This is a vid of me deadlifting 225 lbs. It's a bit sloppy as my back was sore from the previous day, I just did this set for the video. I think I am rounding my back too much/pulling with it. Here is the vid
Why was your back sore? If your lower back is sore or tired the last thing you should be doing is deadlifts.
Having said that your form was pretty bad but got better as the set went on and your hips were staying down as the bar broke the floor.
But if your lower back was sore/tired, its not a good time to be analyzing things that could improve with a fresh lower back. The position the lower back wants to be in the least is the best position since the lever is longest and it has to do a ton of work to resist the load.
Do it again with a fresh back.
Sore back aside.
When setting up for the lift, push hips back first, then bend at knees.
By doing this you load the stronger muscles, posterior chain, creating tension which will make the pull smoother than trying to lift with your legs.
Imagine pushing your butt back until your torso is almost horizontal with floor. Then bend knees, attempting to have vertical shins, shoulders in line or behind bar.
Initial breaking off the floor is quadriceps, pull bar into you and back, using your back muscles, lats.
After breaking bar from floor: Below knee, strong hamstring contribution, at knee and above knee, glutes will finish the terminal hip extension.
Try looking down a little bit more instead of looking straight ahead. Going into cervical(neck) extension can happen on maximal attempts but shouldn’t be regular technique.
You have happy feet. Which means they move between reps. Don’t do that.
If your not doing a maximal attempt ditch the mixed grip and save your biceps. Depending on goals straps/hook grip could be better options.
And if, IF, you have any control over it, don’t know your gym, ditch hex plates, move to round plates.