Core i5 video out problem

i just purchased a Moshi mini displayport to HDMI adapter, and connected my Macbook pro 15" core i5 to my HDTV (1080p). I noticed that every 30 secs or so, while watching even standard res avi video I'll get a dropped frame or two. Even if the video is playing on the computer display, as long as the TV is connected, it will drop frames occasionally on both. I tried MP4 video on Itunes and got the same.
Is this normal? The Core i5's have discrete graphics cards, dont think this should be occurring.
Any one else had this experience?
Audio is outputting fine by the way.

Thanks

 

Thanks for the reply
Tried VLC and DVD player. It seems to be a generalized issue with the interface, not just while playing video. The hole system seems to stutter every once in a while (not the audio, just on screen).