The 'Codecs' and 'Profiles' Parameters for "Bucket" Media Types
draft-gellens-mime-bucket-bis-09
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6381.
|
|
|---|---|---|---|
| Authors | Per Frojdh , David Singer , Randall Gellens | ||
| Last updated | 2018-12-20 (Latest revision 2011-08-03) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 6381 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Pete Resnick | ||
| Send notices to | (None) |
draft-gellens-mime-bucket-bis-09
Network Working Group R. Gellens
Internet-Draft QUALCOMM Incorporated
Obsoletes: 4281 (if approved) D. Singer
Updates: 3839,4393,4337 Apple Inc.
(if approved) P. Frojdh
Intended status: Standards Track Ericsson AB
Expires: February 4, 2012 August 3, 2011
The Codecs and Profiles Parameters for "Bucket" Media Types
draft-gellens-mime-bucket-bis-09.txt
Abstract
Several MIME type/subtype combinations exist that can contain
different media formats. A receiving agent thus needs to examine the
details of such media content to determine if the specific elements
can be rendered given an available set of codecs. Especially when
the end system has limited resources, or the connection to the end
system has limited bandwidth, it is helpful to know from the Content-
Type alone if the content can be rendered.
This document specifies two parameters, "codecs" and "profiles",
which are used with various MIME types or type/subtype combinations
to allow for unambiguous specification of the codecs employed by the
media formats contained within, or the profile(s) of the overall
container format. This document obsoletes RFC 4281; RFC 4281 defines
the "codecs" parameter, which this document retains in a backwards
compatible manner with minor clarifications; the "profiles" parameter
is added by this document.
By labeling content with the specific codecs indicated to render the
contained media, receiving systems can determine if the codecs are
supported by the end system, and if not, can take appropriate action
(such as rejecting the content, sending notification of the
situation, transcoding the content to a supported type, fetching and
installing the required codecs, further inspection to determine if it
will be sufficient to support a subset of the indicated codecs, etc.)
Similarly, the profiles can provide an overall indication, to the
receiver, of the specifications with which the content complies.
This is an indication of the compatibility of the container format
and its contents to some specification. The receiver may be able to
work out the extent to which it can handle and render the content by
examining to see which of the declared profiles it supports, and what
they mean.
Status of this Memo
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This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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 February 4, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions Used in This Document . . . . . . . . . . . . . . 6
3. The Codecs Parameter . . . . . . . . . . . . . . . . . . . . . 7
3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Generic Syntax . . . . . . . . . . . . . . . . . . . . . . 9
3.3. ISO File Format Name Space . . . . . . . . . . . . . . . . 10
3.4. ISO Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Use in Additional Media Types . . . . . . . . . . . . . . 12
3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.7. Additional Media Feature Details . . . . . . . . . . . . . 13
4. The Profiles Parameter . . . . . . . . . . . . . . . . . . . . 15
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 15
4.2. Formal Declaration . . . . . . . . . . . . . . . . . . . . 15
4.3. Profiles Parameter Definition . . . . . . . . . . . . . . 16
4.4. Profiles for files carrying MP4RA registered brands . . . 17
4.5. Profiles Parameter BNF Definition . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6. Registration . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. Differences from RFC 4281 . . . . . . . . . . . . . . . . . . 21
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . . 23
10.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
One of the original motivations for MIME is the ability to identify
the specific media type of a message part. However, due to various
factors, it is not always possible from looking at the MIME type and
subtype to know which specific media formats are contained in the
body part, or which codecs are indicated in order to render the
content.
There are several media type/subtypes (either currently registered or
deployed with registration pending) that contain codecs chosen from a
set. In the absence of the parameters described here, it is
necessary to examine each media element in order to determine the
codecs or other features required to render the content. For
example, video/3gpp may contain any of the video formats H.263
Profile 0, H.263 Profile 3, H.264, MPEG-4 Simple Profile, and/or any
of the audio formats Adaptive Multi Rate (AMR), Adaptive Multi Rate -
WideBand (AMR-WB), Extended AMR-WB, Advanced Audio Coding (AAC), or
Enhanced aacPlus, as specified in [3GPP-Formats].
In some cases, the specific codecs can be determined by examining the
header information of the media content. While this isn't as bad as
examining the entire content, it still requires specialized knowledge
of each format and is resource consumptive.
This ambiguity can be a problem for various clients and servers. For
example, it presents a significant burden to Multimedia Messaging
(MMS) servers, which must examine the media sent in each message in
order to determine which codecs are required to render the content.
Only then can such a server determine if the content requires
transcoding or specialized handling prior to being transmitted to the
handset.
Additionally, it presents a challenge to smart clients on devices
with constrained memory, processing power, or transmission bandwidth
(such as cellular telephones and PDAs). Such clients often need to
determine in advance if they are currently capable of rendering the
content contained in an MMS or email message.
Ambiguity:
o audio/3gpp can contain AMR, AAC, AMR-WB, Extended AMR-WB, or
Enhanced aacPlus contents as specified in [3GPP-Formats].
o audio/3gpp2 can contain AMR, AAC, 13K (as per [RFC3625]), Enhanced
Variable Rate Codec (EVRC), Selectable Mode Vocoder (SMV), or
VMR-WB, as specified in [3GPP2-Formats].
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o video/3gpp can contain H.263 Profile 0, H.263 Profile 3, H.264,
MPEG-4 Simple Profile, and/or AMR, AMR-WB, Extended AMR-WB, AAC,
or Enhanced aacPlus, as specified in [3GPP-Formats].
o video/3gpp2 can contain H.263 Profile 0, H.263 Profile 3, H.264,
MPEG-4 Simple Profile, and/or AMR, AAC, 13K (as per [RFC3625]),
EVRC, SMV, or VMR-WB, as specified in [3GPP2-Formats].
o audio/mp4 can include any codec defined in MPEG-1, MPEG-2, MPEG-4
or registered at the MP4 registration authority [MP4RA].
o video/mp4 has the same issues as audio/mp4, and in addition many
video codecs, and especially the MPEG codecs, have a variety of
profiles and levels, not all of which are supported by every
implementation.
Note that there are additional media types that are ambiguous, but
are outside the scope of this document, including:
o video/mpeg4-generic, which can contain anything allowed by the
MPEG-4 specification, or any codec registered with the MP4
registration authority [MP4RA];
With each "bucket" type, a receiving agent only knows that it has a
container format. It doesn't even know whether content labeled
video/3gpp or video/3gpp2 contains video; it might be audio only,
audio and video, or video only.
A solution that permits a receiving agent to determine the specific
codecs or profiles required to render media content would help
provide efficient and scalable servers, especially for Multimedia
Messaging (MMS), and aid the growth of multimedia services in
wireless networks.
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2. Conventions Used in This Document
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 "Key words for use in
RFCs to Indicate Requirement Levels" [RFC2119] .
The syntax in this document uses the BNF rules specified in [RFC2045]
and [RFC2231].
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3. The Codecs Parameter
3.1. Introduction
This section adds a parameter to allow unambiguous specification of
all codecs indicated to render the content in the MIME part. This
parameter is optional in all current types to which it is added.
Future types that contain ambiguity are strongly encouraged to
include this parameter.
This parameter applies to:
1. Files in the family based on the ISO Base Media File Format
[ISO14496-12].
2. The QuickTime file format, owned by Apple Inc.
This includes the media types:
1. audio/3gpp, video/3gpp [RFC3839]
2. audio/3gpp2, video/3gpp2 [RFC4393]
3. audio/mp4, video/mp4, application/mp4 [RFC4337]
4. video/quicktime
5. application/mp21 (see note below)
Note that MPEG-21 files under the type application/mp21 may, but are
not required to, contain a top-level 'moov' atom providing a timed,
coded, resource. The codecs parameter SHOULD only be used for
MPEG-21 files when this timed material is also present in the file.
Parameter name: codecs
Parameter value: A single value, or a comma-separated list of values
identifying the codec(s) indicated to render the content in the body
part.
Each value consists of one or more dot-separated elements. The name
space for the first element is determined by the MIME type. The name
space for each subsequent element is determined by the preceding
element. The precise syntax is given below in the Generic Syntax
(Section 3.2).
Note that, per [RFC2045], some characters (including the comma used
to separate multiple values) require that the entire parameter value
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be enclosed in quotes.
An element MAY include an octet that [RFC2045] requires to be
encoded. In this case, [RFC2231] is used: an asterisk ("*") is
placed at the end of the parameter name (becoming "codecs*" instead
of "codecs"), the parameter value usually starts with two single
quote ("'") characters (indicating that neither character set nor
language is specified), and each octet that requires encoding is
represented as a percent sign ("%") followed by two hexadecimal
digits. Note that, when the [RFC2231] form is used, the percent
sign, asterisk, and single quote characters have special meaning and
so MUST themselves be percent encoded.
Examples of Generic Syntax:
codecs=a.bb.ccc.d
codecs="a.bb.ccc.d, e.fff"
codecs*=''fo%2e
codecs*="''%25%20xz, gork"
When the codecs parameter is used, it MUST contain all codecs
indicated by the content present in the body part. The codecs
parameter MUST NOT include any codecs that are not indicated by any
media elements in the body part.
In some cases, not all indicated codecs are absolutely required in
order to render the content. Therefore, when a receiver does not
support all listed codecs, special handling might be required. For
example, the media element(s) could be examined in order to determine
if an unsupported codec is actually required (e.g., there may be
alternative tracks (such as English and Spanish audio), there may be
timed text that can be dropped, etc.)
Although the encoder MUST create parameter values that are complete
and accurate in 'breadth' (that is, the encoder MUST report all four-
character codes used in all tracks for ISO-family files, for example)
receivers MUST NOT rely on the parameter values being complete in
'depth'. (If the hierarchical rules for a given code (e.g., 'qvxy')
were written after a server was implemented, for example, that server
will not know what elements to place after 'qvxy').
Although a mismatch is not permitted by this specification, the body-
part is definitive of the actual codecs needed; the parameter
supplied here is informative. If a receiver encounters a body part
whose codecs parameter contains codecs that are not indicated by any
media elements, then the receiver SHOULD process the body part by
discarding the information in the codecs parameter.
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If a receiver encounters a body part whose codecs parameter does not
contain all codecs indicated by the media elements, then the receiver
MAY process the body part by discarding the information in the codecs
parameter.
3.2. Generic Syntax
The codecs parameter takes either of two forms. The first form is
used when the value does not contain any octets that require
encoding. The second form uses [RFC2231] to allow arbitrary octets
to be encoded. With either form, quotes allow for commas and other
characters in <tspecials> (quotes MAY be used even when not
required).
This BNF uses the rules specified in [RFC2045] and [RFC2231].
While [RFC2231] allows specification of character set and language,
this parameter does not contain items intended for human consumption,
and hence makes no use of language. The language element SHOULD be
omitted; the character set SHOULD also be omitted. A receiver MAY
ignore language and MAY choose to support only US-ASCII [RFC1345] and
UTF-8 [RFC3629].
Implementations MUST NOT add CFWS between the tokens except after
",". TOKEN is defined in [RFC2045], and <ext-octet> and <attribute-
char> are defined in [RFC2231].
The BNF syntax is as follows:
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codecs := cod-simple / cod-fancy
cod-simple := "codecs" "=" unencodedv
unencodedv := id-simple / simp-list
simp-list := DQUOTE id-simple *( "," id-simple ) DQUOTE
id-simple := element
; "." reserved as hierarchy delimiter
element := 1*octet-sim
octet-sim := <any TOKEN character>
; Within a codecs parameter value, "." is reserved
; as a hierarchy delimiter
cod-fancy := "codecs*" "=" encodedv
encodedv := fancy-sing / fancy-list
fancy-sing := [charset] "'" [language] "'" id-encoded
; Parsers MAY ignore <language>
; Parsers MAY support only US-ASCII and UTF-8
fancy-list := DQUOTE [charset] "'" [language] "'" id-list DQUOTE
; Parsers MAY ignore <language>
; Parsers MAY support only US-ASCII and UTF-8
id-list := id-encoded *( "," id-encoded )
id-encoded := encoded-elm *( "." encoded-elm )
; "." reserved as hierarchy delimiter
encoded-elm := 1*octet-fancy
octet-fancy := ext-octet / attribute-char
DQUOTE := %x22 ; " (double quote)
Initial name space: This document only defines values for files in
the ISO Base Media File Format, and QuickTime, families. Other file
formats may also define codec naming.
3.3. ISO File Format Name Space
For the ISO Base Media File Format, and the QuickTime movie file
format, the first element of a codecs parameter value is a sample
description entry four-character code as registered by the MP4
Registration Authority [MP4RA]. Values are case sensitive.
Note that there are potentially multiple tracks in a file, each
potentially carrying multiple sample entries (some but not all uses
of the ISO File Format restrict the number of sample entries in a
track to one).
When the first element of a value is 'mp4a' (indicating some kind of
MPEG-4 audio), or 'mp4v' (indicating some kind of MPEG-4 part-2
video), or 'mp4s' (indicating some kind of MPEG-4 Systems streams
such as MPEG-4 BIFS), the second element is the hexadecimal
representation of the MP4 Registration Authority ObjectTypeIndication
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(OTI), as specified in [MP4RA] and [MP41] (including amendments).
Note that [MP4RA] uses a leading "0x" with these values, which is
omitted here and hence implied.
One of the OTI values for 'mp4a' is 40 (identifying MPEG-4 audio).
For this value, the third element identifies the audio
ObjectTypeIndication (OTI) as defined in [MP4A] (including
amendments), expressed as a decimal number.
For example, AAC low complexity has the value 2, so a complete string
for AAC-LC would be "mp4a.40.2".
One of the OTI values for 'mp4v' is 20 (identifying MPEG-4 part-2
video). For this value, the third element identifies the video
ProfileLevelIndication as defined in [MP4V] (including amendments),
expressed as a decimal number.
For example, MPEG-4 Visual Simple Profile Level 0 has the value 9, so
a complete string for MPEG-4 Visual Simple Profile Level 0 would be
"mp4v.20.9".
When the first element of a value is a code indicating a codec from
the Advanced Video Coding specification [AVC], specifically one of
the sample entries defined in [AVC-Formats] (such as 'avc1', 'avc2',
'svc1', 'mvc1' and 'mvc2') - indicating AVC (H.264), Scalable Video
Coding (SVC) or Multiview Video Coding (MVC), the second element
(referred to as 'avcoti' in the formal syntax) is the hexadecimal
representation of the following three bytes in the (subset) sequence
parameter set NAL unit specified in [AVC]:
(1) profile_idc,
(2) the byte containing the constraint_set flags (currently
constraint_set0_flag through constraint_set5_flag, and the
reserved_zero_2bits) and
(3) level_idc.
Note that the sample entries 'avc1' and 'avc2' do not necessarily
indicate that the media only contains AVC NAL units. In fact, the
media may be encoded as an SVC or MVC profile and thus contain SVC or
MVC NAL units. In order to be able to determine which codec is used
further information is necessary (profile_idc). Note also that
reserved_zero_2bits is required to be equal to 0 in [AVC], but other
values for it may be specified in the future by ITU-T or ISO/IEC.
This is as previously defined in the 3GPP File Format specification
3GPP TS 26.244 [3GPP-Formats], section A.2.2.
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When SVC or MVC content is coded in an AVC-compatible fashion, the
sample description may include both an AVC configuration record and
an SVC or MVC configuration record. Under those circumstances, it is
recommended that the two configuration records both be reported as
they may contain different AVC profile, level, and compatibility
indicator values. Thus the codecs reported would include the sample
description code (e.g. 'avc1') twice, with the values from one of the
configuration records forming the 'avcoti' information in each.
3.4. ISO Syntax
id-simple :=/ id-iso
id-encoded :=/ id-iso
id-iso := iso-gen / iso-mpega / iso-mpegv / iso-avc
iso-gen := cpid *( element / encoded-elm )
; <element> used with <codecs-simple>
; <encoded-elm> used with <codecs-fancy>
;
; Note that the BNF permits "." within <element>
; and <encoded-elm> but "." is reserved as the
; hierarchy delimiter
iso-mpega := mp4a "." oti [ "." aud-oti ]
iso-mpegv := mp4v "." oti [ "." vid-pli ]
iso-avc := avc1 / avc2 / svc1 / mvc1 / mvc2 [ "." avcoti ]
cpid := 4(octet-simple / octet-fancy)
; <octet-simple> used with <codecs-simple>
; <octet-fancy> used with <codecs-fancy>
mp4a := %x6d.70.34.61 ; 'mp4a'
oti := 2(DIGIT / "A" / "B" / "C" / "D" / "E" / "F")
; leading "0x" omitted
avc1 := %x61.76.63.31 ; 'avc1'
avc2 := %x61.76.63.32 ; 'avc2'
svc1 := %x73.76.63.31 ; 'svc1'
mvc1 := %x6d.76.63.31 ; 'mvc1'
mvc2 := %x6d.76.63.32 ; 'mvc2'
avcoti := 6(DIGIT / "A" / "B" / "C" / "D" / "E" / "F")
; leading "0x" omitted
aud-oti := 1*DIGIT
mp4v := %x6d.70.34.76 ; 'mp4v'
vid-pli := 1*DIGIT
3.5. Use in Additional Media Types
This parameter MAY be specified for use with additional MIME media
types.
For ISO file formats where the name space as defined here is
sufficient, all that needs to be done is to update the media type
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registration to specify the codecs parameter with a reference to this
document. For existing media types, it is generally advisable for
the parameter to be optional; for new media types, the parameter MAY
be optional or required, as appropriate.
For ISO file formats where the name space as defined here needs to be
expanded, a new document MAY update this one by specifying the
additional detail.
For non-ISO formats, a new document MAY update this one by specifying
the name space for the media type(s).
3.6. Examples
Content-Type: video/3gpp2; codecs="sevc, s263"
(EVRC audio plus H.263 video)
Content-Type: audio/3gpp; codecs=samr
(AMR audio)
Content-Type: video/3gpp; codecs="s263, samr"
(H.263 video plus AMR audio)
Content-Type: audio/3gpp2; codecs=mp4a.E1
(13k audio)
Content-Type: video/3gpp2; codecs="mp4v.20.9, mp4a.E1"
(MPEG-4 Visual Simple Profile Level 0 plus 13K voice)
Content-Type: video/mp4; codecs="avc1.640028"
(H.264/AVC video, High Profile, Level 40,
e.g. DVB 720p 50Hz HDTV)
Content-Type: video/mp4; codecs="svc1.56401E, avc1.4D401E"
(SVC video, Scalable High Profile, Level 30,
with a Main Profile AVC base layer, e.g. DVB 25 Hz SDTV)
Content-Type: video/mp4; codecs="mvc1.800030, avc1.640030"
(MVC video, Stereo High Profile, Level 42,
with a High Profile base layer, e.g. as adopted in Blu-ray)
Note: OTI value 20 ("0x20" in [MP4RA]) says "Includes associated
Amendment(s) and Corrigendum(a). The actual object types are defined
in [MP4V] and are conveyed in the DecoderSpecificInfo as specified in
[MP4V], Annex K." (references adjusted).
3.7. Additional Media Feature Details
It is sometimes helpful to provide additional details for a media
element (e.g., the number of X and Y pixels, the color depth, etc.).
These details are sometimes called "media features" or "media
characteristics".
When such additional features are included, the content-features
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[RFC2912] header provides a handy way to do so.
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4. The Profiles Parameter
4.1. Introduction
Just as some codecs have a variety of profiles (subsets of their
functionality within which a bitstream can be coded), so also some
media files can be profiled, and be associated with one or more
profile identifiers of the profiles to which they conform. These
profiles can indicate features of the file format itself, which
codecs may be present, the profiles of those codecs, and so on. It
can be advantageous to a receiving system to know the overall file
profile(s) of a file; indeed, under these circumstances it may not be
necessary to know the codecs themselves if they are implied by the
profile.
The 'profiles' parameter reports on the profile(s) of the overall
container format. A profile of the container format may have
restrictions on not only the features of the container format itself,
but also on what codecs may be included, and indeed have restrictions
on the profiles of those codecs. The 'profiles' parameter does not,
however, report directly any profiles of the contained media: when
such codec-specific profiles are reported, this report is part of the
'codecs' parameter. The 'profiles' parameter reports only the
profile(s) applying to the complete container.
When the use of the profiles parameter is defined for a given format,
that definition SHOULD indicate that it directly reflects information
in the body-part, i.e. that it does not convey information beyond, or
different from, what can be learnt by inspecting the body-part.
Although a mismatch is not permitted by this specification, the body-
part is definitive of the actual profiles; the parameter supplied
here is informative.
4.2. Formal Declaration
This section adds a parameter to allow unambiguous specification of
the profiles to which a file claims conformance. This parameter is
OPTIONAL in all current types to which it is added.
This parameter applies to:
1. Box-structured (also known as atom-structured) files that have an
initial box containing compatibility brands, as registered at the
MP4 Registration Authority [MP4RA], such as a filetype or
segment-type box. This includes principally files in the family
based on the ISO Base Media File Format [ISO14496-12], and also
the QuickTime file format, owned by Apple Inc. (A brand can
indicate conformance with restrictions regarding which codecs and
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file format features are used, adherence to quantitative limits
such as the length/size of the file, and so on.)
This includes the media types:
1. audio/3gpp, video/3gpp [RFC3839]
2. audio/3gpp2, video/3gpp2 [RFC4393]
3. audio/mp4, video/mp4 [RFC4337]
4. video/quicktime
5. application/mp21
Parameter name: profiles
Parameter value: A single value, or a comma-separated list of values
identifying the profiles(s) to which the file claims conformance.
The name space is determined by the MIME type.
Note that, per [RFC2045], some characters (including the comma used
to separate multiple values) require that the entire parameter value
be enclosed in quotes.
An element MAY include an octet that [RFC2045] requires to be
encoded. In this case, [RFC2231] is used: an asterisk ("*") is
placed at the end of the parameter name (becoming "profiles*" instead
of "profiles"), the parameter value usually starts with two single
quote ("'") characters(indicating that neither character set nor
language is specified), and each octet that requires encoding is
represented as a percent sign ("%") followed by two hexadecimal
digits. Note that, when the [RFC2231] form is used, the percent
sign, asterisk, and single quote characters have special meaning and
so MUST themselves be percent encoded.
Examples of Generic Syntax:
profiles="isom,mp41,qvXt"
profiles*="''%25%20xz, gork"
4.3. Profiles Parameter Definition
The 'profiles' parameter is an OPTIONAL parameter that indicates one
or more profiles to which the file claims conformance. Like the
'codecs' parameter described above, it may occur as either 'profiles'
or 'profiles*', with the same encoding rules. The value is, as for
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the codecs parameter, a comma-separated list of profile identifiers.
4.4. Profiles for files carrying MP4RA registered brands
For any file format carrying a brand registered at the MP4
Registration Authority [MP4RA], notably files based on the ISO Base
Media File Format ISO/IEC 14496-12 [ISO14496-12] and QuickTime movie
files, the profiles parameter MUST list exactly the major brand,
followed by the compatible-brands, as listed in the filetype box
('ftyp') or segment-type box ('styp'). The major-brand MUST be
first, and MAY be removed from the compatible-brands list. (The file
format requires that it be repeated in the compatible brands, but
this requirement is relaxed here for compactness.)
An example might be profiles="mp41,isom,qvXt", indicating that MPEG-4
version 1 is the major brand and preferred use, that the file is
compatible with the version of the base file format identified by
'isom', and that it is also compatible with the specification/profile
'qvXt' (whatever that may be).
4.5. Profiles Parameter BNF Definition
profil := pro-simple / pro-fancy
pro-simple := "profiles" "=" unencodedv
; Within a codecs parameter value, "." is reserved
; as a hierarchy delimiter
pro-fancy := "profiles*" "=" encodedv
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5. IANA Considerations
IANA has acted on the "MIME Media Types registry" and either added a
reference, or replaced the reference to [RFC4281], with a reference
to this document, thereby indicating that the "codecs" and/or
"profiles" parameters are optional for the following media types (as
listed in Sections 3 and 4):
1. audio/3gpp, video/3gpp [RFC3839]
2. audio/3gpp2, video/3gpp2 [RFC4393]
3. audio/mp4, video/mp4, application/mp4 [RFC4337]
4. video/quicktime
5. application/mp21
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6. Registration
The MPEG4 Registration Authority can be consulted for the most up-to-
date registration of sub-parameters for the codecs type, for specific
codecs.
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7. Security Considerations
The codecs parameter itself does not alter the security
considerations of any of the media types with which it is used. Each
audio and video media type has its own set of security considerations
that continue to apply, regardless of the use of the codecs
parameter.
An incorrect codecs parameter might cause media content to be
received by a device that is not capable of rendering it, or might
cause media content to not be sent to a device that is capable of
receiving it. An incorrect codecs parameter is therefore capable of
some types of denial-of-service attacks. However, this is most
likely to arise by accident, as an attacker capable of altering media
data in transit could cause more harm by altering the media format
itself, or even the content type header, rather than just the codecs
parameter of the content type header.
To the extent that a receiver reacts to a 'codecs' parameter that
indicates an unsupported codec, by fetching and installing the
required codecs, such reaction needs to be performed carefully and in
accord with the system's normal validity and security checks and
procedures.
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8. Differences from RFC 4281
1. Improved the introduction and other supporting and explanatory
text;
2. improved the references;
3. clarified the MIME types to which the parameters apply, and
clarified the consequent IANA actions;
4. added the 'profiles' parameter;
5. fixed an error in the BNF, where it did not correspond to either
the examples or common usage;
6. added the definition of the sub-parameters for the AVC family of
codecs;
7. switched to the latest boilerplate, and XML2RFC;
8. added a security consideration for possible triggering of
downloads;
9. updated acknowledgments.
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9. Acknowledgements
Harinath Garudadri provided a great deal of help, which is very much
appreciated. Mary Barnes and Bruce Lilly provided detailed and
helpful comments. Reviews and comments by Sam Hartman, Russ Housley,
and Bert Wijnen were much appreciated. Chris Newman carefully
reviewed and improved the BNF.
Christian Timmerer helped with the MPEG-21 material, and Thomas
Schierl and Yago Sanchez helped with SVC and MVC.
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10. References
10.1. Normative References
[3GPP-Formats]
3rd Generation Partnership Project, "Technical
Specification Group Services and System Aspects;
Transparent end-to-end packet switched streaming service
(PSS); 3GPP file format (3GP)", 3GPP TS 26.244.
[AVC] "Advanced video coding for generic audiovisual services",
ITU-T Recommendation H.264, ISO/IEC 14496-10:2009.
[AVC-Formats]
"Information technology -- Coding of audio-visual objects
-- Part 15: Advanced Video Coding (AVC) file format", ISO/
IEC 14496-15:2010.
[ISO14496-12]
"Information technology -- Coding of audio-visual objects
-- Part 12: ISO base media file format", ISO/
IEC 14496-12:2008.
[MP4RA] "MP4REG, The MPEG-4 Registration Authority",
<http://www.mp4ra.org>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
Word Extensions:
Character Sets, Languages, and Continuations", RFC 2231,
November 1997.
[RFC2912] Klyne, G., "Indicating Media Features for MIME Content",
RFC 2912, September 2000.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3839] Castagno, R. and D. Singer, "MIME Type Registrations for
3rd Generation Partnership Project (3GPP) Multimedia
files", RFC 3839, July 2004.
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[RFC4281] Gellens, R., Singer, D., and P. Frojdh, "The Codecs
Parameter for "Bucket" Media Types", RFC 4281,
November 2005.
[RFC4337] Y Lim and D. Singer, "MIME Type Registration for MPEG-4",
RFC 4337, March 2006.
[RFC4393] Garudadri, H., "MIME Type Registrations for 3GPP2
Multimedia Files", RFC 4393, March 2006.
10.2. Informative References
[3GPP2-Formats]
Third Generation Partnership Project 2, "3GPP2 File
Formats for Multimedia Service", <http://www.3gpp2.org/
Public_html/specs/C.S0050-0_v1.0_121503.pdf>.
[MP41] "Information technology--Coding of audio-visual objects--
Part 1: Systems", ISO/IEC 14496-1:2010.
[MP4A] "Information technology--Coding of audio-visual
objects--3: Audio", ISO/IEC 14496-3:2009.
[MP4V] "Information technology--Coding of audio-visual objects--
Part 2: Visual", ISO/IEC 14496-2:2004.
[RFC1345] Simonsen, K., "Character Mnemonics and Character Sets",
RFC 1345, June 1992.
[RFC3625] Gellens, R. and H. Garudadri, "The QCP File Format and
Media Types for Speech Data", RFC 3625, September 2003.
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Authors' Addresses
Randall Gellens
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92121
US
Email: randy@qualcomm.com
David Singer
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
US
Phone: +1 408 996 1010
Email: singer@apple.com
Per Frojdh
Ericsson AB
Ericsson Research
Stockholm SE-164 80
Sweden
Phone: +46 8 7190000
Email: Per.Frojdh@ericsson.com
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