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http://tools.ietf.org/html/draft-pantos-http-live-streaming-12
Informational R. Pantos, Ed.
Internet-Draft W. May
Intended status: Informational Apple Inc.
Expires: April 17, 2014 October 14, 2013
HTTP Live Streaming
draft-pantos-http-live-streaming-12
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 6 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and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.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 17, 2014.
Copyright Notice
Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4. New Tags . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.4.1. EXT-X-BYTERANGE . . . . . . . . . . . . . . . . . . . 7
3.4.2. EXT-X-TARGETDURATION . . . . . . . . . . . . . . . . . 8
3.4.3. EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . . . . 8
3.4.4. EXT-X-KEY . . . . . . . . . . . . . . . . . . . . . . 9
3.4.5. EXT-X-PROGRAM-DATE-TIME . . . . . . . . . . . . . . . 10
3.4.6. EXT-X-ALLOW-CACHE . . . . . . . . . . . . . . . . . . 11
3.4.7. EXT-X-PLAYLIST-TYPE . . . . . . . . . . . . . . . . . 11
3.4.8. EXT-X-ENDLIST . . . . . . . . . . . . . . . . . . . . 11
3.4.9. EXT-X-MEDIA . . . . . . . . . . . . . . . . . . . . . 11
3.4.9.1. Rendition Groups . . . . . . . . . . . . . . . . . 14
3.4.10. EXT-X-STREAM-INF . . . . . . . . . . . . . . . . . . . 15
3.4.10.1. Alternative Renditions . . . . . . . . . . . . . . 16
3.4.11. EXT-X-DISCONTINUITY . . . . . . . . . . . . . . . . . 17
3.4.12. EXT-X-DISCONTINUITY-SEQUENCE . . . . . . . . . . . . . 18
3.4.13. EXT-X-I-FRAMES-ONLY . . . . . . . . . . . . . . . . . 18
3.4.14. EXT-X-MAP . . . . . . . . . . . . . . . . . . . . . . 19
3.4.15. EXT-X-I-FRAME-STREAM-INF . . . . . . . . . . . . . . . 20
3.4.16. EXT-X-START . . . . . . . . . . . . . . . . . . . . . 20
3.4.17. EXT-X-VERSION . . . . . . . . . . . . . . . . . . . . 21
4. Media segments . . . . . . . . . . . . . . . . . . . . . . . . 22
5. Key files . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 23
5.2. IV for [AES_128] . . . . . . . . . . . . . . . . . . . . . 24
6. Client/Server Actions . . . . . . . . . . . . . . . . . . . . 24
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 24
6.2. Server Process . . . . . . . . . . . . . . . . . . . . . . 24
6.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . 24
6.2.2. Live Playlists . . . . . . . . . . . . . . . . . . . . 27
6.2.3. Encrypting media segments . . . . . . . . . . . . . . 27
6.2.4. Providing variant streams . . . . . . . . . . . . . . 28
6.3. Client Process . . . . . . . . . . . . . . . . . . . . . . 29
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6.3.1. Introduction . . . . . . . . . . . . . . . . . . . . . 29
6.3.2. Loading the Playlist file . . . . . . . . . . . . . . 29
6.3.3. Playing the Playlist file . . . . . . . . . . . . . . 30
6.3.4. Reloading the Playlist file . . . . . . . . . . . . . 31
6.3.5. Determining the next segment to load . . . . . . . . . 31
6.3.6. Decrypting encrypted media segments . . . . . . . . . 32
7. Protocol version compatibility . . . . . . . . . . . . . . . . 32
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
8.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 33
8.2. Simple Media Playlist file . . . . . . . . . . . . . . . . 34
8.3. Live Media Playlist, using HTTPS . . . . . . . . . . . . . 34
8.4. Playlist file with encrypted media segments . . . . . . . 34
8.5. Master Playlist file . . . . . . . . . . . . . . . . . . . 35
8.6. Master Playlist with I-Frames . . . . . . . . . . . . . . 35
8.7. Master Playlist with Alternative audio . . . . . . . . . . 35
8.8. Master Playlist with Alternative video . . . . . . . . . . 36
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 37
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11. Security Considerations . . . . . . . . . . . . . . . . . . . 38
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.1. Normative References . . . . . . . . . . . . . . . . . . . 39
12.2. Informative References . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
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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 allows clients to choose from among different encodings of
the presentation. 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 presentation, 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 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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A Playlist is known as a Media Playlist if all URI lines in the
Playlist identify media segments. A Playlist is known as a Master
Playlist if all URI lines in the Playlist identify Media Playlists.
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 Media 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.
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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 ("), 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
characters within a quoted-string MUST NOT include linefeed (0xA),
carriage-return (0xD) or double quote (0x22). Attributes that
wish to carry these characters must do so in an escaped form, such
as percent-encoded for a URI.
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. This tag MUST be included
in both Media Playlists and Master Playlists. Its format is:
#EXTM3U
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3.3.2. EXTINF
The EXTINF tag specifies the duration of a media segment. It applies
only to the media segment that follows it, and MUST be followed by a
media segment URI. Each media segment MUST be preceded by an EXTINF
tag. Its format is:
#EXTINF:<duration>,<title>
where duration is an decimal-integer or decimal-floating-point number
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. Durations SHOULD be floating-
point if the version is equal to or greater than 3. The remainder 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, EXT-X-DISCONTINUITY-SEQUENCE, EXT-X-
START, 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. It
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MUST NOT appear in a Master Playlist.
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, when rounded to the nearest integer, MUST be less than or equal
to the target duration. This tag MUST appear once in a Media
Playlist file. It applies to the entire Playlist file. Its format
is:
#EXT-X-TARGETDURATION:<s>
where s is a decimal-integer indicating the target duration in
seconds.
The EXT-X-TARGETDURATION tag MUST NOT appear in a Master Playlist.
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>
where number is a decimal-integer. The sequence number MUST NOT
decrease.
A Media Playlist file MUST NOT contain more than one EXT-X-MEDIA-
SEQUENCE tag. If the Media 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 Media
Playlists contain matching content.
A media URI is not required to contain its sequence number.
See Section 6.2.1, Section 6.3.2 and Section 6.3.5 for information on
handling the EXT-X-MEDIA-SEQUENCE tag.
The EXT-X-MEDIA-SEQUENCE tag MUST NOT appear in a Master Playlist.
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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 REQUIRED.
The methods defined are: NONE, AES-128, and SAMPLE-AES.
An encryption method of NONE means that media segments are not
encrypted. If the encryption method is NONE, the following
attributes MUST NOT be present: URI; IV; KEYFORMAT;
KEYFORMATVERSIONS.
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.
A client MUST NOT not attempt to decrypt any segments whose EXT-X-KEY
tag has a METHOD attribute that it does not recognize.
URI
The value is a quoted-string containing a URI [RFC3986] that
specifies how to obtain the key. This attribute is REQUIRED unless
the METHOD is NONE.
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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. See Section 5.2 for when the IV attribute is
used.
KEYFORMAT
The value is a quoted-string that specifies how the key is
represented in the resource identified by the URI; see Section 5 for
more detail. This attribute is OPTIONAL; its absence indicates, an
implicit value of "identity". 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 Media Playlist file does not contain an EXT-X-KEY tag then
media segments are not encrypted.
See Section 5 for the format of the key file, and Section 5.2,
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-
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X-PROGRAM-DATE-TIME tag.
The EXT-X-PROGRAM-DATE-TIME tag MUST NOT appear in a Master Playlist.
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 a Media 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.
The EXT-X-PLAYLIST-TYPE tag MUST NOT appear in a Master Playlist.
3.4.8. EXT-X-ENDLIST
The EXT-X-ENDLIST tag indicates that no more media segments will be
added to the Media Playlist file. It MAY occur anywhere in the
Playlist file; it MUST NOT occur more than once. Its format is:
#EXT-X-ENDLIST
The EXT-X-ENDLIST tag MUST NOT appear in a Master Playlist.
3.4.9. EXT-X-MEDIA
The EXT-X-MEDIA tag is used to relate Media Playlists that contain
alternative renditions of the same content. For example, three EXT-
X-MEDIA tags can be used to identify audio-only Media Playlists that
contain English, French and Spanish renditions of the same
presentation. Or two EXT-X-MEDIA tags can be used to identify video-
only Media Playlists that show two different camera angles.
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The EXT-X-MEDIA tag stands alone, in that it does not apply to a
particular URI in the Master Playlist. Its format is:
#EXT-X-MEDIA:<attribute-list>
The following attributes are defined:
TYPE
The value is enumerated-string; valid strings are AUDIO, VIDEO,
SUBTITLES and CLOSED-CAPTIONS. 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. If the value is
CLOSED-CAPTIONS, the media segments for the video renditions can
include closed captions. This attribute is REQUIRED.
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. If
the TYPE is CLOSED-CAPTIONS, the URI attribute MUST NOT be present.
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. This attribute is REQUIRED.
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.
ASSOC-LANGUAGE
The value is a quoted-string containing an RFC 5646 [RFC5646]
language tag that identifies a language that is associated with the
rendition. An associated language is often used in a different role
than the language specified by the LANGUAGE attribute (e.g. written
vs. spoken, or as a fallback dialect). This attribute is OPTIONAL.
NAME
The value is a quoted-string containing a human-readable description
of the rendition. If the LANGUAGE attribute is present then this
description SHOULD be in that language. This attribute is REQUIRED.
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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. If it is present, its value MUST be YES
if the value of the DEFAULT attribute is YES. 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.
INSTREAM-ID
The value is a quoted-string that specifies a rendition within the
segments in the Media Playlist. This attribute is REQUIRED if the
TYPE attribute is CLOSED-CAPTIONS, in which case it MUST have one of
the values: "CC1", "CC2", "CC3", "CC4". For all other TYPE values,
the INSTREAM-ID SHOULD NOT be specified.
CHARACTERISTICS
The value is a quoted-string containing one or more Uniform Type
Identifiers [UTI] separated by comma (,) characters. This attribute
is OPTIONAL. Each UTI indicates an individual characteristic of the
rendition.
A SUBTITLES rendition MAY include the following characteristics:
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"public.accessibility.transcribes-spoken-dialog";
"public.accessibility.describes-music-and-sound"; "public.easy-to-
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. The EXT-
X-MEDIA tag MUST NOT appear in a Media Playlist.
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.
A Playlist MAY contain multiple groups of the same TYPE in order to
provide multiple encodings of each group. If it does so, each group
of the same TYPE MUST contain identical attributes, with the
exception of the URI attribute.
Each member in a group of renditions MAY have a different sample
format. However, any EXT-X-STREAM-INF tag or EXT-X-I-FRAME-STREAMINF
tag which references that group MUST have a CODECS attribute that
lists every sample format present in any rendition in the group.
Please see Section 3.4.10 and Section 3.4.15.
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3.4.10. EXT-X-STREAM-INF
The EXT-X-STREAM-INF tag specifies a variant stream, which is a set
of renditions which can be combined to play the presentation. The
attributes of the tag provide information about the variant stream.
The EXT-X-STREAM-INF tag identifies the next URI line in the Playlist
as a rendition of the variant stream.
The EXT-X-STREAM-INF tag MUST NOT appear in a Media Playlist.
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.
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 Media Playlist file. Valid format
identifiers are those in the ISO Base Media 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.
The RESOLUTION attribute is OPTIONAL but is recommended if the
variant stream includes video.
AUDIO
The value is a quoted-string. It MUST match the value of the
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GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is AUDIO. It indicates the set of
audio renditions that MAY be used when playing the presentation. See
Section 3.4.10.1.
The AUDIO attribute is OPTIONAL.
VIDEO
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is VIDEO. It indicates the set of
video renditions that MAY be used when playing the presentation. See
Section 3.4.10.1.
The VIDEO attribute is OPTIONAL.
SUBTITLES
The value is a quoted-string. It MUST match the value of the
GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in the Master
Playlist whose TYPE attribute is SUBTITLES. It indicates the set of
subtitle renditions that MAY be used when playing the presentation.
See Section 3.4.10.1.
The SUBTITLES attribute is OPTIONAL.
CLOSED-CAPTIONS
The value can be either a quoted-string or an enumerated-string with
the value NONE. If the value is a quoted-string, it MUST match the
value of the GROUP-ID attribute of an EXT-X-MEDIA tag elsewhere in
the Playlist whose TYPE attribute is CLOSED-CAPTIONS, and indicates
the set of closed-caption renditions that may be used when playlist
the presentation. See Section 3.4.10.1.
If the value is the enumerated-string value NONE, all EXT-X-STREAM-
INF tags MUST have this attribute with a value of NONE. This
indicates that there are no closed captions in any variant stream in
the Master Playlist.
The CLOSED-CAPTIONS attribute is OPTIONAL.
3.4.10.1. Alternative Renditions
When an EXT-X-STREAM-INF tag contains an AUDIO, VIDEO, SUBTITLES, or
CLOSED-CAPTIONS attribute, it indicates that alternative renditions
of the content are available for playback of that variant stream.
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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 is REQUIRED if the media type is SUBTITLES, but
OPTIONAL if the media type is VIDEO or AUDIO. If the media type is
VIDEO or AUDIO, a missing URI attribute indicates that the media data
for this rendition is included in the Media playlist of any EXT-X-
STREAM-INF tag referencing this MEDIA tag. If the media type is
AUDIO, the audio data for this rendition MUST also be present in any
video renditions specified by the EXT-X-STREAM-INF tag.
The URI attribute MUST NOT be included if the media type is CLOSED-
CAPTIONS.
Note that if a client chooses to play renditions of audio and video
that are not present in the main Media 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
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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.
The EXT-X-DISCONTINUITY tag MUST NOT appear in a Master Playlist.
3.4.12. EXT-X-DISCONTINUITY-SEQUENCE
The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between
different renditions of the same variant stream or different variant
streams that have EXT-X-DISCONTINUITY tags in their Media Playlists.
Its format is:
#EXT-X-DISCONTINUITY-SEQUENCE:<number>
where number is a decimal-integer. The discontinuity sequence number
MUST NOT decrease.
A Media Playlist MUST NOT contain more than one EXT-X-DISCONTINUITY-
SEQUENCE tag. If the Media Playlist does not contain an EXT-X-
DISCONTINUITY-SEQUENCE tag, then the discontinuity sequence number of
the first segment in the playlist SHALL be considered to be 0.
The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any EXT-X-
DISCONTINUITY tag.
A media playlist MUST NOT contain a EXT-X-DISCONTINUITY-SEQUENCE if
its EXT-X-PLAYLIST-TYPE is VOD or EVENT.
An EXT-X-DISCONTINUITY-SEQUENCE tag MUST ONLY appear in a Media
Playlist.
See Section 6.2.1 and Section 6.2.2 for more information about the
EXT-X-DISCONTINUITY-SEQUENCE tag.
3.4.13. 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.
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The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its
format is:
#EXT-X-I-FRAMES-ONLY
In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the media segment
duration (EXTINF tag value) is the time between the presentation time
of the I-frame in the media segment and the presentation time of the
next I-frame in the Playlist, or the end of the presentation if it is
the last I-frame in the Playlist.
Media resources containing I-frame segments MUST begin with either a
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.
The EXT-X-I-FRAMES-ONLY tag MUST NOT appear in a Master Playlist.
3.4.14. EXT-X-MAP
The EXT-X-MAP tag specifies how to obtain header information required
to parse the applicable media segments, such as the Transport Stream
PAT/PMT or the WebVTT header. 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.
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 segment header information. This attribute is
REQUIRED.
BYTERANGE
The value is a quoted-string specifying a byte range into the
resource identified by the URI attribute. This range SHOULD contain
only the header information. 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.
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The EXT-X-MAP tag appeared in version 5 of the protocol for use in
Media Playlist that contain the EXT-X-I-FRAMES-ONLY tag. In protocol
version 6, it may appear in any Media Playlist.
The EXT-X-MAP tag MUST NOT appear in a Master Playlist.
3.4.15. EXT-X-I-FRAME-STREAM-INF
The EXT-X-I-FRAME-STREAM-INF tag identifies a Media Playlist file
containing the I-frames of a multimedia presentation. It stands
alone, in that it does not apply to a particular URI in the Master
Playlist. Its format is:
#EXT-X-I-FRAME-STREAM-INF:<attribute-list>
All attributes defined for the EXT-X-STREAM-INF tag (Section 3.4.10)
are also defined for the EXT-X-I-FRAME-STREAM-INF tag, except for the
AUDIO, SUBTITLES and CLOSED-CAPTIONS attributes. In addition, the
following attribute is defined:
URI
The value is a quoted-string containing a URI that identifies the
I-frame 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 Master Playlist that specifies alternative VIDEO renditions and
I-frame Playlists SHOULD include an alternative I-frame VIDEO
rendition for each regular VIDEO rendition, with the same NAME and
LANGUAGE attributes.
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. The EXT-X-I-FRAME-STREAM-INF tag MUST NOT appear in
a Media Playlist.
3.4.16. EXT-X-START
The EXT-X-START tag indicates a preferred point at which to start
playing a Playlist. By default, clients SHOULD start playback at
this point when beginning a playback session. It MUST NOT appear
more than once in a Playlist. This tag is OPTIONAL.
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If the EXT-X-START tag appears in a Master Playlist, it indicates the
preferred starting point of every Media Playlist in the Master
Playlist. If this tag appears in a Media Playlist that is referenced
by a Master Playlist, then every other Media Playlist in the Master
Playlist MUST also contain an EXT-X-START tag with the same
attributes and values.
Its format is:
#EXT-X-START:<attribute list>
The following attributes are defined:
TIME-OFFSET
The value of TIME-OFFSET is a decimal-floating-point number of
seconds. A positive number indicates a time offset from the
beginning of the Playlist. A negative number indicates a negative
time offset from the end of the last segment in the Playlist. This
attribute is REQUIRED.
The absolute value of TIME-OFFSET MUST NOT be larger than the
Playlist duration.
If the Playlist does not contain the EXT-X-ENDLIST tag, the TIME-
OFFSET SHOULD NOT be within three target durations of the end of the
Playlist file.
PRECISE
The value is an enumerated-string; valid strings are YES and NO. If
the value is YES, clients SHOULD start playback at the segment
containing the TIME-OFFSET, but SHOULD NOT render media samples in
that segment whose presentation times are prior to the TIME-OFFSET.
If the value is NO, clients SHOULD attempt to render every media
sample in that segment. This attribute is OPTIONAL. If it is
missing, its value should be treated as NO.
The EXT-X-START tag appeared in version 6 of the protocol.
3.4.17. 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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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.
The EXT-X-VERSION tag MAY appear in either Master Playlist or Media
Playlist. It MUST appear in all playlists containing tags or
attributes that are not compatible with protocol version 1.
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.
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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.
The encoding parameters for samples in a media segment and across
multiple media segments in a Media Playlist SHOULD remain consistent.
However clients SHOULD deal with encoding changes as they are
encountered, for example by scaling video content to accommodate a
resolution change.
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 subtitle segment MUST either start with a WebVTT header or have
an EXT-X-MAP tag applied to it in the Media Playlist.
Within each WebVTT header there MUST be an X-TIMESTAMP-MAP metadata
header. This header synchronizes the cue timestamps in the WebVTT
file with the MPEG-2 (PES) timestamps in other renditions of the
variant stream. Its format is:
X-TIMESTAMP-MAP=LOCAL:<cue time>,MPEGTS:<MPEG-2 time>
e.g. X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
The cue timestamp in the LOCAL attribute MAY fall outside the range
of time covered by the segment.
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.
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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.
6.2. Server Process
6.2.1. Introduction
The production of the source media is outside the scope of this
document, which simply presumes a source of continuous encoded media
containing the presentation.
The server MUST divide the source media into individual media
segments whose duration is less than or equal to a constant target
duration. The server SHOULD attempt to divide the source media at
points that support effective decode of individual media segments,
e.g. on packet and key frame boundaries.
The server MUST create a URI for every media segment that enables its
clients to obtain the segment data. If a server supports partial
loading of resources (e.g. via HTTP Range requests), it MAY specify
segments as sub-ranges of larger resources using the EXT-X-BYTERANGE
tag.
If WebVTT segments are distributed by HTTP, the server SHOULD support
client requests to use the "gzip" Content-Encoding.
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The server MUST create a Media 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
Media 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 Media Playlist file MUST contain an EXT-X-TARGETDURATION tag.
Its value MUST be equal to or greater than the EXTINF duration of any
media segment that appears or will appear in the Playlist file,
rounded to the nearest integer. Its value MUST NOT change. A
typical target duration is 10 seconds.
The Playlist file SHOULD contain one EXT-X-VERSION tag which
indicates its compatibility version. 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.
The server MUST NOT change the Media 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 or EXT-X-
DISCONTINUITY-SEQUENCE tags (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 Master 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
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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.
Each segment in a Media Playlist has an integer discontinuity
sequence number. The discontinuity sequence number can be used in
addition to the timestamps within the media to synchronize media
segments across different renditions.
A segment's discontinuity sequence number is the value of the EXT-X-
DISCONTINUITY-SEQUENCE tag (or zero if none) plus the number of EXT-
X-DISCONTINUITY tags in the playlist preceding the URI line of the
segment.
A Media Playlist that contains an EXT-X-PLAYLIST-TYPE tag with a
value of EVENT or VOD MUST NOT contain an EXT-X-DISCONTINUITY-
SEQUENCE tag.
The server MAY associate an absolute date and time with a media
segment by applying an EXT-X-PROGRAM-DATE-TIME tag to it. This
defines an informative mapping of the (wall-clock) date and time
specified by the tag to the first media timestamp in the segment,
which may be used as a basis for seeking, for display, or for other
purposes. If a server provides this mapping, it SHOULD apply an EXT-
X-PROGRAM-DATE-TIME tag to every segment that has an EXT-X-
DISCONTINUITY tag applied to it.
If the Media Playlist contains the final media segment of the
presentation then the Playlist file MUST contain the EXT-X-ENDLIST
tag.
If a Media Playlist does not contain the EXT-X-ENDLIST tag, the
server MUST make a new version of the Playlist file available that
contains at least one new media segment. It MUST be made available
relative to the time that the previous version of the Playlist file
was made available: no earlier than one-half the target duration
after that time, and no later than 1.5 times the target duration
after that time.
If the server wishes to remove an entire presentation, it MUST make
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.
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6.2.2. Live Playlists
The server MAY limit the availability of media segments by removing
media segments from the Playlist file (Section 6.2.1). If media
segments are to be removed, the Playlist file MUST contain 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 the server wishes to remove segments from a Media Playlist
containing an EXT-X-DISCONTINUITY tag, the playlist MUST contain an
EXT-X-DISCONTINUITY-SEQUENCE tag.
If the server removes a EXT-X-DISCONTINUITY tag from the Media
Playlist, it MUST increment the value of the EXT-X-DISCONTINUITY-
SEQUENCE tag so that the discontinuity sequence numbers of the
segments still in the playlist remain unchanged.
If a server plans to remove a media segment after it is delivered to
clients over HTTP, it SHOULD ensure that the HTTP response contains
an Expires header that reflects the planned time-to-live.
A Live Playlist MUST NOT contain the EXT-X-PLAYLIST-TYPE tag.
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.
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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
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 Media Playlist files to provide different
encodings of the same presentation. If it does so it SHOULD provide
a Master Playlist file that lists each variant stream to allow
clients to switch between encodings dynamically.
Master Playlists MUST contain an EXT-X-STREAM-INF tag or EXT-X-I-
FRAME-STREAM-INF tag for each variant stream.
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 is
part of the variant stream, including in any rendition.
The server MUST meet the following constraints when producing variant
streams:
Each variant stream MUST present the same content, including EXT-
X-DISCONTINUITY tags at the same points in each rendition.
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Matching content in variant streams MUST have matching timestamps.
This allows clients to synchronize the media.
Each Media Playlist in each variant stream 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.
Content that appears in a Media Playlist of one variant stream but
not in another MUST appear either at the beginning or at the end
of the Media Playlist file and MUST NOT be longer than the target
duration.
If any Media Playlist in a Master Playlist contains an EXT-X-
PROGRAM-DATE-TIME tag, then all Media Playlists in that Master
Playlist MUST contain EXT-X-PROGRAM-DATE-TIME tags with consistent
mappings of date and time to media timestamps.
In addition, for broadest compatibility, variant streams SHOULD
contain the same encoded audio bitstream. This allows clients to
switch between variant streams without audible glitching.
The rules for variant streams also apply to alternative renditions -
see Section 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 Master Playlist, the client MUST
obtain the Media Playlist file from the Master 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.
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The client SHOULD ignore any tags and attributes it does not
recognize.
The client MUST determine the next media segment to load, as
described in Section 6.3.5.
If the Media Playlist contains the EXT-X-MEDIA-SEQUENCE tag, the
client SHOULD assume that each media segment in it will become
unavailable at the time that the Playlist file was loaded plus the
duration of the Playlist file.
6.3.3. Playing the Playlist file
The client SHALL choose which media segment to play first from the
Media Playlist when playback starts. If the EXT-X-ENDLIST tag is not
present and the client intends to play the media 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.
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6.3.4. Reloading the Playlist file
The client MUST periodically reload the Media 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 at least the target duration
before attempting to reload the Playlist file again, measured from
the last time the client began loading the Playlist file.
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 or alternate renditions that are
not currently being played. If it decides to switch playback to a
different variant stream, it SHOULD stop reloading the Playlist of
the old variant stream and begin loading the Playlist of the new
variant stream. It can use the EXTINF durations and the constraints
in Section 6.2.4 to determine the approximate location of
corresponding media. Once media from the new variant stream has been
loaded, the timestamps in the media segments can be used to
synchronize the old and new timelines precisely. A client MUST NOT
assume that segments with the same media sequence number in different
variant streams or different renditions contain matching content.
6.3.5. Determining the next segment to load
The client MUST examine the Media Playlist file every time it is
loaded or reloaded to determine the next media segment to load.
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
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file contains the EXT-X-MEDIA-SEQUENCE tag then the next media
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 Media 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 3.4.13) 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:
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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.
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.
Clients and servers MUST implement protocol version 6 or higher to
use:
o The EXT-X-MAP tag in a Media playlist that does not contain EXT-X-
I-FRAMES-ONLY.
The PROGRAM-ID attribute of the EXT-X-STREAM-INF and the EXT-X-I-
FRAME-STREAM-INF tags has been removed in protocol version 6.
8. Examples
8.1. Introduction
This section contains several example Playlist files.
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8.2. Simple Media Playlist file
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:5220
#EXTINF:5219.2,
http://media.example.com/entire.ts
#EXT-X-ENDLIST
8.3. Live Media Playlist, using HTTPS
#EXTM3U
#EXT-X-VERSION:3
#EXT-X-TARGETDURATION:8
#EXT-X-MEDIA-SEQUENCE:2680
#EXTINF:7.975,
https://priv.example.com/fileSequence2680.ts
#EXTINF:7.941,
https://priv.example.com/fileSequence2681.ts
#EXTINF:7.975,
https://priv.example.com/fileSequence2682.ts
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
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8.5. Master Playlist file
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000
http://example.com/low.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=2560000
http://example.com/mid.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=7680000
http://example.com/hi.m3u8
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
http://example.com/audio-only.m3u8
8.6. Master Playlist with I-Frames
#EXTM3U
#EXT-X-STREAM-INF:BANDWIDTH=1280000
low/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=86000,URI="low/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=2560000
mid/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=150000,URI="mid/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=7680000
hi/audio-video.m3u8
#EXT-X-I-FRAME-STREAM-INF:BANDWIDTH=550000,URI="hi/iframe.m3u8"
#EXT-X-STREAM-INF:BANDWIDTH=65000,CODECS="mp4a.40.5"
audio-only.m3u8
8.7. Master Playlist with Alternative audio
In this example, the CODECS attributes have been condensed for space.
A '\' is used to indicate that the tag continues on the following
line with whitespace removed:
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#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="English", \
DEFAULT=YES,AUTOSELECT=YES,LANGUAGE="en", \
URI="main/english-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Deutsch", \
DEFAULT=NO,AUTOSELECT=YES,LANGUAGE="de", \
URI="main/german-audio.m3u8"
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="aac",NAME="Commentary", \
DEFAULT=NO,AUTOSELECT=NO,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. Master Playlist with Alternative video
In this example, the CODECS attributes have been condensed for space.
A '\' is used to indicate that the tag continues on the following
line with whitespace removed:
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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, Alan Tseng, and
Eryk Vershen.
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.
[WebVTT] World Wide Web Consortium (W3C), "WebVTT: The Web Video
Text Tracks Format", July 2013,
<http://dev.w3.org/html5/webvtt/>.
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>.
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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