I obtained approval from the manufacturer for the type and position of my GoPro mounts. I used the surfboard mounts rather than the standard GoPro mounts as they have a larger adhesive area. I usually have one camera mounted on one of the stick on mounts under the wing, and one mounted on a strap on mount on the opposite strut. I have never experienced any interference with the control surfaces or the aerodynamics of the airplane (no change in stall speed, or drag imbalance). That said, I would never mount anything on the top of the wing because of the disturbance to the lifting airflow.
If you fly a GA aircraft, I would definitely advise going through the CASA approval process to mount external cameras and not post any video online unless you have done that.
RA Aus has a (soft) policy of actually encouraging us to have cameras as it might help investigators in case of accident. I'm not sure if it is in black and white, but I have read references to it in Sport Pilot. Also, if you fly an LSA, anything you do to the aircraft by way of modifications requires approval. So be careful about that.
Finally, FWIW, don't be stupid about flying videos. Don't post footage of yourself deliberately breaking rules or doing dangerous flying. It WILL get you into trouble and it will bring attention to the rest of us. There's lots of legal stuff to video and we are privileged to see the world the way few others get to see it.
Post your videos, I love to watch them all.