What does it mean when encode a yuv422 file to yuv420 by libx264 lossless encoding? I have an AVI file input.avi encoded in HQ which has yuv422 format according to ffprobe.

Now, if I run the following command

ffmpeg -i input.avi -c:v libx264 -crf 0 -pix_fmt yuv420p out.mp4


Will the out.mp4 be lossless compared with input.avi? or it will be 'lossless' except half of the U and V information is lost?
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 -