D3D12_VIDEO_MOTION_ESTIMATOR_INPUT.pHintMotionVectorHeap use case

As mentioned, pHintMotionVectorHeap representing the buffer containing the hardware-dependent output of the previous motion estimator operation which may be used for hinting the current operation. First I tried passing motion vector heap obtained after estimating the previous pair of frames, the result did not change a single pixel. Then I thought that maybe it should be used for the case when the flow is estimated in coarse-to-fine manner, so I passed the previous motion vector heap of a smaller size, but the result is the same. Then tried all this on a GPU from another chip manufacturer. No, either. What specific use case should this work for?