- From: Remco <remco47@gmail.com>
- Date: Mon, 10 Aug 2009 16:42:36 +0200
On Mon, Aug 10, 2009 at 8:53 AM, Benjamin Hawkes-Lewis<bhawkeslewis at googlemail.com> wrote: > 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": > > http://dev.w3.org/html5/spec/Overview.html#the-figure-element > >> An alt is a textual alternative for the content. > > [snip] > >> For video, audio, object, iframe, this is a little sparse. > > [snip] > >> 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." > > http://www.w3.org/TR/WCAG20/#alt-time-based-mediadef > > 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"): > > http://www.w3.org/2009/06/Text-Alternatives-in-HTML5 > > WCAG 2 Technique "G159: Providing an alternative for time-based media for > video-only content": > > http://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/G159 > > WCAG 2 Technique G58: Placing a link to the alternative for time-based media > immediately next to the non-text content" > > http://www.w3.org/TR/2008/NOTE-WCAG20-TECHS-20081211/G58.html > > Do these features meet your requirements? If not, why not? > > -- > Benjamin Hawkes-Lewis > A longdesc is not the same as an alt, in that a longdesc is a long description of the content, while an alt is alternative actual content. This distinction may in practice be unnecessary though. And I see that the WAI has redefined alt to mean a short description. Does this mean that the alt attribute and longdesc attribute for images can be combined and deprecated in favor of aria-describedby or a figure/legend combo? It would make the HTML spec more consistent. So instead of this: <img title="Tank Man" alt="A man stands in front of a column of three tanks." longdesc="page-about-tank-man-photo.html" src="tankman.jpg"> We would get this: <img title="Tank Man" aria-describedby="tank-desc" src="tankman.jpg"> <p id="tank-desc">A man stands in front of a column of three tanks. <a href="page-about-tank-man-photo.html">More information</a>.</p> Or this: <figure> <legend>Tank Man</legend> <img src="tankman.jpg"> <details><legend>Alternative content</legend>A man stands in front of a column of three tanks. <a href="page-about-tank-man-photo.html">More information</a></details> </figure> And for an iframe: <iframe title="Cool Widget" aria-describedby="widget-desc" src="http://cool-widget.example.com/user/remco"> <p id="widget-desc">All visiting IP addresses and their browsing history as tracked by Example Inc. are displayed in a list. <a href="bigbrother.html">More information</a>.</p> Or: <figure> <legend>Cool Widget</legend> <iframe src="http://cool-widget.example.com/user/remco"> <details><legend>Description</legend>All visiting IP addresses and their browsing history as tracked by Example Inc. are displayed in a list. <a href="bigbrother.html">More information</a>.</details> </figure> One advantage of this is that the alternative content is now by default always visible (or can be made visible in the case of <details>). That makes it much more useful for normal use cases (no network problems or disabled audience), which means it would be provided a lot more. This is a lot better than the current situation with alt. The question now is: why would we need both <figure> and aria-describedby? Remco
Received on Monday, 10 August 2009 07:42:36 UTC