Before we get to your video a couple of things you should do before you post on this forum
1) Read the stickies on each forum. They'll teach you certain things that you SHOULD know before you post. For example, camera angle: preferbably, we shoot from a 45 degree angle so we can see proper depth, knee angle, and back angle.
2) Did you buy the book (Starting Strength)? I ask because your squat lacks the most fundamental part of a lowbar squat - it's in a high bar position. If you did not, please consider purchasing it. Mark provides us with so many FREE resources on his forum; the least we can do as part of the community is support him through the purchase of his books. Also, it's THE BOOK. The basics you need to know about the 5 lifts (Squat, Deadlift, Press, Bench, Power Clean) are in that book!
3) Joint pain. Joint pain can arise from a multitude of reasons: bad form, genetically weaker soft tissue integrity, previous injuries, and just the wear and tear of age. In order to understand why you have joint pain we would need more than a single video.
Lifting background
Age
BW
Previous History of Joint pain or injuries
etc
Please, take the time to carefully read through these forums, the stickies, old posts (There's a search function on the top right hand corner of the screen), and the book before you post again.