Film From the Right Angle
Set the camera at hip height, side on, far enough back to see the bar and your feet in one frame.
A second clip from the front at 45 degrees shows knee tracking better.
Depth
For a competition squat, the crease of the hip drops below the top of the knee. For training, use the depth you can control with a neutral back.
Compare the first and last rep. Depth often shrinks as a set gets hard.
Bar Path
From the side, the bar should travel close to a straight vertical line over the middle of your foot.
A bar that drifts forward usually means your hips rose faster than your chest.
Knees and Back
Knees should track roughly in line with your toes. Some inward movement under a heavy load is common; large or sudden knee cave is worth fixing.
Your back angle should stay steady out of the bottom. A sudden rounding or a hip shoot is the rep to study.