Reality,
Your back is not rounding but it will eventually if you do not start pausing at the bottom each rep and re-set your back. Bouncing your reps like that will at some point lead to a loss of tightness and proper back position. This is besides that fact that it defeats the purpose of performing deadlifts, which is to build concentric pulling strength from a dead stop.
Other than that, your set-up and pulling mechanics look pretty good.
JP