TromboneChat

Sooo, I decided to watch this instructional video and overall it seems pretty solid. I noticed that he kind of dances around saying anything about specific embouchure motions (wise!) and watching him play through some of those exercises, it looks like he's going through some pretty significant shifting. I'm wondering if this is just more noticeable on french horn? Check out the slurs at 8:29 - it looks to me like 2 distinct shifts going on there: one moving the lower jaw forward, and another lower one moving the entire mouthpiece up and dropping his jaw. Some of the shifting (I suspect) may be due to holding the horn at a constant position, where he may be using his lower jaw and head position to adjust where otherwise the horn angle should be changing. Whatever complexity he's doing, embouchure-wise, it seems to be working for him.

Horn is a little bit different because of the small mouthpiece compared to the long tubing. When you get into the lower partials of the horn I think you see more shifting there than you would in the same partials on trombone.

A lot of the shifting we see in Austris's video I think is because he deliberately is dropping the jaw. It certainly works, but it does result in reversals of embouchure form and shifting. I feel it's better in the long term to reduce or eliminate the need to do that, rather than practicing to smooth out the shift. Some of that might be helped by making the correct horn angle adjustments for his face, as you pointed out.