I want to cut out a part of a clip that is moving around and superimpose it on top of another clip, just like using bluescreen... Problem is that I don't have a one-colored background in this clip so that I can use Blue/GreenScreen.

With FinalCut on Mac I was able to do this, but in Premiere I only find the transparency settings.... I can't figure out how to move my mask around in the clip ..... anyone know how to do this?