the reason why these things happen - is that when play audio is used-
the real movie frame rate is used-
the real movie frame rate might be exactly 30fps or 25fps -
DOES NOT match the vga or dvi timings-
vga/dvi timings are different at different screen sizes-
they are 60.02 or 75.03 or 59.94 - very rarely exactly 75Hz or 60Hz
so your movie is playing back NOT locked to the screen outputs-
There arent any drop frames - or any stuttering - the frames are not being output locked to the screen output rate - so at certain times - usually every 30 secs dont have any chance to get displayed- as the movie playback goes out of sync with the screen rate
you want to do audio and dropped frames are critical-
you need to use single or dual output - at exact same size-
do not use triple heads-
do not mix monitor resolutions-
use 1920x1080 or 1280x720 or 800x600 similar-
run catalyst playback at 60fps or 50fps or 75fps -
this give more of a chance for frames which dont line up with the screen refresh rate to get displayed.