[FFmpeg-user] Command line -b:v 20M Bitrate spikes to 65000

[Brian Kneeland]

I am attempting to re-encode some HD material to playback on my  Xbox 360. 

Source: (according to mediainfo)
Video: AVC,1080p, High at 4.1 profile in an MKV container 
Audio: DTS 6 channels at 510 Kbps

Here is the command i am running:
ffmpeg.exe -i .\test.mkv -vcodec mpeg2video -f mpegts -b:v 20M -r 23.98 -acodec ac3 -ac 6 -ab 448k .\test.ts


the resulting file is great and plays fine on my PC but according to Bitrate Viewer (http://www.winhoros.de/docs/bitrate-viewer/) there are peaks of 65126 kbps at one point and several in the 45,000-50,000 range. 

Using the same program (Bitrate Viewer) on the original MKV file, there are no peaks higher than 46,000 kbps and most more in the 30-35,000 range.

Is there a way to modify my command to hard cap the bitrate of the file at 20,000 or 25,000 kbps?

Thanks!