Re: proposed updated response to MPEG on codecs

Hi Glenn,

Am 19.10.2014 um 18:02 schrieb Glenn Adams:
>
>>     Given these requirements, I'm not sure how to deal with an
>>     informal profile that doesn't have an associated TTML Profile
>>     Definition Document.
>     I can understand that. The term "informal profile" is pretty vague.
>
>>     It would seem much simpler to define such a document and
>>     associate it with this informal profile.
>>
>>     [1]
>>     https://www.w3.org/wiki/TTML/CodecsRegistry#Registration_Entry_Requirements_and_Update_Process
>
>     But my conclusion would be different. It is more to allow the
>     signalling of specs that do not use the TTML profiling mechanism.
>
>
> Since I haven't seen a rationale for avoiding use of the TTML profile 
> mechanism in a specification defining activity, I am not willing to 
> concede. Note that one can use the TTML profile mechanism in a 
> defining activity without necessarily requiring a processor to use it.

The profiling mechanism is useful to have an informative reference what 
is supported in different TTML profiles. It helps for an informative (!) 
overview. Therefore it can be used and is used in a specification 
defining activity. But I have some concerns to use it as a normative 
reference. Discussion on this mechanism and different views on this 
mechanisms have been expressed on this list in previous discussion. One 
of my concerns is that different "profiles" list the same feature but 
require only a limited support for that feature. The limitation can vary 
per profile/dialect. As far as I know there is no way to express this 
with the TTML profile mechanisms.

This is not a proposal to add a "subsetting mechanisms" for TTML 
features. This would add more semantics to this architecture and would 
not help adoption.

Best regards,

Andreas

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