The trumpet is played by forcing air through stiffened lips producing a fast vibration of the inside of the lips only. When doing this the lips are pointed, slightly pulled in and tight. The didj is played by allowing all of the lips to vibrate but at a slower rate and using a gentler airstream. When doing this the lips are pushed out as in kissing and relaxed. Once you get it you can feel the lips virating inside the mouthpiece.
Babies do it naturally.
The didgeridoo only amplifies the vibration of the lips. I'm fascinated by the sound of the didgeridoo, but my efforts have been restricted by poor circular breathing technique. Now you close the back of the mouth with the root of your tonge. There are many tricks and exercises to train these steps and co-ordinate them. The one-hour video with David Blanasi is mostly about learning the circular breathing.