You can see during the final extension that the bar is out over your toes instead of over the heels. Probably because of this you are rising onto your toes much too early.
Try pushing your hips back further during the first pull. I good drill (from Dan John) is to do the first pull in slow motion, Stop when the bar is just at knee level and you should feel a lot of tension in your hamstrings, as well as all the weight being on your heels.