Power management: How to not idle the monitor while viewing a movie?

[Sergey Mironov]

Hi List! I have an idle problem. Xfce seems to turn off my display
when it thinks I am out of the computer. It works OK most of the time,
but not when I am viewing a movie using mplayer/vlc etc. Is it
possible to temporary disable the power management for this cases?
More, is it possible to do it with a script?

Thanks in advance,
Sergey