[MPlayer-users] Can't change volume on surround sound files

[Sasha Z]

Even though I have mplayer set to control the master volume, it is
insufficient to control the volume of all the speakers. I can watch
alsamixer's master channel go down, but that doesn't seem to affect
all the channels. In effect, I don't have control overal total volume.

I've got an nforce2 onboard audio chip, and I use the analog outs to a
normal set of computer speakers.

How should I set up mplayer to give me control of the volume? There
should be no assumptions about the previous state of the mixer, as
this is accessed from mythtv, so PCM will always be 100%, and the
master mixer will be anywhere.