HI GalaxieMusique,
I'm french too, but I'm going to write this post in english so that everyone may understand it 😉
I have the same problem in Mavericks, but I'd say, more important, with QuickLook.
Indeed Quicklook can't read avi movies anymore. Actually it always been the case, but with Perian we were able to fix it. The problem is that Perian is no longer available for Mac OS 10.9....
I'd assume that our only hope is Apple themselves... It would be nice from Apple to creat an add-on for quicklook to be able to preview the avi movies.
In regards with quicktime, you can download QuickTime 7 here:
http://www.01net.com/telecharger/windows/Multimedia/lecteurs_video_dvd/fiches/10 0.html
and ask all the .avi movies to be played by QuickTime 7 and not QuickTime X (included into Mac OS).
Sorry for the english, we french people can make mistakes sometimes 😉
If anyone has a solution for QuickLook, please do not hesitate. This topic is becoming a real mess....