My first first solo was extremely spontaneous, and definitely not briefed. Indeed, it was such a poor weather day, that I was sure I would not be going solo, so I asked for and got the brand new aircraft. He sent me solo, and was chewed out for sending me in a brand new plane.
My second first solo was thoroughly briefed the day before, so I knew I would be doing it. However, if I had started rigging up a camera in the cockpit, my instructor would have not let me go. Even if the new pilot is not fiddling with the camera, the sheer distraction of thinking to "perform" for it, would be a significant safety reduction.
I have since used the "GoPro" cameras with excellent success for collecting cockpit flight test data.