They are professional videographers that go around to a lot of the events and film everyone's rides. Most videos have all three phases and are about 10 minutes long. You can put the channel on AutoPlay and have the chance to see a lot of different horses in riders across all levels at a lot of different venues.
If you would like to work on your dressage theory/knowledge, I highly recommend watching the Steffen Peters and Janet Brown-Foy judge's symposium. Fabulous series with great audio and an absolute gold mine of information. Here is the link to one of the sessions to start you off: http://www.youtube.com/watch?v=zkUcQi2Wz_4