How do you programmatically change volume in Gnome on Ubuntu, either from the command line or an API (Python preferrably)?
The only answers I found to similar questions use amixer, which seems to have no effect on Ubuntu 12.04. Running:
amixer set Headphone 10-
shows:
Simple mixer control 'Headphone',0
Capabilities: pvolume pswitch penum
Playback channels: Front Left - Front Right
Limits: Playback 0 - 115
Mono:
Front Left: Playback 0 [57%] [-57.50dB] [on]
Front Right: Playback 0 [57%] [-57.50dB] [on]
The x% changes each time I run it. Unfortunately, it has no effect on the actual volume. Eventually it says 0%, but volume is still at full blast.
The other downside is I have to specify the exact active output device, which I might not know if there are multiple devices. For example, if I have a "Master" and "Headphone", how do I determine which one is the active device?
Ubuntu uses pulseaudio as sounderver. It can be controlled from the command line using the pactl and pacmd utilities, for example:
pactl set-sink-volume 0 20%
would set the volume of the sink #0 to 20%.
see: man pactl and pacmd help
edit:
to avoid -xx being interpreted as command line option you must prefix it with --. That stops option parsing from that point:
pactl set-sink-volume 0 -- -20% # or:
pactl -- set-sink-volume 0 -20% # doesn't matter where the `--` goes