Which codec is required?

If I've got a video/audio file, how can I tell what Codec it needs? I want
to be able to let the user upload a file to a server but I want to make sure
before hand that the codec is already installed on the machine. If not I'll
tell them it won't work.

Any ideas how to do this?

(I don't want them to download codec - I just want to use the codecs I have
on the machine already.)

TIA - Jeff.


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