Software :: Mencoder Ignores Audio Bitrate Parameter

When I convert files with mencoder I get the output with incorrect audio bitrate. Seems that mencoder ignores the bitrate I pass to it. Here's my script:

Code:
#!/bin/bash
vbitrate=800
abitrate=128
#mkdir $2/../$2_rip
unlink frameno.avi 2> /dev/null
mencoder $1 -ovc frameno -oac mp3lame -lameopts abr:br=$abitrate -o frameno.avi
mencoder $1 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=$vbitrate:v4mv:mbd=2:trell:cmp=10:subcmp=3:vpass=1 -ffourcc DX50 -o /dev/null
mencoder $1 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=$vbitrate:v4mv:mbd=2:trell:cmp=10:subcmp=3:vpass=2 -ffourcc DX50 -o $2
unlink frameno.avi 2> /dev/null
unlink divx2pass.log 2> /dev/null

Result file should have 128kbps audio bitrate, but here are the results:
Input file:
02_seminar.avi, 42Mb
video: 432x320 00:05:10 25fps DivX5 1Mbps
audio: 48KHz 00:05:10 Stereo 138Kbps mp3

Output file:
02.avi, 34Mb
video: 432x320 00:05:10 25fps FMP4 802Kbps
audio: 48KHz 00:05:10 Stereo 138Kbps mp3

Why audio bitrate remains unchanged?