Video combination (elementary question)

(noob alert)

If I want to make a video (I’m not yet sure of what’s a clip and what’s a sequence) where there are two people over a static background and time moves faster for one than the other, how would I do that?

Intuitively, I’d film both… clips? from the same viewpoint and then I’d have to combine them in such a way that the parts that are equal, or constant, are combined/shared, while the parts of each frame that are different, or changing, are taken from only one of the videos.

One way of doing that would be to cut one of the persons from one of the clips and superpose that on the other but I don’t know how difficult that is.

As an additional question, how much harder would it be to to that same video with an equal but changing background? (I’d have to find the mechanical means of filming the same movement twice but that’s a more mundane problem).

via Video Editing Forums: Digital Director – Adobe Premiere, Premiere Elements, and After Effects http://www.videoforums.co.uk/adobe-premiere-premiere-elements-after-effects/43450-video-combination-elementary-question.html