This will happen to me every once in a while, I'll either be watching a movie on Blu-Ray or I'll have a movie in iTunes playing, and after about an hour it will turn the screen saver on, and I've looked everywhere in the control panel for an option to turn it off selectively, and I cannot find one, is there a way to do this?
Not sure I would turn off the screensaver completely, but I would use power management to set the options for movie watching preferences.
One way is to go to Control panel>Appearance and personalization>change Screen saver> and set the wait time to 2 hours or whatever you feel comfortable with. Then click on Change power settings to adjust monitor shutdown etc. for movie viewing.