This is painful to watch.
Re-read the deadlift chapter of SS.
You start off with your shoulders directly over the bar - BAD. The weight only comes off the floor after your hips shoot up to a position that gets the bar under your scapulas, which is where the bar needs to be.
Your are probably setting up with your hips too low. It would be helpful to include your setup procedure in the video to see if you are complying with the SS setup procedure.
The back rounding is bad and it's gonna hurt when the weight gets heavier.