^ VLC is exactly what I use. It's the newest edition available for mac. . It's not a biggie tho, since I prefer avi's or mp4s. I can study the animation frame by frame. Also I can import it into Adobe Flash my animation program of choice ^_^. I've downloaded and tried using mkv to avi/flv/mp4/etc converters but none of them really work well. Usually the beginning plays ok then it freezes. Sometimes It'll convert without a problem tho..
I tried mplayerOSX. It's different than mplayerX. Stupid that they're named similar. Anyways it plays on my computer but it doesn't do any better than VLC player. But anyways like I said it's no biggie.