Originally Posted by NomadDemon
This is theoretically possible with xrandr, but I have never tested that exact setup (I don't have a TV). As it requires xrandr 1.3 you'll need at least xserver 1.6 and xf86-video-ati 6.13.0, but I recommend using a later version if it is available in the distribution of your choice.
Originally Posted by bridgman
1. First figure out the output names and native modes of your displays. The easiest way to do this is to connect the displays and run xrandr with no arguments and look through the output. If you are running an old kernel or are using UMS you might have to reboot your computer after connecting the displays before running xrandr.
For the purpose of this guide I'm assuming the primary display is named "DVI-0" and has a native mode of 1280x1024, and the tv display is named "DIN" and has a native mode of 1024x768.
2. Turn of the tv display using xrandr:
Use the name of your tv display as output.
xrandr --output DIN --off
Strictly speaking this should not be necessary, but I have found that turning of any secondary displays first avoids a lot of problems later...
3. Configure the primary display using xrandr:
Use the name of your primary display as output, and the native mode of your primary display as mode.
xrandr --output DVI-0 --mode 1280x1024 --pos 0x0 --primary
Your primary display is most likely already correctly configured, but reconfiguring it anyway doesn't hurt.
4. Configure the tv display using xrandr:
Use the native mode of your primary display as fb, the name of your tv display as output, the native mode of your tv display as mode, and the name of your primary display as same-as. Scale is calculated by dividing the x and y values of your primary display mode with the corresponding value of your tv display mode.
xrandr --fb 1280x1024 --output DIN --mode 1024x768 --scale 1.25x1.333 --same-as DVI-0