W3C home > Mailing lists > Public > public-html@w3.org > April 2011

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

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Fri, 22 Apr 2011 17:19:09 +1000
Message-ID: <BANLkTim4Gs35bFe1DA3ZqBeUs9-OjhS6yw@mail.gmail.com>
To: public-html <public-html@w3.org>, Paul Cotton <Paul.Cotton@microsoft.com>, Sam Ruby <rubys@intertwingly.net>, Maciej Stachowiak <mjs@apple.com>, Eric Carlson <eric.carlson@apple.com>
This is a reply by Eric and myself.

Eric and I hereby confirm that we withdraw our change proposal 3
http://www.w3.org/WAI/PF/HTML/wiki/Media_Multitrack_Change_Proposal
since we are in amicable consensus with change proposal 4, even if the
5 changes listed below are not applied immediately, but registered as
bugs on the spec and dealt with post LC.

Best Regards,
Silvia & Eric.


On Fri, Apr 22, 2011 at 5:18 PM, Silvia Pfeiffer
<silviapfeiffer1@gmail.com> wrote:
> (sending this on behalf of the accessibility task force)
>
> 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 with 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
>
Received on Friday, 22 April 2011 07:19:57 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 9 May 2012 00:17:28 GMT