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[media] text alternatives for video

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 19 May 2011 14:24:03 +1000
Message-ID: <BANLkTik6M=LLJ+A7Ri+uh0tvPM90XVDkzw@mail.gmail.com>
To: HTML Accessibility Task Force <public-html-a11y@w3.org>
Hi all,

In today's media subgroup call, the discussions on how to do text
alternatives for video continued.


We tightened up the requirements, which can now be summarized as follows:

1. need to support graphical and text-only browsers

2. need to support HTML5 and legacy browsers (i.e. <video> element support)

3. need to allow describing the default and custom video player layout

4. need to allow for short and long text alternative for placeholder image

5. need to allow for short and long text alternative for video

6. need to work when text alternative is on page / not on page


After lengthy discussions, we eventually came up with the following
markup example:

<video src="file.mp4" poster="poster.png" aria-describedby="posteralt
videosummary"
  transcript="transcript.html" aria-label="MyPlayer video player">
  <p id="videosummary">A Clockwork Orange Trailer (<a
href="transcript.html">Transcript</a>)</p>
  <p id="posteralt">Poster frame is a clockwork orange movie poster (<a
  href="posterlongdesc.html">long description</a>)</p>
  <p><a href="file.mp4">Download the video file</a></p>
</video>

This type of markup satisfies the above requirements as follows:

1.
Graphical browsers display the video with poster.png as the
placeholder image (or the first frame if no @poster attribute is
given)
Text-only browsers can display similar text to what is now inside the <video>

2.
HTML5 browsers display the video with poster.png as the placeholder
image (or the first frame if no @poster attribute is given)
Legacy browsers display the paragraphs from inside the video element

3.
Default layout would have a controls attribute and no text in aria-label
Custom layout announced through the aria-label attribute

4.
Short text alternative for the placeholder image is provided through
aria-describedby
Long text alternative for the placeholder image is provided through
the link inside the paragraph for the short text alternative for the
image

5.
Short text alternative for the video is provided through aria-describedby
Long text alternative for the video is provided through the link
inside the paragraph for the short text alternative for the video, and
also as an additional attribute on the video element so that a context
menu can bring up a link to the transcript for sighted users

6.
Example above is how it would work for when the text alternatives are
not on the page
When they are, aria-describedby can link to those paragraphs, but may
want to add still links to long description inside the <video>


Have we overlooked anything?

Cheers,
Silvia.
Received on Thursday, 19 May 2011 04:24:50 GMT

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