http://www.wotsit.org 
This is the greatest page that I ever seen about file formats. It includes not only audio/video file formats; but also other document formats; such as MS Applications. Worths trying ! 

http://www.real.com 
This is almost the inventor of the idea of streaming media. Visit here frequently to get the latest player for your audio and video files. It also presents education material for video/audio formats. 

http://ourworld.compuserve.com/homepages/jimj/stream/streamtxt.htm 
This is where you can find various streaming media resources. 

http://www.vegasmusicandfilm.com/streaming.html 
This is another place for streaming media. This is said to be streaming media gallery. 

http://www.microsoft.com/windows/windowsmedia/technologies/formats.htm 
Microsoft's formats about multimedia technologies. 

http://developer.apple.com/techpubs/quicktime/qtdevdocs/RM/pdfframe.htm 
Apple's QuickTime movie specifications. 

http://www.xanadu.com.au/sc/audio.html 
A comparison of Internet Audio Formats 

http://www.cs.tut.fi/%7Eleopold/Ld/AudioFormats.html 
Another comparison of audio formats. 

http://www.nzine.co.nz/features/rave6aa.html 
Streaming video format comparison. 

http://www.rahul.net/jfm/avi.html 
AVI Overview