You need to tell more.
.avi is NO Video-Codec - it is a container and can hold Codecs that works and not.
If it opens with QuickTime-Player then
open Inspector [cmd+I]
Video formatted (Codecs) : nnnnnnnnnnnn
Frames per second : YY.yy fps
What does they say ?
If QT-player do not opens Your .avi files - try VLC-player (download from Internet) and see what it says.
Yours Bengt W