I think this is a good idea, but one rapidly runs into the problems
talked about in the 'bucket' RFC, notably that there is not a
universal language for naming codecs (4ccs etc). But it's proved
useful in the past.
In general, the source fallbacks are also a way to 'probe' this,
albeit in a very different way.
I'm not sure you can always get a definitive answer to the question
"if I gave you a file with this (extended) MIME type, could you play
it?" and I am fairly sure that asking the implementation to enumerate
all the types it could support would be hard.
But this kind of query is really useful on a 'portal' page -- entry
points to sites. A script can detect that you need to download oh,
say, Theora, in order to see the videos in the rest of the site, and
shows a frame or page that would help you load it. :-)
--
David Singer
Apple/QuickTime
