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Informational                                             R. Pantos, Ed.
Internet-Draft                                                    W. May
Intended status: Informational                                Apple Inc.
Expires: October 2, 2011                                  March 31, 2011


                          HTTP Live Streaming
                  draft-pantos-http-live-streaming-06

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 3 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   and derivative works of it may not be created, and it may not be
   published except as an Internet-Draft.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 October 2, 2011.

Copyright Notice

   Copyright (c) 2011 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.  New Tags . . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.1.  EXT-X-TARGETDURATION . . . . . . . . . . . . . . . . .  7
       3.3.2.  EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . . . .  7
       3.3.3.  EXT-X-KEY  . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.4.  EXT-X-PROGRAM-DATE-TIME  . . . . . . . . . . . . . . .  8
       3.3.5.  EXT-X-ALLOW-CACHE  . . . . . . . . . . . . . . . . . .  8
       3.3.6.  EXT-X-PLAYLIST-TYPE  . . . . . . . . . . . . . . . . .  9
       3.3.7.  EXT-X-ENDLIST  . . . . . . . . . . . . . . . . . . . .  9
       3.3.8.  EXT-X-STREAM-INF . . . . . . . . . . . . . . . . . . .  9
       3.3.9.  EXT-X-DISCONTINUITY  . . . . . . . . . . . . . . . . . 10
       3.3.10. EXT-X-VERSION  . . . . . . . . . . . . . . . . . . . . 10
   4.  Media files  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Key files  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 12
     5.2.  IV for AES-128 . . . . . . . . . . . . . . . . . . . . . . 12
   6.  Client/Server Actions  . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  Server Process . . . . . . . . . . . . . . . . . . . . . . 12
       6.2.1.  Introduction . . . . . . . . . . . . . . . . . . . . . 12
       6.2.2.  Sliding Window Playlists . . . . . . . . . . . . . . . 14
       6.2.3.  Encrypting media files . . . . . . . . . . . . . . . . 15
       6.2.4.  Providing variant streams  . . . . . . . . . . . . . . 15
     6.3.  Client Process . . . . . . . . . . . . . . . . . . . . . . 16
       6.3.1.  Introduction . . . . . . . . . . . . . . . . . . . . . 16
       6.3.2.  Loading the Playlist file  . . . . . . . . . . . . . . 16
       6.3.3.  Playing the Playlist file  . . . . . . . . . . . . . . 17
       6.3.4.  Reloading the Playlist file  . . . . . . . . . . . . . 18
       6.3.5.  Determining the next file to load  . . . . . . . . . . 18
       6.3.6.  Decrypting encrypted media files . . . . . . . . . . . 19
   7.  Protocol version compatibility . . . . . . . . . . . . . . . . 19
   8.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     8.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . 19
     8.2.  Simple Playlist file . . . . . . . . . . . . . . . . . . . 20
     8.3.  Sliding Window Playlist, using HTTPS . . . . . . . . . . . 20
     8.4.  Playlist file with encrypted media files . . . . . . . . . 20



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     8.5.  Variant Playlist file  . . . . . . . . . . . . . . . . . . 21
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 21
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
     12.2. Informative References . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24











































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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.  Each media URI refers to a media file which is a
   segment of a single contiguous stream.

   To play the stream, the client first obtains the Playlist file and
   then obtains and plays each media file 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 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, a blank,
   or starts with the comment 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 file or a variant Playlist file (see
   Section 3.3.8).

   URIs MAY be relative.  A relative URI MUST be resolved against the



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   URI of the Playlist file that contains it.

   Lines that start with the comment character '#' are either comments
   or tags.  Tags begin with #EXT.  All other lines that begin with '#'
   are comments and SHOULD be ignored.

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

   M3U 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).

   The Extended M3U file format defines two tags: EXTM3U and EXTINF.  An
   Extended M3U file is distinguished from a basic M3U file by its first
   line, which MUST be #EXTM3U.

   EXTINF is a record marker that describes the media file identified by
   the URI that follows it.  Each media file URI 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 file in
   seconds.  Integer durations 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 of the line following the comma
   is the title of the media file, which is an optional human-readable
   informative title of the media segment.

   This document defines the following new tags: 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-ENDLIST,
   EXT-X-DISCONTINUITY, and EXT-X-VERSION.

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.



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   An attribute/value pair has the following syntax:

   AttributeName=AttributeValue

   An AttributeName is an unquoted string containing characters from the
   set [A-Z].

   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.

   o  quoted-string: a string of characters within a pair of double-
      quotes (").  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, indicating horizontal and vertical pixel dimensions.

   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.

   Attribute/value pairs of type enumerated-string that contain
   unrecognized values SHOULD be ignored by the client.






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3.3.  New Tags

3.3.1.  EXT-X-TARGETDURATION

   The EXT-X-TARGETDURATION tag specifies the maximum media file
   duration.  The EXTINF duration of each media file in the Playlist
   file MUST be less than or equal to the target duration.  This tag
   MUST appear once in the Playlist file.  Its format is:

   #EXT-X-TARGETDURATION:<s>

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

3.3.2.  EXT-X-MEDIA-SEQUENCE

   Each media file URI in a Playlist has a unique integer sequence
   number.  The sequence number of a URI is equal to the sequence number
   of the URI that preceded it plus one.  The EXT-X-MEDIA-SEQUENCE tag
   indicates the sequence number of the first URI 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 URI in the playlist SHALL
   be considered to be 0.

   A media file's sequence number is not required to appear in its URI.

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

3.3.3.  EXT-X-KEY

   Media files MAY be encrypted.  The EXT-X-KEY tag provides information
   necessary to decrypt media files that follow it.  Its format is:

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

   The following attributes are defined:

   The METHOD attribute specifies the encryption method.  It is of type
   enumerated-string.  Each EXT-X-KEY tag MUST contain a METHOD
   attribute.

   Two methods are defined: NONE and AES-128.




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   An encryption method of NONE means that media files are not
   encrypted.  If the encryption method is NONE, the URI and the IV
   attributes MUST NOT be present.

   An encryption method of AES-128 means that media files are 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.

   The URI attribute specifies how to obtain the key.  Its value is a
   quoted-string that contains a URI [RFC3986] for the key.

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

   A new EXT-X-KEY supersedes any prior EXT-X-KEY.

   If the Playlist file does not contain an EXT-X-KEY tag then media
   files are not encrypted.

   See Section 5 for the format of the key file, and Section 5.2,
   Section 6.2.3 and Section 6.3.6 for additional information on media
   file encryption.

3.3.4.  EXT-X-PROGRAM-DATE-TIME

   The EXT-X-PROGRAM-DATE-TIME tag associates the beginning of the next
   media file with an absolute date and/or time.  The date/time
   representation is ISO/IEC 8601:2004 [ISO_8601] and SHOULD indicate a
   time zone.  For example:

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

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

3.3.5.  EXT-X-ALLOW-CACHE

   The EXT-X-ALLOW-CACHE tag indicates whether the client MAY or MUST
   NOT cache downloaded media files 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>




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

3.3.6.  EXT-X-PLAYLIST-TYPE

   The EXT-X-PLAYLIST-TYPE tag provides mutability information about the
   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.

3.3.7.  EXT-X-ENDLIST

   The EXT-X-ENDLIST tag indicates that no more media files 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

3.3.8.  EXT-X-STREAM-INF

   The EXT-X-STREAM-INF tag indicates that the next URI in the Playlist
   file identifies another Playlist file.  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 file, 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.



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   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 file in the Playlist file.  Valid format
   identifiers are those in the ISO File Format Name Space defined by
   RFC 4281 [RFC4281].

   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 stream.

3.3.9.  EXT-X-DISCONTINUITY

   The EXT-X-DISCONTINUITY tag indicates an encoding discontinuity
   between the media file 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.

3.3.10.  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.






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   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.


4.  Media files

   Each media file URI in a Playlist file MUST identify a media file
   which is a segment of the overall presentation.  Each media file MUST
   be formatted as an MPEG-2 Transport Stream or an MPEG-2 audio
   elementary stream [ISO_13818].

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

   A media file in a Playlist MUST be the continuation of the encoded
   stream at the end of the media file with the previous sequence number
   unless it was the first media file ever to appear in the Playlist
   file or it is prefixed by an EXT-X-DISCONTINUITY tag.

   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 one 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 within a stream inside a media
   file and between corresponding streams across multiple media files
   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.


5.  Key files







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5.1.  Introduction

   An EXT-X-KEY tag with the URI attribute identifies a Key file.  A Key
   file contains the cipher key that MUST be used to decrypt subsequent
   media files in the Playlist.

   The AES-128 encryption method uses 16-octet keys.  The format of the
   Key file is simply a packed array of these 16 octets in binary
   format.

5.2.  IV for AES-128

   128-bit AES 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 the EXT-X-KEY tag has the IV attribute, 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 hexadecimal number
   and MUST be prefixed with 0x or 0X.

   If the EXT-X-KEY tag does not have the IV attribute, implementations
   MUST use the sequence number of the media file as the IV when
   encrypting or decrypting that media file.  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 files and how the client should download and play them.

6.2.  Server Process

6.2.1.  Introduction

   The production of the MPEG-2 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 files 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 files, e.g. on packet and key
   frame boundaries.



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

   The server MUST create a Playlist file.  The Playlist file MUST
   conform to the format described in Section 3.  A URI for each media
   file 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
   file 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
   file 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 files all comply.

   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 the "gzip" Content-Encoding.

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

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

      Append lines to it (Section 6.2.1).

      Remove media file URIs from the Playlist in the order that they
      appear, along with any tags that apply only to those media files
      (Section 6.2.2).

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

      Add or remove EXT-X-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



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   present and has a value of VOD, the Playlist file MUST NOT change.

   Every media file URI in a Playlist MUST be prefixed with an EXTINF
   tag indicating the duration of the media file.

   The server MAY associate an absolute date and time with a media file
   by prefixing its URI with an EXT-X-PROGRAM-DATE-TIME tag.  The value
   of the date and time 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 place an EXT-X-PROGRAM-DATE-TIME tag
   after every EXT-X-DISCONTINUITY tag in the Playlist file.

   If the Playlist contains the final media file 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 file URI.  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
   the Playlist file unavailable to clients.  It SHOULD ensure that all
   media files 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 files to those which
   have been most recently added to the Playlist.  To do so the Playlist
   file MUST ALWAYS contain exactly one EXT-X-MEDIA-SEQUENCE tag.  Its
   value MUST be incremented by 1 for every media file URI that is
   removed from the Playlist file.

   Media file URIs MUST be removed from the Playlist file in the order
   in which they were added.

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

   When the server removes a media file URI from the Playlist, the media
   file SHOULD remain available to clients for a period of time equal to
   the duration of the media file plus the duration of the longest
   Playlist file in which the media file has appeared.



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   If a server plans to remove a media file 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 files

   If media files 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.

   If the encryption METHOD is AES-128, AES-128 CBC encryption SHALL be
   applied to individual media files.  The entire file MUST be
   encrypted.  Cipher Block Chaining MUST NOT be applied across media
   files.  The IV used for encryption MUST be either the sequence number
   of the media file or the value of the IV attribute of the EXT-X-KEY
   tag, as described in Section 5.2.

   The server MUST encrypt every media file in a Playlist using the
   method and other attributes specified by the EXT-X-KEY tag that most
   immediately precedes its URI in the Playlist file.  Media files
   preceded by an EXT-X-KEY tag whose METHOD is NONE, or not preceded by
   any EXT-X-KEY tag, MUST NOT be encrypted.

   The server MUST NOT remove an EXT-X-KEY tag from the Playlist file if
   the Playlist file contains a URI to a media file encrypted with that
   key.

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 for each
   variant stream.  Each EXT-X-STREAM-INF tag for 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 contains the CODECS attribute, the
   attribute value MUST include every format defined by [RFC4281] that
   is present in any media file that appears or will appear in the
   Playlist file.




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   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.

      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.

      Elementary Audio Stream files MUST signal the timestamp of the
      first sample in the file by prepending an ID3 PRIV tag [ID3] with
      an owner identifier of
      "com.apple.streaming.transportStreamTimestamp".  The binary data
      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.

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



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      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.

      The client MUST determine the next media file 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 file in it will become unavailable at
   the time that the Playlist file was loaded plus the duration of the
   Playlist file.  The duration of a Playlist file is the sum of the
   durations of the media files within it.

6.3.3.  Playing the Playlist file

   The client SHALL choose which media file 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 file 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 files 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 file that is preceded by an EXT-X-
   DISCONTINUITY tag.

   The client SHOULD attempt to load media files 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 files after they
   have been played.  Otherwise the client MAY cache downloaded media
   files 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.




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   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.

   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
   file in the Playlist.  Media file 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 time before retrying.  The
   minimum delay is a multiple of the target duration.  This multiple is
   0.5 for the first attempt, 1.5 for the second, and 3.0 thereafter.

   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 files can be
   used to synchronize the old and new timelines precisely.

6.3.5.  Determining the next file to load

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

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

   If the first file 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



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   loaded media file at the offset it was originally found at, halting
   playback if it does not.  The next media file to load MUST be the
   first media file URI following the last-loaded URI in the Playlist.

   If the first file to be played has been loaded and the Playlist file
   contains the EXT-X-MEDIA-SEQUENCE tag then the next media file to
   load SHALL be the one with the lowest sequence number that is greater
   than the sequence number of the last media file loaded.

6.3.6.  Decrypting encrypted media files

   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 files following the EXT-X-KEY tag until
   another EXT-X-KEY tag is encountered.

   If the encryption METHOD is AES-128, AES-128 CBC decryption SHALL be
   applied to individual media files.  The entire file MUST be
   decrypted.  Cipher Block Chaining MUST NOT be applied across media
   files.  The IV used for decryption MUST be either the sequence number
   of the media file or the value of the IV attribute of the EXT-X-KEY
   tag, as described in Section 5.2.

   If the encryption METHOD is NONE, the client MUST treat all media
   files following the EXT-X-KEY tag as cleartext (not encrypted) until
   another EXT-X-KEY tag is encountered.


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.

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

   o  Floating-point EXTINF duration values.


8.  Examples

8.1.  Introduction

   This section contains several example Playlist files.





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8.2.  Simple Playlist file

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

8.3.  Sliding Window Playlist, using HTTPS

   #EXTM3U
   #EXT-X-TARGETDURATION:8
   #EXT-X-MEDIA-SEQUENCE:2680

   #EXTINF:8,
   https://priv.example.com/fileSequence2680.ts
   #EXTINF:8,
   https://priv.example.com/fileSequence2681.ts
   #EXTINF:8,
   https://priv.example.com/fileSequence2682.ts

8.4.  Playlist file with encrypted media files

   #EXTM3U
   #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:15,
   http://media.example.com/fileSequence52-1.ts
   #EXTINF:15,
   http://media.example.com/fileSequence52-2.ts
   #EXTINF:15,
   http://media.example.com/fileSequence52-3.ts

   #EXT-X-KEY:METHOD=AES-128,URI="https://priv.example.com/key.php?r=53"

   #EXTINF:15,
   http://media.example.com/fileSequence53-1.ts











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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


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"

   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 (OS 3.0) and QuickTime Player in Mac OS X
   Snow Leopard.



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   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 files received from a server so
   that non-compliant files are rejected.

   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 2965 [RFC2965].  See
   also the Security Considerations section of RFC 2965, 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




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12.1.  Normative References

   [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>.

   [ISO_13818]
              International Organization for Standardization, "ISO/IEC
              International Standard 13818; Generic coding of moving
              pictures and associated audio information", October 2007,
              <http://www.iso.org/iso/catalogue_detail?csnumber=44169>.

   [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.

   [RFC2965]  Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, 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.

   [RFC4281]  Gellens, R., Singer, D., and P. Frojdh, "The Codecs
              Parameter for "Bucket" Media Types", RFC 4281,
              November 2005.




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

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

   [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>.


Authors' Addresses

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

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


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

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













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