[MPlayer-users] Quiet AC3 with 2-speaker setup

[Jeff_Mitchell at accessbusinessgroup.com]

First off, I want to thank the developers for their hard work.  MPlayer can
play pretty much anything I throw at it, and it's supremely useful on my
set-top box.  I've been using it to rip some of our DVDs to hard drive for
posterity (we've got a small child in the house, and I'd rather not buy the
same DVD multiple times because of breakage/scratches/random acts of
jelly.), and I've run into a bit of a snag with AC3 5.1 audio.  My set-top
box and desktop are both connected to recievers via a standard 1/8" stereo
plug -> 2 RCA cable, running from the motherboard's onboard sound card.
When I rip a DVD, I'm using -aid 128, which is generally the English 5.1
track, and I'm using -oac copy, so the full audio information is getting
preserved in the resulting .avi.

When I play a ripped VOB, and MPlayer gives this in its output (this is
most of my DVDs):

AC3: 5.1 (3f+2r+lfe)  48000 Hz  448.0 kbit/s

The output volume is very quiet.  If I turn up the stereo loud enough to
hear dialog, I start getting a lot of background hiss.

When I play a ripped VOB, and MPlayer gives this in its output (this is
rare -- mostly a few Baby Einstein titles I ripped for my son):

AC3: 2.0 (stereo)  48000 Hz  192.0 kbit/s

The output volume is at a level I would expect.  I can set the volume
reasonably, and what little dialog I can find is clear, without any kind of
background noise.

I assume that the observed behavior is an artifact of the downmixing
process done by liba52.  This process is probably doing everything
correctly -- it's just not quite working for the way I have my system set
up.  One solution I can think of is to find a way to skip the 5.1 track
altogether (via -aid X) and use the stereo audio track provided on most
DVDs, but if I'm going to rip a DVD, I'd like to be able to preserve the
full 5.1, in case my set-top box ever becomes 5.1-capable.  So I'd love to
hear about some sort of tweak or configuration I can do to make my current
output (straight stereo from a cheap sound card) play 5.1 at the volume I
get from the rarer stereo-only DVDs.

In case you're wondering, I'm using Mandrake 10.1, with these RPMs:
mplayer-1.0-0.pre5.9plf
mplayer-gui-1.0-0.pre5.9plf
liba52dec0-0.7.4-6mdk

Xine seems to handle the 5.1 -> 2.0 downmixing differently, so that either
file sounds fine.  This makes it look like liba52 is doing its thing just
fine.  Unfortunately, I'd rather use MPlayer to play the files.  Thanks in
advance for any help.

-Jeff