h.264 – ffmpeg, libx264: encode h264 stream with motion vectors for every 4×4 block

I’m trying to encode an h264 stream that consists of mostly P frames and where there are motion vectors for every 4×4 pixel partition

The following is my ffmpeg command line:

!ffmpeg -framerate 60  -i 'frame_%06d.png' -c:v libx264 -crf 0 -partitions p4x4 -direct-pred none -me_method tesa -motion-est tesa -x264-params keyint=infinite:bframes=0:ref=1:subme=2:merange=8 'encoded.mp4'

however, this results in motion vectors only on 16×16 block boundaries

what’s wrong?