Setting video-conf inf command line for diffferent qualities is not working

[jj001]

c:\TEMP\VLC2>set | grep codec
audiocodec=MP3
videocodec=Xvid

c:\TEMP\VLC2>%avidemux% --video-codec %videocodec% --video-conf=cbr=512 --audio-codec %audiocodec% --force-alt-h264 --load %f%.mp4 --save %f%-conv_cbr_512.mp4 --quit

c:\TEMP\VLC2>%avidemux% --video-codec %videocodec% --video-conf=cbr=128 --audio-codec %audiocodec% --force-alt-h264 --load %f%.mp4 --save %f%-conv_cbr_128.mp4 --quit



I just get a files of the same size than %f%