already do the third world squat hold (http://www.T-Nation.com/free_online_article/sports_body_training_performance/the_thirdworld_squat)
as well as facing the wall squats, foam rolling (pvc pipe), mobility drills for t-spine, ankles and hips. Lower body training focused mostly around posterior chain movements. Advice appreciated 
EDIT:
ADDED A SECOND FORM VIDEO (last two reps look any better?)
BAM! #1. treat every damn rep with respect, get tight under the bar. chest up and full, shoulder blades pinched horizontally together, elbows forward, lower back arched, belly full of air.
#2. how wide is your stance? your back is rounding at the bottom and your chest is caving in. the wider the stance, the more you can sit down between your hips, push your knees out and keep good form. this + point one should help.
#3. practise form with goblet squats