So, all those weapon videos are used in fullscreen GUIs (in PDAs).
Check out windowDef VidFrame inside \base\guis\movies\uac_welcome.gui
So I think it should just be:
So it just plays in a loop (if it's looped). I think....
I haven't really worked yet with RoQs in GUIs, but if that doesn't work, then it will be a bit tricky. You'd have to make windowDef with animation, onTime 0 to onTime <length of you RoQ> and on that last frame you would have to resetCinematics to make it loop.