In a way it's the same with helmet mounted lights. Sometimes takes a while to get them dialed in and then if your head starts to droop ( from tiredness ) you might have to readjust the angle of the lamp. Then there's the issue of helmet movement during the course of a ride. Almost impossible to control all these things, even more difficult the more weight you put on your helmet.

Of course with video you can't tell these things are even happening because there's no feedback once you start riding. One thing is certain, if you do finally get the video to look right you might consider "Not removing the camera from the helmet." This means having a dedicated helmet for video. This is also true for helmet lamps. Once you take them off you have to dial them in all over again. This is why it is extremely helpful if you have a helmet lamp that easily tilts "on the fly". ( such as the Gloworm products ). Those O-ring helmet mounts are simply a PITA once you start the ride.