You will be surprized at the task loading a camera brings. I have seen good divers go totally to pieces once they had a camera in their hands. Your skills have to be instinctive once you take on a camera, wheather you realize it or not, my bet is you are still doing a lot of "thinking" about buoyancy. While not exactly for video, here is the "Am I ready for photography" test I recommend.
In a safe place (pool- quarry- somewhere you can't hurt yourself or the enviroment) find a small object on a post/wall/rock to be your photo subject. Hold your hands out at arms length in frount of you and form a square with both hands- this is your imaginary camera's viewfinder. Center the object in your "fiewfinder", while in mid water hovering, swim up to within 6 inches of it, hold that postion for at least 15 seconds while you focus, take the photo then back away without using your hands (they are holding the camera), turn using your fins then swim off. Once you can do that with ease, you are ready to pick up a camera. Concentrate on the "camera" in your hands and forget about diving, your bouyancy should be instinctive at this point. If you accend, decend (crash into the bottom
)or can't hold position without thinking about it, you need to practice your diving skills more.
While I am at it, you also need to have an instinctive feel for you air pressure and where your dive buddy is. As photographers/videographers we tend to be horrible buddies. It is way too easy to get caught up in the camera and forget about everything else.