GB - I've been meaning to comment but not much time these days. I've put up some squat video but no critique yet. So we'll help each other.
Like me, you are ever so close and in some cases you are hitting parallel or just below. (like the first rep of your last set) So you have the flexibility to get there. The problem we all have is, as the weight gets more difficult, our mind tells us, "don't go too deep or gravity will win". Just trust the safety bars or whatever you have for bailing.
I'm no expert squatter and struggling with getting consistently past parallel myself, but FWIW there are a couple of things.
Stance slightly wider, or a wide as you can effectively keep the knees tracking the feet. Always push the knees outward.
You could try low bar squatting. You'll need more hip drive coming out of the hole ala Rippletoe.
Go down aggressively, but under control for a full stretch at the bottom. A full stretch will help on the rebound.
Stay tight. Use as close a grip as flexibility will allow. Grip the bar tight. keep the upper back tight.
Come out of the rack with full control. Try limiting feet movement to three steps. Back, out, out. four steps max.
Take in as much air as you can before decending.
Determine where parallel is using some marker, such as a rack pin hole, then try to go past it with the bar each time. I set the safety bar one pin below parallel, then try to get the bar as close to the safety bar as I can at the bottom. After a while, I think you'll get the feel for parallel, but its good to check video once in a while.
Also set up a box at or below parallel and do some box squats. A great tool for learning to sit back and getting deeper.
When shooting a video, wear clothes that you can easily see the hip crease at the bottom.
Anyway - those are some of the things I'm working on that might help.