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weird how hard it is to find real knowledge on these issues.



If you get off the PC and go to the MAC you don't have to worry about it. You just can't play it period.

It is rather complex because anyone can write a CODEC and use it and not need to follow any "standard". It's own popularity makes it it's own standard.
The more people that use it to create works and then publish with it the more other people have to find, download, and install a new codec to play the music or video.
I'm not sure if any site has a conclusive list of CODECS but it must easily surpass 100 by now.
 
http://www.videohelp.com/
http://www.doom9.org/

Are some of the popular sites I've been to when I neeed to track down something (but I'm sure you've already been to these sites by now)