I am making a new short movie/film and have quite a few gunfight scenes. One of the shots is the gunner shooting while moving. As he keeps moving he goes behind a pole, still shooting. I want to make the muzzle flash behind the pole, however I am only going to do this in Final Cut Pro. I tried putting the Matte around the area where you should not be able to see the muzzle flash. I thought I was set to go, then I click render and nothing happened. Am I using the mask completely wrong?