Just another squat check(/wreck)

[JayvH]

Hello coach,
I'd like to get a view on my squats and hope you are so kind or move it to the training discussion part.
I'm stuck in the area of 67,5 to 70 kg for two months now. This is not to not getting 5 reps done but to net getting 5 perfect reps done.
First of all I am not sure if I'm doing this hip drive thing right. I think I should feel the bounce of the hamstrings when I am starting the ascend, if I am recalling SS 2nd edition correctly. I can't feel a stretch in the hamstrings or the adductors, but I am also not sure if this only to occur when handling higher weights. Second problem is that the knees are buckling in sometimes especially on the last reps of a set. No matter how much I tell myself “knees out, knees out, knees out” they won't follow my orders at the end of a set.
OK, here is the video material.
1.
http://www.youtube.com/user/JayvH#p/u/1/2NWd2YOYk5w
First set until 00:40. Second set until 1:23 and than number three. Are there by any chance one or two reps which look OK, so I can build up on those? On the fifth rep of set 2 (1:21) I had a hard way up, maybe a loss of tightness in the lower back.
I am aware that hamstring tension is killed as soon as the knees buckle in, so we definitely can't see anything on rep 3. Set 3 and the knees are a complete mess. So here is a video shot two days earlier from the front. Set 2 until 00:40, Set 3 till the end. My equipment is only capable of recording 40sec peaces so not every rep of the set is available.
2.
http://www.youtube.com/watch?v=ls6pxrr33fM
It was deadlift day so I wore sweatpants that hide the knee activities a little bit, but I hope it's assessable and the first reps are OK. 00:36 show knees going in and 1:07 and 1:20 do the same.

Could it be that my stance is too wide? This feels most comfortable to squat, but I am not so sure that most comfortable means best chance to squat correct.

[Mark Rippetoe]

Here is a new cue that we've been having good results from. Visualize a vertical slot directly over the mid-foot that the bar will slide up and down in. Keep the bar in that slot when you squat.