No no, I'm not saying AVS opens them, I'm saying Any Video Converter.
"I can guarantee you, that if you download the latest version of Any Video Converter, (5.5 I think is the most current) and it's free, it will convert your .264 files to .avi, or other formats very easily. Open the program, then you can either drag your .264 files into the window to convert, or add manually by browsing. Select the type of output you want, ie. .avi, .mp4 etc, (there are LOTS!!) then click Convert Now.
If you are still having problems, post back. Personally Any Video Converter does more in my opinion than AVS, as I have used both in my job. I still have both pograms but Any Video Converter has so far been able to convert all of my different files to date.