Now for a break-down of your squats:
Your form actually looks pretty solid for a low-bar squat. You will always have a bit of a forward lean with those but you managed to not fold over like a pancake at the bottom, or good-morning it on the way up, so good job.
The only have two criticisms.
One of them is obviously depth. But you hit parallel, it seems. Your lower back does seem like it would round a little bit if you went lower. This brings me to my second criticism. You need to arch your back a tiny bit more. If you don't arch it makes it harder for you to keep a tight lower back when you're going deeper in the squat, which causes "butt winking". So remember to really squeeze tight when you sit back and keep that arch.
Oh, and point your toes out a bit more.
Otherwise, your form is perfect!
BUT....on the other hand....your set of 21 reps was a little uglier in the lower back area. There was definitely more rounding because you were attempting to go fast, and you had even less of an arch with your heavier set. Always make sure to squeeze and keep the arch in your back and lock-out COMPLETELY at the end of each rep.
The first thing that jumped out at me is how you started the squat. You walked it out, sat back, and then started bouncing the reps, never really locking out fully. And then when you do lock-out on a rep (presumably out of breathlessness), you repeat the same thing over again.
Remember, a front squat is not a back squat. You NEVER sit back with a front squat. Don't shift your hips. A front squat is about keeping your chest way up, and dropping straight down, using the stretch reflex from your hamstrings to bounce you back up.
Always force your knees out to the sides when you drop down, and when you're coming back up. Don't be concerned with your knees going over your toes either. Don't think about arching your back. Un-rack the bar with your chest way up, step back, and drop.
-It really is important that you lock out completely with all free-weight squats.
-Point your toes out to the sides more, because this will be easier on your hips and allow you to get deeper into the squat as well as help you bring your hips through on the lock-out.
-And keep those elbows up! Don't let em drop!
Hope that helps.