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Informational                                             R. Pantos, Ed.
Internet-Draft                                                    W. May
Intended status: Informational                                Apple Inc.
Expires: April 18, 2013                                 October 15, 2012


                          HTTP Live Streaming
                  draft-pantos-http-live-streaming-10

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 5 of this protocol.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 18, 2013.

Copyright Notice

   Copyright (c) 2012 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 Informational Internet Draft is submitted as an RFC Editor



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   Contribution and/or non-IETF Document (not as a Contribution, IETF
   Contribution, nor IETF Document) in accordance with BCP 78 and BCP
   79.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The Playlist file  . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Attribute Lists  . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Standard Tags  . . . . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  EXTM3U . . . . . . . . . . . . . . . . . . . . . . . .  6
       3.3.2.  EXTINF . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  New Tags . . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.4.1.  EXT-X-BYTERANGE  . . . . . . . . . . . . . . . . . . .  7
       3.4.2.  EXT-X-TARGETDURATION . . . . . . . . . . . . . . . . .  7
       3.4.3.  EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . . . .  8
       3.4.4.  EXT-X-KEY  . . . . . . . . . . . . . . . . . . . . . .  8
       3.4.5.  EXT-X-PROGRAM-DATE-TIME  . . . . . . . . . . . . . . . 10
       3.4.6.  EXT-X-ALLOW-CACHE  . . . . . . . . . . . . . . . . . . 10
       3.4.7.  EXT-X-PLAYLIST-TYPE  . . . . . . . . . . . . . . . . . 10
       3.4.8.  EXT-X-ENDLIST  . . . . . . . . . . . . . . . . . . . . 11
       3.4.9.  EXT-X-MEDIA  . . . . . . . . . . . . . . . . . . . . . 11
         3.4.9.1.  Rendition Groups . . . . . . . . . . . . . . . . . 13
       3.4.10. EXT-X-STREAM-INF . . . . . . . . . . . . . . . . . . . 14
         3.4.10.1. Alternative Renditions . . . . . . . . . . . . . . 15
       3.4.11. EXT-X-DISCONTINUITY  . . . . . . . . . . . . . . . . . 16
       3.4.12. EXT-X-I-FRAMES-ONLY  . . . . . . . . . . . . . . . . . 16
       3.4.13. EXT-X-MAP  . . . . . . . . . . . . . . . . . . . . . . 17
       3.4.14. EXT-X-I-FRAME-STREAM-INF . . . . . . . . . . . . . . . 17
       3.4.15. EXT-X-VERSION  . . . . . . . . . . . . . . . . . . . . 18
   4.  Media segments . . . . . . . . . . . . . . . . . . . . . . . . 19
   5.  Key files  . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     5.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 20
     5.2.  IV for [AES_128] . . . . . . . . . . . . . . . . . . . . . 20
   6.  Client/Server Actions  . . . . . . . . . . . . . . . . . . . . 20
     6.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 20
     6.2.  Server Process . . . . . . . . . . . . . . . . . . . . . . 21
       6.2.1.  Introduction . . . . . . . . . . . . . . . . . . . . . 21
       6.2.2.  Sliding Window Playlists . . . . . . . . . . . . . . . 23
       6.2.3.  Encrypting media segments  . . . . . . . . . . . . . . 23
       6.2.4.  Providing variant streams  . . . . . . . . . . . . . . 24
     6.3.  Client Process . . . . . . . . . . . . . . . . . . . . . . 25
       6.3.1.  Introduction . . . . . . . . . . . . . . . . . . . . . 25
       6.3.2.  Loading the Playlist file  . . . . . . . . . . . . . . 25



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       6.3.3.  Playing the Playlist file  . . . . . . . . . . . . . . 26
       6.3.4.  Reloading the Playlist file  . . . . . . . . . . . . . 26
       6.3.5.  Determining the next segment to load . . . . . . . . . 27
       6.3.6.  Decrypting encrypted media segments  . . . . . . . . . 28
   7.  Protocol version compatibility . . . . . . . . . . . . . . . . 28
   8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     8.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 29
     8.2.  Simple Playlist file . . . . . . . . . . . . . . . . . . . 29
     8.3.  Sliding Window Playlist, using HTTPS . . . . . . . . . . . 30
     8.4.  Playlist file with encrypted media segments  . . . . . . . 30
     8.5.  Variant Playlist file  . . . . . . . . . . . . . . . . . . 30
     8.6.  Variant Playlist with I-Frames . . . . . . . . . . . . . . 31
     8.7.  Variant Playlist with Alternative audio  . . . . . . . . . 31
     8.8.  Variant Playlist with Alternative video  . . . . . . . . . 31
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 32
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 32
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 33
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 34
     12.2. Informative References . . . . . . . . . . . . . . . . . . 36
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36






























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1.  Introduction

   This document describes a protocol for transferring unbounded streams
   of multimedia data.  The protocol supports the encryption of media
   data and the provision of alternate versions (e.g. bitrates) of a
   stream.  Media data can be transferred soon after it is created,
   allowing it to be played in near real-time.  Data is usually carried
   over HTTP [RFC2616].

   External references that describe related standards such as HTTP are
   listed in Section 11.


2.  Summary

   A multimedia presentation is specified by a URI [RFC3986] to a
   Playlist file, which is an ordered list of media URIs and
   informational tags.  The URIs and their associated tags specify a
   series of media segments.

   To play the stream, the client first obtains the Playlist file and
   then obtains and plays each media segment in the Playlist.  It
   reloads the Playlist file as described in this document to discover
   additional segments.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


3.  The Playlist file

3.1.  Introduction

   Playlists MUST be Extended M3U Playlist files [M3U].  This document
   extends the M3U file format further by defining additional tags.

   An M3U Playlist is a text file that consists of individual lines.
   Lines are terminated by either a single LF character or a CR
   character followed by an LF character.  Each line is a URI, blank, or
   starts with the character '#'.  Blank lines are ignored.  White space
   MUST NOT be present, except for elements in which it is explicitly
   specified.

   A URI line identifies a media segment or a variant Playlist file (see
   Section 3.4.10).  Each media segment is specified by a media URI and
   the tags that apply to it.




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   Lines that start with the character '#' are either comments or tags.

   Tags begin with #EXT.  All other lines that begin with '#' are
   comments and SHOULD be ignored.

   A URI in a Playlist, whether it is a URI line or part of a tag, MAY
   be relative.  Relative URIs MUST be resolved against the URI of the
   Playlist file that contains it.

   The duration of a Playlist file is the sum of the durations of the
   media segments within it.

   Playlist files whose names end in .m3u8 and/or have the HTTP Content-
   Type "application/vnd.apple.mpegurl" are encoded in UTF-8 [RFC3629].
   Files whose names end with .m3u and/or have the HTTP Content-Type
   [RFC2616] "audio/mpegurl" are encoded in US-ASCII [US_ASCII].

   Playlist files MUST have names that end in .m3u8 and/or have the
   Content-Type "application/vnd.apple.mpegurl" (if transferred over
   HTTP), or have names that end in .m3u and/or have the HTTP Content-
   Type type "audio/mpegurl" (for compatibility).

3.2.  Attribute Lists

   Certain extended M3U tags have values which 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] and '-'.

   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.

   o  hexadecimal-integer: an unquoted string of characters from the set
      [0..9] and [A..F] that is prefixed with 0x or 0X and which
      expresses an integer in base-16 arithmetic.

   o  decimal-floating-point: an unquoted string of characters from the
      set [0..9] and '.' which expresses a floating-point number in
      decimal positional notation.




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   o  quoted-string: a string of characters within a pair of double-
      quotes ("), including Uniform Type Identifiers [UTI].  The set of
      characters allowed in the string and any rules for escaping
      special characters are specified by the Attribute definition, but
      any double-quote (") character and any carriage-return or linefeed
      will always be replaced by an escape sequence.

   o  enumerated-string: an unquoted character string from a set which
      is explicitly defined by the Attribute.  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.

   An Attribute/value pair with an unrecognized AttributeName MUST be
   ignored by the client.

   Any tag containing an attribute/value pair of type enumerated-string
   whose AttributeName is recognized but whose AttributeValue is not
   recognized MUST be ignored by the client.

3.3.  Standard Tags

3.3.1.  EXTM3U

   An Extended M3U file is distinguished from a basic M3U file by its
   first line, which MUST be the tag #EXTM3U.

3.3.2.  EXTINF

   The EXTINF tag specifies the duration of a media segment.  It applies
   only to the media segment that follows it.  Each media segment MUST
   be preceded by an EXTINF tag.  Its format is:

   #EXTINF:<duration>,<title>

   "duration" is an integer or floating-point number in decimal
   positional notation that specifies the duration of the media segment
   in seconds.  Durations that are reported as integers SHOULD be
   rounded to the nearest integer.  Durations MUST be integers if the
   protocol version of the Playlist file is less than 3.  The remainder



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   of the line following the comma is an optional human-readable
   informative title of the media segment.

3.4.  New Tags

   This document defines the following new tags: EXT-X-BYTERANGE, EXT-X-
   TARGETDURATION, EXT-X-MEDIA-SEQUENCE, EXT-X-KEY, EXT-X-PROGRAM-DATE-
   TIME, EXT-X-ALLOW-CACHE, EXT-X-PLAYLIST-TYPE, EXT-X-STREAM-INF, EXT-
   X-I-FRAME-STREAM-INF, EXT-X-I-FRAMES-ONLY, EXT-X-MEDIA, EXT-X-
   ENDLIST, EXT-X-DISCONTINUITY, and EXT-X-VERSION.

3.4.1.  EXT-X-BYTERANGE

   The EXT-X-BYTERANGE tag indicates that a media segment is a sub-range
   of the resource identified by its media URI.  It applies only to the
   next media URI 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.

   A media URI with no EXT-X-BYTERANGE tag applied to it specifies a
   media segment that consists of the entire resource.

   The EXT-X-BYTERANGE tag appeared in version 4 of the protocol.

3.4.2.  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 MUST be less than or equal to the target duration.  This tag
   MUST appear once in the Playlist file.  It applies to the entire
   Playlist file.  Its format is:

   #EXT-X-TARGETDURATION:<s>

   where s is an integer indicating the target duration in seconds.







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3.4.3.  EXT-X-MEDIA-SEQUENCE

   Each media segment in a Playlist has a unique integer sequence
   number.  The sequence number of a segment is equal to the sequence
   number of the segment that preceded it plus one.  The EXT-X-MEDIA-
   SEQUENCE tag indicates the sequence number of the first segment that
   appears in a Playlist file.  Its format is:

   #EXT-X-MEDIA-SEQUENCE:<number>

   A Playlist file MUST NOT contain more than one EXT-X-MEDIA-SEQUENCE
   tag.  If the Playlist file does not contain an EXT-X-MEDIA-SEQUENCE
   tag then the sequence number of the first segment in the playlist
   SHALL be considered to be 0.  A client MUST NOT assume that segments
   with the same sequence number in different variants or renditions
   contain matching content.

   A media URI is not required to contain its sequence number.

   See Section 6.3.2 and Section 6.3.5 for information on handling the
   EXT-X-MEDIA-SEQUENCE tag.

3.4.4.  EXT-X-KEY

   Media segments MAY be encrypted.  The EXT-X-KEY tag specifies how to
   decrypt them.  It applies to every media segment 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, in which case they MUST resolve to the same key.
   Its 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 mandatory.

   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, the following
   attributes MUST NOT be present: URI; IV; KEYFORMAT;
   KEYFORMATVERSIONS.




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   An encryption method of AES-128 means that media segments are
   completely encrypted using the Advanced Encryption Standard [AES_128]
   with a 128-bit key and PKCS7 padding [RFC5652].  If the encryption
   method is AES-128, the URI attribute MUST be present.  The IV
   attribute MAY be present; see Section 5.2.

   An encryption method of SAMPLE-AES means that the media segments
   contain elementary streams of audio, video, or other samples that are
   encrypted using the Advanced Encryption Standard [AES_128].  How an
   elementary stream is encrypted depends on the media encoding.  The
   encryption format for H.264 [H_264], AAC [ISO_14496] and AC-3 [AC_3]
   elementary streams is described by [SampleEnc].  The IV attribute MAY
   be present; see Section 5.2.

   URI

   The value is a quoted-string containing a URI [RFC3986] that
   specifies how to obtain the key.  This attribute is mandatory unless
   the METHOD is NONE.

   IV

   The value is a hexadecimal-integer that specifies the Initialization
   Vector to be used with the key.  The IV attribute appeared in
   protocol version 2.

   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".  The KEYFORMAT attribute appeared in
   protocol version 5.

   KEYFORMATVERSIONS

   The value is a quoted-string containing one or more positive integers
   separated by the "/" character (for example, "1/3").  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".  The KEYFORMATVERSIONS attribute appeared in
   protocol version 5.

   If the 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 Section 5.2,



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   Section 6.2.3 and Section 6.3.6 for additional information on media
   segment encryption.

3.4.5.  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.

   The date/time representation is ISO/IEC 8601:2004 [ISO_8601] and
   SHOULD indicate a time zone:

   #EXT-X-PROGRAM-DATE-TIME:<YYYY-MM-DDThh:mm:ssZ>

   For example:

   #EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00

   See Section 6.2.1 and Section 6.3.3 for more information on the EXT-
   X-PROGRAM-DATE-TIME tag.

3.4.6.  EXT-X-ALLOW-CACHE

   The EXT-X-ALLOW-CACHE tag indicates whether the client MAY or MUST
   NOT cache downloaded media segments for later replay.  It MAY occur
   anywhere in the Playlist file; it MUST NOT occur more than once.  The
   EXT-X-ALLOW-CACHE tag applies to all segments in the playlist.  Its
   format is:

   #EXT-X-ALLOW-CACHE:<YES|NO>

   See Section 6.3.3 for more information on the EXT-X-ALLOW-CACHE tag.

3.4.7.  EXT-X-PLAYLIST-TYPE

   The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
   Playlist file.  It applies to the entire Playlist file.  It is
   optional.  Its format is:

   #EXT-X-PLAYLIST-TYPE:<EVENT|VOD>

   Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE
   tag.








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3.4.8.  EXT-X-ENDLIST

   The EXT-X-ENDLIST tag indicates that no more media segments will be
   added to the Playlist file.  It MAY occur anywhere in the Playlist
   file; it MUST NOT occur more than once.  Its format is:

   #EXT-X-ENDLIST

3.4.9.  EXT-X-MEDIA

   The EXT-X-MEDIA tag is used to relate Playlists that contain
   alternative renditions of the same content.  For example, three EXT-
   X-MEDIA tags can be used to identify audio-only 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 Playlists that show two different camera angles.

   The EXT-X-MEDIA tag stands alone, in that it does not apply to a
   particular URI in the Playlist.  Its format is:

   #EXT-X-MEDIA:<attribute-list>

   The following attributes are defined:

   URI

   The value is a quoted-string containing a URI that identifies the
   Playlist file.  This attribute is optional; see Section 3.4.10.1.

   TYPE

   The value is enumerated-string; valid strings are AUDIO, VIDEO and
   SUBTITLES.  If the value is AUDIO, the Playlist described by the tag
   MUST contain audio media.  If the value is VIDEO, the Playlist MUST
   contain video media.  If the value is SUBTITLES, the Playlist MUST
   contain subtitle media.

   GROUP-ID

   The value is a quoted-string identifying a mutually-exclusive group
   of renditions.  The presence of this attribute signals membership in
   the group.  See Section 3.4.9.1.

   LANGUAGE

   The value is a quoted-string containing an RFC 5646 [RFC5646]
   language tag that identifies the primary language used in the
   rendition.  This attribute is optional.



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   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.

   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.

   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 which 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 which is
   intended to be played in response to explicit user request.

   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"; "public.easy-to-



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   read" (which indicates that the subtitles have been edited for ease
   of reading).

   An AUDIO rendition MAY include the following characteristics:
   "public.accessibility.describes-video".

   The CHARACTERISTICS attribute MAY include private UTIs.

   The EXT-X-MEDIA tag appeared in version 4 of the protocol.

3.4.9.1.  Rendition Groups

   A set of EXT-X-MEDIA tags with the same GROUP-ID value forms a group
   of renditions.  Each member of the group MUST represent an
   alternative rendition of the same content.

   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 the same TYPE
      attribute.

   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  All members of a group whose AUTOSELECT attribute has a value of
      YES MUST have LANGUAGE [RFC5646] attributes with unique values.

   o  All members of a group with TYPE=AUDIO MUST use the same audio
      sample format.

   o  All members of a group with TYPE=VIDEO MUST use the same video
      sample format.

   A Playlist MAY contain multiple groups of the same TYPE in order to
   provide multiple encodings of each rendition.  If it does so, each
   group of the same TYPE SHOULD contain corresponding members with the
   same NAME attribute, LANGUAGE attribute, and rendition.










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3.4.10.  EXT-X-STREAM-INF

   The EXT-X-STREAM-INF tag identifies a media URI as a Playlist file
   containing a multimedia presentation and provides information about
   that presentation.  It applies only to the URI that follows it.  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 MUST be an
   upper bound of the overall bitrate of each media segment (calculated
   to include container overhead) that appears or will appear in the
   Playlist.

   Every EXT-X-STREAM-INF tag MUST include the BANDWIDTH attribute.

   PROGRAM-ID

   The value is a decimal-integer that uniquely identifies a particular
   presentation within the scope of the Playlist file.

   A Playlist file MAY contain multiple EXT-X-STREAM-INF tags with the
   same PROGRAM-ID to identify different encodings of the same
   presentation.  These variant playlists MAY contain additional EXT-X-
   STREAM-INF tags.

   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 a media segment in the Playlist file.  Valid format
   identifiers are those in the ISO File Format Name Space defined by
   RFC 6381 [RFC6381].

   Every EXT-X-STREAM-INF tag SHOULD include a CODECS attribute.

   RESOLUTION

   The value is a decimal-resolution describing the approximate encoded
   horizontal and vertical resolution of video within the presentation.






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   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 Playlist
   whose TYPE attribute is AUDIO.  It indicates the set of audio
   renditions that MAY be used when playing the presentation.  See
   Section 3.4.10.1.

   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 Playlist
   whose TYPE attribute is VIDEO.  It indicates the set of video
   renditions that MAY be used when playing the presentation.  See
   Section 3.4.10.1.

   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 Playlist
   whose TYPE attribute is SUBTITLES.  It indicates the set of subtitle
   renditions that MAY be used when playing the presentation.  See
   Section 3.4.10.1.

3.4.10.1.  Alternative Renditions

   When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, or SUBTITLE
   attribute, it indicates that alternative renditions of the content
   are available for playback of that variant.

   When defining alternative renditions, the following constraints MUST
   be met:

   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 match
      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.

   The URI attribute of an EXT-X-MEDIA tag is optional.  If it is
   missing, it indicates that the rendition described by the EXT-X-MEDIA
   tag is present in the main Playlist described by the EXT-X-STREAM-INF



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   tag.

   Note that if a client chooses to play renditions of audio and video
   that are not present in the main Playlist described by the EXT-X-
   STREAM-INF tag, or if the client chooses to play an audio rendition
   and the main Playlist is audio-only, then the client MAY ignore the
   main Playlist and its media.

3.4.11.  EXT-X-DISCONTINUITY

   The EXT-X-DISCONTINUITY tag indicates an encoding discontinuity
   between the media segment that follows it and the one that preceded
   it.  The set of characteristics that MAY change is:

   o  file format

   o  number and type of tracks

   o  encoding parameters

   o  encoding sequence

   o  timestamp sequence

   Its format is:

   #EXT-X-DISCONTINUITY

   See Section 4, Section 6.2.1, and Section 6.3.3 for more information
   about the EXT-X-DISCONTINUITY tag.

3.4.12.  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 (or Intra frames) are
   encoded video frames whose encoding does not depend on any other
   frame.

   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.



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   Media resources containing I-frame segments MUST begin with either a
   Transport Stream PAT/PMT or be accompanied by an EXT-X-MAP tag
   indicating the proper PAT/PMT.  The byte range of an I-frame segment
   with an EXT-X-BYTERANGE tag applied to it (Section 3.4.1) MUST NOT
   include a PAT/PMT.

   The EXT-X-I-FRAMES-ONLY tag appeared in version 4 of the protocol.

3.4.13.  EXT-X-MAP

   The EXT-X-MAP tag specifies how to obtain the Transport Stream PAT/
   PMT for the applicable media segment.  It applies to every media
   segment that appears after it in the Playlist until the next EXT-X-
   DISCONTINUITY tag, or until the end of the playlist.

   The EXT-X-MAP tag MUST NOT appear unless the Playlist also contains
   the EXT-X-I-FRAMES-ONLY tag.  It is RECOMMENDED that the EXT-X-MAP
   tag only be used for segments whose resource does not start with a
   PAT/PMT.

   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 Transport Stream PAT/PMT.  This attribute
   is mandatory.

   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 Transport Stream PAT/PMT.  The format of the byte range is
   described in Section 3.4.1.  This attribute is optional; if it is not
   present, the byte range is the entire resource indicated by the URI.

   The EXT-X-MAP tag appeared in version 5 of the protocol.

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

   The EXT-X-I-FRAME-STREAM-INF tag identifies a 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 Playlist.
   Its format is:



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   #EXT-X-I-FRAME-STREAM-INF:<attribute-list>

   All attributes defined for the EXT-X-STREAM-INF tag (Section 3.4.10)
   are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
   AUDIO and SUBTITLES attributes.  In addition, the following attribute
   is defined:

   URI

   The value is a quoted-string containing a URI that identifies the
   I-frame Playlist file.

   Every EXT-X-I-FRAME-STREAM-INF tag MUST include a BANDWIDTH attribute
   and a URI attribute.

   The provisions in Section 3.4.10.1 also apply to EXT-X-I-FRAME-
   STREAM-INF tags with a VIDEO attribute.

   A 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.

   The EXT-X-I-FRAME-STREAM-INF tag appeared in version 4 of the
   protocol.  Clients that do not implement protocol version 4 or higher
   MUST ignore it.

3.4.15.  EXT-X-VERSION

   The EXT-X-VERSION tag indicates the compatibility version of the
   Playlist file.  The Playlist file, its associated media, and its
   server MUST comply with all provisions of the most-recent version of
   this document describing the protocol version indicated by the tag
   value.

   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 version.

   A Playlist file MUST NOT contain more than one EXT-X-VERSION tag.  A
   Playlist file that does not contain an EXT-X-VERSION tag MUST comply
   with version 1 of this protocol.






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4.  Media segments

   Each media URI in a Playlist file specifies a media segment which is
   part of the overall presentation.  If a media URI has an EXT-X-
   BYTERANGE tag applied to it, the segment is a sub-range of the media
   file identified by the URI.  Otherwise, the segment is the entire
   media file.

   Each media segment MUST be formatted as an MPEG-2 Transport Stream
   [ISO_13818], an MPEG audio elementary stream [ISO_11172], or a WebVTT
   [WebVTT] file.

   Transport Stream segments MUST contain a single MPEG-2 Program.
   There SHOULD be a Program Association Table (PAT) and a Program Map
   Table (PMT) at the start of each segment.  A segment that contains
   video SHOULD have at least one key frame and enough information to
   completely initialize a video decoder.

   A Transport Stream or audio elementary stream segment MUST be the
   continuation of the encoded media at the end of the segment with the
   previous sequence number, where values in a continuous series, such
   as timestamps and Continuity Counters, continue uninterrupted -
   unless the media segment was the first ever to appear in the Playlist
   file or has an EXT-X-DISCONTINUITY tag applied to it.

   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 PID that it can play.

   Clients MUST ignore private streams inside Transport Streams that
   they do not recognize.

   The encoding parameters for samples in a stream inside a media
   segment and between corresponding streams across multiple media
   segments 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.

   Subtitle segments MUST be formatted as WebVTT [WebVTT] files.  Each
   subtitle 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 that time range
   extends beyond the EXTINF duration.  A WebVTT segment MAY contain no
   cues; this indicates that no subtitles are to be displayed during
   that period.

   Each WebVTT segment MUST have an X-TIMESTAMP-MAP metadata header.



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   This header synchronizes the cue timestamps in the WebVTT file with
   the MPEG-2 (PES) timestamps in other streams.  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.


5.  Key files

5.1.  Introduction

   An EXT-X-KEY tag with a URI attribute identifies a Key file.  A Key
   file contains the cipher key that MUST be used to decrypt subsequent
   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 Initialization Vector (IV) to be
   supplied when encrypting and decrypting.  Varying this IV increases
   the strength of the cipher.

   If an EXT-X-KEY tag has a KEYFORMAT of "identity" and an IV attribute
   is present, implementations MUST use the attribute value as the IV
   when encrypting or decrypting with that key.  The value MUST be
   interpreted as a 128-bit number.

   If an EXT-X-KEY tag with a KEYFORMAT of "identity" does not have the
   IV attribute, implementations MUST use the sequence number of the
   media segment as the IV when encrypting or decrypting that media
   segment.  The big-endian binary representation of the sequence number
   SHALL be placed in a 16-octet buffer and padded (on the left) with
   zeros.


6.  Client/Server Actions

6.1.  Introduction

   This section describes how the server generates the Playlist and
   media segments and how the client should download and play them.




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6.2.  Server Process

6.2.1.  Introduction

   The production of the media stream is outside the scope of this
   document, which simply presumes a source of a continuous stream
   containing the presentation.

   The server MUST divide the stream into individual media segments
   whose duration is less than or equal to a constant target duration.
   The server SHOULD attempt to divide the stream 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.

   If WebVTT segments are distributed by HTTP, the server SHOULD support
   client requests to use the "gzip" Content-Encoding.

   The server MUST create a Playlist file.  The Playlist file MUST
   conform to the format described in Section 3.  A URI for each media
   segment that the server wishes to make available MUST appear in the
   Playlist in the order in which it is to be played.  The entire media
   segment MUST be available to clients if its URI is in the Playlist
   file.

   The Playlist file MUST contain an EXT-X-TARGETDURATION tag.  Its
   value MUST be equal to or greater than the EXTINF value of any media
   segment that appears or will appear in the Playlist file.  Its value
   MUST NOT change.  A typical target duration is 10 seconds.

   The Playlist file SHOULD contain one EXT-X-VERSION tag which
   indicates the compatibility version of the stream.  Its value MUST be
   the lowest protocol version with which the server, Playlist file, and
   associated media segments all comply.  Its value MUST NOT change.

   The server MUST create a URI for the Playlist file that will allow
   its clients to obtain the file.

   If the Playlist file is distributed by HTTP, the server SHOULD
   support client requests to use "gzip" Content-Encoding.

   Changes to the Playlist file MUST be made atomically from the point
   of view of the clients.



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   The server MUST NOT change the Playlist file, except to:

      Append lines to it (Section 6.2.1).

      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).

      Increment the value of the EXT-X-MEDIA-SEQUENCE tag
      (Section 6.2.2).

      Add or remove EXT-X-STREAM-INF tags or EXT-X-I-FRAME-STREAM-INF
      tags (Section 6.2.4).  Note that clients are not required to
      reload variant Playlist files, so changing them may not have
      immediate effect.

      Add an EXT-X-ENDLIST tag to the Playlist (Section 6.2.1).

   Furthermore, the Playlist file MAY contain an EXT-X-PLAYLIST-TYPE tag
   with a value of either EVENT or VOD.  If the tag is present and has a
   value of EVENT, the server MUST NOT change or delete any part of the
   Playlist file (although it MAY append lines to it).  If the tag is
   present and has a value of VOD, the Playlist file MUST NOT change.

   Every media segment in a Playlist MUST have an EXTINF tag applied to
   it indicating the duration of the media segment.

   The server MAY associate an absolute date and time with a media
   segment by applying an EXT-X-PROGRAM-DATE-TIME tag to the segment.
   The date and time value provides an informative mapping of the
   timeline of the media to an appropriate wall-clock time, 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.

   If the Playlist contains the final media segment of the presentation
   then the Playlist file MUST contain the EXT-X-ENDLIST tag.

   If the 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.

   If the server wishes to remove an entire presentation, it MUST make



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   the Playlist file unavailable to clients.  It SHOULD 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.

6.2.2.  Sliding Window 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 exactly
   one EXT-X-MEDIA-SEQUENCE tag.  Its value MUST be incremented by 1 for
   every media segment that is removed from the Playlist file.

   Media segments MUST be removed from the Playlist file in the order
   that they appear in the Playlist.

   The server MUST NOT remove a media segment from the Playlist file if
   the duration of the Playlist file minus the duration of the segment
   is less than three times the target duration.

   When the server removes a media segment from the Playlist, the
   corresponding media URI SHOULD 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.

   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.

6.2.3.  Encrypting media segments

   If media segments are to be encrypted the server MUST define a URI
   which will allow authorized clients to obtain a Key file containing a
   decryption key.  The Key file MUST conform to the format described in
   Section 5.

   The server MAY set the HTTP Expires header in the key response to
   indicate that the key may be cached.

   The server MUST encrypt every media segment in a Playlist according
   to the EXT-X-KEY tag that applies to its URI in the Playlist file.
   Media segments with an EXT-X-KEY tag whose METHOD is NONE, or which
   do not have an EXT-X-KEY tag applied to them, MUST NOT be encrypted.

   If the encryption METHOD is AES-128 and the Playlist does not contain
   the EXT-X-I-FRAMES-ONLY tag, AES-128 CBC encryption with PKCS7
   padding [RFC5652] SHALL be applied to individual media segments.  The
   entire segment MUST be encrypted.  Cipher Block Chaining MUST NOT be



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   applied across media segments.  The IV used for encryption MUST be
   either the 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.

   If the encryption METHOD is AES-128 and the Playlist contains an EXT-
   X-I-FRAMES-ONLY tag, AES-128 CBC encryption with PKCS7 padding
   [RFC5652] MUST be applied to the entire resource.  The entire
   resource MUST be encrypted.  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 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.

   If the encryption METHOD is SAMPLE-AES, certain elementary streams
   MAY be encrypted prior to encapsulation in a media segment.  The
   encryption format for H.264, AAC and AC-3 elementary streams is
   described by [SampleEnc].

   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.

6.2.4.  Providing variant streams

   A server MAY offer multiple Playlist files to provide different
   encodings of the same presentation.  If it does so it SHOULD provide
   a variant Playlist file that lists each variant stream to allow
   clients to switch between encodings dynamically.

   Variant Playlists MUST contain an EXT-X-STREAM-INF tag or EXT-X-I-
   FRAME-STREAM-INF tag for each variant stream.  Each tag identifying
   an encoding of the same presentation MUST have the same PROGRAM-ID
   attribute value.  The PROGRAM-ID value for each presentation MUST be
   unique within the variant Playlist.

   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 format
   defined by [RFC6381] that is present in any media segment that
   appears or will appear in the Playlist file.

   The server MUST meet the following constraints when producing variant
   streams:

      Each variant stream MUST present the same content, including
      stream discontinuities.

      Each variant Playlist file MUST have the same target duration.
      The only exception is that SUBTITLES renditions with a EXT-X-
      PLAYLIST-TYPE of VOD MAY have longer target durations.



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      Content that appears in one variant Playlist file but not in
      another MUST appear either at the beginning or at the end of the
      Playlist file and MUST NOT be longer than the target duration.

      Matching content in variant streams MUST have matching timestamps.
      This allows clients to synchronize the streams.

      Each Elementary Audio Stream segment MUST signal the timestamp of
      its first sample with an ID3 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.

   In addition, all variant streams SHOULD contain the same encoded
   audio bitstream.  This allows clients to switch between streams
   without audible glitching.

   The rules for variant streams also apply to alternate renditions -
   see Section 3.4.10.1.

6.3.  Client Process

6.3.1.  Introduction

   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 MUST obtain the Playlist file from the URI.  If the
   Playlist file so obtained is a variant Playlist, the client MUST
   obtain the Playlist file from the variant Playlist.

   This document does not specify the treatment of variant streams by
   clients.

6.3.2.  Loading the Playlist file

   Every time a Playlist file is loaded or reloaded from the Playlist
   URI:

      The client MUST ensure that the Playlist file begins with the
      EXTM3U tag and that the EXT-X-VERSION tag, if present, specifies a
      protocol version supported by the client; if not, the client MUST
      NOT attempt to use the Playlist.

      The client SHOULD ignore any tags and attributes it does not
      recognize.



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      The client MUST determine the next media segment to load, as
      described in Section 6.3.5.

   If the 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.

6.3.3.  Playing the Playlist file

   The client SHALL choose which media segment to play first from the
   Playlist when playback starts.  If the EXT-X-ENDLIST tag is not
   present and the client intends to play the media regularly (i.e. in
   playlist order at the nominal playback rate), the client SHOULD NOT
   choose a segment which starts less than three target durations from
   the end of the Playlist file.  Doing so can trigger playback stalls.

   To achieve regular playback, media segments MUST be played in the
   order that they appear in the Playlist file.  The client MAY present
   the available media in any way it wishes, including regular playback,
   random access, and trick modes.

   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.

   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.

   If the Playlist file contains the EXT-X-ALLOW-CACHE tag and its value
   is NO, the client MUST NOT cache downloaded media segments after they
   have been played.  Otherwise the client MAY cache downloaded media
   segments indefinitely for later replay.

   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,
   but if it does not the client MUST NOT infer an originating time
   zone.

   The client MUST NOT depend upon the correctness or the consistency of
   the value of the EXT-X-PROGRAM-DATE-TIME tag.

6.3.4.  Reloading the Playlist file

   The client MUST periodically reload the Playlist file unless it
   contains the EXT-X-ENDLIST tag.



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   However the client MUST NOT attempt to reload the Playlist file more
   frequently than specified by this section.

   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 a period of time before
   attempting to reload the Playlist file again.  This period is called
   the initial minimum reload delay.  It is measured from the time that
   the client began loading the Playlist file.

   The initial minimum reload delay is the duration of the last media
   segment in the Playlist.  Media segment duration is specified by the
   EXTINF tag.

   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.

   In order to reduce server load, the client SHOULD NOT reload the
   Playlist files of variant streams that are not currently being
   played.  If it decides to switch playback to a different variant, it
   SHOULD stop reloading the Playlist of the old variant and begin
   loading the Playlist of the new variant.  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 has been loaded, the timestamps in the media segments can be
   used to synchronize the old and new timelines precisely.  A client
   MUST NOT assume that segments with the same media sequence number in
   different variants or renditions contain matching content.

6.3.5.  Determining the next segment to load

   The client MUST examine the Playlist file every time it is loaded or
   reloaded to determine the next media segment to load.

   The first segment to load MUST be the segment that the client has
   chosen to play first, as described in Section 6.3.3.

   If the first segment to be played has been loaded and the Playlist
   file does not contain the EXT-X-MEDIA-SEQUENCE tag then the client
   MUST verify that the current Playlist file contains the URI of the
   last loaded media segment at the offset it was originally found at,
   halting playback if it does not.  The next media segment to load MUST
   be the first media segment following the last-loaded segment in the
   Playlist.

   If the first segment to be played has been loaded and the Playlist
   file contains the EXT-X-MEDIA-SEQUENCE tag then the next media



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   segment to load SHALL be the one with the lowest sequence number that
   is greater than the sequence number of the last media segment loaded.

6.3.6.  Decrypting encrypted media segments

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

   A client MUST NOT attempt to use an EXT-X-KEY tag with an unsupported
   or unrecognized KEYFORMAT attribute.  A client SHOULD fail playback
   if the Playlist contains a media segment to which only EXT-X-KEY tags
   with unrecognized or unsupported KEYFORMAT attributes are applied.

   If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
   applied to individual media segments.  The entire segment MUST be
   decrypted.  Cipher Block Chaining MUST NOT be applied across media
   segments.  The IV used for decryption MUST be either the 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.

   If the encryption METHOD is AES-128 and the media segment is part of
   an I-frame playlist (Section 3.4.12) special care MUST 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 (offset 0).  The sub-range specified by the EXT-X-BYTERANGE
   tag MUST be widened to include the 16-byte blocks in which the
   beginning and end of the sub-range fall.  Next, it MUST be widened
   further to include the previous 16-byte block.  That range MUST be
   loaded and decrypted with AES-128 CBC using an arbitrary IV.  The
   decrypted segment will then be in the original (unwidened) sub-range.

   If the encryption METHOD is SAMPLE-AES, AES-128 decryption SHALL be
   applied to encrypted elementary streams within the media segment.
   The encryption format for H.264, AAC and AC-3 elementary streams is
   described by [SampleEnc].

   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

   Clients and servers MUST implement protocol version 2 or higher to
   use:

   o  The IV attribute of the EXT-X-KEY tag.




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   Clients and servers MUST implement protocol version 3 or higher to
   use:

   o  Floating-point EXTINF duration values.

   Clients and servers MUST implement protocol version 4 or higher to
   use:

   o  The EXT-X-BYTERANGE tag.

   o  The EXT-X-I-FRAME-STREAM-INF tag.

   o  The EXT-X-I-FRAMES-ONLY tag.

   o  The EXT-X-MEDIA tag.

   o  The AUDIO and VIDEO attributes of the EXT-X-STREAM-INF tag.

   Clients and servers MUST implement protocol version 5 or higher to
   use:

   o  The KEYFORMAT and KEYFORMATVERSIONS attributes of the EXT-X-KEY
      tag.

   o  The EXT-X-MAP tag.


8.  Examples

8.1.  Introduction

   This section contains several example Playlist files.

8.2.  Simple Playlist file

   #EXTM3U
   #EXT-X-VERSION:3
   #EXT-X-TARGETDURATION:5220
   #EXTINF:5219.2,
   http://media.example.com/entire.ts
   #EXT-X-ENDLIST










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8.3.  Sliding Window 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

8.4.  Playlist file 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

8.5.  Variant Playlist file

   #EXTM3U
   #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1280000
   http://example.com/low.m3u8
   #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2560000
   http://example.com/mid.m3u8
   #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=7680000
   http://example.com/hi.m3u8
   #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=65000,CODECS="mp4a.40.5"
   http://example.com/audio-only.m3u8





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8.6.  Variant Playlist with I-Frames

   In this example, the PROGRAM-ID attributes have been left out:

   #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

8.7.  Variant Playlist with Alternative audio

   In this example, the PROGRAM-ID attributes have been left out.  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="Deutsche", \
      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,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

8.8.  Variant Playlist with Alternative video

   In this example, the PROGRAM-ID attributes have been left out.  The
   CODECS attributes have been condensed for space.  A '\' is used to
   indicate that the tag continues on the following line with whitespace
   removed:



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   #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

   #EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
   main/audio-only.m3u8


9.  Contributors

   Significant contributions to the design of this protocol were made by
   Jim Batson, David Biderman, Bill May, Roger Pantos, and Alan Tseng.


10.  IANA Considerations

   This memo requests that the following MIME type [RFC2046] be
   registered with the IANA:

   Type name: "application"




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   Subtype name: "vnd.apple.mpegurl"

   Required parameters: (none)

   Optional parameters: (none)

   Encoding considerations: encoded as text.  See Section 3 for more
   information.

   Security considerations: See Section 11.

   Compression: this media type does not employ compression.

   Interoperability considerations: There are no byte-ordering issues,
   since files are 7- or 8-bit text.  Applications could encounter
   unrecognized tags, which SHOULD be ignored.

   Published specification: see Section 3.

   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.

   Additional information: files begin with the magic number #EXTM3U.
   Filenames normally end with .m3u8 or .m3u (see Section 3).  No
   Macintosh file type codes have been registered.

   Person & email address to contact for further information: David
   Singer, singer AT apple.com.

   Intended usage: LIMITED USE

   Restrictions on usage: (none)

   Author: Roger Pantos

   Change Controller: David Singer


11.  Security Considerations

   Since the protocol generally uses HTTP to transfer data, most of the
   same security considerations apply.  See section 15 of RFC 2616
   [RFC2616].

   Media file parsers are typically subject to "fuzzing" attacks.
   Clients SHOULD take care when parsing segments received from a server
   that non-compliant segments are rejected.



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   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 RFC 3986 [RFC3986].

   Clients SHOULD load resources identified by URI lazily 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 RFC 6265 [RFC6265].  See
   also the Security Considerations section of RFC 6265, and RFC 2964
   [RFC2964].

   Encryption keys are specified by URI.  The delivery of these keys
   SHOULD be secured by a mechanism such as HTTP over TLS [RFC5246]
   (formerly SSL) in conjunction with a secure realm or a session
   cookie.


12.  References

12.1.  Normative References

   [AC_3]     Advanced Television Systems Committee, "ATSC Standard:
              A/52:2010: Digital Audio Compression (AC-3) (E-AC-3)
              Standard", November 2010,
              <http://www.atsc.org/cms/standards/a_52-2010.pdf>.

   [AES_128]  U.S. Department of Commerce/National Institute of
              Standards and Technology, "Advanced Encryption Standard
              (AES), FIPS PUB 197", November 2001, <http://
              csrc.nist.gov/publications/fips/fips197/fips-197.pdf>.

   [H_264]    International Telecommunications Union, "Advanced video
              coding for generic audiovisual services", January 2012,
              <http://www.itu.int/rec/T-REC-H.264>.

   [ISO_11172]
              International Organization for Standardization, "ISO/IEC
              International Standard 11172-1; Coding of moving pictures
              and associated audio for digital storage media -- Part 1:
              Systems", 1993,
              <http://www.iso.org/iso/catalogue_detail?csnumber=19180>.

   [ISO_13818]
              International Organization for Standardization, "ISO/IEC
              International Standard 13818; Generic coding of moving



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              pictures and associated audio information", October 2007,
              <http://www.iso.org/iso/catalogue_detail?csnumber=44169>.

   [ISO_14496]
              International Organization for Standardization, "ISO/IEC
              14496-3:2009 Information technology -- Coding of audio-
              visual objects -- Part 3: Audio", 2009,
              <http://www.iso.org/iso/catalogue_detail?csnumber=53943>.

   [ISO_8601]
              International Organization for Standardization, "ISO/IEC
              International Standard 8601:2004; Data elements and
              interchange formats -- Information interchange --
              Representation of dates and times", December 2004,
              <http://www.iso.org/iso/catalogue_detail?csnumber=40874>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2964]  Moore, K. and N. Freed, "Use of HTTP State Management",
              BCP 44, RFC 2964, October 2000.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5646]  Phillips, A. and M. Davis, "Tags for Identifying
              Languages", BCP 47, RFC 5646, September 2009.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
              April 2011.



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   [RFC6381]  Gellens, R., Singer, D., and P. Frojdh, "The 'Codecs' and
              'Profiles' Parameters for "Bucket" Media Types", RFC 6381,
              August 2011.

   [US_ASCII]
              American National Standards Institute, "ANSI X3.4-1986,
              Information Systems -- Coded Character Sets 7-Bit American
              National Standard Code for Information Interchange (7-Bit
              ASCII)", December 1986.

12.2.  Informative References

   [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",
              <http://wikipedia.org/wiki/M3U>.

   [SampleEnc]
              Apple Inc., "MPEG-2 Stream Encryption Format for HTTP Live
              Streaming", <https://developer.apple.com/library/ios/
              documentation/AudioVideo/Conceptual/
              HLS_Sample_Encryption/>.

   [UTI]      Apple Inc., "Uniform Type Identifier", <http://
              developer.apple.com/library/ios/#documentation/general/
              conceptual/DevPedia-CocoaCore/UniformTypeIdentifier.html>.

   [WebVTT]   World Wide Web Consortium (W3C), "WebVTT Standard",
              September 2012, <http://dev.w3.org/html5/webvtt/>.


Authors' Addresses

   Roger Pantos (editor)
   Apple Inc.
   Cupertino, California
   United States

   Email: http-live-streaming-review@group.apple.com










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   William May, Jr.
   Apple Inc.
   Cupertino, California
   United States

   Email: http-live-streaming-review@group.apple.com













































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