I have installed ubuntu 11.04 on my computer. I have also instaled xbmc media center to see my movies. I have tried to play an HD movie (MKV with x264) and it doesn't go as smooth as it does in Windows (with Core AVC codec).

Following the information found in may forums, I tried to install:
- x264 package
- Ubuntu restricted extras
- w32codec package (from medibuntu)
- non-free codecs (from medibuntu)

After doing that, I tried it but nothing changed. I rebooted the machine with the same result. I don't know if it uses the new codecs or not. Is there any way to see what codec uses xbmc to reproduce a movie?

Any idea to solve the problem?