go from 16:9 to 4:3

Hey, I'm trying to make a Counterstrike video, but i play the game in 4:3 1280 x 960. Is there a way I can make the timeline I'm working on 4:3? When I try to in the master settings, and in the timeline settings, 4:3 is grayed out and I cant seem to figure out how to make i selectable.