Doppleganger effect?

[BobbyP]

You know those scenes when, for example, kevjumba is sitting on the right side of the sofa and on the left side he is also sitting? And they verbaly interact?
With after effects how do you do that? I know i need to film multiple times but i have no idea how to create the actual effect

 

[LeHenoy]

Yes, i know how this goes. So, First you need a static camera. Then you film
you first on the right or the left site, and then the other site. In after effects you
import both clips, then you pull both in, and then you have to make a mask around
one of the clips and Tada! There you are!
PS: It's important that nothing has been changed during you are filming

 

[LeHenoy]

For the dialog you only have to time it good