That is *big*. A lot more than the 2 mm chrome-plated steel shaft of an audio cassette or audio reel-to-reel recorder!
I wonder how they overcame the tendency for the tape to "stick" to the capstan instead of exiting cleanly. They'll have found a way - a pair of rollers, perhaps. I was wondering whether there were ducts inside to ensure that the capstan was only "sticky" for part of its rotation, but there was no sign of that. The guy in the video should have rehearsed what he wanted to say so he could "present" a little bit more authoritatively. ;-) But where would we be without amateur experts like him?