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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Informational R. Pantos, Ed. 3 Internet-Draft W. May 4 Intended status: Informational Apple Inc. 5 Expires: April 18, 2016 October 16, 2015 7 HTTP Live Streaming 8 draft-pantos-http-live-streaming-17 10 Abstract 12 This document describes a protocol for transferring unbounded streams 13 of multimedia data. It specifies the data format of the files and 14 the actions to be taken by the server (sender) and the clients 15 (receivers) of the streams. It describes version 7 of this protocol. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on April 18, 2016. 34 Copyright Notice 36 Copyright (c) 2015 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. 46 This document may not be modified, and derivative works of it may not 47 be created, and it may not be published except as an Internet-Draft. 49 This Informational Internet Draft is submitted as an RFC Editor 50 Contribution and/or non-IETF Document (not as a Contribution, IETF 51 Contribution, nor IETF Document) in accordance with BCP 78 and BCP 52 79. 54 Table of Contents 56 1. Introduction to HTTP Live Streaming . . . . . . . . . . . . . 3 57 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 3. Media Segments . . . . . . . . . . . . . . . . . . . . . . . 5 59 4. Playlists . . . . . . . . . . . . . . . . . . . . . . . . . . 7 60 4.1. Definition of a Playlist . . . . . . . . . . . . . . . . 7 61 4.2. Attribute Lists . . . . . . . . . . . . . . . . . . . . . 8 62 4.3. Playlist Tags . . . . . . . . . . . . . . . . . . . . . . 9 63 4.3.1. Basic Tags . . . . . . . . . . . . . . . . . . . . . 10 64 4.3.1.1. EXTM3U . . . . . . . . . . . . . . . . . . . . . 10 65 4.3.1.2. EXT-X-VERSION . . . . . . . . . . . . . . . . . . 10 66 4.3.2. Media Segment Tags . . . . . . . . . . . . . . . . . 10 67 4.3.2.1. EXTINF . . . . . . . . . . . . . . . . . . . . . 11 68 4.3.2.2. EXT-X-BYTERANGE . . . . . . . . . . . . . . . . . 11 69 4.3.2.3. EXT-X-DISCONTINUITY . . . . . . . . . . . . . . . 11 70 4.3.2.4. EXT-X-KEY . . . . . . . . . . . . . . . . . . . . 12 71 4.3.2.5. EXT-X-MAP . . . . . . . . . . . . . . . . . . . . 14 72 4.3.2.6. EXT-X-PROGRAM-DATE-TIME . . . . . . . . . . . . . 15 73 4.3.3. Media Playlist Tags . . . . . . . . . . . . . . . . . 15 74 4.3.3.1. EXT-X-TARGETDURATION . . . . . . . . . . . . . . 15 75 4.3.3.2. EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . 16 76 4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE . . . . . . . . . . 16 77 4.3.3.4. EXT-X-ENDLIST . . . . . . . . . . . . . . . . . . 17 78 4.3.3.5. EXT-X-PLAYLIST-TYPE . . . . . . . . . . . . . . . 17 79 4.3.3.6. EXT-X-I-FRAMES-ONLY . . . . . . . . . . . . . . . 17 80 4.3.4. Master Playlist Tags . . . . . . . . . . . . . . . . 18 81 4.3.4.1. EXT-X-MEDIA . . . . . . . . . . . . . . . . . . . 18 82 4.3.4.1.1. Rendition Groups . . . . . . . . . . . . . . 21 83 4.3.4.2. EXT-X-STREAM-INF . . . . . . . . . . . . . . . . 22 84 4.3.4.2.1. Alternative Renditions . . . . . . . . . . . 25 85 4.3.4.3. EXT-X-I-FRAME-STREAM-INF . . . . . . . . . . . . 25 86 4.3.4.4. EXT-X-SESSION-DATA . . . . . . . . . . . . . . . 26 87 4.3.4.5. EXT-X-SESSION-KEY . . . . . . . . . . . . . . . . 27 88 4.3.5. Media or Master Playlist Tags . . . . . . . . . . . . 27 89 4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS . . . . . . . . . . . 28 90 4.3.5.2. EXT-X-START . . . . . . . . . . . . . . . . . . . 28 91 5. Key files . . . . . . . . . . . . . . . . . . . . . . . . . . 29 92 5.1. Structure of Key files . . . . . . . . . . . . . . . . . 29 93 5.2. IV for [AES_128] . . . . . . . . . . . . . . . . . . . . 29 94 6. Client/Server Responsibilities . . . . . . . . . . . . . . . 29 95 6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 29 96 6.2. Server Responsibilities . . . . . . . . . . . . . . . . . 29 97 6.2.1. General Server Responsibilities . . . . . . . . . . . 30 98 6.2.2. Live Playlists . . . . . . . . . . . . . . . . . . . 32 99 6.2.3. Encrypting Media Segments . . . . . . . . . . . . . . 33 100 6.2.4. Providing Variant Streams . . . . . . . . . . . . . . 34 101 6.3. Client Responsibilities . . . . . . . . . . . . . . . . . 35 102 6.3.1. General Client Responsibilities . . . . . . . . . . . 35 103 6.3.2. Loading the Media Playlist file . . . . . . . . . . . 36 104 6.3.3. Playing the Media Playlist file . . . . . . . . . . . 36 105 6.3.4. Reloading the Media Playlist file . . . . . . . . . . 37 106 6.3.5. Determining the next segment to load . . . . . . . . 38 107 6.3.6. Decrypting encrypted Media Segments . . . . . . . . . 38 108 7. Protocol version compatibility . . . . . . . . . . . . . . . 39 109 8. Playlist Examples . . . . . . . . . . . . . . . . . . . . . . 41 110 8.1. Simple Media Playlist . . . . . . . . . . . . . . . . . . 41 111 8.2. Live Media Playlist, using HTTPS . . . . . . . . . . . . 41 112 8.3. Playlist with encrypted Media Segments . . . . . . . . . 41 113 8.4. Master Playlist . . . . . . . . . . . . . . . . . . . . . 42 114 8.5. Master Playlist with I-Frames . . . . . . . . . . . . . . 42 115 8.6. Master Playlist with Alternative audio . . . . . . . . . 43 116 8.7. Master Playlist with Alternative video . . . . . . . . . 43 117 8.8. Session Data in a Master Playlist . . . . . . . . . . . . 44 118 8.9. CHARACTERISTICS attribute containing multiple 119 characteristics . . . . . . . . . . . . . . . . . . . . . 44 120 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 45 121 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 122 11. Security Considerations . . . . . . . . . . . . . . . . . . . 46 123 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 124 12.1. Normative References . . . . . . . . . . . . . . . . . . 46 125 12.2. Informative References . . . . . . . . . . . . . . . . . 49 126 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49 128 1. Introduction to HTTP Live Streaming 130 HTTP Live Streaming provides a reliable, cost-effective means of 131 delivering continuous and long-form video over the Internet. It 132 allows a receiver to adapt the bit rate of the media to the current 133 network conditions in order to maintain uninterrupted playback at the 134 best possible quality. It supports interstitial content boundaries. 135 It provides a flexible framework for media encryption. It can 136 efficiently offer multiple renditions of the same content, such as 137 audio translations. It offers compatibility with large-scale HTTP 138 caching infrastructure to support delivery to large audiences. 140 Since its first draft publication in 2009, HTTP Live Streaming has 141 been implemented and deployed by a wide array of content producers, 142 tools vendors, distributors, and device manufacturers. 144 The purpose of this document is to facilitate interoperability 145 between HTTP Live Streaming implementations by describing the media 146 transmission protocol. Using this protocol, a client can receive a 147 continuous stream of media from a server for concurrent presentation. 149 This document describes version 7 of the protocol. 151 2. Overview 153 A multimedia presentation is specified by a Uniform Resource 154 Identifier (URI) [RFC3986] to a Playlist. 156 A Playlist is either a Media Playlist or a Master Playlist. Both are 157 UTF-8 text files containing URIs and descriptive tags. 159 A Media Playlist contains a list of Media Segments, which when played 160 sequentially will play the multimedia presentation. 162 Here is an example of a Media Playlist: 164 #EXTM3U 165 #EXT-X-TARGETDURATION:10 167 #EXTINF:9.009, 168 http://media.example.com/first.ts 169 #EXTINF:9.009, 170 http://media.example.com/second.ts 171 #EXTINF:3.003, 172 http://media.example.com/third.ts 174 The first line is the format identifier tag #EXTM3U. The line 175 containing #EXT-X-TARGETDURATION says that all Media Segments will be 176 10 seconds long or less. Then three Media Segments are declared. 177 The first and second are 9.009 seconds long; the third is 3.003 178 seconds. 180 To play this Playlist, the client first downloads it and then 181 downloads and plays each Media Segment declared within it. The 182 client reloads the Playlist as described in this document to discover 183 any added segments. Data SHOULD be carried over HTTP [RFC7230], but 184 in general a URI can specify any protocol that can reliably transfer 185 the specified resource on demand. 187 A more complex presentation can be described by a Master Playlist. A 188 Master Playlist provides a set of Variant Streams, each of which 189 describes a different version of the same content. 191 A Variant Stream includes a Media Playlist that specifies media 192 encoded at a particular bit rate, in a particular format, and at a 193 particular resolution for media containing video. 195 A Variant Stream can also specify a set of Renditions. Renditions 196 are alternate versions of the content, such as audio produced in 197 different languages or video recorded from different camera angles. 199 Clients should switch between different Variant Streams to adapt to 200 network conditions. Clients should choose Renditions based on user 201 preferences. 203 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 204 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 205 document are to be interpreted as described in RFC 2119 [RFC2119]. 207 3. Media Segments 209 A Media Playlist contains a series of Media Segments which make up 210 the overall presentation. A Media Segment is specified by a URI and 211 optionally a byte range. 213 The duration of each Media Segment is indicated in the Media Playlist 214 by its EXTINF tag (Section 4.3.2.1). 216 Each segment in a Media Playlist has a unique integer Media Sequence 217 Number. The Media Sequence Number of the first segment in the Media 218 Playlist is either 0, or declared in the Playlist (Section 4.3.3.2). 219 The Media Sequence Number of every other segment is equal to the 220 Media Sequence Number of the segment that precedes it plus one. 222 Each Media Segment MUST be formatted as an MPEG-2 Transport Stream 223 [ISO_13818], a WebVTT [WebVTT] file, or a Packed Audio file, which is 224 a file containing packed encoded audio samples and ID3 tags, such as 225 AAC with ADTS framing [ISO_13818_7], MP3 [ISO_13818_3] or AC-3 226 [AC_3]. Transport of other media file formats is not defined. 228 Some media formats require that a parser be initialized with a common 229 sequence of bytes before a Media Segment can be parsed. This format- 230 specific sequence is called the Media Initialization Section. The 231 Media Initialization Section of an MPEG-2 Transport Stream segment is 232 the Program Association Table (PAT) followed by the Program Map 233 Table (PMT). The Media Initialization Section of a WebVTT segment is 234 the WebVTT header. A Packed Audio segment has no Media 235 Initialization Section. 237 Transport Stream segments MUST contain a single MPEG-2 Program; 238 playback of Multi-Program Transport Streams is not defined. Each 239 Transport Stream segment SHOULD contain a PAT and a PMT at the start 240 of the segment - or have a Media Initialization Section declared in 241 the Media Playlist (Section 4.3.2.5). 243 A Media Segment that contains video SHOULD have at least one key 244 frame and enough information to completely initialize a video 245 decoder. 247 Each Media Segment MUST be the continuation of the encoded media at 248 the end of the segment with the previous Media Sequence Number, where 249 values in a continuous series such as timestamps and Continuity 250 Counters continue uninterrupted. The only exceptions are the first 251 Media Segment ever to appear in a Media Playlist, and Media Segments 252 which are explicitly signaled as discontinuities (Section 4.3.2.3). 253 Unmarked media discontinuities can trigger playback errors. 255 Each Packed Audio segment MUST signal the timestamp of its first 256 sample with an ID3 PRIV tag [ID3] at the beginning of the segment. 257 The ID3 PRIV owner identifier MUST be 258 "com.apple.streaming.transportStreamTimestamp". The ID3 payload MUST 259 be a 33-bit MPEG-2 Program Elementary Stream timestamp expressed as a 260 big-endian eight-octet number, with the upper 31 bits set to zero. A 261 Packed Audio segment without such an ID3 tag can trigger playback 262 errors. 264 Subtitle segments are formatted as WebVTT [WebVTT] files. Each 265 subtitle segment MUST contain all subtitle cues that are intended to 266 be displayed during the period indicated by the segment EXTINF 267 duration. The start time offset and end time offset of each cue MUST 268 indicate the total display time for that cue, even if part of the cue 269 time range is outside the segment period. A WebVTT segment MAY 270 contain no cues; this indicates that no subtitles are to be displayed 271 during that period. 273 Each subtitle segment MUST either start with a WebVTT header or have 274 a Media Initialization Section declared in the Media Playlist 275 (Section 4.3.2.5). 277 In order to synchronize timestamps between audio/video and subtitles, 278 a X-TIMESTAMP-MAP metadata header SHOULD be added to each WebVTT 279 header. This header maps WebVTT cue timestamps to MPEG-2 (PES) 280 timestamps in other Renditions of the Variant Stream. Its format is: 282 X-TIMESTAMP-MAP=LOCAL:,MPEGTS: 283 e.g. X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 285 The cue timestamp in the LOCAL attribute MAY fall outside the range 286 of time covered by the segment. 288 If a WebVTT segment does not have the X-TIMESTAMP-MAP, the client 289 MUST assume that the WebVTT cue time of 0 maps to an MPEG-2 timestamp 290 of 0. 292 4. Playlists 294 This section describes the Playlist files used by HTTP Live 295 Streaming. In this section, "MUST" and "MUST NOT" specify the rules 296 for the syntax and structure of legal Playlist files. Playlists that 297 violate these rules are invalid; clients MUST fail to parse them. 298 See Section 6.3.2. 300 The format of the Playlist files is derived from the M3U [M3U] 301 playlist file format and inherits two tags from that earlier file 302 format: EXTM3U (Section 4.3.1.1) and EXTINF (Section 4.3.2.1). 304 In this section, tags are specified using a BNF-style syntax. 306 Each Playlist file MUST be identifiable by either the path component 307 of its URI or by HTTP Content-Type. In the first case, the path MUST 308 end with either .m3u8 or .m3u. In the second, the HTTP Content-type 309 MUST be "application/vnd.apple.mpegurl" or "audio/mpegurl". Clients 310 SHOULD refuse to parse Playlists that are not so identified. 312 4.1. Definition of a Playlist 314 Playlist files MUST be encoded in UTF-8 [RFC3629]. They MUST NOT 315 contain any byte order mark (BOM); Clients SHOULD reject Playlists 316 which contain a BOM or do not parse as UTF-8. PLaylist files MUST 317 NOT contain UTF-8 control characters (U+0000 to U+001F and U+007F to 318 U+009F), with the exceptions of CR (U+000D) and LF (U+000A). All 319 character sequences MUST be normalized according to Unicode 320 normalization form "NFC". Note that US-ASCII [US_ASCII] conforms to 321 these rules. 323 Lines in a Playlist file are terminated by either a single line feed 324 character or a carriage return character followed by an line feed 325 character. Each line is a URI, blank, or starts with the character 326 '#'. Blank lines are ignored. White space MUST NOT be present, 327 except for elements in which it is explicitly specified. 329 Lines that start with the character '#' are either comments or tags. 330 Tags begin with #EXT. They are case-sensitive. All other lines that 331 begin with '#' are comments and SHOULD be ignored. 333 A URI line identifies a Media Segment or a Playlist file (see 334 Section 4.3.4.2). Each Media Segment is specified by a URI and the 335 tags that apply to it. 337 A Playlist is a Media Playlist if all URI lines in the Playlist 338 identify Media Segments. A Playlist is a Master Playlist if all URI 339 lines in the Playlist identify Media Playlists. A Playlist MUST be 340 either a Media Playlist or a Master Playlist; all other Playlists are 341 invalid. 343 A URI in a Playlist, whether it is a URI line or part of a tag, MAY 344 be relative. Any relative URI is considered to be relative to the 345 URI of the Playlist that contains it. 347 The duration of a Media Playlist file is the sum of the durations of 348 the Media Segments within it. 350 The segment bit rate of a Media Segment is the size of the Media 351 Segment divided by its EXTINF duration (Section 4.3.2.1). Note that 352 this includes container overhead but does not include overhead 353 imposed by the delivery system, such as HTTP, TCP or IP headers. 355 The peak bit rate of a Media Playlist is the largest segment bit rate 356 of all segments in the Media Playlist. 358 The average segment bit rate of a Media Playlist is the sum of the 359 sizes (in bits) of every Media Segment in the Media Playlist, divided 360 by the Media Playlist duration. Note that this includes container 361 overhead, but not HTTP or other overhead imposed by the delivery 362 system. 364 4.2. Attribute Lists 366 Certain tags have values which are Attribute Lists. An Attribute 367 List is a comma-separated list of attribute/value pairs with no 368 whitespace. 370 An attribute/value pair has the following syntax: 372 AttributeName=AttributeValue 374 An AttributeName is an unquoted string containing characters from the 375 set [A..Z], [0..9] and '-'. Therefore, AttributeNames contain only 376 uppercase letters, not lowercase. There MUST NOT be any whitespace 377 between the AttributeName and the '=' character, nor between the '=' 378 character and the AttributeValue. 380 An AttributeValue is one of the following: 382 o decimal-integer: an unquoted string of characters from the set 383 [0..9] expressing an integer in base-10 arithmetic in the range 384 from 0 to 2^64-1 (18446744073709551615). A decimal-integer may be 385 from 1 to 20 characters long. 387 o hexadecimal-sequence: an unquoted string of characters from the 388 set [0..9] and [A..F] that is prefixed with 0x or 0X. The maximum 389 length of a hexadecimal-sequence depends on its AttributeName. 391 o decimal-floating-point: an unquoted string of characters from the 392 set [0..9] and '.' which expresses a non-negative floating-point 393 number in decimal positional notation. 395 o signed-decimal-floating-point: an unquoted string of characters 396 from the set [0..9], '-' and '.' which expresses a signed 397 floating-point number in decimal positional notation. 399 o quoted-string: a string of characters within a pair of double- 400 quotes (0x22). The following characters MUST NOT appear in a 401 quoted-string: line feed (0xA), carriage return (0xD), or double 402 quote (0x22). Quoted-string AttributeValues SHOULD be constructed 403 so that byte-wise comparison is sufficient to test two quoted- 404 string AttributeValues for equality. Note that this implies case- 405 sensitive comparison. 407 o enumerated-string: an unquoted character string from a set which 408 is explicitly defined by the Attribute. An enumerated-string will 409 never contain double-quotes ("), commas (,), or whitespace. 411 o decimal-resolution: two decimal-integers separated by the "x" 412 character. The first integer is a horizontal pixel dimension 413 (width); the second is a vertical pixel dimension (height). 415 The type of the AttributeValue for a given AttributeName is specified 416 by the Attribute definition. 418 A given AttributeName MUST NOT appear more than once in a given 419 Attribute List. Clients SHOULD refuse to play such Playlists. 421 4.3. Playlist Tags 423 Playlist tags specify either global parameters of the Playlist, or 424 information about the Media Segments or Media Playlists that appear 425 after them. 427 4.3.1. Basic Tags 429 These tags are allowed in both Media Playlists and Master Playlists. 431 4.3.1.1. EXTM3U 433 The EXTM3U tag indicates that the file is an Extended M3U [M3U] 434 Playlist file. It MUST be the first line of every Media Playlist and 435 every Master Playlist. Its format is: 437 #EXTM3U 439 4.3.1.2. EXT-X-VERSION 441 The EXT-X-VERSION tag indicates the compatibility version of the 442 Playlist file, its associated media, and its server. 444 The EXT-X-VERSION tag applies to the entire Playlist file. Its 445 format is: 447 #EXT-X-VERSION: 449 where n is an integer indicating the protocol compatibility version 450 number. 452 It MUST appear in all Playlists containing tags or attributes that 453 are not compatible with protocol version 1 to support 454 interoperability with older clients. Section 7 specifies the minimum 455 value of the compatibility version number for any given Playlist 456 file. 458 A Playlist file MUST NOT contain more than one EXT-X-VERSION tag. If 459 a client encounters a Playlist with multiple EXT-X-VERSION tags, it 460 MUST reject it. 462 4.3.2. Media Segment Tags 464 Each Media Segment is specified by a series of Media Segment tags 465 followed by a URI. Some Media Segment tags apply to just the next 466 segment; others apply to all subsequent segments until another 467 instance of the same tag. 469 A Media Segment tag MUST NOT appear in a Master Playlist. Clients 470 MUST reject Playlists that contain both Media Segment Tags and Master 471 Playlist tags (Section 4.3.4). 473 4.3.2.1. EXTINF 475 The EXTINF tag specifies the duration of a Media Segment. It applies 476 only to the next Media Segment. This tag is REQUIRED for each Media 477 Segment. Its format is: 479 #EXTINF:[,] 481 where duration is a decimal-integer or decimal-floating-point number 482 (as described in Section 4.2) that specifies the duration of the 483 Media Segment in seconds. Durations that are reported as integers 484 SHOULD be rounded to the nearest integer. Durations MUST be integers 485 if the compatibility version number is less than 3 to support older 486 clients. Durations SHOULD be floating-point if the compatibility 487 version number is 3 or greater. The remainder of the line following 488 the comma is an optional human-readable informative title of the 489 Media Segment expressed as raw UTF-8 text. 491 4.3.2.2. EXT-X-BYTERANGE 493 The EXT-X-BYTERANGE tag indicates that a Media Segment is a sub-range 494 of the resource identified by its URI. It applies only to the next 495 URI line that follows it in the Playlist. Its format is: 497 #EXT-X-BYTERANGE:<n>[@<o>] 499 where n is a decimal-integer indicating the length of the sub-range 500 in bytes. If present, o is a decimal-integer indicating the start of 501 the sub-range, as a byte offset from the beginning of the resource. 502 If o is not present, the sub-range begins at the next byte following 503 the sub-range of the previous Media Segment. 505 If o is not present, a previous Media Segment MUST appear in the 506 Playlist file and MUST be a sub-range of the same media resource, or 507 the Media Segment is undefined and the Playlist MUST be rejected. 509 A Media Segment without an EXT-X-BYTERANGE tag consists of the entire 510 resource identified by its URI. 512 Use of the EXT-X-BYTERANGE tag REQUIRES a compatibility version 513 number of 4 or greater. 515 4.3.2.3. EXT-X-DISCONTINUITY 517 The EXT-X-DISCONTINUITY tag indicates a discontinuity between the 518 Media Segment that follows it and the one that preceded it. 520 Its format is: 522 #EXT-X-DISCONTINUITY 524 The EXT-X-DISCONTINUITY tag MUST be present if there is a change in 525 any of the following characteristics: 527 o file format 529 o number, type and identifiers of tracks 531 o timestamp sequence 533 The EXT-X-DISCONTINUITY tag SHOULD be present if there is a change in 534 any of the following characteristics: 536 o encoding parameters 538 o encoding sequence 540 See Section 3, Section 6.2.1, and Section 6.3.3 for more information 541 about the EXT-X-DISCONTINUITY tag. 543 4.3.2.4. EXT-X-KEY 545 Media Segments MAY be encrypted. The EXT-X-KEY tag specifies how to 546 decrypt them. It applies to every Media Segment that appears between 547 it and the next EXT-X-KEY tag in the Playlist file with the same 548 KEYFORMAT attribute (or the end of the Playlist file). Two or more 549 EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to the 550 same Media Segment if they ultimately produce the same decryption 551 key. The format is: 553 #EXT-X-KEY:<attribute-list> 555 The following attributes are defined: 557 METHOD 559 The value is an enumerated-string that specifies the encryption 560 method. This attribute is REQUIRED. 562 The methods defined are: NONE, AES-128, and SAMPLE-AES. 564 An encryption method of NONE means that Media Segments are not 565 encrypted. If the encryption method is NONE, other attributes 566 MUST NOT be present. 568 An encryption method of AES-128 signals that Media Segments are 569 completely encrypted using the Advanced Encryption Standard 570 [AES_128] with a 128-bit key, Cipher Block Chaining, and PKCS7 571 padding [RFC5652]. CBC is restarted on each segment boundary, 572 using either the IV attribute value or the Media Sequence Number 573 as the IV; see Section 5.2. The URI attribute is REQUIRED for 574 this METHOD. 576 An encryption method of SAMPLE-AES means that the Media Segments 577 contain media samples, such as audio or video, that are encrypted 578 using the Advanced Encryption Standard [AES_128]. How these media 579 streams are encrypted and encapsulated in a segment depends on the 580 media encoding and the media format of the segment. The 581 encryption format for H.264 [H_264], AAC [ISO_14496], AC-3 [AC_3], 582 and Enhanced AC-3 [AC_3] media streams is described in the HLS 583 Sample Encryption specification [SampleEnc]. The IV attribute MAY 584 be present; see Section 5.2. 586 URI 588 The value is a quoted-string containing a URI that specifies how 589 to obtain the key. This attribute is REQUIRED unless the METHOD 590 is NONE. 592 IV 594 The value is a hexadecimal-sequence that specifies a 128-bit 595 unsigned integer Initialization Vector to be used with the key. 596 Use of the IV attribute REQUIRES a compatibility version number of 597 2 or greater. See Section 5.2 for when the IV attribute is used. 599 KEYFORMAT 601 The value is a quoted-string that specifies how the key is 602 represented in the resource identified by the URI; see Section 5 603 for more detail. This attribute is OPTIONAL; its absence 604 indicates an implicit value of "identity". Use of the KEYFORMAT 605 attribute REQUIRES a compatibility version number of 5 or greater. 607 KEYFORMATVERSIONS 609 The value is a quoted-string containing one or more positive 610 integers separated by the "/" character (for example, "1", "1/2", 611 or "1/2/5"). If more than one version of a particular KEYFORMAT 612 is defined, this attribute can be used to indicate which 613 version(s) this instance complies with. This attribute is 614 OPTIONAL; if it is not present, its value is considered to be "1". 616 Use of the KEYFORMATVERSIONS attribute REQUIRES a compatibility 617 version number of 5 or greater. 619 If the Media Playlist file does not contain an EXT-X-KEY tag then 620 Media Segments are not encrypted. 622 See Section 5 for the format of the key file, and Section 5.2, 623 Section 6.2.3 and Section 6.3.6 for additional information on Media 624 Segment encryption. 626 4.3.2.5. EXT-X-MAP 628 The EXT-X-MAP tag specifies how to obtain the Media Initialization 629 Section (Section 3) required to parse the applicable Media Segments. 630 It applies to every Media Segment that appears after it in the 631 Playlist until the next EXT-X-MAP tag or until the end of the 632 playlist. 634 Its format is: 636 #EXT-X-MAP:<attribute-list> 638 The following attributes are defined: 640 URI 642 The value is a quoted-string containing a URI that identifies a 643 resource that contains the Media Initialization Section. This 644 attribute is REQUIRED. 646 BYTERANGE 648 The value is a quoted-string specifying a byte range into the 649 resource identified by the URI attribute. This range SHOULD 650 contain only the Media Initialization Section. The format of the 651 byte range is described in Section 4.3.2.2. This attribute is 652 OPTIONAL; if it is not present, the byte range is the entire 653 resource indicated by the URI. 655 An EXT-X-MAP tag SHOULD be supplied for Media Segments in Playlists 656 with the EXT-X-I-FRAMES-ONLY tag when the first Media Segment (i.e., 657 I-frame) in the Playlist (or the first segment following an 658 EXT-X-DISCONTINUITY tag) does not immediately follow the Media 659 Initialization Section at the beginning of its resource. 661 Use of the EXT-X-MAP tag in a Media Playlist that contains the 662 EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 5 663 or greater. Use of the EXT-X-MAP tag in a Media Playlist that DOES 664 NOT contain the EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility 665 version number of 6 or greater. 667 4.3.2.6. EXT-X-PROGRAM-DATE-TIME 669 The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a 670 Media Segment with an absolute date and/or time. It applies only to 671 the next Media Segment. 673 The date/time representation is ISO/IEC 8601:2004 [ISO_8601] and 674 SHOULD indicate a time zone and fractional parts of seconds: 676 #EXT-X-PROGRAM-DATE-TIME:<YYYY-MM-DDThh:mm:ssZ> 678 For example: 680 #EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00 682 EXT-X-PROGRAM-DATE-TIME tags SHOULD provide millisecond accuracy. 684 See Section 6.2.1 and Section 6.3.3 for more information on the EXT-X 685 -PROGRAM-DATE-TIME tag. 687 4.3.3. Media Playlist Tags 689 Media Playlist tags describe global parameters of the Media Playlist. 690 There MUST NOT be more than one Media Playlist tag of each type in 691 any Media Playlist. 693 A Media Playlist Tag MUST NOT appear in a Master Playlist 695 4.3.3.1. EXT-X-TARGETDURATION 697 The EXT-X-TARGETDURATION tag specifies the maximum Media Segment 698 duration. The EXTINF duration of each Media Segment in the Playlist 699 file, when rounded to the nearest integer, MUST be less than or equal 700 to the target duration; longer segments can trigger playback stalls 701 or other errors. It applies to the entire Playlist file. Its format 702 is: 704 #EXT-X-TARGETDURATION:<s> 706 where s is a decimal-integer indicating the target duration in 707 seconds. The EXT-X-TARGETDURATION tag is REQUIRED. 709 4.3.3.2. EXT-X-MEDIA-SEQUENCE 711 The EXT-X-MEDIA-SEQUENCE tag indicates the Media Sequence Number of 712 the first Media Segment that appears in a Playlist file. Its format 713 is: 715 #EXT-X-MEDIA-SEQUENCE:<number> 717 where number is a decimal-integer. 719 If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE 720 tag then the Media Sequence Number of the first Media Segment in the 721 Media Playlist SHALL be considered to be 0. A client MUST NOT assume 722 that segments with the same Media Sequence Number in different Media 723 Playlists contain matching content - see Section 6.3.2. 725 A URI for a Media Segment is not required to contain its Media 726 Sequence Number. 728 See Section 6.2.1 and Section 6.3.5 for more information on setting 729 the EXT-X-MEDIA-SEQUENCE tag. 731 The EXT-X-MEDIA-SEQUENCE tag MUST appear before the first Media 732 Segment in the Playlist. 734 4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE 736 The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between 737 different Renditions of the same Variant Stream or different Variant 738 Streams that have EXT-X-DISCONTINUITY tags in their Media Playlists. 740 Its format is: 742 #EXT-X-DISCONTINUITY-SEQUENCE:<number> 744 where number is a decimal-integer. 746 If the Media Playlist does not contain an EXT-X-DISCONTINUITY- 747 SEQUENCE tag, then the Discontinuity Sequence Number of the first 748 Media Segment in the Playlist SHALL be considered to be 0. 750 The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before the first 751 Media Segment in the Playlist. 753 The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any 754 EXT-X-DISCONTINUITY tag. 756 See Section 6.2.1 and Section 6.2.2 for more information about 757 setting the value of the EXT-X-DISCONTINUITY-SEQUENCE tag. 759 4.3.3.4. EXT-X-ENDLIST 761 The EXT-X-ENDLIST tag indicates that no more Media Segments will be 762 added to the Media Playlist file. It MAY occur anywhere in the Media 763 Playlist file. Its format is: 765 #EXT-X-ENDLIST 767 4.3.3.5. EXT-X-PLAYLIST-TYPE 769 The EXT-X-PLAYLIST-TYPE tag provides mutability information about the 770 Media Playlist file. It applies to the entire Media Playlist file. 771 It is OPTIONAL. Its format is: 773 #EXT-X-PLAYLIST-TYPE:<EVENT|VOD> 775 Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE 776 tag. 778 If the EXT-X-PLAYLIST-TYPE value is EVENT, Media Segments can only be 779 added to the end of the Media Playlist. If the EXT-X-PLAYLIST-TYPE 780 value is VOD, the Media Playlist cannot change. 782 If the EXT-X-PLAYLIST-TYPE tag is omitted from a Media Playlist, the 783 Playlist can be updated according to the rules in Section 6.2.1 with 784 no additional restrictions. For example, a live Playlist 785 (Section 6.2.2) MAY be updated to remove Media Segments in the order 786 that they appeared. 788 4.3.3.6. EXT-X-I-FRAMES-ONLY 790 The EXT-X-I-FRAMES-ONLY tag indicates that each Media Segment in the 791 Playlist describes a single I-frame. I-frames (or Intra frames) are 792 encoded video frames whose encoding does not depend on any other 793 frame. I-frame playlists can be used for trick play, such as fast 794 forward, rapid reverse and scrubbing. 796 The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its 797 format is: 799 #EXT-X-I-FRAMES-ONLY 801 In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the Media Segment 802 duration (EXTINF tag value) is the time between the presentation time 803 of the I-frame in the Media Segment and the presentation time of the 804 next I-frame in the Playlist, or the end of the presentation if it is 805 the last I-frame in the Playlist. 807 Media resources containing I-frame segments MUST begin with either a 808 Media Initialization Section (Section 3) or be accompanied by an 809 EXT-X-MAP tag indicating the Media Initialization Section so that 810 clients can load and decode I-frame segments in any order. The byte 811 range of an I-frame segment with an EXT-X-BYTERANGE tag applied to it 812 (Section 4.3.2.2) MUST NOT include its Media Initialization Section; 813 clients can assume that the Media Initialization Section is defined 814 by EXT-X-MAP tag, or is located from the start of the resource to the 815 offset of the first I-frame segment in that resource. 817 Use of the EXT-X-I-FRAMES-ONLY REQUIRES a compatibility version 818 number of 4 or greater. 820 4.3.4. Master Playlist Tags 822 Master Playlist tags define the Variant Streams, Renditions, and 823 other global parameters of the presentation. 825 Master Playlist Tags MUST NOT appear in a Media Playlist; clients 826 MUST reject any Playlist that contains both a Master Playlist tag and 827 either a Media Playlist tag or a Media Segment tag. 829 4.3.4.1. EXT-X-MEDIA 831 The EXT-X-MEDIA tag is used to relate Media Playlists that contain 832 alternative Renditions (Section 4.3.4.2.1) of the same content. For 833 example, three EXT-X-MEDIA tags can be used to identify audio-only 834 Media Playlists that contain English, French and Spanish Renditions 835 of the same presentation. Or two EXT-X-MEDIA tags can be used to 836 identify video-only Media Playlists that show two different camera 837 angles. 839 Its format is: 841 #EXT-X-MEDIA:<attribute-list> 843 The following attributes are defined: 845 TYPE 847 The value is an enumerated-string; valid strings are AUDIO, VIDEO, 848 SUBTITLES and CLOSED-CAPTIONS. This attribute is REQUIRED. 850 In Transport Streams, Closed captions [CEA608] media is carried in 851 the video stream. Therefore, an EXT-X-MEDIA tag with TYPE of 852 CLOSED-CAPTION does not specify a Rendition; the closed caption 853 media is present in the Media Segments of every video Rendition. 855 URI 857 The value is a quoted-string containing a URI that identifies the 858 Media Playlist file. This attribute is OPTIONAL; see 859 Section 4.3.4.2.1. If the TYPE is CLOSED-CAPTIONS, the URI 860 attribute MUST NOT be present. 862 GROUP-ID 864 The value is a quoted-string which specifies the group to which 865 the Rendition belongs. See Section 4.3.4.1.1. This attribute is 866 REQUIRED. 868 LANGUAGE 870 The value is a quoted-string containing one of the standard Tags 871 for Identifying Languages [RFC5646], which identifies the primary 872 language used in the Rendition. This attribute is OPTIONAL. 874 ASSOC-LANGUAGE 876 The value is a quoted-string containing a language tag [RFC5646] 877 that identifies a language that is associated with the Rendition. 878 An associated language is often used in a different role than the 879 language specified by the LANGUAGE attribute (e.g. written vs. 880 spoken, or as a fallback dialect). This attribute is OPTIONAL. 882 The LANGUAGE and ASSOC-LANGUAGE attributes can be used, for 883 example, to link Norwegian renditions that use different spoken 884 and written languages. 886 NAME 888 The value is a quoted-string containing a human-readable 889 description of the Rendition. If the LANGUAGE attribute is 890 present then this description SHOULD be in that language. This 891 attribute is REQUIRED. 893 DEFAULT 895 The value is an enumerated-string; valid strings are YES and NO. 896 If the value is YES, then the client SHOULD play this Rendition of 897 the content in the absence of information from the user indicating 898 a different choice. This attribute is OPTIONAL. Its absence 899 indicates an implicit value of NO. 901 AUTOSELECT 903 The value is an enumerated-string; valid strings are YES and NO. 904 This attribute is OPTIONAL. Its absence indicates an implicit 905 value of NO. If the value is YES, then the client MAY choose to 906 play this Rendition in the absence of explicit user preference 907 because it matches the current playback environment, such as 908 chosen system language. 910 If the AUTOSELECT attribute is present, its value MUST be YES if 911 the value of the DEFAULT attribute is YES. 913 FORCED 915 The value is an enumerated-string; valid strings are YES and NO. 916 This attribute is OPTIONAL. Its absence indicates an implicit 917 value of NO. The FORCED attribute MUST NOT be present unless the 918 TYPE is SUBTITLES. 920 A value of YES indicates that the Rendition contains content which 921 is considered essential to play. When selecting a FORCED 922 Rendition, a client SHOULD choose the one that best matches the 923 current playback environment (e.g. language). 925 A value of NO indicates that the Rendition contains content which 926 is intended to be played in response to explicit user request. 928 INSTREAM-ID 930 The value is a quoted-string that specifies a Rendition within the 931 segments in the Media Playlist. This attribute is REQUIRED if the 932 TYPE attribute is CLOSED-CAPTIONS, in which case it MUST have one 933 of the values: "CC1", "CC2", "CC3", "CC4", or "SERVICEn" where n 934 MUST be an integer between 1 and 63 (e.g."SERVICE3" or 935 "SERVICE42"). 937 The values "CC1", "CC2", "CC3", and "CC4" identify a Line 21 Data 938 Services channel [CEA608]. The "SERVICE" values identify a 939 Digital Television Closed Captioning [CEA708] service block 940 number. 942 For all other TYPE values, the INSTREAM-ID MUST NOT be specified. 944 CHARACTERISTICS 946 The value is a quoted-string containing one or more Uniform Type 947 Identifiers [UTI] separated by comma (,) characters. This 948 attribute is OPTIONAL. Each UTI indicates an individual 949 characteristic of the Rendition. 951 A SUBTITLES Rendition MAY include the following characteristics: 952 "public.accessibility.transcribes-spoken-dialog"; 953 "public.accessibility.describes-music-and-sound"; "public.easy-to- 954 read" (which indicates that the subtitles have been edited for 955 ease of reading). 957 An AUDIO Rendition MAY include the following characteristics: 958 "public.accessibility.describes-video". 960 The CHARACTERISTICS attribute MAY include private UTIs. 962 4.3.4.1.1. Rendition Groups 964 A set of one or more EXT-X-MEDIA tags with the same GROUP-ID value 965 and the same TYPE value defines a Group of Renditions. Each member 966 of the Group MUST be an alternative rendition of the same content; 967 otherwise playback errors can occur. 969 All EXT-X-MEDIA tags in a Playlist MUST meet the following 970 constraints: 972 o All EXT-X-MEDIA tags in the same Group MUST have different NAME 973 attributes. 975 o A Group MUST NOT have more than one member with a DEFAULT 976 attribute of YES. 978 o All members of a Group whose AUTOSELECT attribute has a value of 979 YES MUST have LANGUAGE [RFC5646] attributes with unique values. 981 A Playlist MAY contain multiple Groups of the same TYPE in order to 982 provide multiple encodings of that media type. If it does so, each 983 Group of the same TYPE MUST have the same set of members, and each 984 corresponding member MUST have identical attributes with the 985 exception of the URI attribute. 987 Each member in a Group of Renditions MAY have a different sample 988 format. However, any EXT-X-STREAM-INF (Section 4.3.4.2) tag or 989 EXT-X-I-FRAME-STREAM-INF (Section 4.3.4.3) tag which references that 990 Group MUST have a CODECS attribute that lists every sample format 991 present in any Rendition in the Group, or client playback failures 992 can occur. 994 4.3.4.2. EXT-X-STREAM-INF 996 The EXT-X-STREAM-INF tag specifies a Variant Stream, which is a set 997 of Renditions which can be combined to play the presentation. The 998 attributes of the tag provide information about the Variant Stream. 1000 The URI line that follows the EXT-X-STREAM-INF tag specifies a Media 1001 Playlist that carries a Rendition of the Variant Stream. The URI 1002 line is REQUIRED. Clients that do not support multiple video 1003 renditions SHOULD play this Rendition 1005 Its format is: 1007 #EXT-X-STREAM-INF:<attribute-list> 1008 <URI> 1010 The following attributes are defined: 1012 BANDWIDTH 1014 The value is a decimal-integer of bits per second. It represents 1015 the peak segment bit rate of the Variant Stream. 1017 If all the Media Segments in a Variant Stream have already been 1018 created, the BANDWIDTH value MUST be the largest sum of peak 1019 segment bit rates that is produced by any playable combination of 1020 Renditions. (For a Variant Stream with a single Media Playlist, 1021 this is just the peak segment bit rate of that Media Playlist.) 1022 An inaccurate value can cause playback stalls or prevent clients 1023 from playing the variant. 1025 If the Master Playlist is to be made available before all Media 1026 Segments in the presentation have been encoded, the BANDWIDTH 1027 value SHOULD be the BANDWIDTH value of a representative period of 1028 similar content, encoded using the same settings. 1030 Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute. 1032 AVERAGE-BANDWIDTH 1034 The value is a decimal-integer of bits per second. It represents 1035 the average segment bit rate of the Variant Stream. 1037 If all the Media Segments in a Variant Stream have already been 1038 created, the AVERAGE-BANDWIDTH value MUST be the largest sum of 1039 average segment bit rates that is produced by any playable 1040 combination of Renditions. (For a Variant Stream with a single 1041 Media Playlist, this is just the average segment bit rate of that 1042 Media Playlist.) An inaccurate value can cause playback stalls or 1043 prevent clients from playing the variant. 1045 If the Master Playlist is to be made available before all Media 1046 Segments in the presentation have been encoded, the AVERAGE- 1047 BANDWIDTH value SHOULD be the AVERAGE-BANDWIDTH value of a 1048 representative period of similar content, encoded using the same 1049 settings. 1051 The AVERAGE-BANDWIDTH attribute is OPTIONAL. 1053 CODECS 1055 The value is a quoted-string containing a comma-separated list of 1056 formats, where each format specifies a media sample type that is 1057 present in one or more Renditions specified by the Variant Stream. 1058 Valid format identifiers are those in the ISO Base Media File 1059 Format Name Space defined by The 'Codecs' and 'Profiles' 1060 Parameters for "Bucket" Media Types [RFC6381]. 1062 For example, a stream containing AAC-LC audio and H.264 Main 1063 Profile Level 3.0 video would have a CODECS value of 1064 "mp4a.40.2,avc1.4d401e". 1066 Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute. 1068 RESOLUTION 1070 The value is a decimal-resolution describing the optimal pixel 1071 resolution at which to display all the video in the Variant 1072 Stream. 1074 The RESOLUTION attribute is OPTIONAL but is recommended if the 1075 Variant Stream includes video. 1077 FRAME-RATE 1079 The value is a decimal-floating-point describing the maximum frame 1080 rate for all the video in the Variant Stream, rounded to 3 decimal 1081 places. 1083 The FRAME-RATE attribute is OPTIONAL but is recommended if the 1084 Variant Stream includes video. The FRAME-RATE attribute SHOULD be 1085 included if any video in a Variant Stream exceeds 30 frames per 1086 second. 1088 AUDIO 1089 The value is a quoted-string. It MUST match the value of the 1090 GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master 1091 Playlist whose TYPE attribute is AUDIO. It indicates the set of 1092 audio Renditions that SHOULD be used when playing the 1093 presentation. See Section 4.3.4.2.1. 1095 The AUDIO attribute is OPTIONAL. 1097 VIDEO 1099 The value is a quoted-string. It MUST match the value of the 1100 GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master 1101 Playlist whose TYPE attribute is VIDEO. It indicates the set of 1102 video Renditions that SHOULD be used when playing the 1103 presentation. See Section 4.3.4.2.1. 1105 The VIDEO attribute is OPTIONAL. 1107 SUBTITLES 1109 The value is a quoted-string. It MUST match the value of the 1110 GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master 1111 Playlist whose TYPE attribute is SUBTITLES. It indicates the set 1112 of subtitle Renditions that can be used when playing the 1113 presentation. See Section 4.3.4.2.1. 1115 The SUBTITLES attribute is OPTIONAL. 1117 CLOSED-CAPTIONS 1119 The value can be either a quoted-string or an enumerated-string 1120 with the value NONE. If the value is a quoted-string, it MUST 1121 match the value of the GROUP-ID attribute of an EXT-X-MEDIA tag 1122 elsewhere in the Playlist whose TYPE attribute is CLOSED-CAPTIONS, 1123 and indicates the set of closed-caption Renditions that can be 1124 used when playing the presentation. See Section 4.3.4.2.1. 1126 If the value is the enumerated-string value NONE, all EXT-X 1127 -STREAM-INF tags MUST have this attribute with a value of NONE, 1128 indicating that there are no closed captions in any Variant Stream 1129 in the Master Playlist. Having closed captions in one Variant 1130 Stream but not another can trigger playback inconsistencies. 1132 The CLOSED-CAPTIONS attribute is OPTIONAL. 1134 4.3.4.2.1. Alternative Renditions 1136 When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, SUBTITLES, or 1137 CLOSED-CAPTIONS attribute, it indicates that alternative Renditions 1138 of the content are available for playback of that Variant Stream. 1140 When defining alternative Renditions, the following constraints MUST 1141 be met to prevent client playback errors: 1143 o All playable combinations of Renditions associated with an EXT-X 1144 -STREAM-INF tag MUST have an aggregate bandwidth less than or 1145 equal to the BANDWIDTH attribute of the EXT-X-STREAM-INF tag. 1147 o If an EXT-X-STREAM-INF tag contains a RESOLUTION attribute and a 1148 VIDEO attribute, then every alternative video Rendition MUST have 1149 an optimal display resolution matching the value of the RESOLUTION 1150 attribute. 1152 o Every alternative Rendition associated with an EXT-X-STREAM-INF 1153 tag MUST meet the constraints for a Variant Stream described in 1154 Section 6.2.4. 1156 The URI attribute of the EXT-X-MEDIA tag is REQUIRED if the media 1157 type is SUBTITLES, but OPTIONAL if the media type is VIDEO or AUDIO. 1158 If the media type is VIDEO or AUDIO, a missing URI attribute 1159 indicates that the media data for this Rendition is included in the 1160 Media Playlist of any EXT-X-STREAM-INF tag referencing this 1161 EXT-X-MEDIA tag. If the media TYPE is AUDIO and the URI attribute is 1162 missing, clients MUST assume that the audio data for this Rendition 1163 is present in every video Rendition specified by the EXT-X-STREAM-INF 1164 tag. 1166 The URI attribute of the EXT-X-MEDIA tag MUST NOT be included if the 1167 media type is CLOSED-CAPTIONS. 1169 4.3.4.3. EXT-X-I-FRAME-STREAM-INF 1171 The EXT-X-I-FRAME-STREAM-INF tag identifies a Media Playlist file 1172 containing the I-frames of a multimedia presentation. It stands 1173 alone, in that it does not apply to a particular URI in the Master 1174 Playlist. Its format is: 1176 #EXT-X-I-FRAME-STREAM-INF:<attribute-list> 1178 All attributes defined for the EXT-X-STREAM-INF tag (Section 4.3.4.2) 1179 are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the 1180 AUDIO, SUBTITLES and CLOSED-CAPTIONS attributes. In addition, the 1181 following attribute is defined: 1183 URI 1185 The value is a quoted-string containing a URI that identifies the 1186 I-frame Media Playlist file. That Playlist file MUST contain an 1187 EXT-X-I-FRAMES-ONLY tag. 1189 Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute 1190 and a URI attribute. 1192 The provisions in Section 4.3.4.2.1 also apply to EXT-X-I-FRAME- 1193 STREAM-INF tags with a VIDEO attribute. 1195 A Master Playlist that specifies alternative VIDEO Renditions and 1196 I-frame Playlists SHOULD include an alternative I-frame VIDEO 1197 Rendition for each regular VIDEO Rendition, with the same NAME and 1198 LANGUAGE attributes. 1200 4.3.4.4. EXT-X-SESSION-DATA 1202 The EXT-X-SESSION-DATA tag allows arbitrary session data to be 1203 carried in a Master Playlist. 1205 Its format is: 1207 #EXT-X-SESSION-DATA:<attribute list> 1209 The following attributes are defined: 1211 DATA-ID 1213 The value of DATA-ID is a quoted-string which identifies that data 1214 value. The DATA-ID SHOULD conform to a reverse DNS naming 1215 convention, such as "com.example.movie.title"; however, there is 1216 no central registration authority, so Playlist authors SHOULD take 1217 care to choose a value which is unlikely to collide with others. 1218 This attribute is REQUIRED. 1220 VALUE 1222 VALUE is a quoted-string. It contains the data identified by 1223 DATA-ID. If the LANGUAGE is specified, VALUE SHOULD contain a 1224 human-readable string written in the specified language. 1226 URI 1228 The value is a quoted-string containing a URI. The resource 1229 identified by the URI MUST be formatted as JSON [RFC7159]; 1230 otherwise, clients may fail to interpret the resource. 1232 LANGUAGE 1234 The value is a quoted-string containing a language tag [RFC5646] 1235 that identifies the language of the VALUE. This attribute is 1236 OPTIONAL. 1238 Each EXT-X-SESSION-DATA tag MUST contain either a VALUE or URI 1239 attribute, but not both. 1241 A Playlist MAY contain multiple EXT-X-SESSION-DATA tags with the same 1242 DATA-ID attribute. A Playlist MUST NOT contain more than one EXT-X 1243 -SESSION-DATA tag with the same DATA-ID attribute and the same 1244 LANGUAGE attribute. 1246 4.3.4.5. EXT-X-SESSION-KEY 1248 The EXT-X-SESSION-KEY tag allows encryption keys from Media Playlists 1249 to be specified in Master Playlist. This allows the client to 1250 preload these keys without having to read the Media Playlist(s) 1251 first. 1253 Its format is: 1255 #EXT-X-SESSION-KEY:<attribute list> 1257 All attributes defined for the EXT-X-KEY tag (Section 4.3.2.4) are 1258 also defined for the EXT-X-SESSION-KEY, except that the value of the 1259 METHOD attribute MUST NOT be NONE. If an EXT-X-SESSION-KEY is used, 1260 the values of the METHOD, KEYFORMAT and KEYFORMATVERSIONS attributes 1261 MUST match any EXT-X-KEY with the same URI value. 1263 EXT-X-SESSION-KEY tags SHOULD be added if multiple Variant Streams or 1264 Renditions use the same encryption keys and formats. 1266 The EXT-X-SESSION-KEY tag is optional. 1268 4.3.5. Media or Master Playlist Tags 1270 The tags in this section can appear in either Master Playlists or 1271 Media Playlists. If one of these tags appears in a Master Playlist, 1272 it SHOULD NOT appear in any Media Playlist referenced by that Master 1273 Playlist. A tag that appears in both MUST have the same value; 1274 otherwise, clients SHOULD ignore the value in the Media Playlist(s). 1276 These tags MUST NOT appear more than once in a Playlist. If a tag 1277 appears more than once, clients MUST reject the playlist. 1279 4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS 1281 The EXT-X-INDEPENDENT-SEGMENTS tag indicates that all media samples 1282 in a Media Segment can be decoded without information from other 1283 segments. It applies to every Media Segment in the Playlist. 1285 Its format is: 1287 #EXT-X-INDEPENDENT-SEGMENTS 1289 If the EXT-X-INDEPENDENT-SEGMENTS tag appears in a Master Playlist, 1290 it applies to every Media Segment in every Media Playlist in the 1291 Master Playlist. 1293 4.3.5.2. EXT-X-START 1295 The EXT-X-START tag indicates a preferred point at which to start 1296 playing a Playlist. By default, clients SHOULD start playback at 1297 this point when beginning a playback session. This tag is OPTIONAL. 1299 Its format is: 1301 #EXT-X-START:<attribute list> 1303 The following attributes are defined: 1305 TIME-OFFSET 1307 The value of TIME-OFFSET is a signed-decimal-floating-point number 1308 of seconds. A positive number indicates a time offset from the 1309 beginning of the Playlist. A negative number indicates a negative 1310 time offset from the end of the last Media Segment in the 1311 Playlist. This attribute is REQUIRED. 1313 The absolute value of TIME-OFFSET SHOULD NOT be larger than the 1314 Playlist duration. If the absolute value of TIME-OFFSET exceeds 1315 the duration of the Playlist, it indicates either the end of the 1316 Playlist (if positive) or the beginning of the Playlist (if 1317 negative). 1319 If the Playlist does not contain the EXT-X-ENDLIST tag, the TIME- 1320 OFFSET SHOULD NOT be within three target durations of the end of 1321 the Playlist file. 1323 PRECISE 1325 The value is an enumerated-string; valid strings are YES and NO. 1326 If the value is YES, clients SHOULD start playback at the Media 1327 Segment containing the TIME-OFFSET, but SHOULD NOT render media 1328 samples in that segment whose presentation times are prior to the 1329 TIME-OFFSET. If the value is NO, clients SHOULD attempt to render 1330 every media sample in that segment. This attribute is OPTIONAL. 1331 If it is missing, its value should be treated as NO. 1333 5. Key files 1335 5.1. Structure of Key files 1337 An EXT-X-KEY tag with a URI attribute identifies a Key file. A Key 1338 file contains a cipher key that can decrypt Media Segments in the 1339 Playlist. 1341 [AES_128] encryption uses 16-octet keys. If the KEYFORMAT of an 1342 EXT-X-KEY tag is "identity", the Key file is a single packed array of 1343 16 octets in binary format. 1345 5.2. IV for [AES_128] 1347 [AES_128] REQUIRES the same 16-octet Initialization Vector (IV) to be 1348 supplied when encrypting and decrypting. Varying this IV increases 1349 the strength of the cipher. 1351 An IV attribute on an EXT-X-KEY tag with a KEYFORMAT of "identity" 1352 specifies an Initialization Vector that can be used when decrypting 1353 Media Segments encrypted with that Key file. IV values for AES-128 1354 are 128-bit numbers. 1356 An EXT-X-KEY tag with a KEYFORMAT of "identity" that does not have an 1357 IV attribute indicates that the Media Sequence Number is to be used 1358 as the IV when decrypting a Media Segment, by putting its big-endian 1359 binary representation into a 16-octet (128-bit) buffer and padding 1360 (on the left) with zeros. 1362 6. Client/Server Responsibilities 1364 6.1. Introduction 1366 This section describes how the server generates the Playlist and 1367 Media Segments and how the client should download them for playback. 1369 6.2. Server Responsibilities 1370 6.2.1. General Server Responsibilities 1372 The production of the source media is outside the scope of this 1373 document, which simply presumes a source of continuous encoded media 1374 containing the presentation. 1376 The server MUST divide the source media into individual Media 1377 Segments whose duration is less than or equal to a constant target 1378 duration. Segments that are longer than the planned target duration 1379 can trigger playback stalls and other errors. 1381 The server SHOULD attempt to divide the source media at points that 1382 support effective decode of individual Media Segments, e.g. on packet 1383 and key frame boundaries. 1385 The server MUST create a URI for every Media Segment that enables its 1386 clients to obtain the segment data. If a server supports partial 1387 loading of resources (e.g. via HTTP Range requests), it MAY specify 1388 segments as sub-ranges of larger resources using the EXT-X-BYTERANGE 1389 tag. 1391 Any Media Segment that is specified in a Playlist loaded by a client 1392 MUST be available for immediate download, or playback errors can 1393 occur. Once download starts, its transfer rate SHOULD NOT be 1394 constrained by the segment production process. 1396 HTTP servers SHOULD transfer text files - such as Playlists and 1397 WebVTT segments - using the "gzip" Content-Encoding if the client 1398 indicates that it is prepared to accept it. 1400 The server must create a Media Playlist file (Section 4) that 1401 contains a URI for each Media Segment that the server wishes to make 1402 available, in the order in which they are to be played. 1404 The value of the EXT-X-VERSION tag (Section 4.3.1.2) SHOULD NOT be 1405 greater than what is required for the tags and attributes in the 1406 Playlist - see Section 7. 1408 Changes to the Playlist file MUST be made atomically from the point 1409 of view of the clients, or playback errors MAY occur. 1411 The server MUST NOT change the Media Playlist file, except to: 1413 Append lines to it (Section 6.2.1). 1415 Remove Media Segment URIs from the Playlist in the order that they 1416 appear, along with any tags that apply only to those segments 1417 (Section 6.2.2). 1419 Increment the value of the EXT-X-MEDIA-SEQUENCE or EXT-X 1420 -DISCONTINUITY-SEQUENCE tags (Section 6.2.2). 1422 Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1). 1424 A Media Playlist has further constraints on its updates if it 1425 contains an EXT-X-PLAYLIST-TYPE tag. An EXT-X-PLAYLIST-TYPE tag with 1426 a value of VOD indicates that the Playlist file MUST NOT change. An 1427 EXT-X-PLAYLIST-TYPE tag with a value of EVENT indicates that the 1428 server MUST NOT change or delete any part of the Playlist file; it 1429 MAY append lines to it. 1431 The value of the EXT-X-TARGETDURATION tag in the Media Playlist MUST 1432 NOT change. A typical target duration is 10 seconds. 1434 Playlist changes other than those allowed here can trigger playback 1435 errors and inconsistent client behavior. 1437 Each Media Segment in a Media Playlist has an integer Discontinuity 1438 Sequence Number. The Discontinuity Sequence Number can be used in 1439 addition to the timestamps within the media to synchronize Media 1440 Segments across different Renditions. 1442 A segment's Discontinuity Sequence Number is the value of the EXT-X 1443 -DISCONTINUITY-SEQUENCE tag (or zero if none) plus the number of 1444 EXT-X-DISCONTINUITY tags in the Playlist preceding the URI line of 1445 the segment. 1447 The server MAY associate an absolute date and time with a Media 1448 Segment by applying an EXT-X-PROGRAM-DATE-TIME tag to it. This 1449 defines an informative mapping of the (wall-clock) date and time 1450 specified by the tag to the first media timestamp in the segment, 1451 which may be used as a basis for seeking, for display, or for other 1452 purposes. If a server provides this mapping, it SHOULD apply an 1453 EXT-X-PROGRAM-DATE-TIME tag to every segment that has an 1454 EXT-X-DISCONTINUITY tag applied to it. 1456 If the Media Playlist contains the final Media Segment of the 1457 presentation then the Playlist file MUST contain the EXT-X-ENDLIST 1458 tag; this allows clients to minimize unproductive Playlist reloads. 1460 If a Media Playlist does not contain the EXT-X-ENDLIST tag, the 1461 server MUST make a new version of the Playlist file available that 1462 contains at least one new Media Segment. It MUST be made available 1463 relative to the time that the previous version of the Playlist file 1464 was made available: no earlier than one-half the target duration 1465 after that time, and no later than 1.5 times the target duration 1466 after that time. This allows clients to utilize the network 1467 efficiently. 1469 If the server wishes to remove an entire presentation, it SHOULD 1470 provide a clear indication to clients that the Playlist file is no 1471 longer available (e.g. with an HTTP 404 or 410 response). It MUST 1472 ensure that all Media Segments in the Playlist file remain available 1473 to clients for at least the duration of the Playlist file at the time 1474 of removal to prevent interruption of in-progress playback. 1476 6.2.2. Live Playlists 1478 The server MAY limit the availability of Media Segments by removing 1479 Media Segments from the Playlist file (Section 6.2.1). If Media 1480 Segments are to be removed, the Playlist file MUST contain an EXT-X 1481 -MEDIA-SEQUENCE tag. Its value MUST be incremented by 1 for every 1482 Media Segment that is removed from the Playlist file; it MUST NOT 1483 decrease or wrap. Clients can malfunction if each Media Segment does 1484 not have a consistent, unique Media Sequence Number. 1486 Media Segments MUST be removed from the Playlist file in the order 1487 that they appear in the Playlist; otherwise, client playback can 1488 malfunction. 1490 The server MUST NOT remove a Media Segment from a Playlist file 1491 without an EXT-X-ENDLIST tag if that would produce a Playlist whose 1492 duration is less than three times the target duration. Doing so can 1493 trigger playback stalls. 1495 When the server removes a Media Segment URI from the Playlist, the 1496 corresponding Media Segment MUST remain available to clients for a 1497 period of time equal to the duration of the segment plus the duration 1498 of the longest Playlist file distributed by the server containing 1499 that segment. Removing a Media Segment earlier than that can 1500 interrupt in-progress playback. 1502 If the server wishes to remove segments from a Media Playlist 1503 containing an EXT-X-DISCONTINUITY tag, the Media Playlist MUST 1504 contain an EXT-X-DISCONTINUITY-SEQUENCE tag. Without the EXT-X 1505 -DISCONTINUITY-SEQUENCE tag, it can be impossible for a client to 1506 locate corresponding segments between Renditions. 1508 If the server removes an EXT-X-DISCONTINUITY tag from the Media 1509 Playlist, it MUST increment the value of the EXT-X-DISCONTINUITY- 1510 SEQUENCE tag so that the Discontinuity Sequence Numbers of the 1511 segments still in the Media Playlist remain unchanged. The value of 1512 the EXT-X-DISCONTINUITY-SEQUENCE tag MUST NOT decrease or wrap. 1514 Clients can malfunction if each Media Segment does not have a 1515 consistent Discontinuity Sequence Number. 1517 If a server plans to remove a Media Segment after it is delivered to 1518 clients over HTTP, it SHOULD ensure that the HTTP response contains 1519 an Expires header that reflects the planned time-to-live. 1521 A Live Playlist MUST NOT contain the EXT-X-PLAYLIST-TYPE tag, as no 1522 value of that tag allows Media Segments to be removed. 1524 6.2.3. Encrypting Media Segments 1526 Media Segments MAY be encrypted. Every encrypted Media Segment MUST 1527 have an EXT-X-KEY tag (Section 4.3.2.4) applied to it with a URI that 1528 the client can use to obtain a Key file (Section 5) containing the 1529 decryption key. 1531 A Media Segment can only be encrypted with one encryption METHOD, 1532 using one encryption key and IV. However, a server MAY offer 1533 multiple ways to retrieve that key by providing multiple EXT-X-KEY 1534 tags, each with a different KEYFORMAT attribute value. 1536 The server MAY set the HTTP Expires header in the key response to 1537 indicate the duration for which the key can be cached. 1539 If an encrypted Media Segment is followed by one or more unencrypted 1540 Media Segments in the Playlist, the unencrypted Media Segments MUST 1541 have an EXT-X-KEY tag whose METHOD is NONE applied to them. 1542 Otherwise, the client will misinterpret those segments as encrypted. 1544 If the encryption METHOD is AES-128 and the Playlist does not contain 1545 the EXT-X-I-FRAMES-ONLY tag, AES encryption as described in 1546 Section 4.3.2.4 SHALL be applied to individual Media Segments. 1548 If the encryption METHOD is AES-128 and the Playlist contains an 1549 EXT-X-I-FRAMES-ONLY tag, the entire resource MUST be encrypted using 1550 AES-128 CBC with PKCS7 padding [RFC5652]. Encryption MAY be 1551 restarted on 16-byte block boundaries, unless the first block 1552 contains an I-frame. The IV used for encryption MUST be either the 1553 Media Sequence Number of the Media Segment or the value of the IV 1554 attribute of the EXT-X-KEY tag, as described in Section 5.2. These 1555 constraints allow a client to load and decrypt individual I-frames 1556 specified as sub-ranges of regular encrypted Media Segments, and 1557 their Media Initialization Sections. 1559 If the encryption METHOD is SAMPLE-AES, media samples MAY be 1560 encrypted prior to encapsulation in a Media Segment. The encryption 1561 format for H.264, AAC, AC-3 and Enhanced AC-3 media streams is 1562 described by the HLS Sample Encryption specification [SampleEnc]. 1564 The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if 1565 it applies to any Media Segment in the Playlist file, or clients who 1566 subsequently load that Playlist will be unable to decrypt those Media 1567 Segments. 1569 6.2.4. Providing Variant Streams 1571 A server MAY offer multiple Media Playlist files to provide different 1572 encodings of the same presentation. If it does so it SHOULD provide 1573 a Master Playlist file that lists each Variant Stream to allow 1574 clients to switch between encodings dynamically. 1576 Master Playlists describe regular Variant Streams with EXT-X-STREAM- 1577 INF tags and I-frame Variant Streams with EXT-X-I-FRAME-STREAM-INF 1578 tags. 1580 If an EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAM-INF tag contains 1581 the CODECS attribute, the attribute value MUST include every media 1582 format [RFC6381] present in any Media Segment in any of the 1583 Renditions specified by the Variant Stream. 1585 The server MUST meet the following constraints when producing Variant 1586 Streams in order to allow clients to switch between them seamlessly: 1588 Each Variant Stream MUST present the same content. 1590 Matching content in Variant Streams MUST have matching timestamps. 1591 This allows clients to synchronize the media. 1593 Matching content in Variant Streams MUST have matching 1594 Discontinuity Sequence Numbers - see Section 4.3.3.3. 1596 Each Media Playlist in each Variant Stream MUST have the same 1597 target duration. The only exception is that SUBTITLES Renditions 1598 with an EXT-X-PLAYLIST-TYPE of VOD MAY have longer target 1599 durations. 1601 Content that appears in a Media Playlist of one Variant Stream but 1602 not in another MUST appear either at the beginning or at the end 1603 of the Media Playlist file and MUST NOT be longer than the target 1604 duration. 1606 If any Media Playlists have an EXT-X-PLAYLIST-TYPE tag, all Media 1607 Playlists MUST have the EXT-X-PLAYLIST-TYPE tag with the same 1608 value. 1610 If the Playlist contains an EXT-X-PLAYLIST-TYPE tag with the value 1611 of VOD, the first segment of every Media Playlist in every Variant 1612 Stream MUST start at the same media timestamp. 1614 If any Media Playlist in a Master Playlist contains an EXT-X 1615 -PROGRAM-DATE-TIME tag, then all Media Playlists in that Master 1616 Playlist MUST contain EXT-X-PROGRAM-DATE-TIME tags with consistent 1617 mappings of date and time to media timestamps. 1619 In addition, for broadest compatibility, Variant Streams SHOULD 1620 contain the same encoded audio bitstream. This allows clients to 1621 switch between Variant Streams without audible glitching. 1623 The rules for Variant Streams also apply to alternative Renditions - 1624 see Section 4.3.4.2.1. 1626 6.3. Client Responsibilities 1628 6.3.1. General Client Responsibilities 1630 How the client obtains the URI to the Playlist file is outside the 1631 scope of this document; it is presumed to have done so. 1633 The client obtains the Playlist file from the URI. If the Playlist 1634 file so obtained is a Master Playlist, the client can select a 1635 Variant Stream to load from the Master Playlist. 1637 Clients MUST ensure that loaded Playlists comply with Section 4 and 1638 that the EXT-X-VERSION tag, if present, specifies a protocol version 1639 supported by the client; if either check fails, the client MUST NOT 1640 attempt to use the Playlist, or unintended behavior could occur. 1642 If any URI element in a Playlist contains an URI scheme that the 1643 client cannot handle, the client MUST stop playback. All clients 1644 MUST support HTTP schemes. 1646 To support forward compatibility, when parsing Playlists, Clients 1647 MUST: 1649 o ignore any unrecognized tags. 1651 o ignore any Attribute/value pair with an unrecognized 1652 AttributeName. 1654 o ignore any tag containing an attribute/value pair of type 1655 enumerated-string whose AttributeName is recognized but whose 1656 AttributeValue is not recognized, unless the definition of the 1657 attribute says otherwise. 1659 Algorithms used by the client to switch between Variant Streams are 1660 beyond the scope of this document. 1662 6.3.2. Loading the Media Playlist file 1664 Every time a Media Playlist is loaded or reloaded from a Playlist 1665 URI, the client MUST determine the next Media Segment to load, as 1666 described in Section 6.3.5, if it intends to play the presentation 1667 normally (i.e., in playlist order at the nominal playback rate). 1669 If the Media Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the 1670 client SHOULD assume that each Media Segment in it will become 1671 unavailable at the time that the Playlist file was loaded plus the 1672 duration of the Playlist file. 1674 A client MAY use the segment Media Sequence Number to track the 1675 location of a Media Segment within a Playlist when the Playlist is 1676 reloaded. 1678 A client MUST NOT assume that segments with the same Media Sequence 1679 Number in different Variant Streams or Renditions have the same 1680 position in the presentation; Playlists MAY have independent Media 1681 Sequence Numbers. Instead, a client MUST use the relative position 1682 of each segment on the Playlist timeline and its Discontinuity 1683 Sequence Number to locate corresponding segments. 1685 A client MUST load the Media Playlist file of every Rendition 1686 selected for playback in order to locate the media specific to that 1687 Rendition. But, to prevent unnecessary load on the server, it SHOULD 1688 NOT load the Playlist file of any other Rendition. 1690 For some Variant Streams, it is possible to select Renditions that do 1691 not include the Rendition specified by the EXT-X-STREAM-INF tag. As 1692 noted above, the client SHOULD NOT load that Rendition in those 1693 cases. 1695 6.3.3. Playing the Media Playlist file 1697 The client SHALL choose which Media Segment to play first from the 1698 Media Playlist when playback starts. If the EXT-X-ENDLIST tag is not 1699 present and the client intends to play the media normally, the client 1700 SHOULD NOT choose a segment which starts less than three target 1701 durations from the end of the Playlist file. Doing so can trigger 1702 playback stalls. 1704 Normal playback can be achieved by playing the Media Segments in the 1705 order that they appear in the Playlist. The client MAY present the 1706 available media in any way it wishes, including normal playback, 1707 random access, and trick modes. 1709 The encoding parameters for samples in a Media Segment and across 1710 multiple Media Segments in a Media Playlist SHOULD remain consistent. 1711 However, clients SHOULD deal with encoding changes as they are 1712 encountered, for example by scaling video content to accommodate a 1713 resolution change. If the Variant Stream includes a RESOLUTION 1714 attribute, clients SHOULD display all video within a rectangle with 1715 the same proportions as that resolution. 1717 Clients SHOULD be prepared to handle multiple tracks of a particular 1718 type (e.g. audio or video). A client with no other preference SHOULD 1719 choose the track with the lowest numerical track identifier that it 1720 can play. 1722 Clients SHOULD ignore private streams inside Transport Streams that 1723 they do not recognize. Private streams can be used to support 1724 different devices with the same stream, although stream authors 1725 SHOULD be sensitive to the additional network load that this imposes. 1727 The client MUST be prepared to reset its parser(s) and decoder(s) 1728 before playing a Media Segment that has an EXT-X-DISCONTINUITY tag 1729 applied to it, otherwise playback errors can occur. 1731 The client SHOULD attempt to load Media Segments in advance of when 1732 they will be required for uninterrupted playback to compensate for 1733 temporary variations in latency and throughput. 1735 The client MAY use the value of the EXT-X-PROGRAM-DATE-TIME tag to 1736 display the program origination time to the user. If the value 1737 includes time zone information, the client SHALL take it into 1738 account; if it does not the client MAY assume the time to be local. 1740 The client MUST NOT depend upon the correctness or the consistency of 1741 the value of the EXT-X-PROGRAM-DATE-TIME tag; its value is 1742 informative. 1744 6.3.4. Reloading the Media Playlist file 1746 The client MUST periodically reload a Media Playlist file to learn 1747 what media is currently available, unless it contains an EXT-X 1748 -PLAYLIST-TYPE tag with a value of VOD, or a value of EVENT and the 1749 EXT-X-ENDLIST tag is also present. 1751 However the client MUST NOT attempt to reload the Playlist file more 1752 frequently than specified by this section, in order to limit the 1753 collective load on the server. 1755 When a client loads a Playlist file for the first time or reloads a 1756 Playlist file and finds that it has changed since the last time it 1757 was loaded, the client MUST wait for at least the target duration 1758 before attempting to reload the Playlist file again, measured from 1759 the last time the client began loading the Playlist file. 1761 If the client reloads a Playlist file and finds that it has not 1762 changed then it MUST wait for a period of one-half the target 1763 duration before retrying. 1765 After reloading a Media Playlist, the client SHOULD verify that each 1766 Media Segment in it has the same URI (and byte range, if specified) 1767 as the Media Segment with the same Media Sequence Number in the 1768 previous Media Playlist. It SHOULD halt playback if it does not, as 1769 this normally indicates a server error. 1771 In order to reduce server load, the client SHOULD NOT reload the 1772 Playlist files of Variant Streams or alternate Renditions that are 1773 not currently being played. If it decides to switch playback to a 1774 different Variant Stream, it SHOULD stop reloading the Playlist of 1775 the old Variant Stream and begin loading the Playlist of the new 1776 Variant Stream. It can use the EXTINF durations and the constraints 1777 in Section 6.2.4 to determine the approximate location of 1778 corresponding media. Once media from the new Variant Stream has been 1779 loaded, the timestamps in the Media Segments can be used to 1780 synchronize the old and new timelines precisely. 1782 A client MUST NOT attempt to use the Media Sequence Number to 1783 synchronize between streams - see Section 6.3.2. 1785 6.3.5. Determining the next segment to load 1787 The client MUST examine the Media Playlist file every time it is 1788 loaded or reloaded to determine the next Media Segment to load, as 1789 the set of available media MAY have changed. 1791 The first segment to load is generally the segment that the client 1792 has chosen to play first - see Section 6.3.3. 1794 In order to play the presentation normally, the next Media Segment to 1795 load is the one with the lowest Media Sequence Number that is greater 1796 than the Media Sequence Number of the last Media Segment loaded. 1798 6.3.6. Decrypting encrypted Media Segments 1800 If a Media Playlist file contains an EXT-X-KEY tag that specifies a 1801 Key file URI, the client can obtain that Key file and use the key 1802 inside it to decrypt all Media Segments to which that EXT-X-KEY tag 1803 applies. 1805 A client MUST ignore any EXT-X-KEY tag with an unsupported or 1806 unrecognized KEYFORMAT attribute, to allow for cross-device 1807 addressibility. If the Playlist contains a Media Segment to which 1808 only EXT-X-KEY tags with unrecognized or unsupported KEYFORMAT 1809 attributes are applied, playback SHOULD fail. 1811 A client MUST NOT attempt to decrypt any segments whose EXT-X-KEY tag 1812 has a METHOD attribute that it does not recognize. 1814 If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be 1815 applied to individual Media Segments, whose encryption format is 1816 described in Section 4.3.2.4. 1818 If the encryption METHOD is AES-128 and the Media Segment is part of 1819 an I-frame playlist (Section 4.3.3.6) and it has an EXT-X-BYTERANGE 1820 tag applied to it, special care needs to be taken in loading and 1821 decrypting the segment, because the resource identified by the URI is 1822 encrypted in 16-byte blocks from the start of the resource. 1824 The decrypted I-frame can be recovered by first widening its byte 1825 range, as specified by the EXT-X-BYTERANGE tag, so that it starts and 1826 ends on 16-byte boundaries from the start of the resource. 1828 Next, the byte range is widened further to include a 16-byte block at 1829 the beginning of the range. This 16-byte block allows the correct IV 1830 for the following block to be calculated. 1832 The widened byte range can then be loaded and decrypted with AES-128 1833 CBC using an arbitrary IV. The number of bytes added to the 1834 beginning and the end of the original byte range are discarded from 1835 the decrypted bytes; what remains is the decrypted I-frame. 1837 If the encryption METHOD is SAMPLE-AES, AES-128 decryption SHALL be 1838 applied to encrypted media samples within the Media Segment. The 1839 format for encrypted H.264, AAC, AC-3 and Enhanced AC-3 media streams 1840 is described by the HLS Sample Encryption specification [SampleEnc]. 1842 An EXT-X-KEY tag with a METHOD of NONE indicates that the Media 1843 Segments it applies to are not encrypted. 1845 7. Protocol version compatibility 1847 Protocol compatibility is specified by the EXT-X-VERSION tag. A 1848 Playlist that contains tags or attributes that are not compatible 1849 with protocol version 1 MUST include an EXT-X-VERSION tag. 1851 A client MUST NOT attempt playback if it does not support the 1852 protocol version specified by the EXT-X-VERSION tag, or unintended 1853 behavior could occur. 1855 A Media Playlist MUST indicate a EXT-X-VERSION of 2 or higher if it 1856 contains: 1858 o The IV attribute of the EXT-X-KEY tag. 1860 A Media Playlist MUST indicate a EXT-X-VERSION of 3 or higher if it 1861 contains: 1863 o Floating-point EXTINF duration values. 1865 A Media Playlist MUST indicate a EXT-X-VERSION of 4 or higher if it 1866 contains: 1868 o The EXT-X-BYTERANGE tag. 1870 o The EXT-X-I-FRAMES-ONLY tag. 1872 A Media Playlist MUST indicate a EXT-X-VERSION of 5 or higher if it 1873 contains: 1875 o The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY 1876 tag. 1878 o The EXT-X-MAP tag. 1880 A Media Playlist MUST indicate a EXT-X-VERSION of 6 or higher if it 1881 contains: 1883 o The EXT-X-MAP tag in a Media Playlist that does not contain 1884 EXT-X-I-FRAMES-ONLY. 1886 A Master Playlist MUST indicate a EXT-X-VERSION of 7 or higher if it 1887 contains: 1889 o "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA 1890 tag. 1892 The EXT-X-MEDIA tag and the AUDIO, VIDEO and SUBTITLES attributes of 1893 the EXT-X-STREAM-INF tag are backward compatible to protocol version 1894 1, but playback on older clients may not be desirable. A server MAY 1895 consider indicating a EXT-X-VERSION of 4 or higher in the Master 1896 Playlist but is not required to do so. 1898 The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I 1899 -FRAME-STREAM-INF tags was removed in protocol version 6. 1901 The EXT-X-ALLOW-CACHE tag was removed in protocol version 7. 1903 8. Playlist Examples 1905 8.1. Simple Media Playlist 1907 #EXTM3U 1908 #EXT-X-TARGETDURATION:10 1909 #EXTINF:9.009, 1910 http://media.example.com/first.ts 1911 #EXTINF:9.009, 1912 http://media.example.com/second.ts 1913 #EXTINF:3.003, 1914 http://media.example.com/third.ts 1915 #EXT-X-ENDLIST 1917 8.2. Live Media Playlist, using HTTPS 1919 #EXTM3U 1920 #EXT-X-VERSION:3 1921 #EXT-X-TARGETDURATION:8 1922 #EXT-X-MEDIA-SEQUENCE:2680 1924 #EXTINF:7.975, 1925 https://priv.example.com/fileSequence2680.ts 1926 #EXTINF:7.941, 1927 https://priv.example.com/fileSequence2681.ts 1928 #EXTINF:7.975, 1929 https://priv.example.com/fileSequence2682.ts 1931 8.3. Playlist with encrypted Media Segments 1932 #EXTM3U 1933 #EXT-X-VERSION:3 1934 #EXT-X-MEDIA-SEQUENCE:7794 1935 #EXT-X-TARGETDURATION:15 1937 #EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=52" 1939 #EXTINF:2.833, 1940 http://media.example.com/fileSequence52-A.ts 1941 #EXTINF:15.0, 1942 http://media.example.com/fileSequence52-B.ts 1943 #EXTINF:13.333, 1944 http://media.example.com/fileSequence52-C.ts 1946 #EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=53" 1948 #EXTINF:15.0, 1949 http://media.example.com/fileSequence53-A.ts 1951 8.4. Master Playlist 1953 #EXTM3U 1954 #EXT-X-STREAM-INF:BANDWIDTH=1280000,AVERAGE-BANDWIDTH=1000000 1955 http://example.com/low.m3u8 1956 #EXT-X-STREAM-INF:BANDWIDTH=2560000,AVERAGE-BANDWIDTH=2000000 1957 http://example.com/mid.m3u8 1958 #EXT-X-STREAM-INF:BANDWIDTH=7680000,AVERAGE-BANDWIDTH=6000000 1959 http://example.com/hi.m3u8 1960 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5" 1961 http://example.com/audio-only.m3u8 1963 8.5. Master Playlist with I-Frames 1965 #EXTM3U 1966 #EXT-X-STREAM-INF:BANDWIDTH=1280000 1967 low/audio-video.m3u8 1968 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8" 1969 #EXT-X-STREAM-INF:BANDWIDTH=2560000 1970 mid/audio-video.m3u8 1971 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8" 1972 #EXT-X-STREAM-INF:BANDWIDTH=7680000 1973 hi/audio-video.m3u8 1974 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8" 1975 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5" 1976 audio-only.m3u8 1978 8.6. Master Playlist with Alternative audio 1980 In this example, the CODECS attributes have been condensed for space. 1981 A '\' is used to indicate that the tag continues on the following 1982 line with whitespace removed: 1984 #EXTM3U 1985 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \ 1986 DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \ 1987 URI="main/english-audio.m3u8" 1988 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsch", \ 1989 DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \ 1990 URI="main/german-audio.m3u8" 1991 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \ 1992 DEFAULT=NO,AUTOSELECT=NO,LANGUAGE="en", \ 1993 URI="commentary/audio-only.m3u8" 1994 #EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",AUDIO="aac" 1995 low/video-only.m3u8 1996 #EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",AUDIO="aac" 1997 mid/video-only.m3u8 1998 #EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",AUDIO="aac" 1999 hi/video-only.m3u8 2000 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5",AUDIO="aac" 2001 main/english-audio.m3u8 2003 8.7. Master Playlist with Alternative video 2005 This example shows 3 different video Renditions (Main, Centerfield 2006 and Dugout), and 3 different Variant Streams (low, mid and high). In 2007 this example, clients that did not support the EXT-X-MEDIA tag and 2008 the VIDEO attribute of the EXT-X-STREAM-INF tag would only be able to 2009 play the video Rendition "Main". 2011 Since the EXT-X-STREAM-INF tag has no AUDIO attribute, all video 2012 Renditions would be required to contain the audio. 2014 In this example, the CODECS attributes have been condensed for space. 2015 A '\' is used to indicate that the tag continues on the following 2016 line with whitespace removed: 2018 #EXTM3U 2019 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Main", \ 2020 DEFAULT=YES,URI="low/main/audio-video.m3u8" 2021 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Centerfield", \ 2022 DEFAULT=NO,URI="low/centerfield/audio-video.m3u8" 2023 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Dugout", \ 2024 DEFAULT=NO,URI="low/dugout/audio-video.m3u8" 2026 #EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",VIDEO="low" 2027 low/main/audio-video.m3u8 2029 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Main", \ 2030 DEFAULT=YES,URI="mid/main/audio-video.m3u8" 2031 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Centerfield", \ 2032 DEFAULT=NO,URI="mid/centerfield/audio-video.m3u8" 2033 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Dugout", \ 2034 DEFAULT=NO,URI="mid/dugout/audio-video.m3u8" 2036 #EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",VIDEO="mid" 2037 mid/main/audio-video.m3u8 2039 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Main", \ 2040 DEFAULT=YES,URI="hi/main/audio-video.m3u8" 2041 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Centerfield", \ 2042 DEFAULT=NO,URI="hi/centerfield/audio-video.m3u8" 2043 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Dugout", \ 2044 DEFAULT=NO,URI="hi/dugout/audio-video.m3u8" 2046 #EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",VIDEO="hi" 2047 hi/main/audio-video.m3u8 2049 8.8. Session Data in a Master Playlist 2051 In this example, only the EXT-X-SESSION-DATA is shown: 2053 #EXT-X-SESSION-DATA:DATA-ID="com.example.lyrics",URI="lyrics.json" 2055 #EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="en", \ 2056 VALUE="This is an example" 2057 #EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="sp", \ 2058 VALUE="Este es un ejemplo" 2060 8.9. CHARACTERISTICS attribute containing multiple characteristics 2062 Certain characteristics are valid in combination, as in: 2064 <CODE BEGINS> 2065 CHARACTERISTICS= 2066 "public.accessibility.transcribes-spoken-dialog,public.easy-to-read" 2067 <CODE ENDS> 2069 9. Contributors 2071 Significant contributions to the design of this protocol were made by 2072 Jim Batson, David Biderman, Bill May, Roger Pantos, Alan Tseng, and 2073 Eryk Vershen. Stuart Cheshire helped edit the specification. 2075 10. IANA Considerations 2077 This memo requests that the following MIME type [RFC2046] be 2078 registered with the IANA: 2080 Type name: "application" 2082 Subtype name: "vnd.apple.mpegurl" 2084 Required parameters: (none) 2086 Optional parameters: (none) 2088 Encoding considerations: encoded as UTF-8 text. See Section 4 for 2089 more information. 2091 Security considerations: See Section 11. 2093 Compression: this media type does not employ compression. 2095 Interoperability considerations: There are no byte-ordering issues, 2096 since files are 7- or 8-bit text. Applications could encounter 2097 unrecognized tags, which SHOULD be ignored. 2099 Published specification: see Section 4. 2101 Applications that use this media type: Multimedia applications such 2102 as the iPhone media player in iOS 3.0 and later and QuickTime Player 2103 in Mac OS X version 10.6 and later. 2105 Additional information: files begin with the magic number #EXTM3U. 2106 Filenames normally end with .m3u8 or .m3u (see Section 4). No 2107 Macintosh file type codes have been registered. 2109 Person & email address to contact for further information: David 2110 Singer, singer AT apple.com. 2112 Intended usage: LIMITED USE 2114 Restrictions on usage: (none) 2116 Author: Roger Pantos 2118 Change Controller: David Singer 2120 11. Security Considerations 2122 Since the protocol generally uses HTTP to transfer data, most of the 2123 same security considerations apply. See section 15 of HTTP 2124 [RFC7230]. 2126 Media file parsers are typically subject to "fuzzing" attacks. 2127 Implementors SHOULD pay particular attention to code that will parse 2128 data received from a server and ensure that all possible inputs are 2129 handled correctly. 2131 Playlist files contain URIs, which clients will use to make network 2132 requests of arbitrary entities. Clients SHOULD range-check responses 2133 to prevent buffer overflows. See also the Security Considerations 2134 section of Uniform Resource Identifier (URI): Generic Syntax 2135 [RFC3986]. 2137 Clients SHOULD limit each playback session to a reasonable number of 2138 concurrent downloads (e.g. 4) to avoid contributing to denial-of- 2139 service attacks. 2141 HTTP requests often include session state ("cookies"), which may 2142 contain private user data. Implementations MUST follow cookie 2143 restriction and expiry rules specified by HTTP State Management 2144 Mechanism [RFC6265] to protect themselves from attack. See also the 2145 Security Considerations section of that document, and Use of HTTP 2146 State Management [RFC2964]. 2148 Encryption keys are specified by URI. The delivery of these keys 2149 SHOULD be secured by a mechanism such as HTTP Over TLS [RFC2818] 2150 (formerly SSL) in conjunction with a secure realm or a session token. 2152 12. References 2154 12.1. Normative References 2156 [AC_3] Advanced Television Systems Committee, "ATSC Standard: 2157 A/52:2010: Digital Audio Compression (AC-3) (E-AC-3) 2158 Standard", November 2010, 2159 <http://www.atsc.org/cms/standards/a_52-2010.pdf>. 2161 [AES_128] U.S. Department of Commerce/National Institute of 2162 Standards and Technology, "Advanced Encryption Standard 2163 (AES), FIPS PUB 197", November 2001, <http://csrc.nist 2164 .gov/publications/fips/fips197/fips-197.pdf>. 2166 [CEA608] Consumer Electronics Association, "CEA-608-E: Line 21 Data 2167 Services", April 2008, <http://www.ce.org/Standards/ 2168 Standard-Listings/R4-3-Television-Data-Systems 2169 -Subcommittee/Line-21-Data-Service.aspx>. 2171 [CEA708] Consumer Electronics Association, "CEA-708-E (ANSI): 2172 Digital Television (DTV) Closed Captioning", August 2013, 2173 <http://www.ce.org/Standards/Standard-Listings/ 2174 R4-3-Television-Data-Systems-Subcommittee/CEA-708-D.aspx>. 2176 [H_264] International Telecommunications Union, "Advanced video 2177 coding for generic audiovisual services", January 2012, 2178 <http://www.itu.int/rec/T-REC-H.264>. 2180 [ISO_13818] 2181 International Organization for Standardization, "ISO/IEC 2182 International Standard 13818; Generic coding of moving 2183 pictures and associated audio information", October 2007, 2184 <http://www.iso.org/iso/catalogue_detail?csnumber=44169>. 2186 [ISO_13818_3] 2187 International Organization for Standardization, "ISO/IEC 2188 International Standard 13818-3:1998; Generic coding of 2189 moving pictures and associated audio information - Part 3: 2190 Audio", April 1998, <http://www.iso.org/iso/home/store/ 2191 catalogue_tc/catalogue_detail.htm?csnumber=26797>. 2193 [ISO_13818_7] 2194 International Organization for Standardization, "ISO/IEC 2195 International Standard 13818-3:2006; Generic coding of 2196 moving pictures and associated audio information - Part 7: 2197 Advanced Audio Coding (AAC)", January 2006, 2198 <http://www.iso.org/iso/home/store/catalogue_tc/ 2199 catalogue_detail.htm?csnumber=43345>. 2201 [ISO_14496] 2202 International Organization for Standardization, "ISO/IEC 2203 14496-3:2009 Information technology -- Coding of audio- 2204 visual objects -- Part 3: Audio", 2009, 2205 <http://www.iso.org/iso/catalogue_detail?csnumber=53943>. 2207 [ISO_8601] 2208 International Organization for Standardization, "ISO/IEC 2209 International Standard 8601:2004; Data elements and 2210 interchange formats -- Information interchange -- 2211 Representation of dates and times", December 2004, 2212 <http://www.iso.org/iso/catalogue_detail?csnumber=40874>. 2214 [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 2215 Extensions (MIME) Part Two: Media Types", RFC 2046, 2216 November 1996. 2218 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2219 Requirement Levels", BCP 14, RFC 2119, March 1997. 2221 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 2223 [RFC2964] Moore, K. and N. Freed, "Use of HTTP State Management", 2224 BCP 44, RFC 2964, October 2000. 2226 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 2227 10646", STD 63, RFC 3629, November 2003. 2229 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2230 Resource Identifier (URI): Generic Syntax", STD 66, RFC 2231 3986, January 2005. 2233 [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying 2234 Languages", BCP 47, RFC 5646, September 2009. 2236 [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, 2237 RFC 5652, September 2009. 2239 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 2240 April 2011. 2242 [RFC6381] Gellens, R., Singer, D., and P. Frojdh, "The 'Codecs' and 2243 'Profiles' Parameters for "Bucket" Media Types", RFC 6381, 2244 August 2011. 2246 [RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data 2247 Interchange Format", RFC 7159, March 2014. 2249 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2250 Protocol (HTTP/1.1): Message Syntax and Routing", RFC 2251 7230, DOI 10.17487/RFC7230, June 2014, 2252 <http://www.rfc-editor.org/info/rfc7230>. 2254 [US_ASCII] 2255 American National Standards Institute, "ANSI X3.4-1986, 2256 Information Systems -- Coded Character Sets 7-Bit American 2257 National Standard Code for Information Interchange (7-Bit 2258 ASCII)", December 1986. 2260 [WebVTT] World Wide Web Consortium (W3C), "WebVTT: The Web Video 2261 Text Tracks Format", July 2013, 2262 <http://dev.w3.org/html5/webvtt/>. 2264 12.2. Informative References 2266 [ID3] ID3.org, "The ID3 audio file data tagging format", 2267 <http://www.id3.org/Developer_Information>. 2269 [M3U] Nullsoft, Inc., "The M3U Playlist format, originally 2270 invented for the Winamp media player", 2271 <http://wikipedia.org/wiki/M3U>. 2273 [SampleEnc] 2274 Apple Inc., "MPEG-2 Stream Encryption Format for HTTP Live 2275 Streaming", <https://developer.apple.com/library/ios/ 2276 documentation/AudioVideo/Conceptual/ 2277 HLS_Sample_Encryption/>. 2279 [UTI] Apple Inc., "Uniform Type Identifier", 2280 <http://developer.apple.com/library/ios/#documentation/ 2281 general/conceptual/DevPedia-CocoaCore/ 2282 UniformTypeIdentifier.html>. 2284 Authors' Addresses 2286 Roger Pantos (editor) 2287 Apple Inc. 2288 Cupertino, California 2289 United States 2291 Email: http-live-streaming-review@group.apple.com 2293 William May, Jr. 2294 Apple Inc. 2295 Cupertino, California 2296 United States 2298 Email: http-live-streaming-review@group.apple.com