A little critique / comment on your body position: I know you didn't specifically ask for ittt, but I thought it might help. When you're posting at the trot, it's very loud, if that makes sense. Not noise wise, but it looks as if you've been riding a long time, so the actual action of posting is second nature to you, so you just do it instead of concentrating on doing it precisely. At a few points, it looks like you're throwing yourself up and plopping back down- even getting a bit too forward at times. It especially seems to happen when he's doing something to distract you.
My old trainer used to comment on how all of the riders she saw seemed to have this problem eventually, so she would have us imagine that there was an egg on the saddle we were trying not to break, in an effort to post more softly and quietly. Maybe I'm just seeing things, but I thought it might help you out. I know that sometimes if there are multiple other things I'm focusing on (trying to get him to slow down, stop tossing his head, stop whinnying at his buddies, etc...) it still happens to me, so that could be the issue with you. But I think your horse will appreciate the time put into adjusting the form. =P