Not a Mac-only solution: But I managed to convert all of my older .avi (IV50) footage to MP4 using Need4 Video Converter for Windows (http://need4video.com/). It costs a few bucks - but it enabled my video in the ancient IV50 format to be converted to the more future-proof MPEG4 format. The MPEG4 files are easily displayed in Quicktime on both Mac and PC.
/Thomas.
