Welcome to the forum.
First, we need to know more about those AVI's. This THREAD will give you background and how to get that info.
My guess is that Bill's tip will solve your issues, but I wonder why so many people persist in using a digital STILL camera for video editing. That makes about as much sense as, when on a warm summer night, you are looking for some ice cubes for your drink in the microwave.
I think that a lot of it is the marketing of so many of these units, as "do-it-all" solutions.
There are some major after-market players, who have developed a whole line of matte-boxes, follow-focus doohickies, and attached monitors for the Canon 5D MK II. Obviously, there is a growing market for these cameras, and many people are availing themselves of them.
Now, with the file handling and the background work that needs to be done first not withstanding, it seems that the results are very good. I've reviewed files from both the Canon 5D and the Nikon D-90, and was impressed with the results. Now, I was not attempting to edit/Export from these test files, but was able to easily Import and preview them, with the proper CODEC's.
However, I do not use my video camera to take stills, and do not use my still cameras to do motion. For me, I keep these operations separate. Still, there is that convenience factor of having one camera and lens set, and doing both. Many has been the time that I regretted lugging two kits around with me, on holiday. Maybe I'll yield to temptation - but all my lenses are Nikon, and I liked the footage from the Canon better...
I can understand (somewhat) that the video capabilities of the D5 and D-90 may appeal to some because of the sensor size and thus the DOF effect, although I would certainly prefer a Letus on my video camera. But for the point-and-shoot variety of still cameras it is a complete disaster with the lack of tripod mounting, focus and the enormous hassle of trying to edit that later, that I find it ridiculous to even try it. But, as can be seen from recent posts, the school vacations are over and the number of students that try PR out without reading the manual or help file is mounting....
God help us.
Cannot argue. However, as you note, there is great popularity, so maybe I should have invested in Canon, or Nikon (actually over the decades, I feel that I have!). Now, it's not just Summer. Gird your loins. The Holiday Season will soon be upon us. You ain't seen nothing yet...
Maybe you need to do a series of articles, so we can just link to those, as the requests for help come flooding in.
Thanks - your answer solved my problem. I just had to install the Codec.
The only reason i am using digital camera video's is because I haven't got a HD camera yet (but soon hopefully). I wanted to try out Adobe premiere to see what I can do with it. :-)