So I've been making short films and the like for a while now, so it is rather surprising that tonight is my first attempt at using After Effets.
My aim is to teleport a character out of a shot. I have two snippets of footage. One is a clean plate of the scene, the other is the actor doing a small motion as he teleports out.
So as far as I know I need to use the pen tool to create a mask around my actor, and then hit the mask shape keyframe. I have done that, then move to the next frame and adjust the mask and hit the shape keyframe again.
What happens is after I hit the shape keyframe the first time the mask seems to be locked. I can't manipulate it like I could BEFORE I hit the first keyframe. When holding V and using the pen tool I can drag the vector points to change the shape fine. After I hit the keyframe is just skewers the vectors as if create a curve and I can't manipulate the shape.
I believe the issue you're describing has to do with how you're working with the mask. Try clicking on the mask feather properties to deselect the mask points while you're working with it. If that's not it, try looking at some of the video tutorials that are linked from that page I linked earlier. They should help.
Also, as someone new to AE, I would highly suggest you start here. AE is not a program that you can just pick up by fiddling with it. You have to get a good foundation in the basics or you'll end up frustrated.
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