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Re: Track kinds

From: Mark Watson <watsonm@netflix.com>
Date: Thu, 28 Apr 2011 22:43:54 -0700
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
CC: HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <C0DA820F-C54D-4DB5-936B-A9C5CE5FA2FA@netflix.com>

On Apr 28, 2011, at 6:07 PM, Silvia Pfeiffer wrote:

> On Fri, Apr 29, 2011 at 6:52 AM, Mark Watson <watsonm@netflix.com> wrote:
>> All,
>> I updated the wiki page (http://www.w3.org/WAI/PF/HTML/wiki/Track_Kinds)
>> based on our discussion yesterday. There are now three tables, the kinds in
>> the current spec, the kinds that have been suggested and the subset that we
>> have agreed should be added to the spec (currently just "captions").
>> If I understand rightly, the general idea is that we should provide precise,
>> container-independent definitions for all the kinds we agree on in a W3C
>> document other than the HTML specification and propose that the HTML
>> specification just define the text labels to be used with HTML.
>> In parallel, various people will work on introducing the same kinds to
>> various container specifications.
>> We decided to continue the discussion of which ones to propose should be
>> added to the specification on the list. To that end the three that Sylvia
>> suggested yesterday were:
>> - supplementary
>> - commentary
>> - clear audio
>> Comments ?
> 
> Thanks for the great work on the wiki page. It is good to pull this together.
> 
> I think the list that we have in the spec right now is a good start
> and should likely be sufficient for a reply to the 3GPP.
> 
> As for further values:
> 
> I think adding "supplementary" makes sense, because it states that a
> track can be active at the same time as the "main" tracks.

The "supplementary" value from 3GPP is rather subtle. Usually the main audio and video tracks have equal "importance" to the overall presentation. "supplementary" was supposed to convey the idea that this track is somehow less important than the "main" one. One use for this information would be that in an extreme bandwidth crunch you should maintain the "main" track in preference to the "supplementary" one. Examples are that for a music video the audio is more important than the video (though I wonder if that is more true of music videos from the 80s than today) or for sports the video is more important than the audio (except perhaps competitive yodeling?!?).

> 
> I am not so fussed about any of the others because I think as we
> implement this the list will likely grow. I don't mind adding
> "captions" and "commentary" because I know there is material that has
> in-line captions and there are commentary tracks. Alternatively,
> "captions" could be marked as "alternative" and "commentary as
> "supplementary" with a description of what it actually is in the
> label.

If they are for well-understood things then explicit values are useful because people can create UI elements specifically for those things. Particularly for captions it would be nice for them to be accessed through the UI in the same way, whether they are burned in or in text tracks.

For UI consistency, also, I would prefer to have a "Directors Commentary" UI element, rather than relying on every directors commentary track having the same label.

Btw, what is the situation with labels in media container formats ? I don't think DASH has anything yet.

> 
> As for "clear audio", I think we first need to clarify what it is
> exactly. As I understood from our requirements discussions, a "clear
> audio" track is a track that has only the speech part of the video so
> that it is possible to turn this sound up through controls in
> comparison to the main audio track. If this is the case, then it
> compares to the "audio/speech" value of the Ogg roles. If instead it
> is as David describes a track which has the speech part amplified in
> comparison to the main audio, then it is actually a replacement for
> the main audio track and would be covered with "alternative" and a
> description in label as "clear audio".

This is a more general question about how to signal whether a track is "additive" or "alternative". I think we discussed this before (or maybe that was a different list, I forget).

In the context of audio descriptions I've seen it stated that sometimes an audio description track is a replacement for the main audio track and in other cases it's intended to be mixed in (i.e. the descriptions fit somehow into gaps in the main audio track.)

Does anyone on this list know whether that is true ?

As with the repetitive stimulus question there are three approaches:
(a) treat it as a new property (additive vs alternative)
(b) allow multiple kinds (so we wold have "alternate clearaudio" and just "clearaudio")
(c) define separate kinds for the different cases, where it makes sense ("clearaudio-alt" and "clearaudio-mix")

Personally, I prefer (c) as I don't think the concept is universal enough to warrant a separate property.

...Mark

> 
> Cheers,
> Silvia.
> 
Received on Friday, 29 April 2011 05:44:24 UTC

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