Informational R. Pantos, Ed.
Internet-Draft Apple Inc.
Intended status: Informational April 2, 2010
Expires: October 4, 2010
HTTP Live Streaming
draft-pantos-http-live-streaming-03
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 2 of this protocol.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Playlist file . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. New Tags . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. EXT-X-TARGETDURATION . . . . . . . . . . . . . . . . . 6
3.2.2. EXT-X-MEDIA-SEQUENCE . . . . . . . . . . . . . . . . . 6
3.2.3. EXT-X-KEY . . . . . . . . . . . . . . . . . . . . . . 6
3.2.4. EXT-X-PROGRAM-DATE-TIME . . . . . . . . . . . . . . . 7
3.2.5. EXT-X-ALLOW-CACHE . . . . . . . . . . . . . . . . . . 7
3.2.6. EXT-X-ENDLIST . . . . . . . . . . . . . . . . . . . . 7
3.2.7. EXT-X-STREAM-INF . . . . . . . . . . . . . . . . . . . 8
3.2.8. EXT-X-DISCONTINUITY . . . . . . . . . . . . . . . . . 8
3.2.9. EXT-X-VERSION . . . . . . . . . . . . . . . . . . . . 9
4. Media files . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Key files . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. IV for AES-128 . . . . . . . . . . . . . . . . . . . . . . 10
6. Client/Server Actions . . . . . . . . . . . . . . . . . . . . 11
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Server Process . . . . . . . . . . . . . . . . . . . . . . 11
6.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . 11
6.2.2. Sliding Window Playlists . . . . . . . . . . . . . . . 12
6.2.3. Encrypting media files . . . . . . . . . . . . . . . . 13
6.2.4. Providing variant streams . . . . . . . . . . . . . . 13
6.3. Client Process . . . . . . . . . . . . . . . . . . . . . . 14
6.3.1. Introduction . . . . . . . . . . . . . . . . . . . . . 14
6.3.2. Loading the Playlist file . . . . . . . . . . . . . . 14
6.3.3. Playing the Playlist file . . . . . . . . . . . . . . 15
6.3.4. Reloading the Playlist file . . . . . . . . . . . . . 16
6.3.5. Determining the next file to load . . . . . . . . . . 16
6.3.6. Decrypting encrypted media files . . . . . . . . . . . 17
7. Protocol version compatibility . . . . . . . . . . . . . . . . 17
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Simple Playlist file . . . . . . . . . . . . . . . . . . . 17
8.3. Sliding Window Playlist, using HTTPS . . . . . . . . . . . 18
8.4. Playlist file with encrypted media files . . . . . . . . . 18
8.5. Variant Playlist file . . . . . . . . . . . . . . . . . . 18
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 19
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
11. Security Considerations . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22
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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 3.2.7).
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 that specifies the duration of the media
file in seconds. Durations SHOULD be rounded to the nearest integer.
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-STREAM-INF, EXT-X-ENDLIST, EXT-X-DISCONTINUITY,
and EXT-X-VERSION.
3.2. New Tags
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3.2.1. 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.
3.2.2. EXT-X-MEDIA-SEQUENCE
Each media file URI in a Playlist has a unique 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.
3.2.3. 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:METHOD=<method>[,URI="<URI>"][,IV=<IV>]
The METHOD attribute specifies the encryption method. Two encryption
methods are defined: NONE and AES-128.
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,
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the URI attribute MUST be present. The IV attribute MAY be present;
see Section 5.2.
The URI attribute, if present, specifies how to obtain the key. The
IV attribute, if present, specifies the Initialization Vector to be
used with the key. 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.
3.2.4. 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.
3.2.5. 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>
See Section 6.3.3 for more information on the EXT-X-ALLOW-CACHE tag.
3.2.6. 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
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3.2.7. 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=value][,attribute=value]*
<URI>
An attribute MUST NOT occur more than once in the same EXT-X-STREAM-
INF tag. The following attributes are defined:
BANDWIDTH=<n>
where n is a number 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.
PROGRAM-ID=<i>
where i is a number that uniquely identifies a particular
presentation within the scope of the Playlist file.
A Playlist file MAY contain multiple EXT-X-STREAM-INF tags with the
same PROGRAM-ID to identify different encodings of the same
presentation. These variant playlists MAY contain additional EXT-X-
STREAM-INF tags.
CODECS="[format][,format]*"
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].
RESOLUTION=<N>x<M>
where N is the approximate encoded horizontal resolution of video
within the stream, expressed as a number of pixels, and M is the
approximate encoded vertical resolution.
3.2.8. 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:
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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.
3.2.9. 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.
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.
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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 to appear in the Playlist file or
if it is preceded by an EXT-X-DISCONTINUITY tag.
Clients SHOULD be prepared to handle multiple tracks of a particular
type (e.g. audio or video) by choosing a reasonable subset. 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
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.
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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 approximately equal. 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.
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. It MUST
indicate the maximum EXTINF value of any media file added to the
Playlist file. Its value MUST remain constant for the entire
presentation. 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 SHOULD
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.
Changes to the Playlist file MUST be made atomically from the point
of view of the clients.
The server MUST NOT change the value of the EXT-X-ALLOW-CACHE tag.
Every media file URI in a Playlist MUST be prefixed with an EXTINF
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tag indicating the rounded 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.
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.
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.
The duration of a Playlist file that does not contain the EXT-X-
ENDLIST tag MUST be at least three times the target duration.
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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 URI of every EXT-X-KEY tag must be distinct from the URI of every
other EXT-X-KEY tag that appears or has appeared in the Playlist
file, unless its METHOD is NONE. An EXT-X-KEY tag with a METHOD of
NONE MUST NOT contain a URI attribute.
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.
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
protocol version supported by the client; if not, the client MUST
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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.
The client MUST NOT depend upon the correctness or the consistency of
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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.
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
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.
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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.
8. Examples
8.1. Introduction
This section contains several example Playlist files.
8.2. Simple Playlist file
#EXTM3U
#EXT-X-TARGETDURATION:5220
#EXTINF:5220,
http://media.example.com/entire.ts
#EXT-X-ENDLIST
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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
8.5. Variant Playlist file
#EXTM3U
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1280000
http://example.com/low.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2560000
http://example.com/mid.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=7680000
http://example.com/hi.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=65000,CODECS="mp4a.40.5"
http://example.com/audio-only.m3u8
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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.
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
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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
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>.
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[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.
[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)",
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.
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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>.
Author's Address
Roger Pantos (editor)
Apple Inc.
Cupertino, California
United States
Email: http-live-streaming-review@group.apple.com
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