There is a console command for It I think, but Im not sure. Any good video editing program will be able to crop the video for you, cuting out all of the hud, just watch that you keep all the action in the center of the frame.
Also, Im asuming you are recording all your shots as demos, and then later converting them into VIDEO files. If so, once all your shots are done, you can make a copy of your ESF directory (just in case) and replace things like the redical sprite with a blank one. and easy way to do this is to replace the sprites with a null.spr. Just copy Null.spr, and re-name it to what you want to replace.
If you are realy serious about this, and you have some people together, I would be more than glad to help out.
Crap, got to go finish making the Zat, good luck!