A question about filming specific scenes in movies and series. [Details inside].

I don’t know how it is done, but if it were me, I would have one actor 10 feet away from the other one being filmed and projected onto the screen, whilst the other one is speaking to the screen. That way the conversation is naturally timed and there is need for extensive sound editing. Then again, I know nothing of the film industry.

I’d rather have it live, timing can just get too tricky.

They can do it both ways depending on the schedules of the actors. Obviously it works best if all those involved in the scene do it at one time, but with good film editors it is nearly impossible to tell the difference.

They explained it in one of those making of the movie cuts for television. I forget the movie, but one actor was on location in some jungle while the rest of the cast was filming on set. The guy that was on location filmed his part later and had it edited in.

They could have easily green screened it and have edited it later. Technology can be tricky sometimes.
But I agree with @XOIIO that it would be easier to have done it live and more natural for the sequence.
But then again it can work both ways. I would prefer to have it acted out live.