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[whatwg] Alt attribute for <video> and <audio>

From: Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>
Date: Mon, 10 Aug 2009 07:53:09 +0100
Message-ID: <4A7FC3D5.9010407@googlemail.com>
On 10/08/2009 04:05, Remco wrote:
> A title is a short description, and could be the movie title in the
> case of a video element.

WCAG 2 1.1.1 requires that:

"If non-text content is time-based media, then text alternatives at 
least provide descriptive identification of the non-text content."

"title" and "aria-labelledby" seem sufficient for this purpose.

So do "figure" and "legend":


> An alt is a textual alternative for the content.


> For video, audio, object, iframe, this is a little sparse.


> But Elephants Dream may not be a good example for a video where an alt
> text would be useful. It's simply too complicated to replace with
> alternative text. But if you have a short video that explains
> something on Wikipedia, it would be tremendously helpful if the alt
> text would convey the same meaning. A video of a ball falling to show
> what gravity is, could have the alt text: "A ball accelerates as it
> moves down. Next to the ball's trajectory, a speedometer increases
> with 9.8 m/s per second.".

If you want to provide an "alternative for time-based media" (in WCAG 
2's phrase), then you want a method that can scale to contain semantic 
information, such as indicating language changes ("lang") or changes of 
speaker ("dialog").

Here's how WCAG 2 defines "alternative for time-based media":

"document including correctly sequenced text descriptions of time-based 
visual and auditory information and providing a means for achieving the 
outcomes of any time-based interaction

"Note: A screenplay used to create the synchronized media content would 
meet this definition only if it was corrected to accurately represent 
the final synchronized media after editing."


Here's just three ways you could do this without changing HTML5, 
assuming the incorporation of WAI-ARIA:

1. <figure><legend>Ball acceleraton.<details>A ball accelerates as it 
moves down. Next to the ball's trajectory, a speedometer increases with 
9.8 m/s per second.</details></legend><video>...</video></figure>

2. <video title="Ball acceleration" 
aria-describedby="alternative"...</video><p id="alternative">A ball 
accelerates as it moves down. Next to the ball's trajectory, a 
speedometer increases with 9.8 m/s per second.</p>

3. <video title="Interview with Barack Obama" 
aria-describedby="transcript-link"...</video><a href="transcript.html" 
id="transcript-link">Transcript of Interview with Barack Obama</a>

See also:

"WAI CG Consensus Resolutions on Text alternatives in HTML 5" (proposal 
for using "aria-describedby" in place of "longdesc"):


WCAG 2 Technique "G159: Providing an alternative for time-based media 
for video-only content":


WCAG 2 Technique G58: Placing a link to the alternative for time-based 
media immediately next to the non-text content"


Do these features meet your requirements? If not, why not?

Benjamin Hawkes-Lewis
Received on Sunday, 9 August 2009 23:53:09 UTC

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