From mboxrd@z Thu Jan  1 00:00:00 1970
From: Raymond Yau <superquad.vortex2@gmail.com>
Subject: Re: explicit commandline control of speakers vs
 headphone output
Date: Thu, 26 Aug 2010 06:48:34 +0800
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2010/8/26 Eric Holstege <eric_holstege@yahoo.com>

> It appears that when I have a headphone plugged in, the speakers are
> automatically disabled and the output sound is sent to the headphone.
>
> However, I want to explicitly control (e.g. via a script or commandline
> - not a GUI) whether the sound from an (arbitrary) application is going
> to the speakers or to the headphone even when the headphone is plugged in.
> (When I say "arbitrary application" that means I can't alter the code of
> the application itself).
>
> Is this possible?
>
> (I have heard that ALSA mutes the speakers when it detects plugged-in
> headphones. Is switching between them as simple as using e.g. amixer(1)
> to unmute the speakers and mute the headphones and vice versa, or is
> there more to it.)
>
>
>
it is really hardware dependent

Which on-board sound driver are you using ?

auto mute is a specific feature for notebook in old day

For the desktop,  the front panel audio connector of the AC97' chassis and
HDA chassis

http://www.intel.com/support/motherboards/desktop/sb/cs-015851.htm

For some HDA codec, the headphone (front panel green jack) can be used
indpendent of the rear panel jacks on desktop