What does it mean when encode a yuv422 file to yuv420 by libx264 lossless encoding?
To directly compare the YUV422P AVI and YUV420P MP4,

ffmpeg -i input.avi -i out.mp4
   -filter_complex
      "[0]format=yuv420p,split[avi-p][avi-s];
       [1][avi-p]psnr;[1][avi-s]ssim" -f null -