I wrote:
The crudest way of doing this would be to provide transcriptions of audio descriptions to supplement the captions. I believe one can do that with SMIL; I don't know what the situation with other container formats or player UIs is however.
I just ran across the Open and Closed Project's proposal for a XEX format including "audio description scripts", which is precisely the sort of inclusion I mentioned:
http://openandclosed.org/docs/AccessibilityExchange.html -- Benjamin Hawkes-Lewis
