I suppose this won't be a very popular view here, but it seems to me that Ms. Bland escalated the situation into a confrontation, and then she lost.
The initial contact between the officer and Ms. Bland was normal, not an indication of any problem whatsoever. But then the officer went back to his car to do his computer checks and write the ticket or warning, and that part of getting a ticket is the part that seems to take forever. So, Ms. Bland was aggravated when the officer went back to her car, and she lost her cool. Not just a minor slip - she kept provoking the officer until he arrested her.
Now, certainly the officer should not have lost his temper, but it's a normal thing to do under constant provocation - and even then, there's nothing in the video that shows the officer did anything improper. On the other hand, it's clear that Ms. Bland was doing all she could to provoke the officer, even though she may not have done anything unlawful. I have a daughter who's mentally ill and convinced that the whole world is out to get her, so she does her best to provoke other people until they react and prove her presupposition that they're out to get her.
It's a shame that this happened, but I think it would not have happened if Ms. Bland would have been just a bit more cooperative. I think there's a good chance she would have gotten off with just a warning.

-Joe-