Sony Vegas 12 Rendering

help please, I'm trying to shoot a video about the game through the action mirillis program. video he shoots well and on the whole screen. but when rendering through sony in avi sony avc, the video comes out in a square format, not on the whole screen, the whole video is clamped in a square screen. help pzhl. or tell me what I'm doing wrong, or you have any codecs that you use.