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[Bug 10642] No alternative text description for video key frame (poster)

From: <bugzilla@jessica.w3.org>
Date: Mon, 04 Oct 2010 19:56:41 +0000
To: public-html-a11y@w3.org
Message-Id: <E1P2r9N-0006BV-5V@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=10642

--- Comment #43 from Maciej Stachowiak <mjs@apple.com> 2010-10-04 19:56:39 UTC ---
(In reply to comment #42)
> (In reply to comment #39)
> > I wonder if this is a confused proposal.  The poster frame is an alternative to
> > the video, before it's playing/loaded.  Surely we should have
> > a) short alternative text for the audio/video
> > b) a link to a transcript
> > c) a link to a long description
> > 
> > of the multimedia itself, not the proxy for it?
> 
> "The poster  attribute gives the address of an image file that the user agent
> can show while no video data is available.
> 
> Note: The image given by the poster attribute, the poster frame, is intended to
> be a representative frame of the video (typically one of the first non-blank
> frames) that gives the user an idea of what the video is like."
> - http://dev.w3.org/html5/spec/Overview.html#attr-video-poster
> 
> We have 2 problems: If I cannot see the 'image' that the poster frame displays,
> how do I know "what the video is like"?
> 
> While the spec suggests that @poster is 'intended' to be a representative frame
> of the movie, it is not however forbidden that the image in question can in
> fact be *any* image, and the fact that authors can specify *any* image leaves
> open the door that not only can they, they likely will.  For this reason we
> must ensure that when they do so, they can so so in an accessible fashion.
> 
> If the poster frame is the first frame of a movie, then likely the short
> alternative text for the audio/video is sufficient, however if the replacement
> image is not a frame of the video than alternative text that tells non-sighted
> users what the image conveys is required.
> 
> I think that enough use-cases have been brought forward to show where there is
> a need, thus the only question remains: how do we achieve this? More than one
> person has championed a new attribute: @posteralt
> 
> * Is there a technical reason why we cannot have this attribute in HTML5? 
> * A philosophical reason that trumps the accessibility requirement? 
> * Are there any other alternative proposals?

My opinion after reading the discussion here is:

a) There may be circumstances where a text equivalent for the poster frame is
useful (in particular in cases where the poster frame does not actually appear
in the video, which is a valid use case; or in cases where it was very
carefully selected).

b) There are circumstances where it is not useful to provide a text equivalent
for the poster frame, because it would not add useful information on top of
describing the video itself; often the poster frame is effectively a
mostly-decorative placeholder.

c) There are also circumstances where it is not practical to provide one (e.g.
in automatically chosen cases).

So it seems like it may be useful to have a way to provide a text equivalent
for the poster frame, but not make it mandatory.

If such a mechanism were to be added, it would be better to use an element
instead of an attribute, so that the text equivalent can use semantic markup
and is not limited to plain text.

(Chair hat off for the above comments, in case it needs mentioning.)

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Received on Monday, 4 October 2010 19:56:43 GMT

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