OK... I use After Effects about 90% of the time... so it always amazes me how rarely editing program and compositing program features cross paths.
Anyway... the question.
Is there any way to do a Set Matte type of effect in FCP 5?... I need one layer which is a B/W rendered luminance matte which I need to apply to one clip below (or above... whichever way FCP wants it)... but not to any other clips below it.