Playing Hi-Def Full Resolution Video. Why staggering?

Hi,

I have a patch that plays a full-res video and displays text at certain time. I set the qmetro to 10, and also try to minimize the number of bangs, but somehow when the video is playing, it would sometimes stagger a little (not all the time). Does anyone know what cause the staggering and how I can fix this issue?

I'm running the patch and video on a Dual 2GHz G5 with 1.5GB SDRam.

Thanks so much!