You probably already know this, but I’ve found that if you keyframe and shape the mask at the beginning and end of the shot, and then one in the middle, and one in between each of those three points, and so on and so forth, the program automatically gets pretty close to where it needs to be. Then it becomes a matter of going through frame by frame and adjusting it. When I first started rotoscoping I just went frame by frame which was really time consuming, and when I learned this I realized how much time I wasted. Sorry if I’m being redundant but this might be useful to you or someone else on here.