[FFmpeg-user] x264 preset (speed) question

[Toerless Eckert]

ffmpeg -i ...  -vcodec libx264 -crf 23 -preset <profile> ...avi

 size                encoding
           preset    time [sec]
 343112796 ultrafast 32
 203951436 superfast 40
 144580586 veryfast  57
 151997548 faster    82
 154328836 fast      115
 153417634 medium    140
 153318596 slow      245
 150477566 slower    408
 141542408 veryslow  785

this looks all very logical - spend more time, get better compression
at same quality.

But how do i explain the result for preset veryfast ?

Thanks