Displaying movieclip on container roll over

I’m trying to make something similar to the Vimeo video player but I can’t figure out how to make the video controls visible only when you roll over the video clip. I tried creating a movieclip in the background the same size as the video that changes the video controls alpha to 100 onRollOver, but when I roll over the controls, they disappear again. I guess I can add _alpha=100 to the controls onRollOver, but is there a better way to control this functionality?