I think we're most likely to resolve this question with some good examples; we seem mostly in agreement on the technical needs:
* short 'alt' text for media elements
* long description
* transcript
As I said before, all of these are a-temporal; they should remain true no matter whether you're considering the initial image or the video attached. Example: a sighted user seeing the 'trailer green screen' will probably understand that a trailer is involved:
but
<video ... alt="The following preview has been approved for Appropriate Audiences by the MPAA" ... src="Theleopardtrailer.mov" ... />
would, IMHO, be quite unhelpful. It doesn't say anything at all about what the sighted user could learn from the entire resource!
David Singer
Multimedia and Software Standards, Apple Inc.
