[MPlayer-users] AC3 stream reordered on encode

[n0dalus]

I am using the following command to generate an mpeg2 file:
nice -n 10 mencoder -of mpeg -vf expand=720:404,scale=720:576,harddup
-oac lavc -ovc lavc -lavcopts
acodec=ac3:abitrate=448:vcodec=mpeg2video:keyint=25:vbitrate=9500000:aspect=16/9:trell:mbd=2:vrc_maxrate=9600:vrc_buf_size=1835:vpass=1
-mpegopts format=dvd -srate 48000 -speed 41708/40000 -ofps 25 -o
video.mpg -channels 6 video.avi

The source sound is 5.1 ac3, and with '-channels 6' the output sound
is also 5.1 ac3, but either mplayer or mencoder is getting the
channels around the wrong way.
The original video.avi has channel order:
0 front left
1 front right
2 rear left
3 rear right
4 centre
5 lfe

Which is the standard AC3 5.1 order.

The encoded video.mpg appears to have channel order:
0 front
1 rear
2 rear
3 centre
4 front
5 lfe

Is there something I can do to fix this? I can't hear the difference
between the left/right channels but I know parts of the video where
the rear channels are different and that's what I listen for. I know I
could use -af channels to reorder them if I knew which ones were in
the wrong place, but I would rather mencoder/mplayer just do it right
in the first place (unles I've done something wrong?).

Any help would be appreciated.

n0dalus.