I have many 720p MKV video files and a mid-2009 13" MBP. The problem is that when I try to play one of them with VLC or MPlayerX, it starts lagging after about 10 mins and the CPU processes are way high in Activity Monitor. Not all of them, but many. I figure it's either because of the file or the app, but the latter seems more likely. So what can I do? Thanks!