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[Bug 13359] <track> A way is needed to identify the type of data in a track element

From: <bugzilla@jessica.w3.org>
Date: Thu, 28 Jun 2012 03:49:58 +0000
Message-Id: <E1Sk5jy-0002gg-7z@jessica.w3.org>
To: public-html-a11y@w3.org
https://www.w3.org/Bugs/Public/show_bug.cgi?id=13359

--- Comment #49 from Ian 'Hixie' Hickson <ian@hixie.ch> 2012-06-28 03:50:03 UTC ---
(In reply to comment #45)
> 
> A timed metadata track contains text if moov:trak:mdia:minf:stbl:stsd contains
> MetaDataSampleEntry('mett'). The type of text data is identified by a MIME
> type. In this case let TYPE = 'mp4-mett' and VALUE =
> TextMetaDataSampleEntry.mime_format ([1] section 8.5.2.2).
> 
> A timed metadata track contains XML if moov:trak:mdia:minf:stbl:stsd contains
> MetaDataSampleEntry('metx'). The format of the XML document is identified by
> its namespace. In this case let TYPE = 'mp4-metx' and VALUE =
> XMLMetaDataSampleEntry.namespace.

I can't reconcile this with the MPEG4 spec, mostly because the MPEG4 spec seems
to be impenetrable.

First, there's no such thing as a "moov:trak:mdia:minf:stbl:stsd box", it seems
that the formal way to refer to this would be "the first stsd box in the first
stbl box in the first minf box in the first mdia box in the first trak box in
the first moov box, if such a box exists". Is that right? Second, I can't work
out how to even formally phrase the stuff about "mett" and "mime_format" and so
forth. I can't find the definition of SDL, and the SDL in the above-cited MPEG
spec is the only place that mentions "mett". The MPEG files don't seem to
actually contain anything called "TextMetaDataSampleEntry", that seems to just
be a concept used in the spec's syntax definitions (?). Really not sure how to
write this.

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Received on Thursday, 28 June 2012 03:50:07 UTC

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