You are leaving your hips back, not driving them forward. As a result you are sliding or hitching to get the weight up - leaning back a bit. This is forcing you to pull the bar over your knees.
Think about driving your head back and hips forward to lockout the deadlift. You are not using your hips enough and losing your power, and simply trying to pull the back up with bent knees and all back.
After you start to lose your power, your knees dip a bit and you hitch. This is common as lifters try to slink under the bar. When they can't lift it, they end up bending the knees to get it higher on the quads.
Once you learn to drive your head back and hips forward you probably won't notice a knee issue. Right now, when you get stuck with the bar below your knees and start to hitch, you are dipping your knees and causing them to get in the way.
From the point you are at in the video...drive your head back and hips forward.