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Re: Tech Discussions on the Multitrack Media (issue-152)

From: Eric Carlson <eric.carlson@apple.com>
Date: Wed, 2 Mar 2011 13:51:52 -0800
Cc: David Singer <singer@apple.com>, Frank Olivier <Frank.Olivier@microsoft.com>, Philip Jägenstedt <philipj@opera.com>, "public-html@w3.org" <public-html@w3.org>
Message-Id: <00C64EB3-C65D-492B-90B1-DEEE9999AD45@apple.com>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>

On Mar 2, 2011, at 1:36 PM, Silvia Pfeiffer wrote:

> On Thu, Mar 3, 2011 at 6:39 AM, David Singer <singer@apple.com> wrote:
>> 
>> On Mar 2, 2011, at 10:01 , Frank Olivier wrote:
>> 
>>> "About multiple text track formats, my working assumption is that we will be able to agree on a single format that everyone supports as there is not really any of the legal of business issues that we have for audio and video."
>>> Yes, this would be a very desirable outcome. However, it would still be prudent to have the ability to reference multiple text track formats for the same content, as some user agents may have the ability to display more-complex-than-baseline text track formats.
>>> 
>> 
>> Also, looking ahead, we should not assume that even if we pick a default and mandate now, it'll be the best for all time. If we (or someone) introduces a new, better, format, there will be a need for a while to offer both.
> 
> All of these concerns are fair enough. However, I also wonder if this
> necessarily means to have <source> elements for them. The <img> tag
> supports multiple formats without needing a <source> selection. Also,
> if you are providing a webvtt and a ttml file, are they really
> considered alternative resources or should they both be listed in a
> selection menu to the user? If we want the latter - and Mark's
> comments seemed to indicate that - then:
> 
>  <video id="v1" poster=“video.png” controls>
>     <track kind="captions"  srclang="en" label="Captions">
>          <source src="captions.vtt" type="text/vtt">
>          <source src="captions.xml" type="application/ttml+xml">
>      </track>
>  </video>
> 
> surely would be better marked up as:
> 
>  <video id="v1" poster=“video.png” controls>
>     <track kind="captions"  srclang="en" label="Captions" src="captions.vtt">
>     <track kind="captions"  srclang="en" label="Captions" src="captions.xml">
>  </video>
> 
> The <source> mechanism has been introduced to allow UAs to pick the
> first format that they understand and ignore the other <source>
> elements in this list. This exposes all the options that the UA
> supports to the user and allows them to pick for themselves without
> the browser making an implicit decision on quality.
> 
  Who said anything about a decision based on quality? The resource selection algorithm for the main resource doesn't make assumptions about quality when selecting among multiple <source> elements, why would we speciry anything else for track?


> I am not convinced that the <source> mechanism should be allowed for
> text tracks - it might cause more damage than good.
> 
  "more damage than good" is a stretch. What "damage" are you talking about?

eric
Received on Wednesday, 2 March 2011 21:52:56 GMT

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