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[media] proposed a11y TF letter on issue-152

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 21 Apr 2011 11:00:22 +1000
Message-ID: <BANLkTikL+rxFokEO5-mLjH7FYsw+pXsM7g@mail.gmail.com>
To: HTML Accessibility Task Force <public-html-a11y@w3.org>
Hi all,

in today's call we discussed outstanding issues on the media
multitrack change proposals, which we would like to see addressed as
part of accepting proposal 4 on our summary list, see
http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposals_Summary#Proposal_4:_Controller_proposal
.

Below is a draft letter of consensus to be sent to the HTML Working
Group to help resolve issue-152.

DEADLINE: this letter will be sent in 24 hours from now, so if you
disagree with anything stated below, please speak up.

IMPORTANT: as part of the letter, the individual change proposals 1-3
on issue-152 are withdrawn, so check if that is in your interest.

(Note that Ian just added a getID() function, so I was able to remove
this from our list of discussed changes form today's call.)

Cheers,
Silvia.


Here is the proposed letter:

---
Subject: Accessibility Task Force consensus on Issue-152, media multitrack

Dear HTML WG chairs,

The undersigned members of the media subgroup of the accessibility
task force have come to a consensus on ISSUE-152, which we'd like to
share with the larger group through this email.

We appreciate the extra time provided to us by the chairs to further
discuss the submitted four change proposals and come to an agreement.
There have indeed been lengthy discussions during the provided time
frame and we have made great progress.

The group has come to a consensus on which proposal to support. While
some of our feedback on that change proposal has already been taken on
board, there is still a list of 5 outstanding changes that need to be
addressed for the specification text to be complete.

The four proposals on the table are as follows:

1. Audio Track Selecction for Media Element
submitted by: Frank Olivier
http://lists.w3.org/Archives/Public/public-html/2011Feb/att-0363/CP_Issue152.htm

2. Media Multitrack Change Proposal 2: Synchronize separate media
elements through attributes
submitted by: Sean Hayes
http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal_2

3. Media Multitrack Change Proposal: Synchronize separate media
elements through attributes
submitted by: Silvia Pfeiffer and Eric Carlson
http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal

4. Proposal for Audio and Video Track Selection and Synchronisation
for Media Elements
submitted by: Ian Hickson
http://lists.w3.org/Archives/Public/public-html/2011Mar/0436.html


CONSENSUS
The undersigned members of the media subgroup of the accessibility
task force have agreed to withdraw proposals 1-3 in favor of proposal
4.

However, we request the following additions to be made to the proposal:

(1) track kind for in-band tracks:

At this point, it is also not possible to discover the functionality
that a in-band track provides through script. A similar problem was
solved for the TextTrack object by introduction of a kind attribute.
This is also necessary for the TrackList object, in particular to
introduce a standard naming scheme across different media container
formats for exposing the kind of data that their tracks provide.

Therefore, we request addition of a getKind(in unsigned long index)
function to the TrackList object, or something of equivalent
functionality.

The proposed list of values that kind should understand are:
for video:
* sign language video (in different sign languages as provided through
getLanguage())
* captions (as in: burnt-in video that may just be overlays)
* different camera angles
* video mosaic
for audio:
* audio descriptions
* language dub
* commentary (such as director's commentary)
* clear audio (see
http://www.w3.org/WAI/PF/HTML/wiki/Media_Accessibility_Requirements#Clear_audio)


(2) loop attribute for grouped multitrack:

The MediaController object currently does not allow for looping of the
grouped resource. This is inconsistent with what is possible on
individual media elements and also inconsistent with what is possible
on in-band multitrack media resources. The same behavior that an
in-band multitrack resource exposes on looping needs to also be
possible on a grouped multitrack resource.

Therefore, we request addition of a loop IDL attribute on the
MediaController object.
When it is set to true, playback on the grouped multitrack must
restart after all slave elements have ended.

It is set to true when at least one of the media elements in the group
have a loop IDL attribute that is set to true, false otherwise.
Alternatively, it would also be acceptable to set it to true only when
all of the media elements in the group have a loop IDL attribute that
is set to true, though that seems overly verbose.


(3) autoplay attribute for grouped multitrack:

The MediaController object currently always autoplay without a means
to control this autoplay behaviour and without consistent autoplay
across all the slave elements. This is inconsistent with in-band
multitrack media resources. One of the main use cases for the
introduction of autoplay attributes was that this allows the UA to
expose a user setting that disables autoplay behaviour, which is
particularly useful to vision-impaired users who cannot easily locate
autoplaying media elements.

Therefore, we request addition of a autoplay IDL attribute on the
MediaController object.
When it is set to true, playback of the grouped multitrack must start
once all slave elements have reached a readyState of HAVE_ENOUGH_DATA
and can play through.

It is set to true when at least one of the media elements in the group
have a autoplay IDL attribute that is set to true, false otherwise.
Alternatively, it would also be acceptable to set it to true only when
all of the media elements in the group have a autoplay IDL attribute
that is set to true, though that seems overly verbose.


(4) readyState for grouped multitrack:

The MediaController object currently does not expose an aggregate view
of the readyState of the slave media elements. It is, however,
impossible for a developer to reliably aggregate the readyState from
the individual slave media elements, since their states may continue
to change. The media framework inside the UA is the only place where
such aggregation is sensibly possible.

Therefore, we request addition of a readyState IDL attribute on the
MediaController object.
It must represent the minimum state that all the slave media elements
have achieved.


(5) onended event:

The MediaController object currently does not expose an onended event.
This is inconsistent with in-band multitrack media resources and a
convenience event that is useful when reacting to the situation of all
slave elements being finished. This would for example be the case for
a grouped multitrack resource with an ordinary video track and a sign
language track, where the ordinary video track should get a display of
further related videos once all tracks have finished playing. It would
e.g. wait until the sign language track is finished before it
displayed further information.

Therefore, we request addition of a onended event to the MediaController object.


Best Regards,

Media Subgroup of the Accessibility Task force

Judy Brewer
Janina Sajka
John Foliot
Sean Hayes
Frank Olivier
Eric Carlson
Mark Watson
Bob Lund
Silvia Pfeiffer
(is there anyone I've missed or wants to be on that list?)
Received on Thursday, 21 April 2011 01:01:10 GMT

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