GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc8216

Independent Submission R. Pantos, Ed. Request for Comments: 8216 Apple, Inc. Category: Informational W. May ISSN: 2070-1721 MLB Advanced Media

                                                           August 2017
                        HTTP Live Streaming

Abstract

 This document describes a protocol for transferring unbounded streams
 of multimedia data.  It specifies the data format of the files and
 the actions to be taken by the server (sender) and the clients
 (receivers) of the streams.  It describes version 7 of this protocol.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8216.

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.
 This document may not be modified, and derivative works of it may not
 be created, except to format it for publication as an RFC or to
 translate it into languages other than English.

Pantos & May Informational [Page 1] RFC 8216 HTTP Live Streaming August 2017

Table of Contents

 1. Introduction to HTTP Live Streaming .............................4
 2. Overview ........................................................4
 3. Media Segments ..................................................6
    3.1. Supported Media Segment Formats ............................6
    3.2. MPEG-2 Transport Streams ...................................7
    3.3. Fragmented MPEG-4 ..........................................7
    3.4. Packed Audio ...............................................8
    3.5. WebVTT .....................................................8
 4. Playlists .......................................................9
    4.1. Definition of a Playlist ..................................10
    4.2. Attribute Lists ...........................................11
    4.3. Playlist Tags .............................................12
         4.3.1. Basic Tags .........................................12
                4.3.1.1. EXTM3U ....................................12
                4.3.1.2. EXT-X-VERSION .............................12
         4.3.2. Media Segment Tags .................................13
                4.3.2.1. EXTINF ....................................13
                4.3.2.2. EXT-X-BYTERANGE ...........................14
                4.3.2.3. EXT-X-DISCONTINUITY .......................14
                4.3.2.4. EXT-X-KEY .................................15
                4.3.2.5. EXT-X-MAP .................................17
                4.3.2.6. EXT-X-PROGRAM-DATE-TIME ...................18
                4.3.2.7. EXT-X-DATERANGE ...........................18
                         4.3.2.7.1. Mapping SCTE-35 into
                                    EXT-X-DATERANGE ................20
         4.3.3. Media Playlist Tags ................................22
                4.3.3.1. EXT-X-TARGETDURATION ......................22
                4.3.3.2. EXT-X-MEDIA-SEQUENCE ......................22
                4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE ..............23
                4.3.3.4. EXT-X-ENDLIST .............................23
                4.3.3.5. EXT-X-PLAYLIST-TYPE .......................24
                4.3.3.6. EXT-X-I-FRAMES-ONLY .......................24
         4.3.4. Master Playlist Tags ...............................25
                4.3.4.1. EXT-X-MEDIA ...............................25
                         4.3.4.1.1. Rendition Groups ...............28
                4.3.4.2. EXT-X-STREAM-INF ..........................29
                         4.3.4.2.1. Alternative Renditions .........32
                4.3.4.3. EXT-X-I-FRAME-STREAM-INF ..................33
                4.3.4.4. EXT-X-SESSION-DATA ........................34
                4.3.4.5. EXT-X-SESSION-KEY .........................35
         4.3.5. Media or Master Playlist Tags ......................35
                4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS ................35
                4.3.5.2. EXT-X-START ...............................36

Pantos & May Informational [Page 2] RFC 8216 HTTP Live Streaming August 2017

 5. Key Files ......................................................37
    5.1. Structure of Key Files ....................................37
    5.2. IV for AES-128 ............................................37
 6. Client/Server Responsibilities .................................37
    6.1. Introduction ..............................................37
    6.2. Server Responsibilities ...................................37
         6.2.1. General Server Responsibilities ....................37
         6.2.2. Live Playlists .....................................40
         6.2.3. Encrypting Media Segments ..........................41
         6.2.4. Providing Variant Streams ..........................42
    6.3. Client Responsibilities ...................................44
         6.3.1. General Client Responsibilities ....................44
         6.3.2. Loading the Media Playlist File ....................44
         6.3.3. Playing the Media Playlist File ....................45
         6.3.4. Reloading the Media Playlist File ..................46
         6.3.5. Determining the Next Segment to Load ...............47
         6.3.6. Decrypting Encrypted Media Segments ................47
 7. Protocol Version Compatibility .................................48
 8. Playlist Examples ..............................................50
    8.1. Simple Media Playlist .....................................50
    8.2. Live Media Playlist Using HTTPS ...........................50
    8.3. Playlist with Encrypted Media Segments ....................51
    8.4. Master Playlist ...........................................51
    8.5. Master Playlist with I-Frames .............................51
    8.6. Master Playlist with Alternative Audio ....................52
    8.7. Master Playlist with Alternative Video ....................52
    8.8. Session Data in a Master Playlist .........................53
    8.9. CHARACTERISTICS Attribute Containing Multiple
         Characteristics ...........................................54
    8.10. EXT-X-DATERANGE Carrying SCTE-35 Tags ....................54
 9. IANA Considerations ............................................54
 10. Security Considerations .......................................55
 11. References ....................................................56
    11.1. Normative References .....................................56
    11.2. Informative References ...................................59
 Contributors ......................................................60
 Authors' Addresses ................................................60

Pantos & May Informational [Page 3] RFC 8216 HTTP Live Streaming August 2017

1. Introduction to HTTP Live Streaming

 HTTP Live Streaming provides a reliable, cost-effective means of
 delivering continuous and long-form video over the Internet.  It
 allows a receiver to adapt the bit rate of the media to the current
 network conditions in order to maintain uninterrupted playback at the
 best possible quality.  It supports interstitial content boundaries.
 It provides a flexible framework for media encryption.  It can
 efficiently offer multiple renditions of the same content, such as
 audio translations.  It offers compatibility with large-scale HTTP
 caching infrastructure to support delivery to large audiences.
 Since the Internet-Draft was first posted in 2009, HTTP Live
 Streaming has been implemented and deployed by a wide array of
 content producers, tools vendors, distributors, and device
 manufacturers.  In the subsequent eight years, the protocol has been
 refined by extensive review and discussion with a variety of media
 streaming implementors.
 The purpose of this document is to facilitate interoperability
 between HTTP Live Streaming implementations by describing the media
 transmission protocol.  Using this protocol, a client can receive a
 continuous stream of media from a server for concurrent presentation.
 This document describes version 7 of the protocol.

2. Overview

 A multimedia presentation is specified by a Uniform Resource
 Identifier (URI) [RFC3986] to a Playlist.
 A Playlist is either a Media Playlist or a Master Playlist.  Both are
 UTF-8 text files containing URIs and descriptive tags.
 A Media Playlist contains a list of Media Segments, which, when
 played sequentially, will play the multimedia presentation.

Pantos & May Informational [Page 4] RFC 8216 HTTP Live Streaming August 2017

 Here is an example of a Media Playlist:
 #EXTM3U
 #EXT-X-TARGETDURATION:10
 #EXTINF:9.009,
 http://media.example.com/first.ts
 #EXTINF:9.009,
 http://media.example.com/second.ts
 #EXTINF:3.003,
 http://media.example.com/third.ts
 The first line is the format identifier tag #EXTM3U.  The line
 containing #EXT-X-TARGETDURATION says that all Media Segments will be
 10 seconds long or less.  Then, three Media Segments are declared.
 The first and second are 9.009 seconds long; the third is 3.003
 seconds.
 To play this Playlist, the client first downloads it and then
 downloads and plays each Media Segment declared within it.  The
 client reloads the Playlist as described in this document to discover
 any added segments.  Data SHOULD be carried over HTTP [RFC7230], but,
 in general, a URI can specify any protocol that can reliably transfer
 the specified resource on demand.
 A more complex presentation can be described by a Master Playlist.  A
 Master Playlist provides a set of Variant Streams, each of which
 describes a different version of the same content.
 A Variant Stream includes a Media Playlist that specifies media
 encoded at a particular bit rate, in a particular format, and at a
 particular resolution for media containing video.
 A Variant Stream can also specify a set of Renditions.  Renditions
 are alternate versions of the content, such as audio produced in
 different languages or video recorded from different camera angles.
 Clients should switch between different Variant Streams to adapt to
 network conditions.  Clients should choose Renditions based on user
 preferences.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

Pantos & May Informational [Page 5] RFC 8216 HTTP Live Streaming August 2017

3. Media Segments

 A Media Playlist contains a series of Media Segments that make up the
 overall presentation.  A Media Segment is specified by a URI and
 optionally a byte range.
 The duration of each Media Segment is indicated in the Media Playlist
 by its EXTINF tag (Section 4.3.2.1).
 Each segment in a Media Playlist has a unique integer Media Sequence
 Number.  The Media Sequence Number of the first segment in the Media
 Playlist is either 0 or declared in the Playlist (Section 4.3.3.2).
 The Media Sequence Number of every other segment is equal to the
 Media Sequence Number of the segment that precedes it plus one.
 Each Media Segment MUST carry the continuation of the encoded
 bitstream from the end of the segment with the previous Media
 Sequence Number, where values in a series such as timestamps and
 Continuity Counters MUST continue uninterrupted.  The only exceptions
 are the first Media Segment ever to appear in a Media Playlist and
 Media Segments that are explicitly signaled as discontinuities
 (Section 4.3.2.3).  Unmarked media discontinuities can trigger
 playback errors.
 Any Media Segment that contains video SHOULD include enough
 information to initialize a video decoder and decode a continuous set
 of frames that includes the final frame in the Segment; network
 efficiency is optimized if there is enough information in the Segment
 to decode all frames in the Segment.  For example, any Media Segment
 containing H.264 video SHOULD contain an Instantaneous Decoding
 Refresh (IDR); frames prior to the first IDR will be downloaded but
 possibly discarded.

3.1. Supported Media Segment Formats

 All Media Segments MUST be in a format described in this section.
 Transport of other media file formats is not defined.
 Some media formats require a common sequence of bytes to initialize a
 parser before a Media Segment can be parsed.  This format-specific
 sequence is called the Media Initialization Section.  The Media
 Initialization Section can be specified by an EXT-X-MAP tag
 (Section 4.3.2.5).  The Media Initialization Section MUST NOT contain
 sample data.

Pantos & May Informational [Page 6] RFC 8216 HTTP Live Streaming August 2017

3.2. MPEG-2 Transport Streams

 MPEG-2 Transport Streams are specified by [ISO_13818].
 The Media Initialization Section of an MPEG-2 Transport Stream
 Segment is a Program Association Table (PAT) followed by a Program
 Map Table (PMT).
 Transport Stream Segments MUST contain a single MPEG-2 Program;
 playback of Multi-Program Transport Streams is not defined.  Each
 Transport Stream Segment MUST contain a PAT and a PMT, or have an
 EXT-X-MAP tag (Section 4.3.2.5) applied to it.  The first two
 Transport Stream packets in a Segment without an EXT-X-MAP tag SHOULD
 be a PAT and a PMT.

3.3. Fragmented MPEG-4

 MPEG-4 Fragments are specified by the ISO Base Media File Format
 [ISOBMFF].  Unlike regular MPEG-4 files that have a Movie Box
 ('moov') that contains sample tables and a Media Data Box ('mdat')
 containing the corresponding samples, an MPEG-4 Fragment consists of
 a Movie Fragment Box ('moof') containing a subset of the sample table
 and a Media Data Box containing those samples.  Use of MPEG-4
 Fragments does require a Movie Box for initialization, but that Movie
 Box contains only non-sample-specific information such as track and
 sample descriptions.
 A Fragmented MPEG-4 (fMP4) Segment is a "segment" as defined by
 Section 3 of [ISOBMFF], including the constraints on Media Data Boxes
 in Section 8.16 of [ISOBMFF].
 The Media Initialization Section for an fMP4 Segment is an ISO Base
 Media File that can initialize a parser for that Segment.
 Broadly speaking, fMP4 Segments and Media Initialization Sections are
 [ISOBMFF] files that also satisfy the constraints described in this
 section.
 The Media Initialization Section for an fMP4 Segment MUST contain a
 File Type Box ('ftyp') containing a brand that is compatible with
 'iso6' or higher.  The File Type Box MUST be followed by a Movie Box.
 The Movie Box MUST contain a Track Box ('trak') for every Track
 Fragment Box ('traf') in the fMP4 Segment, with matching track_ID.
 Each Track Box SHOULD contain a sample table, but its sample count
 MUST be zero.  Movie Header Boxes ('mvhd') and Track Header Boxes
 ('tkhd') MUST have durations of zero.  A Movie Extends Box ('mvex')
 MUST follow the last Track Box.  Note that a Common Media Application
 Format (CMAF) Header [CMAF] meets all these requirements.

Pantos & May Informational [Page 7] RFC 8216 HTTP Live Streaming August 2017

 In an fMP4 Segment, every Track Fragment Box MUST contain a Track
 Fragment Decode Time Box ('tfdt'). fMP4 Segments MUST use movie-
 fragment-relative addressing. fMP4 Segments MUST NOT use external
 data references.  Note that a CMAF Segment meets these requirements.
 An fMP4 Segment in a Playlist containing the EXT-X-I-FRAMES-ONLY tag
 (Section 4.3.3.6) MAY omit the portion of the Media Data Box
 following the intra-coded frame (I-frame) sample data.
 Each fMP4 Segment in a Media Playlist MUST have an EXT-X-MAP tag
 applied to it.

3.4. Packed Audio

 A Packed Audio Segment contains encoded audio samples and ID3 tags
 that are simply packed together with minimal framing and no per-
 sample timestamps.  Supported Packed Audio formats are Advanced Audio
 Coding (AAC) with Audio Data Transport Stream (ADTS) framing
 [ISO_13818_7], MP3 [ISO_13818_3], AC-3 [AC_3], and Enhanced AC-3
 [AC_3].
 A Packed Audio Segment has no Media Initialization Section.
 Each Packed Audio Segment MUST signal the timestamp of its first
 sample with an ID3 Private frame (PRIV) tag [ID3] at the beginning of
 the segment.  The ID3 PRIV owner identifier MUST be
 "com.apple.streaming.transportStreamTimestamp".  The ID3 payload MUST
 be a 33-bit MPEG-2 Program Elementary Stream timestamp expressed as a
 big-endian eight-octet number, with the upper 31 bits set to zero.
 Clients SHOULD NOT play Packed Audio Segments without this ID3 tag.

3.5. WebVTT

 A WebVTT Segment is a section of a WebVTT [WebVTT] file.  WebVTT
 Segments carry subtitles.
 The Media Initialization Section of a WebVTT Segment is the WebVTT
 header.
 Each WebVTT Segment MUST contain all subtitle cues that are intended
 to be displayed during the period indicated by the segment EXTINF
 duration.  The start time offset and end time offset of each cue MUST
 indicate the total display time for that cue, even if part of the cue
 time range is outside the Segment period.  A WebVTT Segment MAY
 contain no cues; this indicates that no subtitles are to be displayed
 during that period.

Pantos & May Informational [Page 8] RFC 8216 HTTP Live Streaming August 2017

 Each WebVTT Segment MUST either start with a WebVTT header or have an
 EXT-X-MAP tag applied to it.
 In order to synchronize timestamps between audio/video and subtitles,
 an X-TIMESTAMP-MAP metadata header SHOULD be added to each WebVTT
 header.  This header maps WebVTT cue timestamps to MPEG-2 (PES)
 timestamps in other Renditions of the Variant Stream.  Its format is:
 X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<MPEG-2 time>
 e.g., X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
 The cue timestamp in the LOCAL attribute MAY fall outside the range
 of time covered by the segment.
 If a WebVTT segment does not have the X-TIMESTAMP-MAP, the client
 MUST assume that the WebVTT cue time of 0 maps to an MPEG-2 timestamp
 of 0.
 When synchronizing WebVTT with PES timestamps, clients SHOULD account
 for cases where the 33-bit PES timestamps have wrapped and the WebVTT
 cue times have not.

4. Playlists

 This section describes the Playlist files used by HTTP Live
 Streaming.  In this section, "MUST" and "MUST NOT" specify the rules
 for the syntax and structure of legal Playlist files.  Playlists that
 violate these rules are invalid; clients MUST fail to parse them.
 See Section 6.3.2.
 The format of the Playlist files is derived from the M3U [M3U]
 playlist file format and inherits two tags from that earlier file
 format: EXTM3U (Section 4.3.1.1) and EXTINF (Section 4.3.2.1).
 In the specification of tag syntax, a string enclosed by <>
 identifies a tag parameter; its specific format is described in its
 tag definition.  If a parameter is further surrounded by [], it is
 optional; otherwise, it is required.
 Each Playlist file MUST be identifiable either by the path component
 of its URI or by HTTP Content-Type.  In the first case, the path MUST
 end with either .m3u8 or .m3u.  In the second, the HTTP Content-Type
 MUST be "application/vnd.apple.mpegurl" or "audio/mpegurl".  Clients
 SHOULD refuse to parse Playlists that are not so identified.

Pantos & May Informational [Page 9] RFC 8216 HTTP Live Streaming August 2017

4.1. Definition of a Playlist

 Playlist files MUST be encoded in UTF-8 [RFC3629].  They MUST NOT
 contain any Byte Order Mark (BOM); clients SHOULD fail to parse
 Playlists that contain a BOM or do not parse as UTF-8.  Playlist
 files MUST NOT contain UTF-8 control characters (U+0000 to U+001F and
 U+007F to U+009F), with the exceptions of CR (U+000D) and LF
 (U+000A).  All character sequences MUST be normalized according to
 Unicode normalization form "NFC" [UNICODE].  Note that US-ASCII
 [US_ASCII] conforms to these rules.
 Lines in a Playlist file are terminated by either a single line feed
 character or a carriage return character followed by a line feed
 character.  Each line is a URI, is blank, or starts with the
 character '#'.  Blank lines are ignored.  Whitespace MUST NOT be
 present, except for elements in which it is explicitly specified.
 Lines that start with the character '#' are either comments or tags.
 Tags begin with #EXT.  They are case sensitive.  All other lines that
 begin with '#' are comments and SHOULD be ignored.
 A URI line identifies a Media Segment or a Playlist file (see
 Section 4.3.4.2).  Each Media Segment is specified by a URI and the
 tags that apply to it.
 A Playlist is a Media Playlist if all URI lines in the Playlist
 identify Media Segments.  A Playlist is a Master Playlist if all URI
 lines in the Playlist identify Media Playlists.  A Playlist MUST be
 either a Media Playlist or a Master Playlist; all other Playlists are
 invalid.
 A URI in a Playlist, whether it is a URI line or part of a tag, MAY
 be relative.  Any relative URI is considered to be relative to the
 URI of the Playlist that contains it.
 The duration of a Media Playlist is the sum of the durations of the
 Media Segments within it.
 The segment bit rate of a Media Segment is the size of the Media
 Segment divided by its EXTINF duration (Section 4.3.2.1).  Note that
 this includes container overhead but does not include overhead
 imposed by the delivery system, such as HTTP, TCP, or IP headers.
 The peak segment bit rate of a Media Playlist is the largest bit rate
 of any contiguous set of segments whose total duration is between 0.5
 and 1.5 times the target duration.  The bit rate of a set is
 calculated by dividing the sum of the segment sizes by the sum of the
 segment durations.

Pantos & May Informational [Page 10] RFC 8216 HTTP Live Streaming August 2017

 The average segment bit rate of a Media Playlist is the sum of the
 sizes (in bits) of every Media Segment in the Media Playlist, divided
 by the Media Playlist duration.  Note that this includes container
 overhead, but not HTTP or other overhead imposed by the delivery
 system.

4.2. Attribute Lists

 Certain tags have values that are attribute-lists.  An attribute-list
 is a comma-separated list of attribute/value pairs with no
 whitespace.
 An attribute/value pair has the following syntax:
 AttributeName=AttributeValue
 An AttributeName is an unquoted string containing characters from the
 set [A..Z], [0..9] and '-'.  Therefore, AttributeNames contain only
 uppercase letters, not lowercase.  There MUST NOT be any whitespace
 between the AttributeName and the '=' character, nor between the '='
 character and the AttributeValue.
 An AttributeValue is one of the following:
 o  decimal-integer: an unquoted string of characters from the set
    [0..9] expressing an integer in base-10 arithmetic in the range
    from 0 to 2^64-1 (18446744073709551615).  A decimal-integer may be
    from 1 to 20 characters long.
 o  hexadecimal-sequence: an unquoted string of characters from the
    set [0..9] and [A..F] that is prefixed with 0x or 0X.  The maximum
    length of a hexadecimal-sequence depends on its AttributeNames.
 o  decimal-floating-point: an unquoted string of characters from the
    set [0..9] and '.' that expresses a non-negative floating-point
    number in decimal positional notation.
 o  signed-decimal-floating-point: an unquoted string of characters
    from the set [0..9], '-', and '.' that expresses a signed
    floating-point number in decimal positional notation.
 o  quoted-string: a string of characters within a pair of double
    quotes (0x22).  The following characters MUST NOT appear in a
    quoted-string: line feed (0xA), carriage return (0xD), or double
    quote (0x22).  Quoted-string AttributeValues SHOULD be constructed
    so that byte-wise comparison is sufficient to test two quoted-
    string AttributeValues for equality.  Note that this implies case-
    sensitive comparison.

Pantos & May Informational [Page 11] RFC 8216 HTTP Live Streaming August 2017

 o  enumerated-string: an unquoted character string from a set that is
    explicitly defined by the AttributeName.  An enumerated-string
    will never contain double quotes ("), commas (,), or whitespace.
 o  decimal-resolution: two decimal-integers separated by the "x"
    character.  The first integer is a horizontal pixel dimension
    (width); the second is a vertical pixel dimension (height).
 The type of the AttributeValue for a given AttributeName is specified
 by the attribute definition.
 A given AttributeName MUST NOT appear more than once in a given
 attribute-list.  Clients SHOULD refuse to parse such Playlists.

4.3. Playlist Tags

 Playlist tags specify either global parameters of the Playlist or
 information about the Media Segments or Media Playlists that appear
 after them.

4.3.1. Basic Tags

 These tags are allowed in both Media Playlists and Master Playlists.

4.3.1.1. EXTM3U

 The EXTM3U tag indicates that the file is an Extended M3U [M3U]
 Playlist file.  It MUST be the first line of every Media Playlist and
 every Master Playlist.  Its format is:
 #EXTM3U

4.3.1.2. EXT-X-VERSION

 The EXT-X-VERSION tag indicates the compatibility version of the
 Playlist file, its associated media, and its server.
 The EXT-X-VERSION tag applies to the entire Playlist file.  Its
 format is:
 #EXT-X-VERSION:<n>
 where n is an integer indicating the protocol compatibility version
 number.

Pantos & May Informational [Page 12] RFC 8216 HTTP Live Streaming August 2017

 It MUST appear in all Playlists containing tags or attributes that
 are not compatible with protocol version 1 to support
 interoperability with older clients.  Section 7 specifies the minimum
 value of the compatibility version number for any given Playlist
 file.
 A Playlist file MUST NOT contain more than one EXT-X-VERSION tag.  If
 a client encounters a Playlist with multiple EXT-X-VERSION tags, it
 MUST fail to parse it.

4.3.2. Media Segment Tags

 Each Media Segment is specified by a series of Media Segment tags
 followed by a URI.  Some Media Segment tags apply to just the next
 segment; others apply to all subsequent segments until another
 instance of the same tag.
 A Media Segment tag MUST NOT appear in a Master Playlist.  Clients
 MUST fail to parse Playlists that contain both Media Segment tags and
 Master Playlist tags (Section 4.3.4).

4.3.2.1. EXTINF

 The EXTINF tag specifies the duration of a Media Segment.  It applies
 only to the next Media Segment.  This tag is REQUIRED for each Media
 Segment.  Its format is:
 #EXTINF:<duration>,[<title>]
 where duration is a decimal-floating-point or decimal-integer number
 (as described in Section 4.2) that specifies the duration of the
 Media Segment in seconds.  Durations SHOULD be decimal-floating-
 point, with enough accuracy to avoid perceptible error when segment
 durations are accumulated.  However, if the compatibility version
 number is less than 3, durations MUST be integers.  Durations that
 are reported as integers SHOULD be rounded to the nearest integer.
 The remainder of the line following the comma is an optional human-
 readable informative title of the Media Segment expressed as UTF-8
 text.

Pantos & May Informational [Page 13] RFC 8216 HTTP Live Streaming August 2017

4.3.2.2. EXT-X-BYTERANGE

 The EXT-X-BYTERANGE tag indicates that a Media Segment is a sub-range
 of the resource identified by its URI.  It applies only to the next
 URI line that follows it in the Playlist.  Its format is:
 #EXT-X-BYTERANGE:<n>[@<o>]
 where n is a decimal-integer indicating the length of the sub-range
 in bytes.  If present, o is a decimal-integer indicating the start of
 the sub-range, as a byte offset from the beginning of the resource.
 If o is not present, the sub-range begins at the next byte following
 the sub-range of the previous Media Segment.
 If o is not present, a previous Media Segment MUST appear in the
 Playlist file and MUST be a sub-range of the same media resource, or
 the Media Segment is undefined and the client MUST fail to parse the
 Playlist.
 A Media Segment without an EXT-X-BYTERANGE tag consists of the entire
 resource identified by its URI.
 Use of the EXT-X-BYTERANGE tag REQUIRES a compatibility version
 number of 4 or greater.

4.3.2.3. EXT-X-DISCONTINUITY

 The EXT-X-DISCONTINUITY tag indicates a discontinuity between the
 Media Segment that follows it and the one that preceded it.
 Its format is:
 #EXT-X-DISCONTINUITY
 The EXT-X-DISCONTINUITY tag MUST be present if there is a change in
 any of the following characteristics:
 o  file format
 o  number, type, and identifiers of tracks
 o  timestamp sequence

Pantos & May Informational [Page 14] RFC 8216 HTTP Live Streaming August 2017

 The EXT-X-DISCONTINUITY tag SHOULD be present if there is a change in
 any of the following characteristics:
 o  encoding parameters
 o  encoding sequence
 See Sections 3, 6.2.1, and 6.3.3 for more information about the EXT-
 X-DISCONTINUITY tag.

4.3.2.4. EXT-X-KEY

 Media Segments MAY be encrypted.  The EXT-X-KEY tag specifies how to
 decrypt them.  It applies to every Media Segment and to every Media
 Initialization Section declared by an EXT-X-MAP tag that appears
 between it and the next EXT-X-KEY tag in the Playlist file with the
 same KEYFORMAT attribute (or the end of the Playlist file).  Two or
 more EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to
 the same Media Segment if they ultimately produce the same decryption
 key.  The format is:
 #EXT-X-KEY:<attribute-list>
 The following attributes are defined:
    METHOD
    The value is an enumerated-string that specifies the encryption
    method.  This attribute is REQUIRED.
    The methods defined are: NONE, AES-128, and SAMPLE-AES.
    An encryption method of NONE means that Media Segments are not
    encrypted.  If the encryption method is NONE, other attributes
    MUST NOT be present.
    An encryption method of AES-128 signals that Media Segments are
    completely encrypted using the Advanced Encryption Standard (AES)
    [AES_128] with a 128-bit key, Cipher Block Chaining (CBC), and
    Public-Key Cryptography Standards #7 (PKCS7) padding [RFC5652].
    CBC is restarted on each segment boundary, using either the
    Initialization Vector (IV) attribute value or the Media Sequence
    Number as the IV; see Section 5.2.
    An encryption method of SAMPLE-AES means that the Media Segments
    contain media samples, such as audio or video, that are encrypted
    using the Advanced Encryption Standard [AES_128].  How these media
    streams are encrypted and encapsulated in a segment depends on the

Pantos & May Informational [Page 15] RFC 8216 HTTP Live Streaming August 2017

    media encoding and the media format of the segment.  fMP4 Media
    Segments are encrypted using the 'cbcs' scheme of Common
    Encryption [COMMON_ENC].  Encryption of other Media Segment
    formats containing H.264 [H_264], AAC [ISO_14496], AC-3 [AC_3],
    and Enhanced AC-3 [AC_3] media streams is described in the HTTP
    Live Streaming (HLS) Sample Encryption specification [SampleEnc].
    The IV attribute MAY be present; see Section 5.2.
    URI
    The value is a quoted-string containing a URI that specifies how
    to obtain the key.  This attribute is REQUIRED unless the METHOD
    is NONE.
    IV
    The value is a hexadecimal-sequence that specifies a 128-bit
    unsigned integer Initialization Vector to be used with the key.
    Use of the IV attribute REQUIRES a compatibility version number of
    2 or greater.  See Section 5.2 for when the IV attribute is used.
    KEYFORMAT
    The value is a quoted-string that specifies how the key is
    represented in the resource identified by the URI; see Section 5
    for more detail.  This attribute is OPTIONAL; its absence
    indicates an implicit value of "identity".  Use of the KEYFORMAT
    attribute REQUIRES a compatibility version number of 5 or greater.
    KEYFORMATVERSIONS
    The value is a quoted-string containing one or more positive
    integers separated by the "/" character (for example, "1", "1/2",
    or "1/2/5").  If more than one version of a particular KEYFORMAT
    is defined, this attribute can be used to indicate which
    version(s) this instance complies with.  This attribute is
    OPTIONAL; if it is not present, its value is considered to be "1".
    Use of the KEYFORMATVERSIONS attribute REQUIRES a compatibility
    version number of 5 or greater.
 If the Media Playlist file does not contain an EXT-X-KEY tag, then
 Media Segments are not encrypted.
 See Section 5 for the format of the Key file and Sections 5.2, 6.2.3,
 and 6.3.6 for additional information on Media Segment encryption.

Pantos & May Informational [Page 16] RFC 8216 HTTP Live Streaming August 2017

4.3.2.5. EXT-X-MAP

 The EXT-X-MAP tag specifies how to obtain the Media Initialization
 Section (Section 3) required to parse the applicable Media Segments.
 It applies to every Media Segment that appears after it in the
 Playlist until the next EXT-X-MAP tag or until the end of the
 Playlist.
 Its format is:
 #EXT-X-MAP:<attribute-list>
 The following attributes are defined:
    URI
    The value is a quoted-string containing a URI that identifies a
    resource that contains the Media Initialization Section.  This
    attribute is REQUIRED.
    BYTERANGE
    The value is a quoted-string specifying a byte range into the
    resource identified by the URI attribute.  This range SHOULD
    contain only the Media Initialization Section.  The format of the
    byte range is described in Section 4.3.2.2.  This attribute is
    OPTIONAL; if it is not present, the byte range is the entire
    resource indicated by the URI.
 An EXT-X-MAP tag SHOULD be supplied for Media Segments in Playlists
 with the EXT-X-I-FRAMES-ONLY tag when the first Media Segment (i.e.,
 I-frame) in the Playlist (or the first segment following an EXT-
 X-DISCONTINUITY tag) does not immediately follow the Media
 Initialization Section at the beginning of its resource.
 Use of the EXT-X-MAP tag in a Media Playlist that contains the EXT-
 X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 5 or
 greater.  Use of the EXT-X-MAP tag in a Media Playlist that DOES NOT
 contain the EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility version
 number of 6 or greater.
 If the Media Initialization Section declared by an EXT-X-MAP tag is
 encrypted with a METHOD of AES-128, the IV attribute of the EXT-X-KEY
 tag that applies to the EXT-X-MAP is REQUIRED.

Pantos & May Informational [Page 17] RFC 8216 HTTP Live Streaming August 2017

4.3.2.6. EXT-X-PROGRAM-DATE-TIME

 The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a
 Media Segment with an absolute date and/or time.  It applies only to
 the next Media Segment.  Its format is:
 #EXT-X-PROGRAM-DATE-TIME:<date-time-msec>
 where date-time-msec is an ISO/IEC 8601:2004 [ISO_8601] date/time
 representation, such as YYYY-MM-DDThh:mm:ss.SSSZ.  It SHOULD indicate
 a time zone and fractional parts of seconds, to millisecond accuracy.
 For example:
 #EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00
 See Sections 6.2.1 and 6.3.3 for more information on the EXT-X-
 PROGRAM-DATE-TIME tag.

4.3.2.7. EXT-X-DATERANGE

 The EXT-X-DATERANGE tag associates a Date Range (i.e., a range of
 time defined by a starting and ending date) with a set of attribute/
 value pairs.  Its format is:
 #EXT-X-DATERANGE:<attribute-list>
 where the defined attributes are:
    ID
    A quoted-string that uniquely identifies a Date Range in the
    Playlist.  This attribute is REQUIRED.
    CLASS
    A client-defined quoted-string that specifies some set of
    attributes and their associated value semantics.  All Date Ranges
    with the same CLASS attribute value MUST adhere to these
    semantics.  This attribute is OPTIONAL.
    START-DATE
    A quoted-string containing the ISO-8601 date at which the Date
    Range begins.  This attribute is REQUIRED.

Pantos & May Informational [Page 18] RFC 8216 HTTP Live Streaming August 2017

    END-DATE
    A quoted-string containing the ISO-8601 date at which the Date
    Range ends.  It MUST be equal to or later than the value of the
    START-DATE attribute.  This attribute is OPTIONAL.
    DURATION
    The duration of the Date Range expressed as a decimal-floating-
    point number of seconds.  It MUST NOT be negative.  A single
    instant in time (e.g., crossing a finish line) SHOULD be
    represented with a duration of 0.  This attribute is OPTIONAL.
    PLANNED-DURATION
    The expected duration of the Date Range expressed as a decimal-
    floating-point number of seconds.  It MUST NOT be negative.  This
    attribute SHOULD be used to indicate the expected duration of a
    Date Range whose actual duration is not yet known.  It is
    OPTIONAL.
    X-<client-attribute>
    The "X-" prefix defines a namespace reserved for client-defined
    attributes.  The client-attribute MUST be a legal AttributeName.
    Clients SHOULD use a reverse-DNS syntax when defining their own
    attribute names to avoid collisions.  The attribute value MUST be
    a quoted-string, a hexadecimal-sequence, or a decimal-floating-
    point.  An example of a client-defined attribute is X-COM-EXAMPLE-
    AD-ID="XYZ123".  These attributes are OPTIONAL.
    SCTE35-CMD, SCTE35-OUT, SCTE35-IN
    Used to carry SCTE-35 data; see Section 4.3.2.7.1 for more
    information.  These attributes are OPTIONAL.
    END-ON-NEXT
    An enumerated-string whose value MUST be YES.  This attribute
    indicates that the end of the range containing it is equal to the
    START-DATE of its Following Range.  The Following Range is the
    Date Range of the same CLASS that has the earliest START-DATE
    after the START-DATE of the range in question.  This attribute is
    OPTIONAL.
 An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST have a
 CLASS attribute.  Other EXT-X-DATERANGE tags with the same CLASS
 attribute MUST NOT specify Date Ranges that overlap.

Pantos & May Informational [Page 19] RFC 8216 HTTP Live Streaming August 2017

 An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST NOT
 contain DURATION or END-DATE attributes.
 A Date Range with neither a DURATION, an END-DATE, nor an END-ON-
 NEXT=YES attribute has an unknown duration, even if it has a PLANNED-
 DURATION.
 If a Playlist contains an EXT-X-DATERANGE tag, it MUST also contain
 at least one EXT-X-PROGRAM-DATE-TIME tag.
 If a Playlist contains two EXT-X-DATERANGE tags with the same ID
 attribute value, then any AttributeName that appears in both tags
 MUST have the same AttributeValue.
 If a Date Range contains both a DURATION attribute and an END-DATE
 attribute, the value of the END-DATE attribute MUST be equal to the
 value of the START-DATE attribute plus the value of the DURATION
 attribute.
 Clients SHOULD ignore EXT-X-DATERANGE tags with illegal syntax.

4.3.2.7.1. Mapping SCTE-35 into EXT-X-DATERANGE

 Splice information carried in source media according to the SCTE-35
 specification [SCTE35] MAY be represented in a Media Playlist using
 EXT-X-DATERANGE tags.
 Each SCTE-35 splice_info_section() containing a splice_null(),
 splice_schedule(), bandwidth_reservation(), or private_cmd() SHOULD
 be represented by an EXT-X-DATERANGE tag with an SCTE35-CMD attribute
 whose value is the big-endian binary representation of the
 splice_info_section(), expressed as a hexadecimal-sequence.
 An SCTE-35 splice out/in pair signaled by a pair of splice_insert()
 commands SHOULD be represented by one or more EXT-X-DATERANGE tags
 carrying the same ID attribute, which MUST be unique to that splice
 out/in pair.  The "out" splice_info_section() (with
 out_of_network_indicator set to 1) MUST be placed in an SCTE35-OUT
 attribute, with the same formatting as SCTE35-CMD.  The "in"
 splice_info_section() (with out_of_network_indicator set to 0) MUST
 be placed in an SCTE35-IN attribute, with the same formatting as
 SCTE35-CMD.
 An SCTE-35 splice out/in pair signaled by a pair of time_signal()
 commands, each carrying a single segmentation_descriptor(), SHOULD be
 represented by one or more EXT-X-DATERANGE tags carrying the same ID
 attribute, which MUST be unique to that splice out/in pair.  The

Pantos & May Informational [Page 20] RFC 8216 HTTP Live Streaming August 2017

 "out" splice_info_section() MUST be placed in an SCTE35-OUT
 attribute; the "in" splice_info_section() MUST be placed in an
 SCTE35-IN attribute.
 Different types of segmentation, as indicated by the
 segmentation_type_id in the segmentation_descriptor(), SHOULD be
 represented by separate EXT-X-DATERANGE tags, even if two or more
 segmentation_descriptor()s arrive in the same splice_info_section().
 In that case, each EXT-X-DATERANGE tag will have an SCTE35-OUT,
 SCTE35-IN, or SCTE35-CMD attribute whose value is the entire
 splice_info_section().
 An SCTE-35 time_signal() command that does not signal a splice out or
 in point SHOULD be represented by an EXT-X-DATERANGE tag with an
 SCTE35-CMD attribute.
 The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-OUT
 attribute MUST be the date and time that corresponds to the program
 time of that splice.
 The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-CMD
 MUST be the date and time specified by the splice_time() in the
 command or the program time at which the command appeared in the
 source stream if the command does not specify a splice_time().
 An EXT-X-DATERANGE tag containing an SCTE35-OUT attribute MAY contain
 a PLANNED-DURATION attribute.  Its value MUST be the planned duration
 of the splice.
 The DURATION of an EXT-X-DATERANGE tag containing an SCTE35-IN
 attribute MUST be the actual (not planned) program duration between
 the corresponding out-point and that in-point.
 The END-DATE of an EXT-X-DATERANGE tag containing an SCTE35-IN
 attribute MUST be the actual (not planned) program date and time of
 that in-point.
 If the actual end date and time is not known when an SCTE35-OUT
 attribute is added to the Playlist, the DURATION attribute and the
 END-TIME attribute MUST NOT be present; the actual end date of the
 splice SHOULD be signaled by another EXT-X-DATERANGE tag once it has
 been established.
 A canceled splice SHOULD NOT appear in the Playlist as an EXT-
 X-DATERANGE tag.

Pantos & May Informational [Page 21] RFC 8216 HTTP Live Streaming August 2017

 An EXT-X-DATERANGE tag announcing a splice SHOULD be added to a
 Playlist at the same time as the last pre-splice Media Segment, or
 earlier if possible.
 The ID attribute of an EXT-X-DATERANGE tag MAY contain a
 splice_event_id and/or a segmentation_event_id, but it MUST be unique
 in the Playlist.  If there is a possibility that an SCTE-35 id will
 be reused, the ID attribute value MUST include disambiguation, such
 as a date or sequence number.

4.3.3. Media Playlist Tags

 Media Playlist tags describe global parameters of the Media Playlist.
 There MUST NOT be more than one Media Playlist tag of each type in
 any Media Playlist.
 A Media Playlist tag MUST NOT appear in a Master Playlist.

4.3.3.1. EXT-X-TARGETDURATION

 The EXT-X-TARGETDURATION tag specifies the maximum Media Segment
 duration.  The EXTINF duration of each Media Segment in the Playlist
 file, when rounded to the nearest integer, MUST be less than or equal
 to the target duration; longer segments can trigger playback stalls
 or other errors.  It applies to the entire Playlist file.  Its format
 is:
 #EXT-X-TARGETDURATION:<s>
 where s is a decimal-integer indicating the target duration in
 seconds.  The EXT-X-TARGETDURATION tag is REQUIRED.

4.3.3.2. EXT-X-MEDIA-SEQUENCE

 The EXT-X-MEDIA-SEQUENCE tag indicates the Media Sequence Number of
 the first Media Segment that appears in a Playlist file.  Its format
 is:
 #EXT-X-MEDIA-SEQUENCE:<number>
 where number is a decimal-integer.
 If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
 tag, then the Media Sequence Number of the first Media Segment in the
 Media Playlist SHALL be considered to be 0.  A client MUST NOT assume
 that segments with the same Media Sequence Number in different Media
 Playlists contain matching content (see Section 6.3.2).

Pantos & May Informational [Page 22] RFC 8216 HTTP Live Streaming August 2017

 A URI for a Media Segment is not required to contain its Media
 Sequence Number.
 See Sections 6.2.1 and 6.3.5 for more information on setting the EXT-
 X-MEDIA-SEQUENCE tag.
 The EXT-X-MEDIA-SEQUENCE tag MUST appear before the first Media
 Segment in the Playlist.

4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE

 The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between
 different Renditions of the same Variant Stream or different Variant
 Streams that have EXT-X-DISCONTINUITY tags in their Media Playlists.
 Its format is:
 #EXT-X-DISCONTINUITY-SEQUENCE:<number>
 where number is a decimal-integer.
 If the Media Playlist does not contain an EXT-X-DISCONTINUITY-
 SEQUENCE tag, then the Discontinuity Sequence Number of the first
 Media Segment in the Playlist SHALL be considered to be 0.
 The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before the first
 Media Segment in the Playlist.
 The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any EXT-
 X-DISCONTINUITY tag.
 See Sections 6.2.1 and 6.2.2 for more information about setting the
 value of the EXT-X-DISCONTINUITY-SEQUENCE tag.

4.3.3.4. EXT-X-ENDLIST

 The EXT-X-ENDLIST tag indicates that no more Media Segments will be
 added to the Media Playlist file.  It MAY occur anywhere in the Media
 Playlist file.  Its format is:
 #EXT-X-ENDLIST

Pantos & May Informational [Page 23] RFC 8216 HTTP Live Streaming August 2017

4.3.3.5. EXT-X-PLAYLIST-TYPE

 The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
 Media Playlist file.  It applies to the entire Media Playlist file.
 It is OPTIONAL.  Its format is:
 #EXT-X-PLAYLIST-TYPE:<type-enum>
 where type-enum is either EVENT or VOD.
 Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE
 tag.
 If the EXT-X-PLAYLIST-TYPE value is EVENT, Media Segments can only be
 added to the end of the Media Playlist.  If the EXT-X-PLAYLIST-TYPE
 value is Video On Demand (VOD), the Media Playlist cannot change.
 If the EXT-X-PLAYLIST-TYPE tag is omitted from a Media Playlist, the
 Playlist can be updated according to the rules in Section 6.2.1 with
 no additional restrictions.  For example, a live Playlist
 (Section 6.2.2) MAY be updated to remove Media Segments in the order
 that they appeared.

4.3.3.6. EXT-X-I-FRAMES-ONLY

 The EXT-X-I-FRAMES-ONLY tag indicates that each Media Segment in the
 Playlist describes a single I-frame.  I-frames are encoded video
 frames whose encoding does not depend on any other frame.  I-frame
 Playlists can be used for trick play, such as fast forward, rapid
 reverse, and scrubbing.
 The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist.  Its
 format is:
 #EXT-X-I-FRAMES-ONLY
 In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the Media Segment
 duration (EXTINF tag value) is the time between the presentation time
 of the I-frame in the Media Segment and the presentation time of the
 next I-frame in the Playlist, or the end of the presentation if it is
 the last I-frame in the Playlist.
 Media resources containing I-frame segments MUST begin with either a
 Media Initialization Section (Section 3) or be accompanied by an EXT-
 X-MAP tag indicating the Media Initialization Section so that clients
 can load and decode I-frame segments in any order.  The byte range of
 an I-frame segment with an EXT-X-BYTERANGE tag applied to it
 (Section 4.3.2.2) MUST NOT include its Media Initialization Section;

Pantos & May Informational [Page 24] RFC 8216 HTTP Live Streaming August 2017

 clients can assume that the Media Initialization Section is defined
 by the EXT-X-MAP tag or is located from the start of the resource to
 the offset of the first I-frame segment in that resource.
 Use of the EXT-X-I-FRAMES-ONLY REQUIRES a compatibility version
 number of 4 or greater.

4.3.4. Master Playlist Tags

 Master Playlist tags define the Variant Streams, Renditions, and
 other global parameters of the presentation.
 Master Playlist tags MUST NOT appear in a Media Playlist; clients
 MUST fail to parse any Playlist that contains both a Master Playlist
 tag and either a Media Playlist tag or a Media Segment tag.

4.3.4.1. EXT-X-MEDIA

 The EXT-X-MEDIA tag is used to relate Media Playlists that contain
 alternative Renditions (Section 4.3.4.2.1) of the same content.  For
 example, three EXT-X-MEDIA tags can be used to identify audio-only
 Media Playlists that contain English, French, and Spanish Renditions
 of the same presentation.  Or, two EXT-X-MEDIA tags can be used to
 identify video-only Media Playlists that show two different camera
 angles.
 Its format is:
 #EXT-X-MEDIA:<attribute-list>
 The following attributes are defined:
    TYPE
    The value is an enumerated-string; valid strings are AUDIO, VIDEO,
    SUBTITLES, and CLOSED-CAPTIONS.  This attribute is REQUIRED.
    Typically, closed-caption [CEA608] media is carried in the video
    stream.  Therefore, an EXT-X-MEDIA tag with TYPE of CLOSED-
    CAPTIONS does not specify a Rendition; the closed-caption media is
    present in the Media Segments of every video Rendition.
    URI
    The value is a quoted-string containing a URI that identifies the
    Media Playlist file.  This attribute is OPTIONAL; see
    Section 4.3.4.2.1.  If the TYPE is CLOSED-CAPTIONS, the URI
    attribute MUST NOT be present.

Pantos & May Informational [Page 25] RFC 8216 HTTP Live Streaming August 2017

    GROUP-ID
    The value is a quoted-string that specifies the group to which the
    Rendition belongs.  See Section 4.3.4.1.1.  This attribute is
    REQUIRED.
    LANGUAGE
    The value is a quoted-string containing one of the standard Tags
    for Identifying Languages [RFC5646], which identifies the primary
    language used in the Rendition.  This attribute is OPTIONAL.
    ASSOC-LANGUAGE
    The value is a quoted-string containing a language tag [RFC5646]
    that identifies a language that is associated with the Rendition.
    An associated language is often used in a different role than the
    language specified by the LANGUAGE attribute (e.g., written versus
    spoken or a fallback dialect).  This attribute is OPTIONAL.
    The LANGUAGE and ASSOC-LANGUAGE attributes can be used, for
    example, to link Norwegian Renditions that use different spoken
    and written languages.
    NAME
    The value is a quoted-string containing a human-readable
    description of the Rendition.  If the LANGUAGE attribute is
    present, then this description SHOULD be in that language.  This
    attribute is REQUIRED.
    DEFAULT
    The value is an enumerated-string; valid strings are YES and NO.
    If the value is YES, then the client SHOULD play this Rendition of
    the content in the absence of information from the user indicating
    a different choice.  This attribute is OPTIONAL.  Its absence
    indicates an implicit value of NO.
    AUTOSELECT
    The value is an enumerated-string; valid strings are YES and NO.
    This attribute is OPTIONAL.  Its absence indicates an implicit
    value of NO.  If the value is YES, then the client MAY choose to
    play this Rendition in the absence of explicit user preference
    because it matches the current playback environment, such as
    chosen system language.

Pantos & May Informational [Page 26] RFC 8216 HTTP Live Streaming August 2017

    If the AUTOSELECT attribute is present, its value MUST be YES if
    the value of the DEFAULT attribute is YES.
    FORCED
    The value is an enumerated-string; valid strings are YES and NO.
    This attribute is OPTIONAL.  Its absence indicates an implicit
    value of NO.  The FORCED attribute MUST NOT be present unless the
    TYPE is SUBTITLES.
    A value of YES indicates that the Rendition contains content that
    is considered essential to play.  When selecting a FORCED
    Rendition, a client SHOULD choose the one that best matches the
    current playback environment (e.g., language).
    A value of NO indicates that the Rendition contains content that
    is intended to be played in response to explicit user request.
    INSTREAM-ID
    The value is a quoted-string that specifies a Rendition within the
    segments in the Media Playlist.  This attribute is REQUIRED if the
    TYPE attribute is CLOSED-CAPTIONS, in which case it MUST have one
    of the values: "CC1", "CC2", "CC3", "CC4", or "SERVICEn" where n
    MUST be an integer between 1 and 63 (e.g., "SERVICE3" or
    "SERVICE42").
    The values "CC1", "CC2", "CC3", and "CC4" identify a Line 21 Data
    Services channel [CEA608].  The "SERVICE" values identify a
    Digital Television Closed Captioning [CEA708] service block
    number.
    For all other TYPE values, the INSTREAM-ID MUST NOT be specified.
    CHARACTERISTICS
    The value is a quoted-string containing one or more Uniform Type
    Identifiers [UTI] separated by comma (,) characters.  This
    attribute is OPTIONAL.  Each UTI indicates an individual
    characteristic of the Rendition.
    A SUBTITLES Rendition MAY include the following characteristics:
    "public.accessibility.transcribes-spoken-dialog",
    "public.accessibility.describes-music-and-sound", and
    "public.easy-to-read" (which indicates that the subtitles have
    been edited for ease of reading).

Pantos & May Informational [Page 27] RFC 8216 HTTP Live Streaming August 2017

    An AUDIO Rendition MAY include the following characteristic:
    "public.accessibility.describes-video".
    The CHARACTERISTICS attribute MAY include private UTIs.
    CHANNELS
    The value is a quoted-string that specifies an ordered, backslash-
    separated ("/") list of parameters.  If the TYPE attribute is
    AUDIO, then the first parameter is a count of audio channels
    expressed as a decimal-integer, indicating the maximum number of
    independent, simultaneous audio channels present in any Media
    Segment in the Rendition.  For example, an AC-3 5.1 Rendition
    would have a CHANNELS="6" attribute.  No other CHANNELS parameters
    are currently defined.
    All audio EXT-X-MEDIA tags SHOULD have a CHANNELS attribute.  If a
    Master Playlist contains two Renditions encoded with the same
    codec but a different number of channels, then the CHANNELS
    attribute is REQUIRED; otherwise, it is OPTIONAL.

4.3.4.1.1. Rendition Groups

 A set of one or more EXT-X-MEDIA tags with the same GROUP-ID value
 and the same TYPE value defines a Group of Renditions.  Each member
 of the Group MUST be an alternative Rendition of the same content;
 otherwise, playback errors can occur.
 All EXT-X-MEDIA tags in a Playlist MUST meet the following
 constraints:
 o  All EXT-X-MEDIA tags in the same Group MUST have different NAME
    attributes.
 o  A Group MUST NOT have more than one member with a DEFAULT
    attribute of YES.
 o  Each EXT-X-MEDIA tag with an AUTOSELECT=YES attribute SHOULD have
    a combination of LANGUAGE [RFC5646], ASSOC-LANGUAGE, FORCED, and
    CHARACTERISTICS attributes that is distinct from those of other
    AUTOSELECT=YES members of its Group.
 A Playlist MAY contain multiple Groups of the same TYPE in order to
 provide multiple encodings of that media type.  If it does so, each
 Group of the same TYPE MUST have the same set of members, and each
 corresponding member MUST have identical attributes with the
 exception of the URI and CHANNELS attributes.

Pantos & May Informational [Page 28] RFC 8216 HTTP Live Streaming August 2017

 Each member in a Group of Renditions MAY have a different sample
 format.  For example, an English Rendition can be encoded with AC-3
 5.1 while a Spanish Rendition is encoded with AAC stereo.  However,
 any EXT-X-STREAM-INF tag (Section 4.3.4.2) or EXT-X-I-FRAME-STREAM-
 INF tag (Section 4.3.4.3) that references such a Group MUST have a
 CODECS attribute that lists every sample format present in any
 Rendition in the Group, or client playback failures can occur.  In
 the example above, the CODECS attribute would include
 "ac-3,mp4a.40.2".

4.3.4.2. EXT-X-STREAM-INF

 The EXT-X-STREAM-INF tag specifies a Variant Stream, which is a set
 of Renditions that can be combined to play the presentation.  The
 attributes of the tag provide information about the Variant Stream.
 The URI line that follows the EXT-X-STREAM-INF tag specifies a Media
 Playlist that carries a Rendition of the Variant Stream.  The URI
 line is REQUIRED.  Clients that do not support multiple video
 Renditions SHOULD play this Rendition.
 Its format is:
 #EXT-X-STREAM-INF:<attribute-list>
 <URI>
 The following attributes are defined:
    BANDWIDTH
    The value is a decimal-integer of bits per second.  It represents
    the peak segment bit rate of the Variant Stream.
    If all the Media Segments in a Variant Stream have already been
    created, the BANDWIDTH value MUST be the largest sum of peak
    segment bit rates that is produced by any playable combination of
    Renditions.  (For a Variant Stream with a single Media Playlist,
    this is just the peak segment bit rate of that Media Playlist.)
    An inaccurate value can cause playback stalls or prevent clients
    from playing the variant.
    If the Master Playlist is to be made available before all Media
    Segments in the presentation have been encoded, the BANDWIDTH
    value SHOULD be the BANDWIDTH value of a representative period of
    similar content, encoded using the same settings.

Pantos & May Informational [Page 29] RFC 8216 HTTP Live Streaming August 2017

    Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute.
    AVERAGE-BANDWIDTH
    The value is a decimal-integer of bits per second.  It represents
    the average segment bit rate of the Variant Stream.
    If all the Media Segments in a Variant Stream have already been
    created, the AVERAGE-BANDWIDTH value MUST be the largest sum of
    average segment bit rates that is produced by any playable
    combination of Renditions.  (For a Variant Stream with a single
    Media Playlist, this is just the average segment bit rate of that
    Media Playlist.)  An inaccurate value can cause playback stalls or
    prevent clients from playing the variant.
    If the Master Playlist is to be made available before all Media
    Segments in the presentation have been encoded, the AVERAGE-
    BANDWIDTH value SHOULD be the AVERAGE-BANDWIDTH value of a
    representative period of similar content, encoded using the same
    settings.
    The AVERAGE-BANDWIDTH attribute is OPTIONAL.
    CODECS
    The value is a quoted-string containing a comma-separated list of
    formats, where each format specifies a media sample type that is
    present in one or more Renditions specified by the Variant Stream.
    Valid format identifiers are those in the ISO Base Media File
    Format Name Space defined by "The 'Codecs' and 'Profiles'
    Parameters for "Bucket" Media Types" [RFC6381].
    For example, a stream containing AAC low complexity (AAC-LC) audio
    and H.264 Main Profile Level 3.0 video would have a CODECS value
    of "mp4a.40.2,avc1.4d401e".
    Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute.
    RESOLUTION
    The value is a decimal-resolution describing the optimal pixel
    resolution at which to display all the video in the Variant
    Stream.
    The RESOLUTION attribute is OPTIONAL but is recommended if the
    Variant Stream includes video.

Pantos & May Informational [Page 30] RFC 8216 HTTP Live Streaming August 2017

    FRAME-RATE
    The value is a decimal-floating-point describing the maximum frame
    rate for all the video in the Variant Stream, rounded to three
    decimal places.
    The FRAME-RATE attribute is OPTIONAL but is recommended if the
    Variant Stream includes video.  The FRAME-RATE attribute SHOULD be
    included if any video in a Variant Stream exceeds 30 frames per
    second.
    HDCP-LEVEL
    The value is an enumerated-string; valid strings are TYPE-0 and
    NONE.  This attribute is advisory; a value of TYPE-0 indicates
    that the Variant Stream could fail to play unless the output is
    protected by High-bandwidth Digital Content Protection (HDCP) Type
    0 [HDCP] or equivalent.  A value of NONE indicates that the
    content does not require output copy protection.
    Encrypted Variant Streams with different HDCP levels SHOULD use
    different media encryption keys.
    The HDCP-LEVEL attribute is OPTIONAL.  It SHOULD be present if any
    content in the Variant Stream will fail to play without HDCP.
    Clients without output copy protection SHOULD NOT load a Variant
    Stream with an HDCP-LEVEL attribute unless its value is NONE.
    AUDIO
    The value is a quoted-string.  It MUST match the value of the
    GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
    Playlist whose TYPE attribute is AUDIO.  It indicates the set of
    audio Renditions that SHOULD be used when playing the
    presentation.  See Section 4.3.4.2.1.
    The AUDIO attribute is OPTIONAL.
    VIDEO
    The value is a quoted-string.  It MUST match the value of the
    GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
    Playlist whose TYPE attribute is VIDEO.  It indicates the set of
    video Renditions that SHOULD be used when playing the
    presentation.  See Section 4.3.4.2.1.
    The VIDEO attribute is OPTIONAL.

Pantos & May Informational [Page 31] RFC 8216 HTTP Live Streaming August 2017

    SUBTITLES
    The value is a quoted-string.  It MUST match the value of the
    GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
    Playlist whose TYPE attribute is SUBTITLES.  It indicates the set
    of subtitle Renditions that can be used when playing the
    presentation.  See Section 4.3.4.2.1.
    The SUBTITLES attribute is OPTIONAL.
    CLOSED-CAPTIONS
    The value can be either a quoted-string or an enumerated-string
    with the value NONE.  If the value is a quoted-string, it MUST
    match the value of the GROUP-ID attribute of an EXT-X-MEDIA tag
    elsewhere in the Playlist whose TYPE attribute is CLOSED-CAPTIONS,
    and it indicates the set of closed-caption Renditions that can be
    used when playing the presentation.  See Section 4.3.4.2.1.
    If the value is the enumerated-string value NONE, all EXT-X-
    STREAM-INF tags MUST have this attribute with a value of NONE,
    indicating that there are no closed captions in any Variant Stream
    in the Master Playlist.  Having closed captions in one Variant
    Stream but not another can trigger playback inconsistencies.
    The CLOSED-CAPTIONS attribute is OPTIONAL.

4.3.4.2.1. Alternative Renditions

 When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, SUBTITLES, or
 CLOSED-CAPTIONS attribute, it indicates that alternative Renditions
 of the content are available for playback of that Variant Stream.
 When defining alternative Renditions, the following constraints MUST
 be met to prevent client playback errors:
 o  All playable combinations of Renditions associated with an EXT-X-
    STREAM-INF tag MUST have an aggregate bandwidth less than or equal
    to the BANDWIDTH attribute of the EXT-X-STREAM-INF tag.
 o  If an EXT-X-STREAM-INF tag contains a RESOLUTION attribute and a
    VIDEO attribute, then every alternative video Rendition MUST have
    an optimal display resolution matching the value of the RESOLUTION
    attribute.
 o  Every alternative Rendition associated with an EXT-X-STREAM-INF
    tag MUST meet the constraints for a Variant Stream described in
    Section 6.2.4.

Pantos & May Informational [Page 32] RFC 8216 HTTP Live Streaming August 2017

 The URI attribute of the EXT-X-MEDIA tag is REQUIRED if the media
 type is SUBTITLES, but OPTIONAL if the media type is VIDEO or AUDIO.
 If the media type is VIDEO or AUDIO, a missing URI attribute
 indicates that the media data for this Rendition is included in the
 Media Playlist of any EXT-X-STREAM-INF tag referencing this EXT-
 X-MEDIA tag.  If the media TYPE is AUDIO and the URI attribute is
 missing, clients MUST assume that the audio data for this Rendition
 is present in every video Rendition specified by the EXT-X-STREAM-INF
 tag.
 The URI attribute of the EXT-X-MEDIA tag MUST NOT be included if the
 media type is CLOSED-CAPTIONS.

4.3.4.3. EXT-X-I-FRAME-STREAM-INF

 The EXT-X-I-FRAME-STREAM-INF tag identifies a Media Playlist file
 containing the I-frames of a multimedia presentation.  It stands
 alone, in that it does not apply to a particular URI in the Master
 Playlist.  Its format is:
 #EXT-X-I-FRAME-STREAM-INF:<attribute-list>
 All attributes defined for the EXT-X-STREAM-INF tag (Section 4.3.4.2)
 are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
 FRAME-RATE, AUDIO, SUBTITLES, and CLOSED-CAPTIONS attributes.  In
 addition, the following attribute is defined:
    URI
    The value is a quoted-string containing a URI that identifies the
    I-frame Media Playlist file.  That Playlist file MUST contain an
    EXT-X-I-FRAMES-ONLY tag.
 Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute
 and a URI attribute.
 The provisions in Section 4.3.4.2.1 also apply to EXT-X-I-FRAME-
 STREAM-INF tags with a VIDEO attribute.
 A Master Playlist that specifies alternative VIDEO Renditions and
 I-frame Playlists SHOULD include an alternative I-frame VIDEO
 Rendition for each regular VIDEO Rendition, with the same NAME and
 LANGUAGE attributes.

Pantos & May Informational [Page 33] RFC 8216 HTTP Live Streaming August 2017

4.3.4.4. EXT-X-SESSION-DATA

 The EXT-X-SESSION-DATA tag allows arbitrary session data to be
 carried in a Master Playlist.
 Its format is:
 #EXT-X-SESSION-DATA:<attribute-list>
 The following attributes are defined:
    DATA-ID
    The value of DATA-ID is a quoted-string that identifies a
    particular data value.  The DATA-ID SHOULD conform to a reverse
    DNS naming convention, such as "com.example.movie.title"; however,
    there is no central registration authority, so Playlist authors
    SHOULD take care to choose a value that is unlikely to collide
    with others.  This attribute is REQUIRED.
    VALUE
    VALUE is a quoted-string.  It contains the data identified by
    DATA-ID.  If the LANGUAGE is specified, VALUE SHOULD contain a
    human-readable string written in the specified language.
    URI
    The value is a quoted-string containing a URI.  The resource
    identified by the URI MUST be formatted as JSON [RFC7159];
    otherwise, clients may fail to interpret the resource.
    LANGUAGE
    The value is a quoted-string containing a language tag [RFC5646]
    that identifies the language of the VALUE.  This attribute is
    OPTIONAL.
 Each EXT-X-SESSION-DATA tag MUST contain either a VALUE or URI
 attribute, but not both.
 A Playlist MAY contain multiple EXT-X-SESSION-DATA tags with the same
 DATA-ID attribute.  A Playlist MUST NOT contain more than one EXT-X-
 SESSION-DATA tag with the same DATA-ID attribute and the same
 LANGUAGE attribute.

Pantos & May Informational [Page 34] RFC 8216 HTTP Live Streaming August 2017

4.3.4.5. EXT-X-SESSION-KEY

 The EXT-X-SESSION-KEY tag allows encryption keys from Media Playlists
 to be specified in a Master Playlist.  This allows the client to
 preload these keys without having to read the Media Playlist(s)
 first.
 Its format is:
 #EXT-X-SESSION-KEY:<attribute-list>
 All attributes defined for the EXT-X-KEY tag (Section 4.3.2.4) are
 also defined for the EXT-X-SESSION-KEY, except that the value of the
 METHOD attribute MUST NOT be NONE.  If an EXT-X-SESSION-KEY is used,
 the values of the METHOD, KEYFORMAT, and KEYFORMATVERSIONS attributes
 MUST match any EXT-X-KEY with the same URI value.
 EXT-X-SESSION-KEY tags SHOULD be added if multiple Variant Streams or
 Renditions use the same encryption keys and formats.  An EXT-X-
 SESSION-KEY tag is not associated with any particular Media Playlist.
 A Master Playlist MUST NOT contain more than one EXT-X-SESSION-KEY
 tag with the same METHOD, URI, IV, KEYFORMAT, and KEYFORMATVERSIONS
 attribute values.
 The EXT-X-SESSION-KEY tag is optional.

4.3.5. Media or Master Playlist Tags

 The tags in this section can appear in either Master Playlists or
 Media Playlists.  If one of these tags appears in a Master Playlist,
 it SHOULD NOT appear in any Media Playlist referenced by that Master
 Playlist.  A tag that appears in both MUST have the same value;
 otherwise, clients SHOULD ignore the value in the Media Playlist(s).
 These tags MUST NOT appear more than once in a Playlist.  If a tag
 appears more than once, clients MUST fail to parse the Playlist.

4.3.5.1. EXT-X-INDEPENDENT-SEGMENTS

 The EXT-X-INDEPENDENT-SEGMENTS tag indicates that all media samples
 in a Media Segment can be decoded without information from other
 segments.  It applies to every Media Segment in the Playlist.
 Its format is:
 #EXT-X-INDEPENDENT-SEGMENTS

Pantos & May Informational [Page 35] RFC 8216 HTTP Live Streaming August 2017

 If the EXT-X-INDEPENDENT-SEGMENTS tag appears in a Master Playlist,
 it applies to every Media Segment in every Media Playlist in the
 Master Playlist.

4.3.5.2. EXT-X-START

 The EXT-X-START tag indicates a preferred point at which to start
 playing a Playlist.  By default, clients SHOULD start playback at
 this point when beginning a playback session.  This tag is OPTIONAL.
 Its format is:
 #EXT-X-START:<attribute-list>
 The following attributes are defined:
    TIME-OFFSET
    The value of TIME-OFFSET is a signed-decimal-floating-point number
    of seconds.  A positive number indicates a time offset from the
    beginning of the Playlist.  A negative number indicates a negative
    time offset from the end of the last Media Segment in the
    Playlist.  This attribute is REQUIRED.
    The absolute value of TIME-OFFSET SHOULD NOT be larger than the
    Playlist duration.  If the absolute value of TIME-OFFSET exceeds
    the duration of the Playlist, it indicates either the end of the
    Playlist (if positive) or the beginning of the Playlist (if
    negative).
    If the Playlist does not contain the EXT-X-ENDLIST tag, the TIME-
    OFFSET SHOULD NOT be within three target durations of the end of
    the Playlist file.
    PRECISE
    The value is an enumerated-string; valid strings are YES and NO.
    If the value is YES, clients SHOULD start playback at the Media
    Segment containing the TIME-OFFSET, but SHOULD NOT render media
    samples in that segment whose presentation times are prior to the
    TIME-OFFSET.  If the value is NO, clients SHOULD attempt to render
    every media sample in that segment.  This attribute is OPTIONAL.
    If it is missing, its value should be treated as NO.

Pantos & May Informational [Page 36] RFC 8216 HTTP Live Streaming August 2017

5. Key Files

5.1. Structure of Key Files

 An EXT-X-KEY tag with a URI attribute identifies a Key file.  A Key
 file contains a cipher key that can decrypt Media Segments in the
 Playlist.
 [AES_128] encryption uses 16-octet keys.  If the KEYFORMAT of an EXT-
 X-KEY tag is "identity", the Key file is a single packed array of 16
 octets in binary format.

5.2. IV for AES-128

 [AES_128] REQUIRES the same 16-octet IV to be supplied when
 encrypting and decrypting.  Varying this IV increases the strength of
 the cipher.
 An IV attribute on an EXT-X-KEY tag with a KEYFORMAT of "identity"
 specifies an IV that can be used when decrypting Media Segments
 encrypted with that Key file.  IV values for AES-128 are 128-bit
 numbers.
 An EXT-X-KEY tag with a KEYFORMAT of "identity" that does not have an
 IV attribute indicates that the Media Sequence Number is to be used
 as the IV when decrypting a Media Segment, by putting its big-endian
 binary representation into a 16-octet (128-bit) buffer and padding
 (on the left) with zeros.

6. Client/Server Responsibilities

6.1. Introduction

 This section describes how the server generates the Playlist and
 Media Segments and how the client should download them for playback.

6.2. Server Responsibilities

6.2.1. General Server Responsibilities

 The production of the source media is outside the scope of this
 document, which simply presumes a source of continuous encoded media
 containing the presentation.
 The server MUST divide the source media into individual Media
 Segments whose duration is less than or equal to a constant target
 duration.  Segments that are longer than the planned target duration
 can trigger playback stalls and other errors.

Pantos & May Informational [Page 37] RFC 8216 HTTP Live Streaming August 2017

 The server SHOULD attempt to divide the source media at points that
 support effective decode of individual Media Segments, e.g., on
 packet and key frame boundaries.
 The server MUST create a URI for every Media Segment that enables its
 clients to obtain the segment data.  If a server supports partial
 loading of resources (e.g., via HTTP Range requests), it MAY specify
 segments as sub-ranges of larger resources using the EXT-X-BYTERANGE
 tag.
 Any Media Segment that is specified in a Playlist loaded by a client
 MUST be available for immediate download, or playback errors can
 occur.  Once download starts, its transfer rate SHOULD NOT be
 constrained by the segment production process.
 HTTP servers SHOULD transfer text files -- such as Playlists and
 WebVTT segments -- using the "gzip" Content-Encoding if the client
 indicates that it is prepared to accept it.
 The server must create a Media Playlist file (Section 4) that
 contains a URI for each Media Segment that the server wishes to make
 available, in the order in which they are to be played.
 The value of the EXT-X-VERSION tag (Section 4.3.1.2) SHOULD NOT be
 greater than what is required for the tags and attributes in the
 Playlist (see Section 7).
 Changes to the Playlist file MUST be made atomically from the point
 of view of the clients, or playback errors MAY occur.
 The server MUST NOT change the Media Playlist file, except to:
 o  Append lines to it (Section 6.2.1).
 o  Remove Media Segment URIs from the Playlist in the order that they
    appear, along with any tags that apply only to those segments
    (Section 6.2.2).
 o  Increment the value of the EXT-X-MEDIA-SEQUENCE or EXT-X-
    DISCONTINUITY-SEQUENCE tags (Section 6.2.2).
 o  Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1).

Pantos & May Informational [Page 38] RFC 8216 HTTP Live Streaming August 2017

 A Media Playlist has further constraints on its updates if it
 contains an EXT-X-PLAYLIST-TYPE tag.  An EXT-X-PLAYLIST-TYPE tag with
 a value of VOD indicates that the Playlist file MUST NOT change.  An
 EXT-X-PLAYLIST-TYPE tag with a value of EVENT indicates that the
 server MUST NOT change or delete any part of the Playlist file; it
 MAY append lines to it.
 The value of the EXT-X-TARGETDURATION tag in the Media Playlist MUST
 NOT change.  A typical target duration is 10 seconds.
 Playlist changes other than those allowed here can trigger playback
 errors and inconsistent client behavior.
 Each Media Segment in a Media Playlist has an integer Discontinuity
 Sequence Number.  The Discontinuity Sequence Number can be used in
 addition to the timestamps within the media to synchronize Media
 Segments across different Renditions.
 A segment's Discontinuity Sequence Number is the value of the EXT-X-
 DISCONTINUITY-SEQUENCE tag (or zero if none) plus the number of EXT-
 X-DISCONTINUITY tags in the Playlist preceding the URI line of the
 segment.
 The server MAY associate an absolute date and time with a Media
 Segment by applying an EXT-X-PROGRAM-DATE-TIME tag to it.  This
 defines an informative mapping of the (wall-clock) date and time
 specified by the tag to the first media timestamp in the segment,
 which may be used as a basis for seeking, for display, or for other
 purposes.  If a server provides this mapping, it SHOULD apply an EXT-
 X-PROGRAM-DATE-TIME tag to every segment that has an EXT-
 X-DISCONTINUITY tag applied to it.
 The Server MUST NOT add any EXT-X-PROGRAM-DATE-TIME tag to a Playlist
 that would cause the mapping between program date and Media Segment
 to become ambiguous.
 The server MUST NOT remove an EXT-X-DATERANGE tag from a Playlist if
 any date in the range maps to a Media Segment in the Playlist.
 The server MUST NOT reuse the ID attribute value of an EXT-
 X-DATERANGE tag for any new Date Range in the same Playlist.
 Once the Following Range of a Date Range with an END-ON-NEXT=YES
 attribute is added to a Playlist, the Server MUST NOT subsequently
 add a Date Range with the same CLASS attribute whose START-DATE is
 between that of the END-ON-NEXT=YES range and its Following Range.

Pantos & May Informational [Page 39] RFC 8216 HTTP Live Streaming August 2017

 For Date Ranges with a PLANNED-DURATION attribute, the Server SHOULD
 signal the actual end of the range once it has been established.  It
 can do so by adding another EXT-X-DATERANGE tag with the same ID
 attribute value and either a DURATION or an END-DATE attribute or, if
 the Date Range has an END-ON-NEXT=YES attribute, by adding a
 Following Range.
 If the Media Playlist contains the final Media Segment of the
 presentation, then the Playlist file MUST contain the EXT-X-ENDLIST
 tag; this allows clients to minimize unproductive Playlist reloads.
 If a Media Playlist does not contain the EXT-X-ENDLIST tag, the
 server MUST make a new version of the Playlist file available that
 contains at least one new Media Segment.  It MUST be made available
 relative to the time that the previous version of the Playlist file
 was made available: no earlier than one-half the target duration
 after that time, and no later than 1.5 times the target duration
 after that time.  This allows clients to utilize the network
 efficiently.
 If the server wishes to remove an entire presentation, it SHOULD
 provide a clear indication to clients that the Playlist file is no
 longer available (e.g., with an HTTP 404 or 410 response).  It MUST
 ensure that all Media Segments in the Playlist file remain available
 to clients for at least the duration of the Playlist file at the time
 of removal to prevent interruption of in-progress playback.

6.2.2. Live Playlists

 The server MAY limit the availability of Media Segments by removing
 Media Segments from the Playlist file (Section 6.2.1).  If Media
 Segments are to be removed, the Playlist file MUST contain an EXT-X-
 MEDIA-SEQUENCE tag.  Its value MUST be incremented by 1 for every
 Media Segment that is removed from the Playlist file; it MUST NOT
 decrease or wrap.  Clients can malfunction if each Media Segment does
 not have a consistent, unique Media Sequence Number.
 Media Segments MUST be removed from the Playlist file in the order
 that they appear in the Playlist; otherwise, client playback can
 malfunction.
 The server MUST NOT remove a Media Segment from a Playlist file
 without an EXT-X-ENDLIST tag if that would produce a Playlist whose
 duration is less than three times the target duration.  Doing so can
 trigger playback stalls.

Pantos & May Informational [Page 40] RFC 8216 HTTP Live Streaming August 2017

 When the server removes a Media Segment URI from the Playlist, the
 corresponding Media Segment MUST remain available to clients for a
 period of time equal to the duration of the segment plus the duration
 of the longest Playlist file distributed by the server containing
 that segment.  Removing a Media Segment earlier than that can
 interrupt in-progress playback.
 If the server wishes to remove segments from a Media Playlist
 containing an EXT-X-DISCONTINUITY tag, the Media Playlist MUST
 contain an EXT-X-DISCONTINUITY-SEQUENCE tag.  Without the EXT-X-
 DISCONTINUITY-SEQUENCE tag, it can be impossible for a client to
 locate corresponding segments between Renditions.
 If the server removes an EXT-X-DISCONTINUITY tag from the Media
 Playlist, it MUST increment the value of the EXT-X-DISCONTINUITY-
 SEQUENCE tag so that the Discontinuity Sequence Numbers of the
 segments still in the Media Playlist remain unchanged.  The value of
 the EXT-X-DISCONTINUITY-SEQUENCE tag MUST NOT decrease or wrap.
 Clients can malfunction if each Media Segment does not have a
 consistent Discontinuity Sequence Number.
 If a server plans to remove a Media Segment after it is delivered to
 clients over HTTP, it SHOULD ensure that the HTTP response contains
 an Expires header that reflects the planned time-to-live.
 A Live Playlist MUST NOT contain the EXT-X-PLAYLIST-TYPE tag, as no
 value of that tag allows Media Segments to be removed.

6.2.3. Encrypting Media Segments

 Media Segments MAY be encrypted.  Every encrypted Media Segment MUST
 have an EXT-X-KEY tag (Section 4.3.2.4) applied to it with a URI that
 the client can use to obtain a Key file (Section 5) containing the
 decryption key.
 A Media Segment can only be encrypted with one encryption METHOD,
 using one encryption key and IV.  However, a server MAY offer
 multiple ways to retrieve that key by providing multiple EXT-X-KEY
 tags, each with a different KEYFORMAT attribute value.
 The server MAY set the HTTP Expires header in the key response to
 indicate the duration for which the key can be cached.
 Any unencrypted Media Segment in a Playlist that is preceded by an
 encrypted Media Segment MUST have an EXT-X-KEY tag applied to it with
 a METHOD attribute of NONE.  Otherwise, the client will misinterpret
 those segments as encrypted.

Pantos & May Informational [Page 41] RFC 8216 HTTP Live Streaming August 2017

 If the encryption METHOD is AES-128 and the Playlist does not contain
 the EXT-X-I-FRAMES-ONLY tag, AES encryption as described in
 Section 4.3.2.4 SHALL be applied to individual Media Segments.
 If the encryption METHOD is AES-128 and the Playlist contains an EXT-
 X-I-FRAMES-ONLY tag, the entire resource MUST be encrypted using
 AES-128 CBC with PKCS7 padding [RFC5652].  Encryption MAY be
 restarted on 16-byte block boundaries, unless the first block
 contains an I-frame.  The IV used for encryption MUST be either the
 Media Sequence Number of the Media Segment or the value of the IV
 attribute of the EXT-X-KEY tag, as described in Section 5.2.  These
 constraints allow a client to load and decrypt individual I-frames
 specified as sub-ranges of regular encrypted Media Segments, and
 their Media Initialization Sections.
 If the encryption METHOD is SAMPLE-AES, media samples MAY be
 encrypted prior to encapsulation in a Media Segment.
 The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if
 it applies to any Media Segment in the Playlist file, or clients who
 subsequently load that Playlist will be unable to decrypt those Media
 Segments.

6.2.4. Providing Variant Streams

 A server MAY offer multiple Media Playlist files to provide different
 encodings of the same presentation.  If it does so, it SHOULD provide
 a Master Playlist file that lists each Variant Stream to allow
 clients to switch between encodings dynamically.
 Master Playlists describe regular Variant Streams with EXT-X-STREAM-
 INF tags and I-frame Variant Streams with EXT-X-I-FRAME-STREAM-INF
 tags.
 If an EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAM-INF tag contains
 the CODECS attribute, the attribute value MUST include every media
 format [RFC6381] present in any Media Segment in any of the
 Renditions specified by the Variant Stream.

Pantos & May Informational [Page 42] RFC 8216 HTTP Live Streaming August 2017

 The server MUST meet the following constraints when producing Variant
 Streams in order to allow clients to switch between them seamlessly:
 o  Each Variant Stream MUST present the same content.
 o  Matching content in Variant Streams MUST have matching timestamps.
    This allows clients to synchronize the media.
 o  Matching content in Variant Streams MUST have matching
    Discontinuity Sequence Numbers (see Section 4.3.3.3).
 o  Each Media Playlist in each Variant Stream MUST have the same
    target duration.  The only exceptions are SUBTITLES Renditions and
    Media Playlists containing an EXT-X-I-FRAMES-ONLY tag, which MAY
    have different target durations if they have an EXT-X-PLAYLIST-
    TYPE of VOD.
 o  Content that appears in a Media Playlist of one Variant Stream but
    not in another MUST appear either at the beginning or at the end
    of the Media Playlist file and MUST NOT be longer than the target
    duration.
 o  If any Media Playlists have an EXT-X-PLAYLIST-TYPE tag, all Media
    Playlists MUST have an EXT-X-PLAYLIST-TYPE tag with the same
    value.
 o  If the Playlist contains an EXT-X-PLAYLIST-TYPE tag with the value
    of VOD, the first segment of every Media Playlist in every Variant
    Stream MUST start at the same media timestamp.
 o  If any Media Playlist in a Master Playlist contains an EXT-X-
    PROGRAM-DATE-TIME tag, then all Media Playlists in that Master
    Playlist MUST contain EXT-X-PROGRAM-DATE-TIME tags with consistent
    mappings of date and time to media timestamps.
 o  Each Variant Stream MUST contain the same set of Date Ranges, each
    one identified by an EXT-X-DATERANGE tag(s) with the same ID
    attribute value and containing the same set of attribute/value
    pairs.
 In addition, for broadest compatibility, Variant Streams SHOULD
 contain the same encoded audio bitstream.  This allows clients to
 switch between Variant Streams without audible glitching.
 The rules for Variant Streams also apply to alternative Renditions
 (see Section 4.3.4.2.1).

Pantos & May Informational [Page 43] RFC 8216 HTTP Live Streaming August 2017

6.3. Client Responsibilities

6.3.1. General Client Responsibilities

 How the client obtains the URI to the Playlist file is outside the
 scope of this document; it is presumed to have done so.
 The client obtains the Playlist file from the URI.  If the Playlist
 file so obtained is a Master Playlist, the client can select a
 Variant Stream to load from the Master Playlist.
 Clients MUST ensure that loaded Playlists comply with Section 4 and
 that the EXT-X-VERSION tag, if present, specifies a protocol version
 supported by the client; if either check fails, the client MUST NOT
 attempt to use the Playlist, or unintended behavior could occur.
 If any URI element in a Playlist contains an URI scheme that the
 client cannot handle, the client MUST stop playback.  All clients
 MUST support HTTP schemes.
 To support forward compatibility, when parsing Playlists, clients
 MUST:
 o  ignore any unrecognized tags.
 o  ignore any attribute/value pair with an unrecognized
    AttributeName.
 o  ignore any tag containing an attribute/value pair of type
    enumerated-string whose AttributeName is recognized but whose
    AttributeValue is not recognized, unless the definition of the
    attribute says otherwise.
 Algorithms used by the client to switch between Variant Streams are
 beyond the scope of this document.

6.3.2. Loading the Media Playlist File

 Every time a Media Playlist is loaded or reloaded from a Playlist
 URI, the client MUST determine the next Media Segment to load, as
 described in Section 6.3.5, if it intends to play the presentation
 normally (i.e., in Playlist order at the nominal playback rate).
 If the Media Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the
 client SHOULD assume that each Media Segment in it will become
 unavailable at the time that the Playlist file was loaded plus the
 duration of the Playlist file.

Pantos & May Informational [Page 44] RFC 8216 HTTP Live Streaming August 2017

 A client MAY use the segment Media Sequence Number to track the
 location of a Media Segment within a Playlist when the Playlist is
 reloaded.
 A client MUST NOT assume that segments with the same Media Sequence
 Number in different Variant Streams or Renditions have the same
 position in the presentation; Playlists MAY have independent Media
 Sequence Numbers.  Instead, a client MUST use the relative position
 of each segment on the Playlist timeline and its Discontinuity
 Sequence Number to locate corresponding segments.
 A client MUST load the Media Playlist file of every Rendition
 selected for playback in order to locate the media specific to that
 Rendition.  But, to prevent unnecessary load on the server, it SHOULD
 NOT load the Playlist file of any other Rendition.
 For some Variant Streams, it is possible to select Renditions that do
 not include the Rendition specified by the EXT-X-STREAM-INF tag.  As
 noted above, the client SHOULD NOT load that Rendition in those
 cases.

6.3.3. Playing the Media Playlist File

 The client SHALL choose which Media Segment to play first from the
 Media Playlist when playback starts.  If the EXT-X-ENDLIST tag is not
 present and the client intends to play the media normally, the client
 SHOULD NOT choose a segment that starts less than three target
 durations from the end of the Playlist file.  Doing so can trigger
 playback stalls.
 Normal playback can be achieved by playing the Media Segments in the
 order that they appear in the Playlist.  The client MAY present the
 available media in any way it wishes, including normal playback,
 random access, and trick modes.
 The encoding parameters for samples in a Media Segment and across
 multiple Media Segments in a Media Playlist SHOULD remain consistent.
 However, clients SHOULD deal with encoding changes as they are
 encountered, for example, by scaling video content to accommodate a
 resolution change.  If the Variant Stream includes a RESOLUTION
 attribute, clients SHOULD display all video within a rectangle with
 the same proportions as that resolution.
 Clients SHOULD be prepared to handle multiple tracks of a particular
 type (e.g., audio or video).  A client with no other preference
 SHOULD choose the track with the lowest numerical track identifier
 that it can play.

Pantos & May Informational [Page 45] RFC 8216 HTTP Live Streaming August 2017

 Clients SHOULD ignore private streams inside Transport Streams that
 they do not recognize.  Private streams can be used to support
 different devices with the same stream, although stream authors
 SHOULD be sensitive to the additional network load that this imposes.
 The client MUST be prepared to reset its parser(s) and decoder(s)
 before playing a Media Segment that has an EXT-X-DISCONTINUITY tag
 applied to it; otherwise, playback errors can occur.
 The client SHOULD attempt to load Media Segments in advance of when
 they will be required for uninterrupted playback to compensate for
 temporary variations in latency and throughput.
 The client MAY use the value of the EXT-X-PROGRAM-DATE-TIME tag to
 display the program origination time to the user.  If the value
 includes time zone information, the client SHALL take it into
 account; if it does not, the client MAY assume the time to be local.
 Note that dates in Playlists can refer to when the content was
 produced (or to other times), which have no relation to the time of
 playback.
 If the first EXT-X-PROGRAM-DATE-TIME tag in a Playlist appears after
 one or more Media Segment URIs, the client SHOULD extrapolate
 backward from that tag (using EXTINF durations and/or media
 timestamps) to associate dates with those segments.  To associate a
 date with any other Media Segment that does not have an EXT-X-
 PROGRAM-DATE-TIME tag applied to it directly, the client SHOULD
 extrapolate forward from the last EXT-X-PROGRAM-DATE-TIME tag
 appearing before that segment in the Playlist.

6.3.4. Reloading the Media Playlist File

 The client MUST periodically reload a Media Playlist file to learn
 what media is currently available, unless it contains an EXT-X-
 PLAYLIST-TYPE tag with a value of VOD, or a value of EVENT and the
 EXT-X-ENDLIST tag is also present.
 However, the client MUST NOT attempt to reload the Playlist file more
 frequently than specified by this section, in order to limit the
 collective load on the server.
 When a client loads a Playlist file for the first time or reloads a
 Playlist file and finds that it has changed since the last time it
 was loaded, the client MUST wait for at least the target duration
 before attempting to reload the Playlist file again, measured from
 the last time the client began loading the Playlist file.

Pantos & May Informational [Page 46] RFC 8216 HTTP Live Streaming August 2017

 If the client reloads a Playlist file and finds that it has not
 changed, then it MUST wait for a period of one-half the target
 duration before retrying.
 After reloading a Media Playlist, the client SHOULD verify that each
 Media Segment in it has the same URI (and byte range, if specified)
 as the Media Segment with the same Media Sequence Number in the
 previous Media Playlist.  It SHOULD halt playback if it does not, as
 this normally indicates a server error.
 In order to reduce server load, the client SHOULD NOT reload the
 Playlist files of Variant Streams or alternate Renditions that are
 not currently being played.  If it decides to switch playback to a
 different Variant Stream, it SHOULD stop reloading the Playlist of
 the old Variant Stream and begin loading the Playlist of the new
 Variant Stream.  It can use the EXTINF durations and the constraints
 in Section 6.2.4 to determine the approximate location of
 corresponding media.  Once media from the new Variant Stream has been
 loaded, the timestamps in the Media Segments can be used to
 synchronize the old and new timelines precisely.
 A client MUST NOT attempt to use the Media Sequence Number to
 synchronize between streams (see Section 6.3.2).

6.3.5. Determining the Next Segment to Load

 The client MUST examine the Media Playlist file every time it is
 loaded or reloaded to determine the next Media Segment to load, as
 the set of available media MAY have changed.
 The first segment to load is generally the segment that the client
 has chosen to play first (see Section 6.3.3).
 In order to play the presentation normally, the next Media Segment to
 load is the one with the lowest Media Sequence Number that is greater
 than the Media Sequence Number of the last Media Segment loaded.

6.3.6. Decrypting Encrypted Media Segments

 If a Media Playlist file contains an EXT-X-KEY tag that specifies a
 Key file URI, the client can obtain that Key file and use the key
 inside it to decrypt all Media Segments to which that EXT-X-KEY tag
 applies.

Pantos & May Informational [Page 47] RFC 8216 HTTP Live Streaming August 2017

 A client MUST ignore any EXT-X-KEY tag with an unsupported or
 unrecognized KEYFORMAT attribute, to allow for cross-device
 addressability.  If the Playlist contains a Media Segment to which
 only EXT-X-KEY tags with unrecognized or unsupported KEYFORMAT
 attributes are applied, playback SHOULD fail.
 A client MUST NOT attempt to decrypt any segments whose EXT-X-KEY tag
 has a METHOD attribute that it does not recognize.
 If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
 applied to individual Media Segments, whose encryption format is
 described in Section 4.3.2.4.
 If the encryption METHOD is AES-128 and the Media Segment is part of
 an I-frame Playlist (Section 4.3.3.6) and it has an EXT-X-BYTERANGE
 tag applied to it, special care needs to be taken in loading and
 decrypting the segment, because the resource identified by the URI is
 encrypted in 16-byte blocks from the start of the resource.
 The decrypted I-frame can be recovered by first widening its byte
 range, as specified by the EXT-X-BYTERANGE tag, so that it starts and
 ends on 16-byte boundaries from the start of the resource.
 Next, the byte range is widened further to include a 16-byte block at
 the beginning of the range.  This 16-byte block allows the correct IV
 for the following block to be calculated.
 The widened byte range can then be loaded and decrypted with AES-128
 CBC using an arbitrary IV.  The number of bytes added to the
 beginning and the end of the original byte range are discarded from
 the decrypted bytes; what remains is the decrypted I-frame.
 If the encryption METHOD is SAMPLE-AES, AES-128 decryption SHALL be
 applied to encrypted media samples within the Media Segment.
 An EXT-X-KEY tag with a METHOD of NONE indicates that the Media
 Segments it applies to are not encrypted.

7. Protocol Version Compatibility

 Protocol compatibility is specified by the EXT-X-VERSION tag.  A
 Playlist that contains tags or attributes that are not compatible
 with protocol version 1 MUST include an EXT-X-VERSION tag.
 A client MUST NOT attempt playback if it does not support the
 protocol version specified by the EXT-X-VERSION tag, or unintended
 behavior could occur.

Pantos & May Informational [Page 48] RFC 8216 HTTP Live Streaming August 2017

 A Media Playlist MUST indicate an EXT-X-VERSION of 2 or higher if it
 contains:
 o  The IV attribute of the EXT-X-KEY tag.
 A Media Playlist MUST indicate an EXT-X-VERSION of 3 or higher if it
 contains:
 o  Floating-point EXTINF duration values.
 A Media Playlist MUST indicate an EXT-X-VERSION of 4 or higher if it
 contains:
 o  The EXT-X-BYTERANGE tag.
 o  The EXT-X-I-FRAMES-ONLY tag.
 A Media Playlist MUST indicate an EXT-X-VERSION of 5 or higher if it
 contains:
 o  The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY
    tag.
 o  The EXT-X-MAP tag.
 A Media Playlist MUST indicate an EXT-X-VERSION of 6 or higher if it
 contains:
 o  The EXT-X-MAP tag in a Media Playlist that does not contain EXT-
    X-I-FRAMES-ONLY.
 A Master Playlist MUST indicate an EXT-X-VERSION of 7 or higher if it
 contains:
 o  "SERVICE" values for the INSTREAM-ID attribute of the EXT-X-MEDIA
    tag.
 The EXT-X-MEDIA tag and the AUDIO, VIDEO, and SUBTITLES attributes of
 the EXT-X-STREAM-INF tag are backward compatible to protocol version
 1, but playback on older clients may not be desirable.  A server MAY
 consider indicating an EXT-X-VERSION of 4 or higher in the Master
 Playlist but is not required to do so.
 The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I-
 FRAME-STREAM-INF tags was removed in protocol version 6.
 The EXT-X-ALLOW-CACHE tag was removed in protocol version 7.

Pantos & May Informational [Page 49] RFC 8216 HTTP Live Streaming August 2017

8. Playlist Examples

8.1. Simple Media Playlist

 #EXTM3U
 #EXT-X-TARGETDURATION:10
 #EXT-X-VERSION:3
 #EXTINF:9.009,
 http://media.example.com/first.ts
 #EXTINF:9.009,
 http://media.example.com/second.ts
 #EXTINF:3.003,
 http://media.example.com/third.ts
 #EXT-X-ENDLIST

8.2. Live Media Playlist Using HTTPS

 #EXTM3U
 #EXT-X-VERSION:3
 #EXT-X-TARGETDURATION:8
 #EXT-X-MEDIA-SEQUENCE:2680
 #EXTINF:7.975,
 https://priv.example.com/fileSequence2680.ts
 #EXTINF:7.941,
 https://priv.example.com/fileSequence2681.ts
 #EXTINF:7.975,
 https://priv.example.com/fileSequence2682.ts

Pantos & May Informational [Page 50] RFC 8216 HTTP Live Streaming August 2017

8.3. Playlist with Encrypted Media Segments

 #EXTM3U
 #EXT-X-VERSION:3
 #EXT-X-MEDIA-SEQUENCE:7794
 #EXT-X-TARGETDURATION:15
 #EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=52"
 #EXTINF:2.833,
 http://media.example.com/fileSequence52-A.ts
 #EXTINF:15.0,
 http://media.example.com/fileSequence52-B.ts
 #EXTINF:13.333,
 http://media.example.com/fileSequence52-C.ts
 #EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=53"
 #EXTINF:15.0,
 http://media.example.com/fileSequence53-A.ts

8.4. Master Playlist

 #EXTM3U
 #EXT-X-STREAM-INF:BANDWIDTH=1280000,AVERAGE-BANDWIDTH=1000000
 http://example.com/low.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=2560000,AVERAGE-BANDWIDTH=2000000
 http://example.com/mid.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=7680000,AVERAGE-BANDWIDTH=6000000
 http://example.com/hi.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
 http://example.com/audio-only.m3u8

8.5. Master Playlist with I-Frames

 #EXTM3U
 #EXT-X-STREAM-INF:BANDWIDTH=1280000
 low/audio-video.m3u8
 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=2560000
 mid/audio-video.m3u8
 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=7680000
 hi/audio-video.m3u8
 #EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
 audio-only.m3u8

Pantos & May Informational [Page 51] RFC 8216 HTTP Live Streaming August 2017

8.6. Master Playlist with Alternative Audio

 In this example, the CODECS attributes have been condensed for space.
 A '\' is used to indicate that the tag continues on the following
 line with whitespace removed:
 #EXTM3U
 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \
    DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \
    URI="main/english-audio.m3u8"
 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsch", \
    DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \
    URI="main/german-audio.m3u8"
 #EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \
    DEFAULT=NO,AUTOSELECT=NO,LANGUAGE="en", \
    URI="commentary/audio-only.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",AUDIO="aac"
 low/video-only.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",AUDIO="aac"
 mid/video-only.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",AUDIO="aac"
 hi/video-only.m3u8
 #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5",AUDIO="aac"
 main/english-audio.m3u8

8.7. Master Playlist with Alternative Video

 This example shows three different video Renditions (Main,
 Centerfield, and Dugout) and three different Variant Streams (low,
 mid, and high).  In this example, clients that did not support the
 EXT-X-MEDIA tag and the VIDEO attribute of the EXT-X-STREAM-INF tag
 would only be able to play the video Rendition "Main".
 Since the EXT-X-STREAM-INF tag has no AUDIO attribute, all video
 Renditions would be required to contain the audio.

Pantos & May Informational [Page 52] RFC 8216 HTTP Live Streaming August 2017

 In this example, the CODECS attributes have been condensed for space.
 A '\' is used to indicate that the tag continues on the following
 line with whitespace removed:
 #EXTM3U
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Main", \
    DEFAULT=YES,URI="low/main/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Centerfield", \
    DEFAULT=NO,URI="low/centerfield/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="low",NAME="Dugout", \
    DEFAULT=NO,URI="low/dugout/audio-video.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=1280000,CODECS="...",VIDEO="low"
 low/main/audio-video.m3u8
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Main", \
    DEFAULT=YES,URI="mid/main/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Centerfield", \
    DEFAULT=NO,URI="mid/centerfield/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="mid",NAME="Dugout", \
    DEFAULT=NO,URI="mid/dugout/audio-video.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=2560000,CODECS="...",VIDEO="mid"
 mid/main/audio-video.m3u8
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Main", \
    DEFAULT=YES,URI="hi/main/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Centerfield", \
    DEFAULT=NO,URI="hi/centerfield/audio-video.m3u8"
 #EXT-X-MEDIA:TYPE=VIDEO,GROUP-ID="hi",NAME="Dugout", \
    DEFAULT=NO,URI="hi/dugout/audio-video.m3u8"
 #EXT-X-STREAM-INF:BANDWIDTH=7680000,CODECS="...",VIDEO="hi"
 hi/main/audio-video.m3u8

8.8. Session Data in a Master Playlist

 In this example, only the EXT-X-SESSION-DATA is shown:
 #EXT-X-SESSION-DATA:DATA-ID="com.example.lyrics",URI="lyrics.json"
 #EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="en", \
         VALUE="This is an example"
 #EXT-X-SESSION-DATA:DATA-ID="com.example.title",LANGUAGE="es", \
         VALUE="Este es un ejemplo"

Pantos & May Informational [Page 53] RFC 8216 HTTP Live Streaming August 2017

8.9. CHARACTERISTICS Attribute Containing Multiple Characteristics

 Certain characteristics are valid in combination, as in:
 CHARACTERISTICS=
 "public.accessibility.transcribes-spoken-dialog,public.easy-to-read"

8.10. EXT-X-DATERANGE Carrying SCTE-35 Tags

 This example shows two EXT-X-DATERANGE tags that describe a single
 Date Range, with an SCTE-35 "out" splice_insert() command that is
 subsequently updated with an SCTE-35 "in" splice_insert() command.
 #EXTM3U
 ...
 #EXT-X-DATERANGE:ID="splice-6FFFFFF0",START-DATE="2014-03-05T11:
 15:00Z",PLANNED-DURATION=59.993,SCTE35-OUT=0xFC002F0000000000FF0
 00014056FFFFFF000E011622DCAFF000052636200000000000A0008029896F50
 000008700000000
 ... Media Segment declarations for 60s worth of media
 #EXT-X-DATERANGE:ID="splice-6FFFFFF0",DURATION=59.993,SCTE35-IN=
 0xFC002A0000000000FF00000F056FFFFFF000401162802E6100000000000A00
 08029896F50000008700000000
 ...

9. IANA Considerations

 IANA has registered the following media type [RFC2046]:
 Type name: application
 Subtype name: vnd.apple.mpegurl
 Required parameters: none
 Optional parameters: none
 Encoding considerations: encoded as UTF-8, which is 8-bit text.  This
 media type may require encoding on transports not capable of handling
 8-bit text.  See Section 4 for more information.
 Security considerations: See Section 10.
 Compression: this media type does not employ compression.

Pantos & May Informational [Page 54] RFC 8216 HTTP Live Streaming August 2017

 Interoperability considerations: There are no byte-ordering issues,
 since files are 8-bit text.  Applications could encounter
 unrecognized tags, which SHOULD be ignored.
 Published specification: see Section 4.
 Applications that use this media type: Multimedia applications such
 as the iPhone media player in iOS 3.0 and later and QuickTime Player
 in Mac OS X version 10.6 and later.
 Fragment identifier considerations: no Fragment Identifiers are
 defined for this media type.
 Additional information:
    Deprecated alias names for this type: none
    Magic number(s): #EXTM3U
    File extension(s): .m3u8, .m3u (see Section 4)
    Macintosh file type code(s): none
 Person & email address to contact for further information: David
 Singer, singer@apple.com.
 Intended usage: LIMITED USE
 Restrictions on usage: none
 Author: Roger Pantos
 Change Controller: David Singer

10. Security Considerations

 Since the protocol generally uses HTTP to transfer data, most of the
 same security considerations apply.  See Section 15 of HTTP
 [RFC7230].
 Media file parsers are typically subject to "fuzzing" attacks.
 Implementors SHOULD pay particular attention to code that will parse
 data received from a server and ensure that all possible inputs are
 handled correctly.
 Playlist files contain URIs, which clients will use to make network
 requests of arbitrary entities.  Clients SHOULD range-check responses
 to prevent buffer overflows.  See also the Security Considerations
 section of "Uniform Resource Identifier (URI): Generic Syntax"
 [RFC3986].

Pantos & May Informational [Page 55] RFC 8216 HTTP Live Streaming August 2017

 Apart from URL resolution, this format does not employ any form of
 active content.
 Clients SHOULD limit each playback session to a reasonable number of
 concurrent downloads (e.g., four) to avoid contributing to denial-of-
 service attacks.
 HTTP requests often include session state ("cookies"), which may
 contain private user data.  Implementations MUST follow cookie
 restriction and expiry rules specified by "HTTP State Management
 Mechanism" [RFC6265] to protect themselves from attack.  See also the
 Security Considerations section of that document, and "Use of HTTP
 State Management" [RFC2964].
 Encryption keys are specified by URI.  The delivery of these keys
 SHOULD be secured by a mechanism such as HTTP Over TLS [RFC2818]
 (formerly SSL) in conjunction with a secure realm or a session token.

11. References

11.1. Normative References

 [AC_3]     Advanced Television Systems Committee, "Digital Audio
            Compression (AC-3) (E-AC-3) Standard", ATSC
            Standard A/52:2010, November 2010, <http://atsc.org/
            wp-content/uploads/2015/03/A52-201212-17.pdf>.
 [AES_128]  National Institute of Standards and Technology, "Advanced
            Encryption Standard (AES)", FIPS PUB 197,
            DOI 10.6028/NIST.FIPS.197, November 2001,
            <http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf>.
 [CEA608]   Consumer Electronics Association, "ANSI/CEA 608-E: Line 21
            Data Services", April 2008.
 [CEA708]   Consumer Technology Association, "Digital Television (DTV)
            Closed Captioning", ANSI/CTA Standard CEA-708-E, August
            2013, <https://standards.cta.tech/kwspub/published_docs/
            ANSI-CTA-708-E-Preview.pdf>.
 [COMMON_ENC]
            International Organization for Standardization,
            "Information technology -- MPEG systems technologies --
            Part 7: Common encryption in ISO base media file format
            files", ISO/IEC 23001-7:2016, February 2016,
            <http://www.iso.org/iso/
            catalogue_detail.htm?csnumber=68042>.

Pantos & May Informational [Page 56] RFC 8216 HTTP Live Streaming August 2017

 [H_264]    International Telecommunications Union, "Advanced video
            coding for generic audiovisual services", January 2012,
            <http://www.itu.int/rec/T-REC-H.264>.
 [HDCP]     Digital Content Protection LLC, "High-bandwidth Digital
            Content Protection System - Mapping HDCP to HDMI",
            February 2013, <http://www.digital-cp.com/
            sites/default/files/specifications/
            HDCP%20on%20HDMI%20Specification%20Rev2_2_Final1.pdf>.
 [ISO_13818]
            International Organization for Standardization, "Generic
            coding of moving pictures and associated audio
            information", ISO/IEC International Standard 13818,
            October 2007,
            <http://www.iso.org/iso/catalogue_detail?csnumber=44169>.
 [ISO_13818_3]
            International Organization for Standardization, "ISO/IEC
            International Standard 13818-3:1998; Generic coding of
            moving pictures and associated audio information - Part 3:
            Audio", April 1998,
            <http://www.iso.org/iso/home/store/catalogue_tc/
            catalogue_detail.htm?csnumber=26797>.
 [ISO_13818_7]
            International Organization for Standardization, "Generic
            coding of moving pictures and associated audio information
            - Part 7: Advanced Audio Coding (AAC)", ISO/IEC
            International Standard 13818-3:2006, January 2006,
            <http://www.iso.org/iso/home/store/catalogue_tc/
            catalogue_detail.htm?csnumber=43345>.
 [ISO_14496]
            International Organization for Standardization,
            "Information technology -- Coding of audio-visual objects
            -- Part 3: Audio", ISO/IEC 14496-3:2009, 2009,
            <http://www.iso.org/iso/catalogue_detail?csnumber=53943>.
 [ISO_8601] International Organization for Standardization, "Data
            elements and interchange formats -- Information
            interchange -- Representation of dates and times", ISO/IEC
            International Standard 8601:2004, December 2004,
            <http://www.iso.org/iso/catalogue_detail?csnumber=40874>.

Pantos & May Informational [Page 57] RFC 8216 HTTP Live Streaming August 2017

 [ISOBMFF]  International Organization for Standardization,
            "Information technology -- Coding of audio-visual objects
            -- Part 12: ISO base media file format",
            ISO/IEC 14496-12:2015, December 2015,
            <http://www.iso.org/iso/
            catalogue_detail.htm?csnumber=68960>.
 [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Two: Media Types", RFC 2046,
            DOI 10.17487/RFC2046, November 1996,
            <https://www.rfc-editor.org/info/rfc2046>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
            DOI 10.17487/RFC2818, May 2000,
            <https://www.rfc-editor.org/info/rfc2818>.
 [RFC2964]  Moore, K. and N. Freed, "Use of HTTP State Management",
            BCP 44, RFC 2964, DOI 10.17487/RFC2964, October 2000,
            <https://www.rfc-editor.org/info/rfc2964>.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
            2003, <https://www.rfc-editor.org/info/rfc3629>.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66,
            RFC 3986, DOI 10.17487/RFC3986, January 2005,
            <https://www.rfc-editor.org/info/rfc3986>.
 [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
            Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
            September 2009, <https://www.rfc-editor.org/info/rfc5646>.
 [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
            RFC 5652, DOI 10.17487/RFC5652, September 2009,
            <https://www.rfc-editor.org/info/rfc5652>.
 [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
            DOI 10.17487/RFC6265, April 2011,
            <https://www.rfc-editor.org/info/rfc6265>.

Pantos & May Informational [Page 58] RFC 8216 HTTP Live Streaming August 2017

 [RFC6381]  Gellens, R., Singer, D., and P. Frojdh, "The 'Codecs' and
            'Profiles' Parameters for "Bucket" Media Types", RFC 6381,
            DOI 10.17487/RFC6381, August 2011,
            <https://www.rfc-editor.org/info/rfc6381>.
 [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
            Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
            2014, <https://www.rfc-editor.org/info/rfc7159>.
 [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Message Syntax and Routing",
            RFC 7230, DOI 10.17487/RFC7230, June 2014,
            <https://www.rfc-editor.org/info/rfc7230>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [SCTE35]   Society of Cable Telecommunications Engineers, "Digital
            Program Insertion Cueing Message for Cable", ANSI/SCTE 35,
            August 2014, <http://www.scte.org/documents/pdf/Standards/
            ANSI_SCTE%2035%202014.pdf>.
 [US_ASCII] American National Standard for Information Systems, "Coded
            Character Sets - 7-Bit American National Standard Code for
            Information Interchange (7-Bit ASCII)", ANSI X3.4,
            December 1986.
 [WebVTT]   World Wide Web Consortium (W3C), "WebVTT: The Web Video
            Text Tracks Format", Draft Community Group Report, June
            2017, <http://dev.w3.org/html5/webvtt/>.

11.2. Informative References

 [CMAF]     International Organization for Standardization,
            "Information technology -- Multimedia application format
            (MPEG-A) -- Part 19: Common media application format
            (CMAF) for segmented media", ISO/IEC FDIS 23000-19,
            <https://www.iso.org/standard/71975.html>.
 [ID3]      ID3.org, "The ID3 audio file data tagging format",
            <http://www.id3.org/Developer_Information>.
 [M3U]      Nullsoft, Inc., "The M3U Playlist format, originally
            invented for the Winamp media player",
            <https://en.wikipedia.org/w/
            index.php?title=M3U7amp;oldid=786631666>.

Pantos & May Informational [Page 59] RFC 8216 HTTP Live Streaming August 2017

 [SampleEnc]
            Apple Inc., "MPEG-2 Stream Encryption Format for HTTP Live
            Streaming",
            <https://developer.apple.com/library/ios/documentation/
            AudioVideo/Conceptual/HLS_Sample_Encryption/>.
 [UNICODE]  The Unicode Consortium, "The Unicode Standard",
            <http://www.unicode.org/versions/latest/>.
 [UTI]      Apple Inc., "Uniform Type Identifier",
            <http://developer.apple.com/library/ios/#documentation/
            general/conceptual/DevPedia-CocoaCore/
            UniformTypeIdentifier.html>.

Contributors

 Significant contributions to the design of this protocol were made by
 Jim Batson, David Biderman, Bill May, Roger Pantos, Alan Tseng, and
 Eryk Vershen.  Stuart Cheshire helped edit the specification.

Authors' Addresses

 Roger Pantos (editor)
 Apple, Inc.
 Cupertino, California
 United States of America
 Email: http-live-streaming-review@group.apple.com
 William May, Jr.
 Major League Baseball Advanced Media
 New York, New York
 United States of America
 Email: bill.may@mlb.com

Pantos & May Informational [Page 60]

/data/webs/external/dokuwiki/data/pages/rfc/rfc8216.txt · Last modified: 2017/08/31 23:39 (external edit)