Your squats aren't bad, but you are moving your back around more than I would like to see. You flex slightly on the way down and go into overextension on the way up. I would rather see you get tight and not move your back much at all. At the top of the squat, stand up as normally as possible. Don't try to overextend your back. Take a big breath and lock everything down. Hold the same position with your torso as you lean over. On the ascent, resist the temptation to point your chest at the wall in front of you while you are still leaned over. Hold together and drive your hips up until you stand up normally again at the top. Narrow your stance a little, too.