Don't make this more difficult than needed. Try out a few things, and use the money you'd spend on the video for an additional dive trip.
A few things that affect breathing:
1. Cold - If you're cold, you'll likely breather faster and your breaths will be more shallow. Warm up, wear a hood that covers your neck. That will help you breathe more slowly and more deeply.
2. Weight - Using more weights than you need will increase your workload and affect your breathing. Do weight checks more frequently, and get rid of any lead that you don't actually need. This will also help you breathe more slowly and more deeply.
3. Trim - stay horizontal in the water. Streamline yourself and your gear. If you're "slippery" in the water you'll use less air. If you plow thru the water, you'll use more.
4. Muscle tone - Don't just relax your mind, relax your muscles. Focus on your shoulders, relax them. Focus on your trunk muscles. Relax them. Focus on your thighs, relax them. The energy it takes to maintain tight muscles increases your weight requirements and alters your breathing. Just by relaxing your neck and shoulders, your breathing will improve.
5. Slow in, slower out. Practice while you sit at the computer: breath in with a slow 3 count, then exhale on a slower 6 count. Try out breathing on this 2-sec exhale for every 1-sec inhale pattern. Make sure at the end of the exhale, you've actually gotten rid of as much of the air as you can (without forcing things). When you dive, every few minutes stop yourself and remind yourself to use the 2/1 breathing ratio for a few breaths. You'll see a major improvement in your breathing.
Write a few "Breathing Reminders" on a slate and stick it in your pocket. On your next dive, sneak a peek at your slate, and spend a few seconds, repeatedly, focused on improving your breathing. You'll see a marked improvement.