Update to media type "application/ttml+xml"

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:
  https://www.w3.org/TR/2016/NOTE-ttml-profile-registry-20160510/#mediatype

[[

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 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.
Security considerations:

     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.
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.
]]
https://www.w3.org/TR/2016/NOTE-ttml-profile-registry-20160510/#mediatype

Thank you,

Philippe

Received on Thursday, 16 June 2016 14:16:06 UTC