Help in Movie export

Hi… wonder if anyone can help me on this…

I created a movie size 300 x 200, and it involves a picture moving from one side to the other.

But i want it to be hidden when it is outside the movie size. I.e. not visible when the object is in the work area. its a scenery pic… so i want to achieve a panning effect without seeing the edge of the picture moving.

I gave some thought and i figure if i put a black layer with a 300x200 hole in middle at top most layer… i can achieve that.

but i am sure Flash MX must be clever than this so must have some build-in function.

any help will be appreciated.