Overall, pretty good, but there are a few things that you need to correct. First of all like the above posters mentioned, you have a chair seat. You need to work on bringing your leg beneath you and under your hip. The reason for chair seat may be that you are pinching with your knees. Try to loosen it off. The grip should be in your calves, not your knees. Try (at a standstill) moving your leg back beneath your hip. Then place a dollar bill between your calf and the horse. Try to ride around the arena like that without it falling out at a walk, trot, and canter. You can also try putting a marshmallow between your knee and the saddle (depending on how big the knee rolls are) and try to ride around without squishing it. Riding bareback and stirrup-less are also good exercises.
I also noticed you really seem to be absorbing the motion in your lower back instead of your legs. Try to keep it supple but not arching. Keep your shoulders tall and do not let your inner shoulder collapse at the corners. Also, when you go over a jump, I notice your lower leg swings back and forth a bit. This could also be the result of gripping with your knees, and a warning that you need to keep a steadier leg and perhaps practice more flatwork and lower jumps.
Overall though, great riding, just fix a few things and you'll be doign excellent. Hope I was helpful. :)
-----In riding horses, we borrow freedom-----