mencoder: voices lost, orchestra still there

[lagu2653]

I want to store my videos in a format which can be read by both Linux and Windows. So I tried this:

Rip:
mencoder dvd://1 -chapter 4-4 -o test.avi -oac copy -ovc lavc -lavcopts vcodec=mpeg4:mbd=2:v4mv:vbitrate=2400:autoaspect -forceidx

Migrate to dx50 for Windows compatibility:
mencoder test.avi -oac copy -ovc copy -ffourcc DX50 -o dx50.avi

The first file came out good, but the second one (a 4:3 film) did worse. The orchestra was still there but the voices was gone.

[lagu2653]

mencoder test.avi -oac mp3lame -ovc copy -ffourcc DX50 -o dx50.avi

got the voices back.