
Re: Timelapse with real-time compositing
When you shoot your green screen foreground with talent, make sure you use the same lens and settings with the same camera set up( lens height, tilt angle, etc.) to keep a correct perspective when you go to shoot your background timelapse. (unless you want weird perspectives of course)
Regarding intervals, if you shoot your timelapse background at say 1 frame per second then your onscreen B/G action will be x 30 realtime. (25 for PAL shooters)
This is a non-scientific basic explanation of the process:
http://www.videojug.com/webvideo/how-to-shoot-on-a-green-screen-effect