Do note that current plugins for Quick Look video do nothing more than be able to display static thumbnails of various video formats even if you have Perian installed. Unlike with Snow Leopard and Perian in the past, you won't see the actual video and audio run in Quick Look with AVI, MKV, etc formats.. That's where the libVLC can come in, I hope.
More info:
https://github.com/Marginal/QLVideo/issues/3