Re: [media-types] Update to media type "application/ttml+xml"

* Philippe Le Hegaret <plh@w3.org> [2016-06-16 10:16-0400]
> 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

PLH indicated that "at first order" is something like an initial claim
about the embedded codecs. Is it the intention that there be some sort
of recovery if that initial claim is incorrect? What should the
processor do if the advertised codec is ogg and the actual codec is
xvid? If you strike "at first order", I think you could avoid having
to define the behavior in the event of invalid parameters.


> 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.

  "TTML2 Profile Comination" has no URL in the reg. The hyptertext version links to
    https://www.w3.org/TR/ttml2/#profile-attribute-processorProfileCombination
  propose instead link to
    https://www.w3.org/TR/ttml2/#processor-profile-combination-table
  and embedding that link in ()s in the text.


> 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
> 
> _______________________________________________
> media-types mailing list
> media-types@ietf.org
> https://www.ietf.org/mailman/listinfo/media-types

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Received on Thursday, 16 June 2016 20:07:40 UTC