[Accessibility-ia2] media a11y

Peter Korn peter.korn at oracle.com
Thu Jun 16 21:28:27 PDT 2011


Silvia,

Reading through your explanation, it seems to me the key issue is the 
division of labor around the rendering of the external file description 
text.  I believe you have made the assumption that the AT will render 
this - at its own pace - while the general approach of accessibility 
APIs is that of exposing GUI/UI elements to AT.

The issue of whether the description text is in the formal DOM or a 
"shadow DOM" is, I think, a red herring.  The user agent has access to 
the text, and the user agent presents all of the media to the user/AT in 
some fashion.  For example, a key facet of the accessibility API is 
exposing the bounding rectangle of all rendered text - something that is 
also not in the DOM but is known to the user agent.  There is no reason 
why the user agent cannot likewise expose the description text in some 
for to the user/AT.


But, returning to what I suspect is the crux of the matter...  I think 
we shouldn't attempt to decide which approach is better before coding up 
a sample of each approach and examining them.  I propose three explorations:

   1. Have the "audio-description-aware" video renderer also render the
      audio descriptions
          * Use one of the new generation of web-based TTS engines, and
            simply have an option in the render to turn description TTS on
          * Note: this doesn't handle Braille; but... how many folks who
            want these descriptions are interested in having an audio
            stream that they can hear be interrupted/paused so that they
            can move their hands to their Braille display to read the
            description, only to then press a key to have the audio
            stream continue?  For Braille-only folks, why would they
            want anything other than the description text - perhaps
            intermingled with the caption text - in "book form"?
   2. Use our existing IA2 API, with a new pattern:
          * Have the "audio-description-aware" video renderer expose an
            AccessibleAction "pause/resume" or some such.
          * Modify some IA2 AT (e.g. NVDA) to recognize this situation,
            and make use of the "pause/resume" action
          * At various moments in the audio/video stream, fire an event
            with the updated description for that video component
          * The modified NVDA would receive this event, call the
            "pause/resume" action, render the description text (in
            speech and/or Braille), and then call "pause/resume" again
   3. Try an experimental new API
          * Call this API something like AccessibleMultimedia;
            potentially model it on AccessibleStreamable (in fact, we
            might have this be options "2a" and "2b" - one that uses
            Streamable with a general pause/resume, and another
            completely new)
          * Modify some AT (e.g. NVDA) to recognize this new API
          * Do whatever you think would be right for this new API

Then interested parties can examine the source code of both approaches, 
play with the resulting applications, and discuss this in a much more 
concrete fashion.  For example, my Braille user assumptions in #1 may be 
totally off base; having coded up examples that use Braille in #2 and #3 
we can try this with users and find out from them what they want.


Regards,

Peter

On 6/16/2011 3:35 PM, Silvia Pfeiffer wrote:
> Hi Pete,
>
> Thanks for your review and questions on the video side of things. I'm
> hoping the combined expertise here will be able to define the best way
> to deal with video and the track specification of HTML5 [1]. I may,
> however, need to go into detail on how tracks and cues are handled in
> HTML5 before we can come to the right solution.
>
> [1] http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#the-track-element
>
> On Fri, Jun 17, 2011 at 5:36 AM, Pete Brunet<pete at a11ysoft.com>  wrote:
>> I've read through the discussion and have these comments and questions:
>>
>> What is the use case to justify an API (and associated synchronization
>> complexity) for access to cues that is not solved by captions for those who
>> can't hear the audio and audio descriptions of visual media for those who
>> can't see the video?
> The<track>  element in HTML5 allows association of external text files
> that provide lists of timed caption cues, subtitle cues, text
> description cues and chapter cues to audio and video elements. This is
> on top of what can come from within a audio or video file, which can
> contain captions and subtitles as text, as well as audio descriptions
> as audio and sign language as video.
>
> Why I approached Alexander was to find out how to deal with text
> descriptions. Text descriptions are something new that you may not
> have seen in traditional accessibility approaches for audio and video:
> they provide the text that is usually spoken in audio descriptions as
> actual timed text cues. The files are essentially the same as caption
> files with cues that have a start and an end time and some text.
> However, it is expected that these text descriptions are read out by a
> screen reader or handed to a braille device to be communicated to
> those who can't hear.
>
> In addition, it should probably be possible to also expose caption
> cues (and subtitle cues for that matter) to AT for those that can
> neither hear nor see and want to consume them through braille. This
> was, however, not my main use case.
>
> Note that none of the text cues are part of the DOM of the Web page
> but only live in the shadow DOM. Therefore, I guess, some method of
> exposure is required.
>
>
>> Since it's early in the discussion of this issue I think this topic needs to
>> be separated from the rest of the discussion.  Alex can you move that to a
>> separate section like you did for the Registry API?
>>
>> At least at this point I'm not in favor of the media control methods.
>> Developers should provide accessible GUI controls.  The developer would have
>> to implement the access in any case and having access through the GUI would
>> eliminate adding the code for these new methods on both sides of the
>> interface.  If the app developer does a correct implementation of the GUI
>> there would be no extra coding required in ATs.
> I guess the idea here was that there may be situations where AT needs
> to overrule what is happening in the UI, for example when there are
> audio and video resources that start autoplaying on a newly opened
> page. However, I am not quite clear on this point either.
>
> The key problem that I saw with text descriptions and video controls
> is that we have quite a special case with text descriptions since the
> author of the text descriptions can identify the breaks in the video
> timeline into which a description cue needs to be fitted, and they can
> provide the text that needs to be spoken in this break, but they
> cannot know how long it will take to actually voice or braille this
> text. Therefore, AT in this case needs to control the video's playback
> timeline and possibly put it on hold when the end time of the cue is
> reached until AT has finished with the text of the cue. I would think
> that this may be one of the only cases where AT actually has to
> control the display of the Web page rather than just being a mere
> observer.
>
> Best Regards,
> Silvia.
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-- 
Oracle <http://www.oracle.com>
Peter Korn | Accessibility Principal
Phone: +1 650 5069522 <tel:+1%20650%205069522>
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