The only thing that worked for turning off screen-blanking when using youtube or vlc was an ugly little hack:
I installed xdotool and ran crontab -e and added:
*/2 * * * * DISPLAY=:0 XAUTHORITY=/home/andy/.Xauthority xdotool key Ctrl
Original post
In spite of not having any screen saver activate and in spite of setting "Blank Screen" to "Never' under Power options, my screen kept on blanking out after 1-3 minutes of watching TV using mythtv. I tried a lot of things, including using xset, but the only thing that worked in the end was editing my /etc/X11/xorg.conf (I use an nvidia driver) and adding the bits in red:
Section "ServerLayout"
Identifier "X.org Configured"
Screen 0 "Screen0" 0 0
Screen 1 "Screen1" RightOf "Screen0"
Screen 2 "Screen2" RightOf "Screen1"
InputDevice "Mouse0" "CorePointer"
InputDevice "Keyboard0" "CoreKeyboard"
Option "BlankTime" "0"
Option "StandbyTime" "0"
Option "SuspendTime" "0"
Option "OffTime" "0"
Option "DPMS" "0"
EndSection
Now the screen never blanks when watching TV using mythtv. On the other hand, it still blanks when watching DVDs in VLC...