When practicing these mouthpiece buzzing examples, remember to keep the mouthpiece on your embouchure with a gentle placement.  Many trombonists like the placement of about 1/3 on the upper lip and 2/3 on the lower.  However, there is much variance in professional players.  Experiment to see what works best for you as you attempt these exercises.  Remember to stop the video, review sections, and rest as needed.