couple of notes:
1. don't think you hit parallel. pretty dang close, though.
2. your stance is wide, and your feet collapse in a bit -- look at your right foot when you're near the bottom, the ankle is rolled in and your foot looks almost flat. your glutes should be engaged enough to keep your feet square and stable on the ground. get squatting shoes, or stick your heels a bit closer together on top of 5lb plates and see what changes. this goes without saying but use light weight when you're messing with stance. as it is the bar is up high on your traps, you're setting your feet for a power-lifting-type squat (i.e., low bar), and you're not allowing your hips to be active enough to keep you stable and push you up and through.
3. great mental fortitude to make the lift.