Accessibility/IA2 1.3: Difference between revisions

Accessibility/IA2 1.3 (view source)

Revision as of 10:04, 6 June 2011

1,617 bytes added , 6 June 2011

added the need to support text descriptions

Silviapfeiffer

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 See [https://lists.linux-foundation.org/pipermail/accessibility-ia2/2010-June/001186.html IA2 list] for discussion.
+==Text Descriptions and Subtitles for Video and Audio==
+The &lt;track> element in HTML5 exposes captions, subtitles and text descriptions to a HTML5 video player.
+See the [http://www.w3.org/TR/html5/the-iframe-element.html#the-track-element HTML5 track element] for the specification.
+The captions have a visual presentation, but are probably not relevant to be exposed to screen readers, because they repeat what is already available in the audio.
+The subtitles have a visual presentation. They could be made available as an alternative to the video's native audio track.
+The text descriptions have no visual presentation, but are supposed to be exposed to screen readers.
+Text description cues (i.e. a single instance of a text description that is to be rendered from a certain start time to a certain stop time) exist in HTML5: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-iframe-element.html#texttrackcue . They need to be exposed through IA2 to screen readers during video playback whenever they become active. Screen readers should, upon receiving a TextTrackCue start reading out the text. However, often the time that is available during the video playback for reading out the description text is not sufficient for the screenreader.
+We therefore need a means for the screenreader to reach back to the browser and pause the video playback until it finishes reading.
+HTML5 has JavaScript interfaces for this to happen, in particular the "pauseOnExit" attribute and the play() function, which will allow the kind of interaction that is required. This needs to be worked out for IA2.