    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.

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    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

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       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

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    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.

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       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.

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    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.

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    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.

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       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.

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       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.

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    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.

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       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.

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       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.

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       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.

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    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

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       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

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          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.

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    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.

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    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.

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          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.

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       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

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       "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.

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       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).

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       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

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    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;

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       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.

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          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.

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          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).

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          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.

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       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.

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          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.

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          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.

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          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.

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       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.

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    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.

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    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

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       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.

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    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.

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       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).

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       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.

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       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.

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       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.

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       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.

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       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).

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    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.

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       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.

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       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.

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       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.

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       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.

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       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.

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    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

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    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

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    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.

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       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"

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    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.

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       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].

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       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>.

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       [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>.

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       [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>.

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       [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>.

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       [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

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