If you run a FPSwatcher like FRAPS or ATITrayTools you will be able to monitor what the GUI is performing at.
With either a sub standard dx9 GPU or a DX8/8.1 GPU (and drivers play apart) the GUI could fall bellow the required FPS for smooth operation.
For example if the video/tv stream is at 50FPS and the GUI drops bellow this then you will get stutter.
You may notice less or no stutter on some of your AVI file as they are running at a much lower FPS ie 25FPS which the GUI has no problems matching (depending on GPU obviously) |