Cloning in Sony Vegas
Record your video with your actor(s) doing whatever the script calls for, Move them to a different spot to act as the "clone" and record it as many times as you want.. Do not put them to close together, You must keep them seperated or they will be cut off during editing. (Tutorial video shot in campaign but works with multiplayer too of course)
source video
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Now open Sony Vegas
Right click Video track one and select Insert Video Track. insert as many tracks as you have clones. For this tutorial I have 2 clones So I made 2 extra tracks.

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Align your clips like this. The bottom clip is my background, The middle clip is Clone 1, The top clip is Clone 2.

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Right click your top clone and select Pan/Crop

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Click the mask Option (1) Then select the Anchor Creation Tool(2) Now draw an outline around your clone(3). Notice how that cuts the other portion of the video out,thus revealing the other clone(4). Apply this for each clone you have. Do not apply it for the background clip.

Final Outcome