In addition to the lower hips, several times you lock your legs completely before you straighten your back. Focus on moving your head in a constant arc: YouTube - Andy Bolton world record dead lift of 457.5kg (1008 lbs).. Notice how his body extends in a fluid motion.
It was hard to find a vid showing great form: Deadlift. He has almost text book form at 0:15. Notice how his hips dip slightly before lifting. More importantly his head is up, chest out, and shoulder back. This puts the majority of the lift on the legs and the back has less ROM to lock out the lift. Watch this vid and yours back to back and you will see how your hips are high resulting in the need for you to use more of your back to lockout the lift.
Sit down into it more. Work on using the leg drive and initial pull together. Finish off at the top by pulling the shoulders back. Very good set. Alot of raw strength.