Media player stuttering when playing DVD MKV files

Hi,

 

Just wondered if anyone else has had this problem.

 

When I try and watch a DVD MKV files using media player, the picture is jerky and stutters, however the sound is perfect.

This does not happen when I am using XBMC installed on the ATV2.

I have movies stored on a Vortxbox, which is wired to a switch which the ATV2 is wired directly into.

Thanks guys.