[alsa-devel] [pulseaudio-discuss] ThinkPad T-510 audio output mute LED non-workingness

[David Henningsson]

On 2015-05-07 02:15, Glenn Golden wrote:
>   8.  ...because [Alsa? Pulseaudio?] maintains two independent mixer mute state
>       variables -- one for headphone port, one for speaker port -- the semantics
>       of both the mute key and the mute LED become less straightforward than
>       with the hardware-based mute in 3.18.

The mute LED follows the state of ALSA's "Master Playback Switch". When 
that one is off, neither 3.5 mm headphone nor internal speakers have 
output - they're both muted.

PulseAudio's abstraction layer sets "Master Playback Switch" according 
to its active port's mute state. PulseAudio's active port (here speaker 
or headphone) will, by default, change automatically as headphones are 
plugged in or unplugged.

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic