I'll learn the parts using any number of resources (by ear, tabs, youtube videos, DAW audio plugins to help isolate the parts, etc). Next is a few weeks of practice so that I can play all parts as well as possible. During this time leading up to filming, I'll create the backing track. (I'm actually the person that creates 95% of GT's backing tracks). Then I'll perform and teach the song on camera. Finally, my play-through performance will be transcribed by one of the GT transcribers, so that the tab 100% matches with the performance video.
Very cool you've done some transcribing work! Fun stuff!
GT Guitar Coach