Quick Look won't play sound of .avi files When I want to use Quick Look to quickly check if an .avi file is corrupt, or if the quality is alright, it does not play the sound anymore.

Is there a way to enhance Quick Look with "proper" divx capabilities, to prevent mishaps like this?

On a related note: I would enjoy .mkv-support, too, if anyone has an idea how to integrate that.

EDIT:
jmlumpkin got it right, Perian solved the problem. I can now quickcheck .avi files again, properly.

Thank you for the quick answer, I would upvote, but it says I need 15 rep first :/
Quick Look won't let you do this. Mainly because the core audio/video stuff behind quicktime doesn't support it.

The easiest way to do this would honestly be to use VLC. This supports both file types you mention. 

The other way is to check out Perian, which gives you a bunch of extra codecs. 

Personally, I would try the VLC way first. You won't be able to view these items with quickview or preview.app, but VLC handles pretty much any file type I have ever thrown at it.