Normal
I was having the same issue when I first started with MediaPortal. Unfortunately, my GeForce 7950GT card wasn't supported by 84.21 (which is considered the last, good, solid version of NVIDIA drivers). Video playback in MP was simply awful, so I went with ZoomPlayer for everything except DRM infected iTunes videos, for which I use QuickTime Player. I couldn't be happier with ZoomPlayer, it works perfectly, and I have never looked back. My HTPC is now rock solid with video playback for both BeyondTV as well as with MP/ZoomPlayer, so I'm not planning to change anything at this point.