Are you sure it's not the camera shaking?
I see the arms moving in relation to the video frame, but not in relation to the trees in the distance, for example (especially watching the right front arm when it's close to the tree line, later in the vid). The hexa seems rock solid. How is the camera attached? Rubber standoffs for the FC can be hit/miss, really depending on the rest of the vibes in the frame. Yours seems to fly well. Post logs... an oscillation like that should be fairly obvious in the accel and motor graphs, I'd think.
-Max