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Re: [media] change proposals for issue-152

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Mon, 28 Mar 2011 22:42:53 -0700
Message-ID: <AANLkTim5Nm8FpYknDpt6nW+9GkKg_qv2MK+HKERjkf8i@mail.gmail.com>
To: HTML Accessibility Task Force <public-html-a11y@w3.org>
OK, so let me see if we can attack the biggest problem of proposal (2)
(and, in fact, proposal (3)).

Right now, these proposals are missing a means to represent in-band
multitrack media elements, which is what proposal (1) is trying to do
for audio resources.

We could do this by adding the following to the HTMLMediaElement:

readonly attribute Video[] videotracks;
readonly attribute Audio[] audiotracks;

These would contain the list of all the tracks from in-band.
For the master video, they would probably also contain the tracks from
the slave media elements, so we have a uniform interface.

Hmm... now the information what is master and what is slave is
somewhat duplicated.

So, I think it would probably be better if instead we recommend that
if you wanted to use in-band tracks, you should use media fragment
addressing, such as:

    <!-- in-band german sign language track -->
    <video id="v3" timeline="v1" kind="signing" srclang="gsg"
label="German Sign Language">
      <source src=“video.webm#track=video_gsg” type=”video/webm”>
      <source src=“video.mp4#track=video_gsg” type=”video/mp4”>

What do people think?


On Sun, Mar 27, 2011 at 11:04 AM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com> wrote:
> Dear Media Subgroup,
> As per decision by the chairs of the HTML WG, we have until Friday to
> continue discussions and come to an agreement on a common change
> proposal: http://lists.w3.org/Archives/Public/public-html/2011Mar/0614.html
> .
> I would recommend to approach this by going one by one through the
> differences of at least the three proposals that have originated from
> this group and either come up with a unified new one, or modify one to
> match all our requirements. The discussions between Ian's proposal and
> ours is one that I would like to see happening afterwards on the main
> list.
> Here are the three proposals under discussion:
> (1) http://lists.w3.org/Archives/Public/public-html/2011Feb/0363.html
> (Frank's original proposal)
> (2) http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal
> (write-up from the F2F)
> (3) http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal_2
> (Sean's proposal)
> Since (2) and (3) are very similar and emerged because we didn't have
> time to finish that discussion at the F2F, I would like to address
> this first.
> So, proposal 3 suggests that rather than having the <track> element as
> a dependent element underneath the <video> element, we should make the
> <track> functionality available as a prime element to Web pages under
> the name <cues>.
> While I can follow the reasoning for this proposal to stem from the
> idea of having a unified approach to all possible types of content
> that can appear in a multi-track resource, I believe this is actually
> taking the purity reasons a step too far. I have two main issues with
> this approach:
> 1. Captions and more generally time-aligned text for videos, are
> always slaved to video content. They do not make sense to exist as an
> entity by themselves. The times in the cues of a cue file only become
> real when attached to a video. A <cues> element on a Web page without
> a video would never display anything because the cues would never
> become active.
> 2. There should be a default rendering of cues and it should be
> attached to the video viewport. Rendering in other positions on the
> page should be regarded as custom rendering and the 20% case - easy to
> achieve, but not the common use case. Proposal 3 puts this on its
> head, making rendering in other positions on the page the default and
> rendering on top of the video a problem of the Web page author.
> For these reasons mainly, I would refrain from trying to re-define how
> the <track> element works.
> Best Regards,
> Silvia.
> On Mon, Mar 21, 2011 at 10:03 PM, Sean Hayes <Sean.Hayes@microsoft.com> wrote:
>> No. we didn't agree on pulling it out. We did however have a unified approach on them all being tracks. I disagree with the move of treating them differently, either they are all tracks or they are all top level elements.
>> I will submit my proposal separately then, I'll also rename <track> to <cues>. I agree that we are not done on this issue.
>> -----Original Message-----
>> From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
>> Sent: 22 March 2011 04:53
>> To: Sean Hayes
>> Cc: HTML Accessibility Task Force
>> Subject: Re: [media] change proposals for issue-152
>> Hi Sean,
>> I don't think we had all agreed on pulling <track> out into a
>> stand-alone tag. I certainly disagree with that move.
>> So, given the lack of time, we will certainly have to submit both
>> proposals now and leave it to the chairs to decide how to move on. I
>> don't think we've finished discussions on this topic though and
>> believe that given time we could still converge. But we'll now have to
>> wait and see what the chairs will allow to happen.
>> Cheers,
>> Silvia.
>> On Tue, Mar 22, 2011 at 1:56 PM, Sean Hayes <Sean.Hayes@microsoft.com> wrote:
>>> [4] Is an interesting CP, it does however fail to capture one fundamental premise of the proposal that we had on the table when I left at 2pm. Namely that the handling of text tracks should be as far as possible the same as the handling of a media track. This would imply under this formulation that <track> (meaning a text track) should be promoted to the same level as audio and video, and with the same model, so no it doesn't have my agreement that it is an equivalent to [1]
>>> I am editing a copy of the page with those changes.
>>> -----Original Message-----
>>> From: public-html-a11y-request@w3.org [mailto:public-html-a11y-request@w3.org] On Behalf Of Silvia Pfeiffer
>>> Sent: 22 March 2011 00:47
>>> To: HTML Accessibility Task Force
>>> Subject: [media] change proposals for issue-152
>>> Hi media subgroup,
>>> A quick status update on where we stand wrt change proposals for issue-152.
>>> Over the weekend we have worked on a change proposal, which we called
>>> the "San Diego Thought Experiment", see [1].
>>> It is based on the ideal markup representation of a multitrack media
>>> resource, where external resources are represented in markup as tracks
>>> of a main resource. As we worked through the markup changes, the
>>> IDL/JavaScript API changes, the CSS changes and the rendering
>>> approaches, we realized that the implementation of this ideal
>>> representation would replicate far too many existing codepaths and at
>>> the same time introduce complex layout requirements that would be
>>> unrealistic to expect to be implemented.
>>> We came to the conclusion that the approach of keeping separate
>>> <video> and <audio> elements around and synchronizing them to a
>>> "master" element (i.e. the "main" resource) would be far easier to
>>> implement and just as powerful. So, we picked up the existing option 6
>>> [2] and continued designing from there to see if that would be
>>> achievable in a simpler manner.
>>> Note that in the meantime Ian has also submitted a change proposal
>>> which is highly interesting [3].
>>> Since Eric and I promised to put the change proposal that was the
>>> outcome of the F2F discussions together, we've worked on this today
>>> and it's now in a readable state [4]. We are going to submit that
>>> proposal as an additional change proposal to the main working group
>>> late today. I don't know if it has general task force approval and
>>> it's too late to do a poll for this. But we certainly want to submit a
>>> change proposal within the deadline. Others should be free to submit
>>> their own if they disagree.
>>> Cheers,
>>> Silvia.
>>> [1] http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Media_API#.2810.29_HTML_Accessibility_Task_Force_proposal_-_.22The_San_Diego_Thought_Experiment.22
>>> [2] http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Media_API#.286.29_Synchronize_separate_media_elements_through_attributes
>>> [3] http://lists.w3.org/Archives/Public/public-html/2011Mar/0436.html
>>> [4] http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal
Received on Tuesday, 29 March 2011 05:43:46 UTC

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