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[Bug 10693] Need a means for navigating between related timed tracks of media elements

From: <bugzilla@jessica.w3.org>
Date: Wed, 12 Jan 2011 23:52:09 +0000
To: public-html-a11y@w3.org
Message-Id: <E1PdAU5-0005bL-PN@jessica.w3.org>

--- Comment #6 from Silvia Pfeiffer <silviapfeiffer1@gmail.com> 2011-01-12 23:52:09 UTC ---
Sorry about the delayed reply.

As an example for a software/system that provides this functionality, you
should look at Daisy players, e.g. http://www.youtube.com/watch?v=WG9Gc-huujk .
In this example, a audio book (which you can regard as a single, lengthy audio
file) is shown to have several different ways of navigating. The navigation is
provided through different markup. For example, it says it has different
navigation levels. In HTML5 they would be provided through multiple text tracks
that are of @kind=chapter and thus provide navigation markers.

Now, if for example one navigation level is book chapters and the next is book
subchapters, then in HTML5 we would provide them as two different text tracks
of @kind=chapter and @label="book chapter" and @label="book subchapter"
respectively. We have, however, no means to determine that one is a higher
resolution to the other. A blind person would want to know this and would want
to be able to navigate e.g. through arrow up/down between the different
resolution levels and e.g. through arrow forward/back within a chapter track.

While the navigation itself is a UA issue, the need to mark one track as
related to the other and as a sub-division of the other is a markup/API issue.

I don't know the best way to solve this. Maybe it is already solved through the
way in which TextTracks are ordered in a media element's list of text tracks,
i.e. if a @kind=chapter track is earlier in the TextTracks list, then it is
implied to be of a higher hierarchical level than the next. Thus, a UA is
expected to allow a blind user to navigate between these tracks in their order
as given in the list of text tracks.

However, there is only limited control over a TextTrack's position in the list
of text tracks, in particular when they originate from different sources.
Therefore, an explicit numbering (similar to the z-level for CSS blocks) might
make more sense.

Either way, a mention of how a UA should interpret the list for navigation
purposes is important.

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Received on Wednesday, 12 January 2011 23:52:11 UTC

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