You could maybe do it with chroma key or green screen. Its the same way they put the weather map behind the weather man and put actors infront of computer made backgrounds in the movies. Ive never tried vegas but Im sure its in there, I have it in several other programs Ive tried. Shoot your first video of everyone moving around and whatever the background is, then shoot the person whoever is going to centered infront of something that a solid color, usually green or blue. Maybe like washing a white bed sheet in green dye would work then try to get it lit as evenly as you can, so the computer can cut it out easiest. You can then stretch or speed up the background clip,add the green screen clip in and add a chroma key filter . You can even slow down the green screen clip if you need more of a speed difference. Then it will look like the person in the 2nd shot is in the first shot, moving at a different speed.
Course the qulaity wont be something from a movie but it should be ok. If thats to hard then try the 1st way.
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