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RE: [media] change proposals for issue-152

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Sun, 27 Mar 2011 18:41:25 +0000
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <8DEFC0D8B72E054E97DC307774FE4B913FB137F2@DB3EX14MBXC313.europe.corp.microsoft.com>
I don't see it as a purity issue. There are 4 main practical reasons that I want to unify the handling of video and text tracks which were present in the version we agreed on at the f2f and were dropped in your CP.

1 - in a multi-video layout it will be important to be able to place the text tracks so that they encompass and are placed with respect to the whole layout, not simply the video it is slaved to. 

2. There does not need to be another special set of rules for downloading the video resource, the same rules and states should work for both.

3. Track should have the same source selection algorithm as <audio> or <video>.

4. The solution should allow having visible captions slaved to an audio only resource without having to pretend that the audio is a video, or giving the audio element a visible rectangle.

I'm not so much concerned with the use case of a text track that is not slaved to a media timeline, however this would be readily achievable simply using a clock since the timeline of a text track is perfectly well defined.

Secondly I see no problem defining that, in the absence of styling to the contrary, the act of slaving to a media timeline causes the default rendering rectangle to be that of the video it is slaved to. I do see a very big problem however with defining the video be a viewport and not simply a containing rectangle and having text track rendering restricted to that rectangle. Which makes proposal (2)

However my main issue is the fact that I don't believe you have adequately justified moving video and audio secondary tracks out of the master video (#10 'the San Diego solution') and an implicit timeline.  The only justification that I can see is that you can apply style, but to my mind that is readily achieved with 

video > track[kind='video'] { ... }

And that avoids having to have to have a bunch of special rules for how to handle the redundant syntactic baggage of slave tracks with controls, poster, etc.

So perhaps if we were to go back to that point at 2pm on Sunday where we seemed to have agreement, and the solution that I thought you were going to write up on behalf of the group as a CP, rather than your modified version, then maybe we can move forward from that point; incorporating a version of the track selection API to incorporate in band tracks.


-----Original Message-----
From: public-html-a11y-request@w3.org [mailto:public-html-a11y-request@w3.org] On Behalf Of Silvia Pfeiffer
Sent: 27 March 2011 19:04
To: HTML Accessibility Task Force
Subject: Re: [media] change proposals for issue-152

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

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,

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 Sunday, 27 March 2011 18:42:10 UTC

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