Right, further to that, I installed the basic codec, and it played in the mala video tester (the mp4). Note that all videos played in media player or vlc, so the computer had the right codecs already for those programs.
However here's what happens in Mala.
When I am on the game with the AVI file, I hear the sound, and see a black square, no video.
When I go to the game with the MP4 file, nothing happens for a few seconds, then MaLa becomes unresponsive and crashes...