The thing that mystifies me about the parts of that video which show the props going round very slowly is that (a) the blades appear to be in the feathered position, and (b) they are exhibing none of the interlacing effects which one normally gets with fast rotating objects on high scan rate HD video.
The blades appear to be rotating very slowly because they're rotating something close to a whole number of turns for each video frame.
They're imaged sharply because the shot is illuminated by bright sunlight and the camera is using a very high shutter speed to control exposure.
(source: I work with cameras for a living)
The really strange effects start when you have a rolling-shutter camera, in which the frame is scanned sequentially from top to bottom. Many modern cameras work this way and when you shoot fast-moving objects, strange things can occur.
https://www.youtube.com/watch?v=ecV7oo68vAc
P