Video playback lag in iTunes when selecting video position

When playing back movies and videos on iTunes 10.4, both bought from the Apple store and imported videos, I am always having issues with the video freezing while the audio continues. For example, if i choose to go to 1 hour into the movie in the navigation bar, the video will freeze but the audio will continue. The only way to fix this is to close the video window, and click 'play movie' again so it can resume from when i closed the window. Even then it sometimes goes back a portion and starts from earlier than i left off.

Also, after watching a video in iTunes, if i go back to playing music, even when the play button is engaged the audio will not start, instead it just stays stuck at 0:00.

Any help with this issue would be appreciated.

-iTunes 10.4

-Apple iMac Snow Leopard 10.6.8

-3.06 GHz Intel Core 2 Duo

-4GB 1067 MHz DDR3