Run a script when mpd wants to play a song

Question

Hi,
I have built a power strip I can control through USB. Now I have teach my computer how to turn on or off a plug , I would like that it turns on automatically  my speakers when my computer play a song and turns it off when it stops.
As the music is controlled by mpd, I would like to know if it is possible to add this functionality to mpd? Or do I have to tell Alsa to make this work (how?)? Or do I have to make a daemon which will check whether a song is played or not?
Thanks

Answer 1

You would write a simple mpd client for such a task usually. (not sure if perhaps 'mpc' has this built-in already)
Example C-program using libmpdclient that wakes up once mpd plays a song or stops playing:
* Compile: gcc mpdsonglisten.c -o mpdsonglisten -lmpdclient -std=c99
* Run: ./mpdsonglisten localhost 6600 <on_play_script> <on_stop_script>
* Example: ./mpdsong localhost 6600 'echo plays!' 'echo stopped!'
* It will call on_play_script once mpd starts playing,
* and on_stop_script once it pauses, stops or does something unknown.
* Error handling is done by ignoring none-fatal erros and trying to reconnect if
* fatal errors happen.
#include <mpd/client.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
static volatile bool not_ctrlc_pressed = true;
static bool check_error(struct mpd_connection * client)
if(mpd_connection_get_error(client) != MPD_ERROR_SUCCESS) {
printf("Error: %s (Retry in 1 second...)\n", mpd_connection_get_error_message(client));
if(!mpd_connection_clear_error(client)) {
mpd_connection_free(client);
sleep(1);
return true;
return (client == NULL);
static struct mpd_connection * connect(const char * host, unsigned port)
struct mpd_connection * client = NULL;
for(;;) {
client = mpd_connection_new(host, port, 2000);
if(check_error(client)) {
continue;
break;
return client;
void cancel_signal(int signal)
if(signal == SIGINT) {
not_ctrlc_pressed = false;
int main(int argc, char const *argv[])
if (argc < 3) {
printf("Usage: prog <hostname> <port>");
return EXIT_FAILURE;
int previous_sond_id = -1;
enum mpd_state prev_state = MPD_STATE_UNKNOWN;
struct mpd_connection * client = connect(argv[1], strtol(argv[2], NULL, 10));
signal(SIGINT, cancel_signal);
while(not_ctrlc_pressed) {
enum mpd_idle events = mpd_run_idle (client);
if(check_error(client)) {
client = connect(argv[1], strtol(argv[2], NULL, 10));
continue;
if (events & MPD_IDLE_PLAYER) {
struct mpd_status * status = mpd_run_status(client);
if (status != NULL) {
enum mpd_state play_state = mpd_status_get_state(status);
int current_song_id = mpd_status_get_song_id(status);
switch(play_state) {
case MPD_STATE_PLAY:
if (current_song_id != previous_sond_id && prev_state != play_state) {
previous_sond_id = current_song_id;
if (argc > 3)
system(argv[3]);
break;
case MPD_STATE_UNKNOWN:
case MPD_STATE_PAUSE:
case MPD_STATE_STOP:
previous_sond_id = -1;
if (argc > 4)
system(argv[4]);
break;
prev_state = play_state;
if(client != NULL) {
mpd_connection_free(client);
return EXIT_SUCCESS;
(also as gist here: https://gist.github.com/sahib/6718139)
Edit: Added error handling // do not consume 100% cpu when connection fails.
Last edited by SahibBommelig (2013-09-26 18:07:56)