There is no need to record video, it is very easy to reproduce:
1. Play a track in deck A.
2. Hit EXT button, next to the gain of channel A. It changes the deck A type to Live Input and the music stops.
I'm not gonna hate more on the design decision, just I think for the solution:
1. If you press EXT it just switches the mode between ext sources
2. EXT goes to LIVE input, only if SHIFT is pressed
You can read my entire post here: