Answer by Hannes R. for Lubuntu 14.04 - Disable screen saver....for real this time?

I know what's going on here. Problem is not how to set the screen saver (it's really easy and the light locker settings work just like they are supposed to work) - but that sometimes it keeps mysteriously resetting to its default position (10 minutes).

How? here's the punchline. Gnome Mplayer resets the screensaver for some reason on pause and exit.

Here's how to fix it:

1. install VLC media player
2. open preferences->default applications
3. set default video player: VLC

and your screen saver will stay the way you want it to be.