How to automatically change volume level when un-/plugging headphones?

During the UDS for Oneiric there has been a session about jack detection. See the blueprint for details. It sounds like this will exactly do what I'm looking for: different volume levels for different devices - just not on every hardware:

<htorque> something i'm curious about: will i be able to have different volume levels for different devices (eg., internal sound muted, headphones 75%) anytime soon?

<coling> this will be supported (on some h/w) yes. Timescales are "soonish" :p
<coling> (I'd also expect OSD to be shown (with current volume) when jacks are plugged/unplugged)

Update for 11.10

This should now be working in Oneiric - unfortunately my ThinkPad T510 seems to be one of the systems that's currently not supported.

Another follow-up from David Henningsson:

Long story short, it’s a desirable feature, and we’re moving in that direction, but slowly, as the feature is more complex than it seems like at first glance.

The good news: in the upcoming Ubuntu Oneiric (11.10), this is actually working. The bad news: it isn’t working for everyone.

More here.

Update for 12.04

It's now working with my ThinkPad T510 (and many other models) in Ubuntu 12.04 (development version).

To set volume level from console use the command amixer. For example:

amixer sset Master playback 0%

Will set your level to 0%

I don't know how to change this when you plug in your headphones... but maybe someone can help you with that

Ear Candy has some functionality for dealing with headphone insertion/removal.

I don't know how much coding experience you have, but you mentioned inotifywait so I'm going to assume you're at least comfortable with shell scripting. The following C program, based on this article, should be able to detect your headphones being plugged or unplugged, after which you can perform whatever actions you want.

#include <linux/input.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>

int main(int argc, char* argv[])
{
    int fd = -1;
    char name[256]= "Unknown";
    struct input_event event;

    if ((fd = open(argv[1], O_RDONLY)) < 0) {
        perror("evdev open");
        exit(1);
    }

    if(ioctl(fd, EVIOCGNAME(sizeof(name)), name) < 0) {
        perror("evdev ioctl");
    }

    printf("The device on %s says its name is %s\n",
            argv[1], name);

    read(fd, &event, sizeof(struct input_event));
    printf("Event type is %d\n", event.type);
    printf("Event code is %d\n", event.code);
    printf("Event value is %d\n", event.value);

    close(fd);
    return 0;
}

The program takes one argument, which should be a path to the input event device for your headphones. This is /dev/input/event7 for me, but you may have to try a few to find which it is on your system. You will need read permissions on that device. The program will print the name of the device, and the type, code, and value of the first event before exiting.

Check dmesg and other log files. Probably plugging in/out fires some particular messages.

Then, you could use a daemon to parse that log file and detect the events. I think you know what to do from this point :)

If you do

amixer sset 'Speaker' playback 0%

the speaker volume will be muted but headphones will carry on working. Unplugging the headphones means no sound. Which is almost what you want...

However...

If you alter the volume control the 'Speaker' volume setting will be set up again. This is because pulseaudio tries to be clever with setting volumes (See http://pulseaudio.org/wiki/PulseAudioStoleMyVolumes for more information). We can stop it from messing with the volumes though.

Open /etc/pulse/default.pa

and find the line

load-module module-udev-detect

and change it to

load-module module-udev-detect ignore_dB=1

Restart pulseaudio.

killall pulseaudio

Now if you mute the speaker volume changing the master volume will not affect it. So headphones will work but the speaker will remain silent.

I think you might achieve what you need using this: https://bbs.archlinux.org/viewtopic.php?pid=1105458#p1105458

Check the ACPID socket for changes, can be done with the help of python or C or shell script, (Python code for controlling the earphone plugin play and pause on rhythmbox). Check for the changes in ACPID voltage to detect earphone plugin and earphone plug out. A seconds delay can be expected though.

Pulseaudio has a module shipped by default that is designed to achieve exactly this:

http://pulseaudio.org/wiki/Modules#module-device-restore