RE: [Media_Piping_TF] New bug in relation to 13358 - removing tracks event

Hi,

I made some changes to the proposed text based on phone conference discussions. I am not able to confirm how DVB's PMT affects how the components are updated between a program and sliced in commercial.

If there are no comments until tomorrow, Tuesday, I will upload it as a new bug. I am concerned weed to get this addressed and waiting will not provide a solution.

Best Regards,
JanL

_____________________________________________
From:   Jan Lindquist
Sent:   den 11 oktober 2011 08:26
To:     Web and TV Interest Group WG
Subject:        [Media_Piping_TF] New bug in relation to 13358 - removing tracks event

Hello,

On recommendation from Ian Hickson I am proposing the following bug to be issues in relationship to 13358 where events for adding tracks are introduced. This bug will address when the tracks are removed. Feel free to comment. I would like to aim to upload it on Thursday after the Media Piping phone conference.

Best Regards,
JanL


Title: <video> change event when tracks are removed

Description:
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 tracks.

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?

[JLI]  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.