Glad that Jeff got you moved to the correct forum.
The first two links that John T. posted will give you all of that information. I would start with the first, "Problem with AVI File... " and read it. Then, for some more background on CODEC's, the building blocks of Audio/Video files, see the "CODEC's a Primer," as it goes in more detail.
If you have any problem understanding the concepts and details in either of those two articles, please let me know, and we can go into more detail, on any aspect.
Good luck, and believe me, with Video editing, every moment spent learning about CODEC's, and how they are contained within file formats, will be time well-spent.
Hunt
