I've encountered this quite a few times now with different Youtube videos. Not just with this video.

I thought I'd see what key he was playing in with the tune at 07:50. The audio is indicating key of F#. That couldn't be right so I slowed it down to see where his fingers were landing. Sure enough....key of F (at 08:05 frame).

Now the odd thing is Jalousie at 06:30 he's doing in C and the pitch sounds like C!

Then....at the frame at 09:30 you can see he's playing in the Key of C but it's coming out as key of D.

Why does this happen with a lot of Youtube videos?