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[whatwg] Proposal for @label attribute associated with kind=metadata TimedTextTracks

From: Eric Winkelman <E.Winkelman@cablelabs.com>
Date: Tue, 22 Mar 2011 10:40:37 -0600
Message-ID: <3C0068AB22D70B4DA32B9A2A965968C76FB2FB6FEB@srvxchg>
On Monday, March 21, 2011 11:17 AM, Tab Atkins Jr. [mailto:jackalmage at gmail.com] wrote:

> >> Use Case:
> >>
> >> Many video streams contain in-band metadata for application signaling,
> and other uses. ?By using this metadata, a web page can synchronize an
> application with the delivered video, or provide other synchronized services.
> >>
> >> An example of this type of metadata is EISS (
> http://www.cablelabs.com/specifications/OC-SP-ETV-AM1.0-I06-110128.pdf
> ) which is used to control applications that are synchronized with a television
> broadcast.
> >>
> >> In general, a media stream can be expected to carry several types of
> metadata and the types of metadata may vary in time.
> >>
> >> Problem:
> >>
> >> For in-band metadata tracks, there is neither a standard way to represent
> the type of metadata in the HTMLTrackElement interface nor is there a
> standard way to represent multiple different types of metadata tracks.
> >>
> >> Proposal:
> >>
> >> For TimedTextTracks with kind=metadata the @label attribute should
> contain a MIME type for the metadata and that a track only contain Cues
> created from metadata of that MIME type.
> >>
> >> This implies that streams with multiple types of metadata require the
> creation of multiple metadata track objects, one for each MIME type.
> >
> >
> > I don't understand. Are you saying that right now all tracks that are
> > of kind=metadata are made available through a single TextTrack? Cause
> > I don't think that's the case.
> >
> > Or are you worried about text track files that contain more than one
> > type of metadata? If the latter, then how is the browser to know how
> > to separate out the individual cues from a single track into
> > multipled?
> >
> > Can you clarify?
> I'm also somewhat confused.  The OP mentions in-band metadata, but then
> proposes adding something to out-of-band <track kind=metadata>
> elements.

I'm not proposing adding anything to out-of-band <track kind=metadata> elements.  In-band metadata tracks are added to the DOM by the media player, and have the same @label attribute that out-of-band tracks do.  I'm suggesting a use for that @label attribute that solves a problem I've encounter using metadata tracks.

> I'm not familiar enough with in-band metadata tracks to know if it would be
> useful to expose additional information about them, but for out-of-band
> tracks I suspect that any information you may need is application-specific,
> and thus can be served with a data-* attribute.

I agree, there are a number of solutions for out-of-band metadata tracks, but  my concern is specifically in-band metadata tracks.  

If an in-band kind=metadata track appears, what kind of information does it contain?  Can you tell by looking at the DOM?  Can you tell by looking at the cue's text?

Received on Tuesday, 22 March 2011 09:40:37 UTC

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