Get-ChildItem -Filter *.mkv | ForEach-Object {
  $out = "$($_.BaseName)_8bit.mkv"
  if (Test-Path $out) { return }

  ffmpeg -i "$($_.FullName)" `
    -map 0 `
    -map_metadata 0 `
    -map_chapters 0 `
    -c:v libx265 -pix_fmt yuv420p -x265-params profile=main `
    -crf 20 -preset slow `
    -c:a copy `
    -c:s copy `
    "$out"
}