I got nvidia card and i use one CRT monitor and LCD television set, connected via HDMI.
By default, when TV is connected (all the time) mode (twinview) is set to :
CRT: 1152x864_75 +0+0, DFP: 1280x720_50 @1280x864 +1152+0 {viewportin=1280x720, viewportout=1212x680+34+20}
and it works fine.
I got two modes which I manually assign through Terminal:
Only TV:
nvidia-settings --assign 0/CurrentMetaMode="DFP-1: 1280x720 { ViewPortIn=1280x720, ViewPortOut=1212x680+34+20 }"
Only Monitor:
nvidia-settings --assign 0/CurrentMetaMode="CRT-1: 1152x864_75"
The problem is, I don`t know how to assign twinview mode manually from Terminal.