get 2 devices
a + b
make sure they both have movie file: testmovie.mpeg (or anything compared matching)
play mplayer on one screen, showing top half the movie content
play mplayer on one screen, showing bottom half the movie content
alter as required.

historical:

http://liqbase.net/liqbase_dualstack.JPG
http://liqbase.net/liqbase_double_tiny.JPG
http://www.youtube.com/watch?v=yk27PenpAz0

recently i've been thinking about collaborative apps where different pieces work together creating data on all:
http://liqbase.net/liq.liqbase.multi...h.S6003750.JPG