Please excuse my ignorance in asking this question.
I was watching the following youtube video,
http://www.youtube.com/watch?v=syCU871iprU of these two young men playing an excellent rendition of Dylan's Knocking on Heaven's Door and noticed they are not in the same key. The one on the 6-string is indeed in the key of G as I play it, but the 12-string player appears to be in Bb. He's capoed on the 3rd fret and playing G-forms. I wasn't aware this was possible. I thought all players had to be in the same key. What am I missing here? Please school me on this.
Could it be that one of them is in an altered tuning? This has to be it, because they both need to be in the same key, right? I'm not getting this at all.