I have a problem masking an object.
The scene is a spaceship flying over a landscape a passing behind a mountain.
The landscape is shot with the camera still, so shapes are not moving.
The spaceship is a composition element created in photoshop smaller than the size of the video.
So I put the spaceship in a layer and move it around.
But when I tried to move it behind the mountain, I created a mask with Ctrl+Shift+N and gave it roughly the shape of the mountain. It looked perfect in the first frame.
But the problem is the layer of the spaceship is moving and the mask moves with it. I want the mask to be still so I guess I'm not using the correct approach to it.
NOTE: I know I could duplicate the background layer, mask all but the mountain and place it on top of the spaceship and original background layers, but I was looking for some masking or Alpha channelling sort of solution
I'm sure this is for the most basic level but I haven't had any luck googleing it.