Most definitely the trumpet corps of 1. Garde-Ulanen-Regiment parading at the Stadtschloß in Potsdam. Depending on the date, the corps is led here by Stabstrompeter/Militär-Musik-Dirigent Leopold Loeser who held that post from 1901-1920. should it date before that, then Stabstrompeter Carl Scharnow.
Regards
Glenn