the Main RTP Sender. 338 Timestamp: 64 bits 340 Indicates the wallclock time when this splicing starts and ends. 341 The full-resolution NTP-format timestamp is used, which is a 64- 342 bit, unsigned, fixed-point number with the integer part in the 343 first 32 bits and the fractional part in the last 32 bits. This 344 format is same as the NTP timestamp field in the RTCP Sender 345 Report (Section 6.4.1 of [RFC3550]). 347 The RTCP splicing notification message can be included in the RTCP 348 compound packet together with RTCP SR generated at the main RTP 349 sender, and hence follows the compound RTCP rules defined in Section 350 6.1 in [RFC3550]. 352 If the use of non-compound RTCP [RFC5506] was previously negotiated 353 between the sender and the splicer, the RTCP splicing notification 354 message may be sent as non-compound RTCP packets. In some cases that 355 the mapping from RTP timestamp to NTP timestamp changes, e.g., clock 356 drift happening before the splicing event, it may be required to send 357 RTCP SR or even updated Splicing Interval information timely to 358 update the timestamp mapping for accurate splicing. 360 When the splicer intercepts the RTCP splicing notification message, 361 it SHOULD NOT forward the message to the down-stream receivers in 362 order to reduce RTCP bandwidth consumption. And if the splicer wishes 363 to prevent the downstream receivers from detecting splicing, it MUST 364 NOT forward the message. 366 4 Reducing Splicing Latency 368 When splicing starts or ends, the splicer outputs the multimedia 369 content from another sender to the receivers. Given that the 370 receivers must first acquire certain information ([RFC6285] refers to 371 this information as Reference Information) to start processing the 372 multimedia data, either the main RTP sender or the substitutive 373 sender SHOULD provide the Reference Information together with its 374 multimedia content to reduce the delay caused by acquiring the 375 Reference Information. The methods by which the Reference Information 376 is distributed to the receivers is out of scope of this memo. 378 Another latency element is synchronization caused delay. The 379 receivers must receive enough synchronization metadata prior to 380 synchronizing the separate components of the multimedia streams when 381 splicing starts or ends. Either the main RTP sender or the 382 substitutive sender SHOULD send the synchronization metadata early 383 enough so that the receivers can play out the multimedia in a 384 synchronized fashion. The main RTP sender and the substitutive sender 385 can be coordinated by some proprietary out-of-band mechanisms to 386 decide when and whom to send the metadata. If both send the 387 information, the splicer SHOULD pick one based on the current 388 situation, e.g., choosing media sender when synchronizing the main 389 media content while choosing the information from the substitutive 390 sender when synchronizing the spliced content. The mechanisms defined 391 in [RFC6051] are RECOMMENDED to be adopted to reduce the possible 392 synchronization delay. 394 5 Failure Cases 396 This section examines the implications of losing RTCP splicing 397 notification message and the other failure case, e.g., the RTP header 398 extension is stripped on the path. 400 Given that there may be a splicing un-aware middlebox on the path 401 between the main RTP sender and the splicer, the main and the 402 substitutive RTP senders can use one heuristic to verify whether or 403 not the Splicing Interval reaches the splicer. 405 The splicer can be implemented to have its own SSRC, and send RTCP 406 reception reports to the senders of the main and substitutive RTP 407 streams. This allows the senders to detect problems on the path to 408 the splicer. Alternatively, it is possible to implement the splicer 409 such that it has no SSRC, and does not send RTCP reports; this 410 prevents the senders from being able to monitor the quality to the 411 path to the splicer. 413 If the splicer has an SSRC and sends its own RTCP reports, it can 414 choose not to pass RTCP reports it receives from the receivers to the 415 senders. This will stop the senders from being able to monitor the 416 quality of the paths from the splicer to the receivers. 418 A splicer that has an SSRC can choose to pass RTCP reception reports 419 from the receivers back to the senders, after modifications to 420 account for the splicing. This will allow the senders the monitor the 421 quality of the paths from the splicer to the receivers. A splicer 422 that does not have its own SSRC has to forward and translation RTCP 423 reports from the receiver, otherwise the senders will not see any 424 receivers in the RTP session. 426 If the splicer is implemented following [RFC6828], it will have its 427 own SSRC and will send its own RTCP reports, and will forward 428 translated RTCP reports from the receivers. 430 Upon the detection of a failure, the splicer can communicate with the 431 main sender and the substitutive sender in some out of band signaling 432 ways to fall back to the payload specific mechanisms it supports, 433 e.g., MPEG-TS splicing solution defined in [SCTE35], or just abandon 434 the splicing. 436 6 Session Description Protocol (SDP) Signaling 438 This document defines the URI for declaring this header extension in 439 an extmap attribute to be "urn:ietf:params:rtp-hdrext:splicing- 440 interval". 442 This document extends the standard semantics defined in SDP Grouping 443 Framework [RFC5888] with a new semantic: SPLICE to represent the 444 relationship between the main RTP stream and the substitutive RTP 445 stream. Only 2 m-lines are allowed in the SPLICE group. The main RTP 446 stream is the one with the extended extmap attribute, and the other 447 one is substitutive stream. A single m-line MUST NOT be included in 448 different SPLICE groups at the same time. The main RTP sender 449 provides the information about both main and substitutive sources. 451 The extended SDP attribute specified in this document is applicable 452 for offer/answer content [RFC3264] and do not affect any rules when 453 negotiating offer and answer. When used with multiple m-lines, 454 substitutive RTP MUST be applied only to the RTP packets whose SDP m- 455 line is in the same group with the substitutive stream using SPLICE 456 and has the extended splicing extmap attribute. This semantic is also 457 applicable for BUNDLE cases. 459 The following examples show how SDP signaling could be used for 460 splicing in different cases. 462 6.1 Declarative SDP 464 v=0 465 o=xia 1122334455 1122334466 IN IP4 splicing.example.com 466 s=RTP Splicing Example 467 t=0 0 468 a=group:SPLICE 1 2 469 m=video 30000 RTP/AVP 100 470 i=Main RTP Stream 471 c=IN IP4 233.252.0.1/127 472 a=rtpmap:100 MP2T/90000 473 a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval 474 a=mid:1 475 m=video 30002 RTP/AVP 100 476 i=Substitutive RTP Stream 477 c=IN IP4 233.252.0.2/127 478 a=sendonly 479 a=rtpmap:100 MP2T/90000 480 a=mid:2 482 Figure 3: Example SDP for a single-channel splicing scenario 484 The splicer receiving the SDP message above receives one MPEG2-TS 485 stream (payload 100) from the main RTP sender (with multicast 486 destination address of 233.252.0.1) on port 30000, and/or receives 487 another MPEG2-TS stream from the substitutive RTP sender (with 488 multicast destination address of 233.252.0.2) on port 30002. But at 489 a particular point in time, the splicer only selects one stream and 490 outputs the content from the chosen stream to the downstream 491 receivers. 493 6.2 Offer/Answer without BUNDLE 495 SDP Offer - from main RTP sender 497 v=0 498 o=xia 1122334455 1122334466 IN IP4 splicing.example.com 499 s=RTP Splicing Example 500 t=0 0 501 a=group:SPLICE 1 2 502 m=video 30000 RTP/AVP 31 100 503 i=Main RTP Stream 504 c=IN IP4 splicing.example.com 505 a=rtpmap:31 H261/90000 506 a=rtpmap:100 MP2T/90000 507 a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval 508 a=sendonly 509 a=mid:1 510 m=video 40000 RTP/AVP 31 100 511 i=Substitutive RTP Stream 512 c=IN IP4 substitutive.example.com 513 a=rtpmap:31 H261/90000 514 a=rtpmap:100 MP2T/90000 515 a=sendonly 516 a=mid:2 518 SDP Answer - from splicer 520 v=0 521 o=xia 1122334455 1122334466 IN IP4 splicer.example.com 522 s=RTP Splicing Example 523 t=0 0 524 a=group:SPLICE 1 2 525 m=video 30000 RTP/AVP 100 526 i=Main RTP Stream 527 c=IN IP4 splicer.example.com 528 a=rtpmap:100 MP2T/90000 529 a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval 530 a=recvonly 531 a=mid:1 532 m=video 40000 RTP/AVP 100 533 i=Substitutive RTP Stream 534 c=IN IP4 splicer.example.com 535 a=rtpmap:100 MP2T/90000 536 a=recvonly 537 a=mid:2 539 6.3 Offer/Answer with BUNDLE: All Media are spliced 541 In this example, the bundled audio and video media have their own 542 substitutive media for splicing: 544 1. An Offer, in which the offerer assigns a unique address and a 545 substitutive media to each bundled "m="line for splicing within the 546 BUNDLE group. 548 2. An answer, in which the answerer selects its own BUNDLE address, 549 and leave the substitutive media untouched. 551 SDP Offer - from main RTP sender 553 v=0 554 o=alice 1122334455 1122334466 IN IP4 splicing.example.com 555 s=RTP Splicing Example 556 c=IN IP4 splicing.example.com 557 t=0 0 558 a=group:SPLICE foo 1 559 a=group:SPLICE bar 2 560 a=group:BUNDLE foo bar 561 m=audio 10000 RTP/AVP 0 8 97 562 a=mid:foo 563 b=AS:200 564 a=rtpmap:0 PCMU/8000 565 a=rtpmap:8 PCMA/8000 566 a=rtpmap:97 iLBC/8000 567 a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval 568 a=sendonly 569 m=video 10002 RTP/AVP 31 32 570 a=mid:bar 571 b=AS:1000 572 a=rtpmap:31 H261/90000 573 a=rtpmap:32 MPV/90000 574 a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval 575 a=sendonly 576 m=audio 20000 RTP/AVP 0 8 97 577 i=Substitutive audio RTP Stream 578 c=IN IP4 substitive.example.com 579 a=rtpmap:0 PCMU/8000 580 a=rtpmap:8 PCMA/8000 581 a=rtpmap:97 iLBC/8000 582 a=sendonly 583 a=mid:1 584 m=video 20002 RTP/AVP 31 32 585 i=Substitutive video RTP Stream 586 c=IN IP4 substitive.example.com 587 a=rtpmap:31 H261/90000 588 a=rtpmap:32 MPV/90000 589 a=mid:2 590 a=sendonly 592 SDP Answer - from the splicer 594 v=0 595 o=bob 2808844564 2808844564 IN IP4 splicer.example.com 596 s=RTP Splicing Example 597 c=IN IP4 splicer.example.com 598 t=0 0 599 a=group:SPLICE foo 1 600 a=group:SPLICE bar 2 601 a=group:BUNDLE foo bar 602 m=audio 30000 RTP/AVP 0 603 a=mid:foo 604 b=AS:200 605 a=rtpmap:0 PCMU/8000 606 a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval 607 a=recvonly 608 m=video 30000 RTP/AVP 32 609 a=mid:bar 610 b=AS:1000 611 a=rtpmap:32 MPV/90000 612 a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval 613 a=recvonly 614 m=audio 30002 RTP/AVP 0 615 i=Substitutive audio RTP Stream 616 c=IN IP4 splicer.example.com 617 a=rtpmap:0 PCMU/8000 618 a=recvonly 619 a=mid:1 620 m=video 30004 RTP/AVP 32 621 i=Substitutive video RTP Stream 622 c=IN IP4 splicer.example.com 623 a=rtpmap:32 MPV/90000 624 a=mid:2 625 a=recvonly 627 6.4 Offer/Answer with BUNDLE: a Subset of Media are Spliced 629 In this example, the substitutive media only applies for video when 630 splicing: 632 1. An Offer, in which the offerer assigns a unique address to each 633 bundled "m="line within the BUNDLE group, and assigns a substitutive 634 media to the bundled video "m=" line for splicing. 636 2. An answer, in which the answerer selects its own BUNDLE address, 637 and leave the substitutive media untouched. 639 SDP Offer - from the main RTP sender: 641 v=0 642 o=alice 1122334455 1122334466 IN IP4 splicing.example.com 643 s=RTP Splicing Example 644 c=IN IP4 splicing.example.com 645 t=0 0 646 a=group:SPLICE bar 2 647 a=group:BUNDLE foo bar 648 m=audio 10000 RTP/AVP 0 8 97 649 a=mid:foo 650 b=AS:200 651 a=rtpmap:0 PCMU/8000 652 a=rtpmap:8 PCMA/8000 653 a=rtpmap:97 iLBC/8000 654 a=sendonly 655 m=video 10002 RTP/AVP 31 32 656 a=mid:bar 657 b=AS:1000 658 a=rtpmap:31 H261/90000 659 a=rtpmap:32 MPV/90000 660 a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval 661 a=sendonly 662 m=video 20000 RTP/AVP 31 32 663 i=Substitutive video RTP Stream 664 c=IN IP4 substitutive.example.com 665 a=rtpmap:31 H261/90000 666 a=rtpmap:32 MPV/90000 667 a=mid:2 668 a=sendonly 670 SDP Answer - from the splicer: 672 v=0 673 o=bob 2808844564 2808844564 IN IP4 splicer.example.com 674 s=RTP Splicing Example 675 c=IN IP4 splicer.example.com 676 t=0 0 677 a=group:SPLICE bar 2 678 a=group:BUNDLE foo bar 679 m=audio 30000 RTP/AVP 0 680 a=mid:foo 681 b=AS:200 682 a=rtpmap:0 PCMU/8000 683 a=recvonly 684 m=video 30000 RTP/AVP 32 685 a=mid:bar 686 b=AS:1000 687 a=rtpmap:32 MPV/90000 688 a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval 689 a=recvonly 690 m=video 30004 RTP/AVP 32 691 i=Substitutive video RTP Stream 692 c=IN IP4 splicer.example.com 693 a=rtpmap:32 MPV/90000 694 a=mid:2 695 a=recvonly 697 7 Security Considerations 699 The security considerations of the RTP specification [RFC3550] and 700 the general mechanism for RTP header extensions [RFC5285] apply. The 701 splicer can either be a mixer or a translator, and has all the 702 security considerations on these two standard RTP intermediaries. 703 However, the splicer replaces some content with other content in RTP 704 packet, thus breaking any RTP-level end-to-end security, such as 705 source authentication and integrity protection. 707 End to end source authentication is not possible with any known 708 existing splicing solution. A new solution can theoretically be 709 developed that enables identifying the participating entities and 710 what each provides, i.e., the different media sources, main and 711 substituting, and the splicer providing the RTP-level integration of 712 the media payloads in a common timeline and synchronization context. 714 Since splicer works as a trusted entity, any RTP-level or outside 715 security mechanism, such IPsec[RFC4301] or Datagram Transport Layer 716 Security [RFC6347], will use a security association between the 717 splicer and the receiver. When using the Secure Real-Time Transport 718 Protocol (SRTP) [RFC3711], the splicer could be provisioned with the 719 same security association as the main RTP sender. 721 If there is a concern about the confidentiality of the splicing time 722 information, header extension encryption [RFC6904] SHOULD be used. 723 However, the malicious endpoint may get the splicing time information 724 by other means, e.g., inferring from the communication between the 725 main and substitutive content sources. To avoid the insertion of 726 invalid substitutive content, the splicer MUST have some mechanisms 727 to authenticate the substitutive stream source. 729 For cases that the splicing time information is changed by a 730 malicious endpoint, the splicing may fail since it will not be 731 available at the right time for the substitutive media to arrive, 732 which may also break an undetectable splicing. To mitigate this 733 effect, the splicer SHOULD NOT forward the splicing time information 734 RTP header extension defined in Section 4.1 to the receivers. And it 735 MUST NOT forward this header extension when considering an 736 undetectable splicing. 738 8 IANA Considerations 740 8.1 RTCP Control Packet Types 742 Based on the guidelines suggested in [RFC5226], a new RTCP packet 743 format has been registered with the RTCP Control Packet Type (PT) 744 Registry: 746 Name: SNM 748 Long name: Splicing Notification Message 750 Value: TBA 752 Reference: This document 754 8.2 RTP Compact Header Extensions 756 The IANA has also registered a new RTP Compact Header Extension 757 [RFC5285], according to the following: 759 Extension URI: urn:ietf:params:rtp-hdrext:splicing-interval 761 Description: Splicing Interval 763 Contact: Jinwei Xia 765 Reference: This document 767 8.3 SDP Grouping Semantic Extension 769 This document request IANA to register the new SDP grouping semantic 770 extension called "SPLICE". 772 Semantics: Splice 774 Token:SPLICE 776 Reference: This document 777 Contact: Jinwei Xia 779 9 Acknowledgement 781 The authors would like to thank the following individuals who help to 782 review this document and provide very valuable comments: Colin 783 Perkins, Bo Burman, Stephen Botzko, Ben Campbell. 785 10 References 787 10.1 Normative References 789 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 790 Requirement Levels", BCP 14, RFC 2119, March 1997. 792 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 793 Jacobson, "RTP: A Transport Protocol for Real-Time 794 Applications", STD 64, RFC 3550, July 2003. 796 [RFC3264] Rosenberg, J., and H. Schulzrinne, "An Offer/Answer Model 797 with the Session Description Protocol (SDP)", RFC 3264, 798 June 2002. 800 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 801 Internet Protocol", RFC 4301, December 2005. 803 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP 804 Header Extensions", RFC 5285, July 2008. 806 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 807 Protocol (SDP) Grouping Framework", RFC 5888, June 2010. 809 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 810 "Network Time Protocol Version 4: Protocol and Algorithms 811 Specification", RFC 5905, June 2010. 813 [RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP 814 Flows", RFC 6051, November 2010. 816 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 817 Security Version 1.2", RFC 6347, January 2012. 819 10.2 Informative References 821 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 822 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 823 RFC 3711, March 2004. 825 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 826 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 827 May 2008. 829 [RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size 830 Real-Time Transport Control Protocol (RTCP): Opportunities 831 and Consequences", RFC 5506, April 2009. 833 [RFC6285] Ver Steeg, B., Begen, A., Van Caenegem, T., and Z. Vax, 834 "Unicast-Based Rapid Acquisition of Multicast RTP 835 Sessions", RFC 6285, June 2011. 837 [RFC6904] Lennox, J.,"Encryption of Header Extensions in the Secure 838 Real-Time Transport Protocol (SRTP)", April 2013. 840 [SCTE35] Society of Cable Telecommunications Engineers (SCTE), 841 "Digital Program Insertion Cueing Message for Cable", 842 2011. 844 [RFC6828] Xia, J., "Content Splicing for RTP Sessions", RFC 6828, 845 January 2013. 847 Authors' Addresses 849 Jinwei Xia 850 Huawei 852 Email: xiajinwei@huawei.com 854 Roni Even 855 Huawei 857 Email: ron.even.tlv@gmail.com 859 Rachel Huang 860 Huawei 862 Email: rachel.huang@huawei.com 864 Lingli Deng 865 China Mobile 867 Email: denglingli@chinamobile.com