TTML Media Type Definition and Profile Registry

2. Media Type Registration

This section updates the media type, "application/ttml+xml" to add a new parameter, codecs . All other provisions of the media type specification remain the same. This updated registration supersedes the initial registration information specified in [ TTML1-1e ], Appendix C, as updated by [ TTML1-2e ], Appendix C.

This section is in conformance with BCP 13 and W3CRegMedia . The information that follows has been submitted to and accepted by the Internet Engineering Steering Group (IESG) for registration with the Internet Assigned Numbers Authority (IANA).

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.

For more information about processor profile combination, see TTML2 Profile Combination .

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.

3. 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 [+|].
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".

4. 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.