Isn't the use of the H.264 motion vector to preserve bit when there is a camera pan? A pan is a case where every pixel in the frame will change, but maybe doesn't have to.
Yes, or when a character moves across the screen. They are quite fine grained. However, when the decoder reads the motion vectors from the bitstream, it is typically not supposed to attach meaning to them: they could point to a patch that is not the same patch in the previous scene, but looks similar enough to serve as a starting point.
