AvatarNathan Richer

i couldn’t see the knee drift forward in the video although i saw a wobble there. 

you may also be unconsciously avoiding hitting your knees on the way down by sliding it fwd. unfortunately you are missing a crucial rite of passage which is to have scrapes all along your shins LOL.
couple of thoughts:
1. make sure you are hinging properly and completely. if you are not, then your pelvis may not rotate properly and you’ll have lower back problems.  a cue would be to pull your way down, using your hip flexors and attempt to clamshell close the space between your abs and top of quads.
2. raise and lower the bar with the feeling of dragging the bar along your shins. of course miss them by a little bit, as joked before, sometimes we miss on the way up or down.  buy some shin guards by Rocktape from Rogue Fitness to protect and keep them pretty. or show off your scars like a real man!
3. rehearse the hip hinge a few times before you do a lift.  do it with your shins against something unmovable like a bench and practice hinging over without your shins touching the bench. this ensures you keep them straight and vertical.
you may also want to experiment with sumo vs conventional and see if there is one you like better.
there are some good articles on t-nation about the DL, and there is some discussion about people using more a squat style or ham style to pull. but if you want to be strict, you should be using glutes and hams and should not be squatting. that doesn’t mean that some people don’t have a bit more quads at the bottom position to start the bar moving.
this t-nation article talks about quad dominant vs hip dominant DLs:
other general tips:

and yes, make sure you do what Thor says – you gotta brace strongly: core, lats, everything – before you start. wind up any slack in the arms, and lift, driving your feet/legs through the floor!  and don’t forget to torque your legs out in ext rotation before you start!