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

From: <bugzilla@jessica.w3.org>
Date: Thu, 25 Aug 2011 19:55:08 +0000
To: public-html-a11y@w3.org
Message-Id: <E1Qwg16-0007Jt-83@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=13359

--- Comment #14 from Bob Lund <b.lund@cablelabs.com> 2011-08-25 19:55:04 UTC ---
(In reply to comment #5)
> 
> How would a general-purpose UA (such as Opera, Chrome, Safari or Firefox)
> recognize IB1, IB2, and IB3? They are not specified in HTML so there is no
> requirement for them to be able to decode them and I haven't seen any moves
> that spans across these and other UAs to make IB1-3 a standard-supported format
> in them.

The types for IB1, IB2 and IB3 could be defined by specifications external to
HTML5. The following language is in
http://dev.w3.org/html5/spec/Overview.html#sourcing-in-band-text-tracks

"A media-resource-specific text track is a text track that corresponds to data
found in the media resource. Rules for processing and rendering such data are
defined by the relevant specifications, e.g. the specification of the video
format if the media resource is a video"

I have made a proposal in the Web and TV IG Media Pipeline task force that
these specs be created for an identified set of metadata and transport formats
http://www.w3.org/2011/webtv/wiki/MPTF/MPTF_Discussions/TV_services_transport_mapping

The idea of a mapping specification was also raised in
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2011-June/031916.html. This
is a long email. The relevant text from Ian was

"There can be a standard way. The idea is that all the types of metadata 
tracks that browsers will support should be specified so that all browsers 
can map them the same way. I'm happy to work with anyone interested in 
writing such a mapping spec, just let me know."

This mapping is necessary but not sufficient to address the problem. There
needs to be a way for the type of the data that results from the mapping to be
conveyed to script - hence bug 13359.

> If there is, then it would make a lot more sense to have actual
> kind=IB1-3 values as part of the spec IMHO.

This is a possible approach but the current use of "kind" seems to be
categorical. What would be most useful to script is an indication of the syntax
and semantics of the metadata - i.e. its type. Also, is can be expected that
for a given category, e.g. advertising insertion point, there will be different
types depending on the transport format. For example, SCTE-35 in MPEG-2 TS and
some, yet to be defined format, in a SMPTE TT track in DASH.

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Received on Thursday, 25 August 2011 19:55:09 GMT

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