After i got my Apple TV 2 jailbroken and installed XBMC on it I started to try and play some mkv files on it. I quickly discovered that it was pure misery. The movie wouldn’t buffer like they should and some wouldn’t even play. I startet googling and discovered a lot of people with the same problems as me. To get it fixed you have to install XBMC Nightly Builds. It has something to do with the lastes version of iOS. After it’s done the files will play like they should. You can see how to install it below.