i've got this annoying issue just with my external monitor but let me explain what machine im running on:
Linux mint 14 on a macbook 4.1 with a Philips 17" external monitor.
The issue is a video lag while playing with vlc (as well as the other players in linux mint), the lag is every 8-10 seconds and it's only when i've got the external monitor plugged in. This means that i've got no lag with my macbook monitor.
don't know if "lag" is the correct word, it's like the video player jump a frame every 8-10 seconds. sometimes is really imperceptible,actually it depends on the film im viewing, but really annoyng.
The monitor configuration in my preferences is:
Ext monitor 1280x1024 75hz;
laptop monitor turned off, "same image in all monitor" not checked as i can use the ext monitor higher resolution.
I keep laptop monitor turned off so i can close its lid whith no video in it.
i hope i explained a little and sorry for my english