- From: John Foliot <jfoliot@stanford.edu>
- Date: Wed, 11 May 2011 22:52:14 -0700 (PDT)
- To: "'HTML Accessibility Task Force'" <public-html-a11y@w3.org>
> > Sorry I can't (yet) post on-list. Feel free to send this on if you'd > like. > > On Wed, May 11, 2011 at 6:45 PM, Silvia Pfeiffer > <silviapfeiffer1@gmail.com> wrote: > > > So, one solution to this is to not have @aria-describedby as the > > solution to longer descriptions of the placeholder image, but instead > > to have it in the resource pointed to by @transcription. I'd be happy > > to just have that. Let's also discuss next week. > > At first glance, this seems to work. This would not, of course, > preclude the use of aria-describedby to reference in-page content (you > can do that anyway). I does seem that @transcription is becoming a > catchall for the video alt, poster alt, transcript, descriptions, etc. > (e.g., anything more than what is appropriate for a short > alternative). > > > The point that nobody seems to understand is that there is no need to > > provide a text alternative for the video. All we need is a text > > alternative for the poster (read: placeholder image). The video's > > content is not presented at the time where a text alternative for the > > video *element* is needed. > > I disagree... mostly. Yes, an alternative to the video content will be > presented some other way (transcript, @transcription, etc.). But an > alternative to the video object itself is still often necessary. > Consider a web page about the Apollo 11 mission. Within that page is a > headered section on the Apollo 11 Launch. Within that section is some > text and a photo of the launch. I think we would all agree that the > image would require @alt even though the visual and even programmatic > context of the image clearly defines what the image is *likely* of. It > could be a photo of mission control or the moon or something else, so > explicit @alt is necessary for accessibility. > > Now consider that the photo is instead a <video> that simply presents > a blank (all black) poster image. If I understand correctly, you are > suggesting that the <video> would have no need for a short > alternative. Why not? Certainly a short alternative presenting the > content of what the video is would be useful for accessibility for > screen reader users (sighted users can, after all, use the entire > visual context to more likely determine the video's content). > > Now consider that the poster frame (whether author defined, random, or > first frame) is an image of the moon, though the video is primarily > about the Apollo 11 launch. A short alternative of "The moon" (or > similar) would be an appropriate alternative for the poster frame, but > would provide little utility (and, in this case, false information) > about what the content of the video actually is. > > This then seems to call for up to 5 (yikes!) types of alternative: > 1. Short alternative for the <video> > 2. Long alternative for the <video> (if necessary) > 3. Short alternative for the poster image (if necessary, when not > identical to #1) > 4. Long alternative for the poster image (if necessary, though I think > this would be somewhat rare) > 5. Alternative for time-based media (e.g., descriptive transcript, as > is defined in WCAG 2.0) > > The proposed solutions generally work well for 1, 2, and 5, but not > for 3 or 4 when poster alt != video alt. > > Of note is that these are all directly supported by WCAG 2.0. SC 1.1.1 > (alt text) would clearly require an alternative for content of the > poster image (if present). But it also states, "If non-text content is > time-based media, then text alternatives at least provide descriptive > identification of the non-text content." See > http://www.w3.org/TR/2010/NOTE-WCAG20-TECHS-20101014/G68 and > http://www.w3.org/TR/2010/NOTE-WCAG20-TECHS-20101014/G100, both of > which would be neglected in my instance of a video with a blank poster > frame. Of course #5 is fully supported by Guideline 1.2. > > > Maybe that is the key problem that we have with @alt and @aria-label. > > We need to find a better name for the attribute so we stop confusion. > > I know Jon has reservations about @alt, but is this not really what > we're looking for (assuming were talking about an alternative for > <video>, not for the poster frame)? > > James would know better of the defined semantics, but @aria-label just > feels wrong - it defines what the object *is*, rather than an > alternative for the object. > > > Thanks for letting me play! > > Jared Smith > WebAIM.org
Received on Thursday, 12 May 2011 05:55:07 UTC