I initially thought they were open for some sort of maintenance. But the video features a takeoff roll of the bomber (around 5:00 minute mark), and I again noticed that the hatches were open during the roll. However, they were retracted immediately after the aircraft left the ground (around 5:25 mark):
This makes me wonder if these hatches serve some special purpose. What are they, and why are they open during the takeoff roll?
Edit: Please don't say you don't see an aircraft, because the landing gear doors are down and radar signature is immense due to that. :)