This is a video of the Mi-24 helicopter. The rotor blades appear not to be moving. Did the pilot and photographer sync the camera and helicopter to make this video and how? I do not know the true source but the video is remarkable.
If the rotor is spinning at 360 RPM, typical of helicopters, that's 6 revolutions per second, and 5 blades go by each revolution. 6 x 5 is 30, so you have 30 blades passing point X in any 1 second period of time. Unlike film at 25fps, video is shot at 30 fps, in perfect sync with the blade passage, so the blades look stopped. If the rotor was going a little faster or slower, the blades would start to move.
The video camera is in effect working like a stop action strobe camera.