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FW: [media] alt technologies for paused video (and using ARIA)

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>
Message-ID: <03bb01cc1068$bcaeb070$360c1150$@edu>
> 
> 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 GMT

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