Re: Inband styling (was Re: Evidence of 'Wide Review' needed for VTT)

On Wed, Oct 21, 2015 at 3:00 PM, David Singer <singer@apple.com> wrote:
>
>> On Oct 21, 2015, at 14:36 , Philip Jägenstedt <philipj@opera.com> wrote:
>>
>> On Wed, Oct 21, 2015 at 2:17 PM, David Singer <singer@apple.com> wrote:
>>>
>>> Yes, the static transcoding case is easier.  It is, alas, not the only one.
>>
>> What we are talking about is the conformance requirements of
>> standalone WebVTT files and what the WebVTT parser will do if
>> encountering style blocks after a cue.
>
> No, I think I must disagree.  Is such a restriction written anywhere (that files cannot be incrementally produced)?  You might argue that the incremental production case isn’t specifically included either, but I think we live in a world with more english than german rules :-)
> <https://en.wikipedia.org/wiki/Everything_which_is_not_forbidden_is_allowed#National_traditions>

The proposed spec text we're talking about only involves conformance
(syntax) and parsing, and currently both of those are defined in a way
that only makes sense for standalone WebVTT files. Incrementally
serializing WebVTT is certainly not disallowed, but it can't be
impacted by *relaxing* conformance and there need be no parser at all.

>> In this context, static
>> resources really is all that exists, as live captioning with
>> <track>+WebVTT [1] hasn't been spec'd. If there are other contexts
>> that use the WebVTT syntax and parser in a streaming mode, then that
>> would be interesting to know. AFAICT, it would only be a situation
>> like that where there could be a problem, and if it's only a
>> hypothetical at this point I don't think that should affect how WebVTT
>> works in the context of <track>.
>
> No, it’s not hypothetical.  DASH/MP4/VTT relies on this, and it was (and is) seen as a core advantage of VTT over TTML.

In the DASH/MP4/VTT software stack, is WebVTT the input or the output,
and is it a file or a stream? AFAICT, the only issue would be with a
WebVTT input stream (using the syntax in the spec, not any other
framing) with STYLE blocks at the end, but since streaming standalone
WebVTT doesn't exist yet I'm uncertain if that's really what you mean.

Philip

Received on Wednesday, 21 October 2015 13:40:03 UTC