1. Start: Take your time. Set your start position before you break the bar from the floor. You're doing a weird dynamic start that you usually only see with really fat people - that is, when you drop your hips, the bar pops off the floor, more like it's being leveraged off rather than lifted by the legs. You may eventually get away with a dynamic start, but not yet. Now it's just throwing you into position, and I'd be willing to bet that position is different every time.
2. During the first pull, keep that chest up - you're letting your hips shoot up and leaving your chest/shoulders behind, which puts you into that RDL type position - too far over the bar, and your weight is way forward on your feet (you can see it pulling you forward very clearly). The moment that bar leaves the floor, force your weight back toward the heels and try to come up with the angle of the back staying teh same until the bar reaches about mid-thigh.
3. You start pulling the bar back and up with your arms when it gets to about the knee. This is usually the result of #2 - you feel it pulling you forward and attempt to pull it back in to keep your balance (generally unconsciously). If you get yourself into a better pulling posture, i.e. correct #2, this will likely go away on its own.
4. Transition between 2nd and 3rd pull needs to be more aggressive. Really snap up and down like you're bouncing off the ceiling.
5. When you pull under, you're doing a weird back bridge thing - like pushing your hips and chest forward to the bar - and throwing your feet out to the sides with straight knees. You need to make that more of a squat under, i.e. pull yourself straight down into a squat, which will push your hips back, not forward. That's why when you first receive the bar, you're in such an unstable position - hips are sliding forward, feet are super wide, and the legs are almost straight. You see immediately your body naturally shifts the hips back in order to support and balance - that's where you need to be headed right away.