Update to media type "application/ttml+xml"
Philippe Le Hegaret <plh <at> w3.org>
2016-06-16 14:16:03 GMT
The W3C Timed Text Working Group would like to update the media type
"application/ttml+xml" as follows. Comments are welcome.
It 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 supercedes the initial registration information in
TTML 1.0 Second Edition.
Text copied below but see also the original text at:
If specified, the charset parameter must match the XML encoding
declaration, or if absent, the actual encoding. See also Encoding
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.
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
For more information about processor profile combination, see
TTML2 Profile Combination.
Same for application/xml, except constrained to either UTF-8 or
UTF-16. See IETF RFC 3023, 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.
As with other XML types and as noted in IETF RFC 3023, 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.
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.
This media type registration is extracted from the TTML Profile
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.
Macintosh file type code(s):
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)
Person & email address to contact for further information:
Timed Text Working Group (public-tt <at> w3.org)
Restrictions on usage:
The published specification is a work product of the World Wide Web
Consortium's Timed Text (TT) Working Group.
The W3C has change control over this specification.