Abstract

This document defines the application/ttml+xml media type and provides a registry of compact (short) identifiers that may be used to identify TTML processor profiles. A processor profile specifies a set of capabilities that a processor must support in order to process a document, where this profile may be defined in a specification document, in a TTML Profile Definition Document, inline within a TTML Document Instance, or by using a combination of these methods. This document only considers the first two of these methods since the third method (the use of inline profile definitions) is not considered to be an identifiable, shared profile definition, but rather, a private profile definition scoped to the document instance in which it is defined.

Purpose

This document serves two purposes: (1) to define the Media Type application/ttml+xml, and (2) to define a registry of compact (short) identifiers of TTML processor profiles.

As a registry, this document is intended to provide a central location for enumerating identified TTML processor profiles, or, more strictly speaking, TTML decoder/processors, where each entry in the registry identifies a particular profile which is understood to implement a processor capable of satisfying the constraints of a defined TTML processor profile that takes the form of a TTML Profile Definition Document. By utilizing a common registry, it is possible to avoid name collisions among different profile defining fora.

In the context of this registry, the term profile means processor profile. It explicitly does not mean content profile. That is, nothing about the use of the profile or codecs parameters described here is intended to be used to identify or make claims about whether a TTML resource conforms with a TTML Content Profile or any type of TTML Profile that may be interpreted in whole or in part as making statements about the conformance of a TTML resource or the features of TTML (or other external specifications) actually used in the resource.

Applications using the entries in this registry are encouraged to support values of the codecs parameter that employ either (or both) of two combination operators, + (AND) and | (OR), which may be used to specify, respectively, that all processor profiles apply (simultaneously) or that any processor profile of a list of profiles may apply individually. If both operators are used, then the + operator has precedence.

The + and | operators are intended to have semantics equivalent to the all(...) and the any(...) function syntax supported by the ttp:processorProfiles attribute as defined by [[TTML2-1e]], §6.2.8. Take note, however, that the combined use of both all(...) and any(...) in a ttp:processorProfiles attribute value expression is not directly supported by [[TTML2-1e]], and, therefore, an application that encounters a combination of both operators in a codecs value expression will need to process such combination semantics as a higher level protocol outside the scope of [[TTML2-1e]] semantics.

The example A+B|C+D|E specifies that a TTML processor that implements any one of the A+B or C+D or E processor profiles satisfies the requirements to fetch and begin decode/processing of a TTML document, where X+Y means that both X and Y processor profiles must be supported, and X|Y means that either X or Y processor profile must be supported.

Media Type Registration

This section defines the media type "application/ttml+xml", and, in conformance with BCP 13 and W3CRegMedia, serves as the registration thereof with the Internet Assigned Numbers Authority (IANA).

This updated definition supersedes the initial registration information specified in [[!TTML1-1e]], Appendix C, as updated by [[!TTML1-2e]], Appendix C.

Type name:

application

Subtype name:

ttml+xml

Required parameters:

None.

Optional parameters:
charset

If specified, the charset parameter must match the XML encoding declaration, or if absent, the actual encoding. See also Encoding Considerations below.

profile

The document profile of a TTMLDocument Instance may be specified using an optional profile parameter, which, if specified, the value of which must adhere to the syntax and semantics of ttp:profile parameter defined by TTML 1.0 Second Edition, Section 6.2.8 ttp:profile of the published specification.

codecs

The optional codecs parameter provides a short form version of the profile parameter with multiple-profile combinatorial capability. If a short (4-character) form of a profile is registered in the TTML Profile Registry, it is recommended that this codecs parameter be used and not the profile parameter. The nominal value of this parameter is a single 4 character code from the registry.

Additionally, applications using the entries in the registry are encouraged to adopt the following combination syntax:

Employ two combination operators, '+' (AND) and '|' (OR), which may be used to specify, respectively, that multiple processor profiles apply (simultaneously) or that any processor profile of a list of profiles may apply individually. If both operators are used in a codecs value, then the '+' operator has precedence.

The example: "A+B|C+D|E" states that a TTML processor that implements any one of A+B or C+D or E processor profiles satisfies, at first order, the requirements to fetch and begin decode/processing of a TTML document, where X+Y means that both X and Y processor profiles must be supported, and X|Y means that either X or Y processor profile must be supported.

Encoding considerations:

Same for application/xml, except constrained to either UTF-8 or UTF-16. See IETF RFC 7303, XML Media Types, Section 3.2. For the purpose of filling out the IANA Application for Media Type (http://www.iana.org/cgi-bin/mediatypes.pl), the value binary applies.

Security considerations:

As with other XML types and as noted in IETF RFC 7303, XML Media Types, Section 10, repeated expansion of maliciously constructed XML entities can be used to consume large amounts of memory, which may cause XML processors in constrained environments to fail.

In addition, because of the extensibility features for TTML and of XML in general, it is possible that "application/ttml+xml" may describe content that has security implications beyond those described here. However, TTML does not provide for any sort of active or executable content, and if the processor follows only the normative semantics of the published specification, this content will be outside TTML namespaces and may be ignored. Only in the case where the processor recognizes and processes the additional content, or where further processing of that content is dispatched to other processors, would security issues potentially arise. And in that case, they would fall outside the domain of this registration document.

Although not prohibited, there are no expectations that XML signatures or encryption would normally be employed.

Interoperability considerations:

The published specification describes processing semantics that dictate behavior that must be followed when dealing with, among other things, unrecognized elements and attributes, both in TTML namespaces and in other namespaces.

Because TTML is extensible, conformant "application/ttml+xml" processors may expect (and enforce) that content received is well-formed XML, but it cannot be guaranteed that the content is valid to a particular DTD or Schema or that the processor will recognize all of the elements and attributes in the document.

Published specification:

This media type registration is extracted from the TTML Profile Registry.

Applications that use this media type:

TTML is used in the television industry for the purpose of authoring, transcoding and exchanging timed text information and for delivering captions, subtitles, and other metadata for television material repurposed for the Web or, more generally, the Internet.

There is partial and full support of TTML in components used by several Web browsers plugins, and in a number of caption authoring tools.

Additional information:
Magic number(s):
File extension(s):

.ttml

Macintosh file type code(s):

"TTML"

Fragment identifiers:

For documents labeled as application/ttml+xml, the fragment identifier notation is intended to be used with xml:id attributes, as described in section 7.2.1 of the Timed Text Markup Language 1 (TTML1) specification.

Person & email address to contact for further information:

Timed Text Working Group (public-tt@w3.org)

Intended usage:

COMMON

Restrictions on usage:

None

Author:

The published specification is a work product of the World Wide Web Consortium's Timed Text (TT) Working Group.

Change controller:

The W3C has change control over this specification.

Registration Entry Requirements and Update Process

  1. Each entry must include a unique identification, where the scope of uniqueness is the set of identifiers defined in this registry. An identifier must conform with the element non-terminal of [[!RFC6381]] and, furthermore, may not contain any of the characters in the regular expression character class [+|].

    As a consequence of the above syntactic constraints, the value space of the codecs parameter described in above is a syntactic subset of the definition of the codecs parameter defined by [[RFC6381]].

  2. Each entry must include an absolute URI that serves as the TTML Profile Designator that identifies the processor profile.
  3. Each entry should include a link that references a TTML Profile Definition Document that formally specifies the processor profile using TTML profile definition vocabulary.
  4. Each entry should include a link that references a public available specification (PAS) that defines the identified processor profile.
  5. Each entry must include contact information of the requestor.

An update to this registry is an addition, change or deletion of an entry. Any person can request an update to this registry by email notice to the chairman of the Timed Text Working Group who will place it on an upcoming meeting agenda and notify the requestor. Consideration and disposition of the request is by consensus of the W3C Timed Text Working Group. The Chair will then notify the requestor of the outcome and update the registry accordingly. Although profiles can be deleted, there is no intent to re-use deleted profile values. That is, the intent is that profile entries are "stable".

Registry

This section is the registry of short form profile identifiers. The first sub-section details how such identifiers should be dereferenced to profile designators, the specifications that define those profiles, and the contact organisation for each profile. The second sub-section describes the mechanism used by each profile to permit identification of the profile of a TTML Document Instance by inspection of that document.

Profile designator and specifications

The following table defines the Profile Designator for each short form Profile Identifier in this Registry, alongside the public specification document in which the profile is defined, and the relevant contact organisation. Entries are ordered alphabetically according to the short profile identifier.

Profile Identifier Profile Designator Public Specification(s) Requestor Contact
cfi1 http://www.decellc.org/profile/cff-tt-image-1.1 [[!UV-DMedia]] DECE
cft1 http://www.decellc.org/profile/cff-tt-text-1.1 [[!UV-DMedia]] DECE
ede1 urn:IRT:ebu-tt-basic-de:2013-07 IRT Technical Guidelines IRT
etd1 urn:ebu:tt:distribution:2014-01 [[!EBU-TT-D-1]] EBU
etd2 urn:ebu:tt:distribution:2018-04 [[!EBU-TT-D-1-0-1]] EBU
etl1 urn:ebu:tt:live:2017-05 [[!EBU-TT-Live-1-0]] EBU
etx1 urn:ebu:tt:exchange:2012-07 [[!EBU-TT-1-0]] EBU
etx2 urn:ebu:tt:exchange:2015-09 [[!EBU-TT-1-1]] EBU
etx3 urn:ebu:tt:exchange:2017-05 [[!EBU-TT-1-2]] EBU
im1i http://www.w3.org/ns/ttml/profile/imsc1/image [[!IMSC1.0.1]] TTWG
im1t http://www.w3.org/ns/ttml/profile/imsc1/text [[!IMSC1.0.1]] TTWG
im2i http://www.w3.org/ns/ttml/profile/imsc1.1/image [[!IMSC1.1]] TTWG
im2t http://www.w3.org/ns/ttml/profile/imsc1.1/text [[!IMSC1.1]] TTWG
tt1f http://www.w3.org/ns/ttml/profile/dfxp-full [[!TTML1-3e]] TTWG
tt1p http://www.w3.org/ns/ttml/profile/dfxp-presentation [[!TTML1-3e]] TTWG
tt1s http://www.w3.org/ns/ttml/profile/sdp-us [[!TTML1-SDP-US]] TTWG
tt1t http://www.w3.org/ns/ttml/profile/dfxp-transformation [[!TTML1-3e]] TTWG
tt2f http://www.w3.org/ns/ttml/profile/ttml2-full [[!TTML2-1e]] TTWG
tt2p http://www.w3.org/ns/ttml/profile/ttml2-presentation [[!TTML2-1e]] TTWG
tt2t http://www.w3.org/ns/ttml/profile/ttml2-transformation [[!TTML2-1e]] TTWG