RFC 8216
HTTP Live Streaming
4. Playlists
This section describes the Playlist files used by HTTP Live Streaming. In this section, "MUST" and "MUST NOT" specify the rules for the syntax and structure of legal Playlist files. Playlists that violate these rules are invalid; clients MUST fail to parse them. See Section 6.3.2. The format of the Playlist files is derived from the M3U [M3U] playlist file format and inherits two tags from that earlier file format: EXTM3U (Section 4.3.1.1) and EXTINF (Section 4.3.2.1). In the specification of tag syntax, a string enclosed by <> identifies a tag parameter; its specific format is described in its tag definition. If a parameter is further surrounded by [], it is optional; otherwise, it is required. Each Playlist file MUST be identifiable either by the path component of its URI or by HTTP Content-Type. In the first case, the path MUST end with either .m3u8 or .m3u. In the second, the HTTP Content-Type MUST be "application/vnd.apple.mpegurl" or "audio/mpegurl". Clients SHOULD refuse to parse Playlists that are not so identified.
4.1. Definition of a Playlist
Playlist files MUST be encoded in UTF-8 [RFC3629]. They MUST NOT contain any Byte Order Mark (BOM); clients SHOULD fail to parse Playlists that contain a BOM or do not parse as UTF-8. Playlist files MUST NOT contain UTF-8 control characters (U+0000 to U+001F and U+007F to U+009F), with the exceptions of CR (U+000D) and LF (U+000A). All character sequences MUST be normalized according to Unicode normalization form "NFC" [UNICODE]. Note that US-ASCII [US_ASCII] conforms to these rules. Lines in a Playlist file are terminated by either a single line feed character or a carriage return character followed by a line feed character. Each line is a URI, is blank, or starts with the character '#'. Blank lines are ignored. Whitespace MUST NOT be present, except for elements in which it is explicitly specified. Lines that start with the character '#' are either comments or tags. Tags begin with #EXT. They are case sensitive. All other lines that begin with '#' are comments and SHOULD be ignored. A URI line identifies a Media Segment or a Playlist file (see Section 4.3.4.2). Each Media Segment is specified by a URI and the tags that apply to it. A Playlist is a Media Playlist if all URI lines in the Playlist identify Media Segments. A Playlist is a Master Playlist if all URI lines in the Playlist identify Media Playlists. A Playlist MUST be either a Media Playlist or a Master Playlist; all other Playlists are invalid. A URI in a Playlist, whether it is a URI line or part of a tag, MAY be relative. Any relative URI is considered to be relative to the URI of the Playlist that contains it. The duration of a Media Playlist is the sum of the durations of the Media Segments within it. The segment bit rate of a Media Segment is the size of the Media Segment divided by its EXTINF duration (Section 4.3.2.1). Note that this includes container overhead but does not include overhead imposed by the delivery system, such as HTTP, TCP, or IP headers. The peak segment bit rate of a Media Playlist is the largest bit rate of any contiguous set of segments whose total duration is between 0.5 and 1.5 times the target duration. The bit rate of a set is calculated by dividing the sum of the segment sizes by the sum of the segment durations.
The average segment bit rate of a Media Playlist is the sum of the sizes (in bits) of every Media Segment in the Media Playlist, divided by the Media Playlist duration. Note that this includes container overhead, but not HTTP or other overhead imposed by the delivery system.4.2. Attribute Lists
Certain tags have values that are attribute-lists. An attribute-list is a comma-separated list of attribute/value pairs with no whitespace. An attribute/value pair has the following syntax: AttributeName=AttributeValue An AttributeName is an unquoted string containing characters from the set [A..Z], [0..9] and '-'. Therefore, AttributeNames contain only uppercase letters, not lowercase. There MUST NOT be any whitespace between the AttributeName and the '=' character, nor between the '=' character and the AttributeValue. An AttributeValue is one of the following: o decimal-integer: an unquoted string of characters from the set [0..9] expressing an integer in base-10 arithmetic in the range from 0 to 2^64-1 (18446744073709551615). A decimal-integer may be from 1 to 20 characters long. o hexadecimal-sequence: an unquoted string of characters from the set [0..9] and [A..F] that is prefixed with 0x or 0X. The maximum length of a hexadecimal-sequence depends on its AttributeNames. o decimal-floating-point: an unquoted string of characters from the set [0..9] and '.' that expresses a non-negative floating-point number in decimal positional notation. o signed-decimal-floating-point: an unquoted string of characters from the set [0..9], '-', and '.' that expresses a signed floating-point number in decimal positional notation. o quoted-string: a string of characters within a pair of double quotes (0x22). The following characters MUST NOT appear in a quoted-string: line feed (0xA), carriage return (0xD), or double quote (0x22). Quoted-string AttributeValues SHOULD be constructed so that byte-wise comparison is sufficient to test two quoted- string AttributeValues for equality. Note that this implies case- sensitive comparison.
o enumerated-string: an unquoted character string from a set that is
explicitly defined by the AttributeName. An enumerated-string
will never contain double quotes ("), commas (,), or whitespace.
o decimal-resolution: two decimal-integers separated by the "x"
character. The first integer is a horizontal pixel dimension
(width); the second is a vertical pixel dimension (height).
The type of the AttributeValue for a given AttributeName is specified
by the attribute definition.
A given AttributeName MUST NOT appear more than once in a given
attribute-list. Clients SHOULD refuse to parse such Playlists.
4.3. Playlist Tags
Playlist tags specify either global parameters of the Playlist or
information about the Media Segments or Media Playlists that appear
after them.
4.3.1. Basic Tags
These tags are allowed in both Media Playlists and Master Playlists.
4.3.1.1. EXTM3U
The EXTM3U tag indicates that the file is an Extended M3U [M3U]
Playlist file. It MUST be the first line of every Media Playlist and
every Master Playlist. Its format is:
#EXTM3U
4.3.1.2. EXT-X-VERSION
The EXT-X-VERSION tag indicates the compatibility version of the
Playlist file, its associated media, and its server.
The EXT-X-VERSION tag applies to the entire Playlist file. Its
format is:
#EXT-X-VERSION:<n>
where n is an integer indicating the protocol compatibility version
number.
It MUST appear in all Playlists containing tags or attributes that are not compatible with protocol version 1 to support interoperability with older clients. Section 7 specifies the minimum value of the compatibility version number for any given Playlist file. A Playlist file MUST NOT contain more than one EXT-X-VERSION tag. If a client encounters a Playlist with multiple EXT-X-VERSION tags, it MUST fail to parse it.4.3.2. Media Segment Tags
Each Media Segment is specified by a series of Media Segment tags followed by a URI. Some Media Segment tags apply to just the next segment; others apply to all subsequent segments until another instance of the same tag. A Media Segment tag MUST NOT appear in a Master Playlist. Clients MUST fail to parse Playlists that contain both Media Segment tags and Master Playlist tags (Section 4.3.4).4.3.2.1. EXTINF
The EXTINF tag specifies the duration of a Media Segment. It applies only to the next Media Segment. This tag is REQUIRED for each Media Segment. Its format is: #EXTINF:<duration>,[<title>] where duration is a decimal-floating-point or decimal-integer number (as described in Section 4.2) that specifies the duration of the Media Segment in seconds. Durations SHOULD be decimal-floating- point, with enough accuracy to avoid perceptible error when segment durations are accumulated. However, if the compatibility version number is less than 3, durations MUST be integers. Durations that are reported as integers SHOULD be rounded to the nearest integer. The remainder of the line following the comma is an optional human- readable informative title of the Media Segment expressed as UTF-8 text.
4.3.2.2. EXT-X-BYTERANGE
The EXT-X-BYTERANGE tag indicates that a Media Segment is a sub-range of the resource identified by its URI. It applies only to the next URI line that follows it in the Playlist. Its format is: #EXT-X-BYTERANGE:<n>[@<o>] where n is a decimal-integer indicating the length of the sub-range in bytes. If present, o is a decimal-integer indicating the start of the sub-range, as a byte offset from the beginning of the resource. If o is not present, the sub-range begins at the next byte following the sub-range of the previous Media Segment. If o is not present, a previous Media Segment MUST appear in the Playlist file and MUST be a sub-range of the same media resource, or the Media Segment is undefined and the client MUST fail to parse the Playlist. A Media Segment without an EXT-X-BYTERANGE tag consists of the entire resource identified by its URI. Use of the EXT-X-BYTERANGE tag REQUIRES a compatibility version number of 4 or greater.4.3.2.3. EXT-X-DISCONTINUITY
The EXT-X-DISCONTINUITY tag indicates a discontinuity between the Media Segment that follows it and the one that preceded it. Its format is: #EXT-X-DISCONTINUITY The EXT-X-DISCONTINUITY tag MUST be present if there is a change in any of the following characteristics: o file format o number, type, and identifiers of tracks o timestamp sequence
The EXT-X-DISCONTINUITY tag SHOULD be present if there is a change in any of the following characteristics: o encoding parameters o encoding sequence See Sections 3, 6.2.1, and 6.3.3 for more information about the EXT- X-DISCONTINUITY tag.4.3.2.4. EXT-X-KEY
Media Segments MAY be encrypted. The EXT-X-KEY tag specifies how to decrypt them. It applies to every Media Segment and to every Media Initialization Section declared by an EXT-X-MAP tag that appears between it and the next EXT-X-KEY tag in the Playlist file with the same KEYFORMAT attribute (or the end of the Playlist file). Two or more EXT-X-KEY tags with different KEYFORMAT attributes MAY apply to the same Media Segment if they ultimately produce the same decryption key. The format is: #EXT-X-KEY:<attribute-list> The following attributes are defined: METHOD The value is an enumerated-string that specifies the encryption method. This attribute is REQUIRED. The methods defined are: NONE, AES-128, and SAMPLE-AES. An encryption method of NONE means that Media Segments are not encrypted. If the encryption method is NONE, other attributes MUST NOT be present. An encryption method of AES-128 signals that Media Segments are completely encrypted using the Advanced Encryption Standard (AES) [AES_128] with a 128-bit key, Cipher Block Chaining (CBC), and Public-Key Cryptography Standards #7 (PKCS7) padding [RFC5652]. CBC is restarted on each segment boundary, using either the Initialization Vector (IV) attribute value or the Media Sequence Number as the IV; see Section 5.2. An encryption method of SAMPLE-AES means that the Media Segments contain media samples, such as audio or video, that are encrypted using the Advanced Encryption Standard [AES_128]. How these media streams are encrypted and encapsulated in a segment depends on the
media encoding and the media format of the segment. fMP4 Media
Segments are encrypted using the 'cbcs' scheme of Common
Encryption [COMMON_ENC]. Encryption of other Media Segment
formats containing H.264 [H_264], AAC [ISO_14496], AC-3 [AC_3],
and Enhanced AC-3 [AC_3] media streams is described in the HTTP
Live Streaming (HLS) Sample Encryption specification [SampleEnc].
The IV attribute MAY be present; see Section 5.2.
URI
The value is a quoted-string containing a URI that specifies how
to obtain the key. This attribute is REQUIRED unless the METHOD
is NONE.
IV
The value is a hexadecimal-sequence that specifies a 128-bit
unsigned integer Initialization Vector to be used with the key.
Use of the IV attribute REQUIRES a compatibility version number of
2 or greater. See Section 5.2 for when the IV attribute is used.
KEYFORMAT
The value is a quoted-string that specifies how the key is
represented in the resource identified by the URI; see Section 5
for more detail. This attribute is OPTIONAL; its absence
indicates an implicit value of "identity". Use of the KEYFORMAT
attribute REQUIRES a compatibility version number of 5 or greater.
KEYFORMATVERSIONS
The value is a quoted-string containing one or more positive
integers separated by the "/" character (for example, "1", "1/2",
or "1/2/5"). If more than one version of a particular KEYFORMAT
is defined, this attribute can be used to indicate which
version(s) this instance complies with. This attribute is
OPTIONAL; if it is not present, its value is considered to be "1".
Use of the KEYFORMATVERSIONS attribute REQUIRES a compatibility
version number of 5 or greater.
If the Media Playlist file does not contain an EXT-X-KEY tag, then
Media Segments are not encrypted.
See Section 5 for the format of the Key file and Sections 5.2, 6.2.3,
and 6.3.6 for additional information on Media Segment encryption.
4.3.2.5. EXT-X-MAP
The EXT-X-MAP tag specifies how to obtain the Media Initialization Section (Section 3) required to parse the applicable Media Segments. It applies to every Media Segment that appears after it in the Playlist until the next EXT-X-MAP tag or until the end of the Playlist. Its format is: #EXT-X-MAP:<attribute-list> The following attributes are defined: URI The value is a quoted-string containing a URI that identifies a resource that contains the Media Initialization Section. This attribute is REQUIRED. BYTERANGE The value is a quoted-string specifying a byte range into the resource identified by the URI attribute. This range SHOULD contain only the Media Initialization Section. The format of the byte range is described in Section 4.3.2.2. This attribute is OPTIONAL; if it is not present, the byte range is the entire resource indicated by the URI. An EXT-X-MAP tag SHOULD be supplied for Media Segments in Playlists with the EXT-X-I-FRAMES-ONLY tag when the first Media Segment (i.e., I-frame) in the Playlist (or the first segment following an EXT- X-DISCONTINUITY tag) does not immediately follow the Media Initialization Section at the beginning of its resource. Use of the EXT-X-MAP tag in a Media Playlist that contains the EXT- X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 5 or greater. Use of the EXT-X-MAP tag in a Media Playlist that DOES NOT contain the EXT-X-I-FRAMES-ONLY tag REQUIRES a compatibility version number of 6 or greater. If the Media Initialization Section declared by an EXT-X-MAP tag is encrypted with a METHOD of AES-128, the IV attribute of the EXT-X-KEY tag that applies to the EXT-X-MAP is REQUIRED.
4.3.2.6. EXT-X-PROGRAM-DATE-TIME
The EXT-X-PROGRAM-DATE-TIME tag associates the first sample of a Media Segment with an absolute date and/or time. It applies only to the next Media Segment. Its format is: #EXT-X-PROGRAM-DATE-TIME:<date-time-msec> where date-time-msec is an ISO/IEC 8601:2004 [ISO_8601] date/time representation, such as YYYY-MM-DDThh:mm:ss.SSSZ. It SHOULD indicate a time zone and fractional parts of seconds, to millisecond accuracy. For example: #EXT-X-PROGRAM-DATE-TIME:2010-02-19T14:54:23.031+08:00 See Sections 6.2.1 and 6.3.3 for more information on the EXT-X- PROGRAM-DATE-TIME tag.4.3.2.7. EXT-X-DATERANGE
The EXT-X-DATERANGE tag associates a Date Range (i.e., a range of time defined by a starting and ending date) with a set of attribute/ value pairs. Its format is: #EXT-X-DATERANGE:<attribute-list> where the defined attributes are: ID A quoted-string that uniquely identifies a Date Range in the Playlist. This attribute is REQUIRED. CLASS A client-defined quoted-string that specifies some set of attributes and their associated value semantics. All Date Ranges with the same CLASS attribute value MUST adhere to these semantics. This attribute is OPTIONAL. START-DATE A quoted-string containing the ISO-8601 date at which the Date Range begins. This attribute is REQUIRED.
END-DATE
A quoted-string containing the ISO-8601 date at which the Date
Range ends. It MUST be equal to or later than the value of the
START-DATE attribute. This attribute is OPTIONAL.
DURATION
The duration of the Date Range expressed as a decimal-floating-
point number of seconds. It MUST NOT be negative. A single
instant in time (e.g., crossing a finish line) SHOULD be
represented with a duration of 0. This attribute is OPTIONAL.
PLANNED-DURATION
The expected duration of the Date Range expressed as a decimal-
floating-point number of seconds. It MUST NOT be negative. This
attribute SHOULD be used to indicate the expected duration of a
Date Range whose actual duration is not yet known. It is
OPTIONAL.
X-<client-attribute>
The "X-" prefix defines a namespace reserved for client-defined
attributes. The client-attribute MUST be a legal AttributeName.
Clients SHOULD use a reverse-DNS syntax when defining their own
attribute names to avoid collisions. The attribute value MUST be
a quoted-string, a hexadecimal-sequence, or a decimal-floating-
point. An example of a client-defined attribute is X-COM-EXAMPLE-
AD-ID="XYZ123". These attributes are OPTIONAL.
SCTE35-CMD, SCTE35-OUT, SCTE35-IN
Used to carry SCTE-35 data; see Section 4.3.2.7.1 for more
information. These attributes are OPTIONAL.
END-ON-NEXT
An enumerated-string whose value MUST be YES. This attribute
indicates that the end of the range containing it is equal to the
START-DATE of its Following Range. The Following Range is the
Date Range of the same CLASS that has the earliest START-DATE
after the START-DATE of the range in question. This attribute is
OPTIONAL.
An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST have a
CLASS attribute. Other EXT-X-DATERANGE tags with the same CLASS
attribute MUST NOT specify Date Ranges that overlap.
An EXT-X-DATERANGE tag with an END-ON-NEXT=YES attribute MUST NOT contain DURATION or END-DATE attributes. A Date Range with neither a DURATION, an END-DATE, nor an END-ON- NEXT=YES attribute has an unknown duration, even if it has a PLANNED- DURATION. If a Playlist contains an EXT-X-DATERANGE tag, it MUST also contain at least one EXT-X-PROGRAM-DATE-TIME tag. If a Playlist contains two EXT-X-DATERANGE tags with the same ID attribute value, then any AttributeName that appears in both tags MUST have the same AttributeValue. If a Date Range contains both a DURATION attribute and an END-DATE attribute, the value of the END-DATE attribute MUST be equal to the value of the START-DATE attribute plus the value of the DURATION attribute. Clients SHOULD ignore EXT-X-DATERANGE tags with illegal syntax.4.3.2.7.1. Mapping SCTE-35 into EXT-X-DATERANGE
Splice information carried in source media according to the SCTE-35 specification [SCTE35] MAY be represented in a Media Playlist using EXT-X-DATERANGE tags. Each SCTE-35 splice_info_section() containing a splice_null(), splice_schedule(), bandwidth_reservation(), or private_cmd() SHOULD be represented by an EXT-X-DATERANGE tag with an SCTE35-CMD attribute whose value is the big-endian binary representation of the splice_info_section(), expressed as a hexadecimal-sequence. An SCTE-35 splice out/in pair signaled by a pair of splice_insert() commands SHOULD be represented by one or more EXT-X-DATERANGE tags carrying the same ID attribute, which MUST be unique to that splice out/in pair. The "out" splice_info_section() (with out_of_network_indicator set to 1) MUST be placed in an SCTE35-OUT attribute, with the same formatting as SCTE35-CMD. The "in" splice_info_section() (with out_of_network_indicator set to 0) MUST be placed in an SCTE35-IN attribute, with the same formatting as SCTE35-CMD. An SCTE-35 splice out/in pair signaled by a pair of time_signal() commands, each carrying a single segmentation_descriptor(), SHOULD be represented by one or more EXT-X-DATERANGE tags carrying the same ID attribute, which MUST be unique to that splice out/in pair. The
"out" splice_info_section() MUST be placed in an SCTE35-OUT attribute; the "in" splice_info_section() MUST be placed in an SCTE35-IN attribute. Different types of segmentation, as indicated by the segmentation_type_id in the segmentation_descriptor(), SHOULD be represented by separate EXT-X-DATERANGE tags, even if two or more segmentation_descriptor()s arrive in the same splice_info_section(). In that case, each EXT-X-DATERANGE tag will have an SCTE35-OUT, SCTE35-IN, or SCTE35-CMD attribute whose value is the entire splice_info_section(). An SCTE-35 time_signal() command that does not signal a splice out or in point SHOULD be represented by an EXT-X-DATERANGE tag with an SCTE35-CMD attribute. The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-OUT attribute MUST be the date and time that corresponds to the program time of that splice. The START-DATE of an EXT-X-DATERANGE tag containing an SCTE35-CMD MUST be the date and time specified by the splice_time() in the command or the program time at which the command appeared in the source stream if the command does not specify a splice_time(). An EXT-X-DATERANGE tag containing an SCTE35-OUT attribute MAY contain a PLANNED-DURATION attribute. Its value MUST be the planned duration of the splice. The DURATION of an EXT-X-DATERANGE tag containing an SCTE35-IN attribute MUST be the actual (not planned) program duration between the corresponding out-point and that in-point. The END-DATE of an EXT-X-DATERANGE tag containing an SCTE35-IN attribute MUST be the actual (not planned) program date and time of that in-point. If the actual end date and time is not known when an SCTE35-OUT attribute is added to the Playlist, the DURATION attribute and the END-TIME attribute MUST NOT be present; the actual end date of the splice SHOULD be signaled by another EXT-X-DATERANGE tag once it has been established. A canceled splice SHOULD NOT appear in the Playlist as an EXT- X-DATERANGE tag.
An EXT-X-DATERANGE tag announcing a splice SHOULD be added to a Playlist at the same time as the last pre-splice Media Segment, or earlier if possible. The ID attribute of an EXT-X-DATERANGE tag MAY contain a splice_event_id and/or a segmentation_event_id, but it MUST be unique in the Playlist. If there is a possibility that an SCTE-35 id will be reused, the ID attribute value MUST include disambiguation, such as a date or sequence number.4.3.3. Media Playlist Tags
Media Playlist tags describe global parameters of the Media Playlist. There MUST NOT be more than one Media Playlist tag of each type in any Media Playlist. A Media Playlist tag MUST NOT appear in a Master Playlist.4.3.3.1. EXT-X-TARGETDURATION
The EXT-X-TARGETDURATION tag specifies the maximum Media Segment duration. The EXTINF duration of each Media Segment in the Playlist file, when rounded to the nearest integer, MUST be less than or equal to the target duration; longer segments can trigger playback stalls or other errors. It applies to the entire Playlist file. Its format is: #EXT-X-TARGETDURATION:<s> where s is a decimal-integer indicating the target duration in seconds. The EXT-X-TARGETDURATION tag is REQUIRED.4.3.3.2. EXT-X-MEDIA-SEQUENCE
The EXT-X-MEDIA-SEQUENCE tag indicates the Media Sequence Number of the first Media Segment that appears in a Playlist file. Its format is: #EXT-X-MEDIA-SEQUENCE:<number> where number is a decimal-integer. If the Media Playlist file does not contain an EXT-X-MEDIA-SEQUENCE tag, then the Media Sequence Number of the first Media Segment in the Media Playlist SHALL be considered to be 0. A client MUST NOT assume that segments with the same Media Sequence Number in different Media Playlists contain matching content (see Section 6.3.2).
A URI for a Media Segment is not required to contain its Media Sequence Number. See Sections 6.2.1 and 6.3.5 for more information on setting the EXT- X-MEDIA-SEQUENCE tag. The EXT-X-MEDIA-SEQUENCE tag MUST appear before the first Media Segment in the Playlist.4.3.3.3. EXT-X-DISCONTINUITY-SEQUENCE
The EXT-X-DISCONTINUITY-SEQUENCE tag allows synchronization between different Renditions of the same Variant Stream or different Variant Streams that have EXT-X-DISCONTINUITY tags in their Media Playlists. Its format is: #EXT-X-DISCONTINUITY-SEQUENCE:<number> where number is a decimal-integer. If the Media Playlist does not contain an EXT-X-DISCONTINUITY- SEQUENCE tag, then the Discontinuity Sequence Number of the first Media Segment in the Playlist SHALL be considered to be 0. The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before the first Media Segment in the Playlist. The EXT-X-DISCONTINUITY-SEQUENCE tag MUST appear before any EXT- X-DISCONTINUITY tag. See Sections 6.2.1 and 6.2.2 for more information about setting the value of the EXT-X-DISCONTINUITY-SEQUENCE tag.4.3.3.4. EXT-X-ENDLIST
The EXT-X-ENDLIST tag indicates that no more Media Segments will be added to the Media Playlist file. It MAY occur anywhere in the Media Playlist file. Its format is: #EXT-X-ENDLIST
4.3.3.5. EXT-X-PLAYLIST-TYPE
The EXT-X-PLAYLIST-TYPE tag provides mutability information about the Media Playlist file. It applies to the entire Media Playlist file. It is OPTIONAL. Its format is: #EXT-X-PLAYLIST-TYPE:<type-enum> where type-enum is either EVENT or VOD. Section 6.2.1 defines the implications of the EXT-X-PLAYLIST-TYPE tag. If the EXT-X-PLAYLIST-TYPE value is EVENT, Media Segments can only be added to the end of the Media Playlist. If the EXT-X-PLAYLIST-TYPE value is Video On Demand (VOD), the Media Playlist cannot change. If the EXT-X-PLAYLIST-TYPE tag is omitted from a Media Playlist, the Playlist can be updated according to the rules in Section 6.2.1 with no additional restrictions. For example, a live Playlist (Section 6.2.2) MAY be updated to remove Media Segments in the order that they appeared.4.3.3.6. EXT-X-I-FRAMES-ONLY
The EXT-X-I-FRAMES-ONLY tag indicates that each Media Segment in the Playlist describes a single I-frame. I-frames are encoded video frames whose encoding does not depend on any other frame. I-frame Playlists can be used for trick play, such as fast forward, rapid reverse, and scrubbing. The EXT-X-I-FRAMES-ONLY tag applies to the entire Playlist. Its format is: #EXT-X-I-FRAMES-ONLY In a Playlist with the EXT-X-I-FRAMES-ONLY tag, the Media Segment duration (EXTINF tag value) is the time between the presentation time of the I-frame in the Media Segment and the presentation time of the next I-frame in the Playlist, or the end of the presentation if it is the last I-frame in the Playlist. Media resources containing I-frame segments MUST begin with either a Media Initialization Section (Section 3) or be accompanied by an EXT- X-MAP tag indicating the Media Initialization Section so that clients can load and decode I-frame segments in any order. The byte range of an I-frame segment with an EXT-X-BYTERANGE tag applied to it (Section 4.3.2.2) MUST NOT include its Media Initialization Section;
clients can assume that the Media Initialization Section is defined by the EXT-X-MAP tag or is located from the start of the resource to the offset of the first I-frame segment in that resource. Use of the EXT-X-I-FRAMES-ONLY REQUIRES a compatibility version number of 4 or greater.
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