No Locking
when you don't want it to; like in the middle of a movie.

Mouse Mover

Mouse Mover: Go to Menu --> Sound & Video --> Mouse Mover before watching a video. This should prevent the screen from blanking. If you can watch a video for over 10 minutes without the screen going black, full-length movie watching will be fine.

If the screen still blanks; you'll need to deactivate screen locking altogether.

1. Go to Menu --> Preferences --> Default applications for LXSession

Default applications for LXSession

The database will show it's updating

database is updating

2. Click the Autostart tab, scroll down and uncheck Screen Locker

uncheck Screen Locker

3. Click the Core applications tab, scroll down to Lock screen manager
4. Delete lxlock and "X" out of LXSession configuration

Delete lxlock

5. Go to Menu --> Preferences --> Power Manager

Power Manager

6. Click the Security tab, uncheck Lock screen when system is going for sleep and click the "X Close" button

uncheck Lock screen

7. Go to Menu --> System Tools --> LXTerminal (or Ctrl+Alt+T) and type: sudo apt remove light-locker -y[Enter]

remove light locker

8. Type: sudo apt autoremove -y[Enter]
9. Reboot

You may now use XScreenSaver

The Screen lock deactivation method above and a lot more is available from Linux - A New Beginning