I selected a bit of footage in the time line, went to filters and added the image mask selection. Now the image mask control area is set up for that objec/piece of footage. There is a square space where you are suppose to drag a still image or Quicktime movie to make a mask. Neither one works. (As a side note) In FCP you can import a still and it works but when you inport a movie as a mask you only see the first frame. Rendering the file doesn't help.
I went back and recreated the Quicktime maske making sure an alpha channel was included but that didn't help.
Little Men Entertainment