[Bug 14492] New: <video> change event when tracks are removed


           Summary: <video> change event when tracks are removed
           Product: HTML WG
           Version: unspecified
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: LC1 HTML5 spec (editor: Ian Hickson)
        AssignedTo: ian@hixie.ch
        ReportedBy: jan.lindquist@ericsson.com
         QAContact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,

The Bug 13358 (http://www.w3.org/Bugs/Public/show_bug.cgi?id=13358) provides a
means of receiving an event for when tracks are added. In the discussion over
how the bug is resolved it was proposed to create a seperate bug for addressing
when tracks are removed. Below is a description of the use case.

Support of events for when tracks are adding will create problems for
application developers that need to get information when tracks are removed.
This is particularly a problem when working with live broadcast (as discussed
from webtv IG) or playlists controlled from the video server (single URL is
used to initiate the stream). Both cases will have different content or
programs being streamed with possibly each content or program having different

An example for how an application developer may have problem is when a user has
language preferences beyond a single language for subtitles or audio. The user
preference may be (1) spanish, (2) english, and (3) french. The application may
indicate spanish based on available audio/subtitle tracks for a program in a
live broadcast but then next scheduled program the spanish audio/subtitle is
removed. How does an application keep track of the removed track and change it
to english?

There may additonal considerations on how a UA may handle the track list. The
<video> is long lived and may go for days or weeks. The list of tracks may
become very large. A means of refreshing the tracks and remove from the list
tracks that are outdated is desired. This may be supported by the application
(*author*) fetching the tracks on a track change event. 

Additionally considerations should be made for UA behaving differently when
handling modifications to details on a track. Changes may generate a new track
instead of reusing an existing track. For example if a track has an audio track
which starts with support stereo and then changes to 5.1 surround. A UA may
keep track list unchanged but simply modify one description, other UA may
create a new track. It is not possible to dictate exactly how UA shall behave
and it is necessary to have a solution that accmodates for frequent changes to
tracks overtime.

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Received on Tuesday, 18 October 2011 13:20:19 UTC