Your back is rounded, though not horribly so. Good call on seeking advice.
In this humble man's opinion (feel free to correct me, guys), your hips' starting point might be a few inches high - however, although lowering them will help, the most useful cue for you will be to lift your chest (draw from the "Superman Cue" in the book), so that its midpoint is facing a little more forward rather than down, which it appears to be in your videos. It'll almost feel like your chest is rotating a bit between your shoulders. It's also important to note that you need to fight hard to constrict your back into a flat position - you'll have to work until you feel a complete tension from your upper back to your lumbar, and it can be a bitch at first.