All the afficiandos seem to think he's playing a trumpet in this performance, if I'm not mistaken that is a B flat cornet which I've only been playing for a mere 52 years......
I saw Antonsen when he was a featured performer at the International Trumpet Guild conference in Baltimore more than 30 years ago. Very young, and a flawless performer in front of hundreds other trumpet players. Carnival of Venice among other difficult pieces.