Crazy Bandwith when Transcoding/Streaming Live

[captainloc]

Hi Guys,
I have a problem with transcoding to stream live an input from my capture card

I'm using this command : vlc -I dummy --v4l2-input 2 --v4l2-audio-input 1 --v4l2-caching 3000 v4l2:///dev/video0:width=720:height=572 --demux avformat --sout '#transcode{venc=x264{qcomp=0,cabac,vbv-maxrate=400k,vbv-bufsize=1200k,profile=baseline},vcodec=x264,vb=400k,height=360,width=640,deinterlace,fps=25,acodec=mp3,ab=96k,channels=2}:std{access=http,mux=ts,dst=0.0.0.0:1122}'

But i dont know why, even if i restrict the bitrate using vbv-maxrate, the bandwidth used is crazy, oscillating between 300k and 800k.
Do you know what's wrong with that ?
I'm not asking for strict CBR but i want a bitrate always under 550k for both Audio+Video. Do you have an idea how to do it ?

Thanks