How to set exact stream output bandwidth (without spikes)

[woj]

Hello,

I'm transcoding from v4l interface (live analog input), and I don't want to go over the 3.5 Mbit.
But very often VLC encode proces is generating spikes - for about 6Mbits. The parameters vb and ab are set for correct values.

How can I make hard output bitrate limit?

Thanks for any help...