Thanks, that was enormously helpful and gives me a great starting point. One place I’m getting tripped up, though, is exactly how to keyframe / move the mask points. For instance, through most of the shot, the hand is positioned more or less the same way — all five fingers are more or less extended. Towards the end of the overlapping portion (see note below), however, the hand dips down, forming more of a fist shape (i.e., no fingers). Should I create a new mask / new layer at this point, or should I keyframe the hand-shaped mask so that it forms a fist shape? To make matters more complicated, the character then stands up, again requiring an entirely different mask shape. What’s the best way to divide up these masks?
Note: The general shape of the shot is of one version of the actor sitting in a chair, and another version of the same actor squatting on the floor to the side / slightly behind him. At one point, the foreground character moves his hand in front of the other’s face — later, he stands up and begins to move across the second character. So I started with a simple “curved line down the center of the frame” mask, then added another version of the topmost layer (with the seated character), in which I masked the hand separately, starting when the hand first moves over the BG character’s face. Should I then create a third mask for the segment where the first character moves bodily across the second, or am I approaching this in the wrong way? Let me know if this is difficult to visualize and I will attach some screenshots. And thanks again for the advice!