Mask a doorway as door opens.
I created a video of me opening a door and a dino comes up and roars. However I can't seem to get it right with masks. The mask is permanent and so there is a hole not a door and it shows thru to my under layer of the yard outside before I open the door. What do I do to have the closed door and then when I open it, reveal the outside as the door opens? I have 3 layers, 1 - closed door, 2-dino that was on green screen, 3 - clean plate of outside yard. I want to see the yard when I open the door, then the dino comes up and I hide. Easy? I don't think so. When I open the door, I am partially blocking the opening and I disappear because of the mask. Any help on this would be appreciated. Is there a way to start masking as the door is opened and not have it just sitting there the whole time??