Your back is too vertical. From the top, knees forward and out, hips back and chest pointed to the floor. Your knees should stop traveling forward 1/3 to 1/2 way down and then it's just sitting back and down.
Looks like you're going forward onto your toes at the bottom, so sit back more and keep the bar over the midfoot. Think of the Master Cue - vertical bar path.
Make sure you keep shoving your knees out.
Also, you might want to think about getting some squat shoes. They would help a great deal.