Lots of tweaks need to be made. You look very uncomfortable and your knees track over your toes before you even start the lift. You need to sit back on your heels a lot more in your starting position. Start doing some stretching to loosen up your quads, lower back, and hammies. Your legs are straightening out too quickly. Everything should be coming together at the top of the lift: your legs straight and your back by driving your hips forward. Before you begin the lift make sure you put tension on your arms so there is no "slack" when you start to push.
And especially your hip flexors!
You're trying to start with your hips too low. You hips move up before you ever break the weight off the floor. Look at your shin angle...your shins should be pretty close to perpendicular to the floor. Basically, you will not break the weight off the floor until your shins are at or close to perpendicular & if you watch, you can see that the weight stays on the floor until you reach a point where your shins are perpendicular. The bar should also be in contact with your shins/quads the entire way up. Looks like you need to engage your lats more & pull the bar into you.
It's hard to tell about your back because of the low video quality & what it's doing to those overhead lights. It doesn't look too bad though. Lower back needs to be flat, thoracic region of the spine, not so much so don't worry too much if there's rounding there.
Stretch & mobility work. Probably your biggest concern right now.
