Audacious

Here is a skeleton example plugin. It should get you started. You may also want to look at existing plugins in the "audacious-plugins" source code to see how they do things ("notify" and "mpris2" are somewhat close to what you are trying to do). The API available to plugins is fairly extensive, and there is some documentation in the C headers (/usr/include/audacious, /usr/include/libaudcore, and /usr/include/libaudgui).

/* Example plugin for Audacious 3.5 */
/* Will not work with earlier Audacious versions */

#include <stdio.h>

#include <audacious/drct.h>
#include <audacious/misc.h>
#include <audacious/plugin.h>
#include <audacious/preferences.h>

#include <libaudcore/hook.h>

/* Default values for any configurable settings */
/* Note that Boolean values have to be in ALL CAPS */
const char * const plugin_defaults[] = {
   "print_filenames", "TRUE",
   "custom_string", "I am a custom string",
   NULL
};

/* Define a simple dialog box for those settings */
/* More complex layouts are possible; see <audacious/preferences.h> */
const PreferencesWidget prefs_widgets[] = {
  { WIDGET_CHK_BTN, "Print song filenames",
    .cfg_type = VALUE_BOOLEAN, .csect = "example", .cname = "print_filenames" },
  { WIDGET_ENTRY, "Print custom string",
    .cfg_type = VALUE_STRING, .csect = "example", .cname = "custom_string" }
};

/* Also for the settings dialog; mostly uninteresting */
const PluginPreferences plugin_prefs = {
   .widgets = prefs_widgets,
   .n_widgets = ARRAY_LEN (prefs_widgets)
};

/* Function to be called when the song changes */
void song_changed (void * data1, void * data2)
{
    /* Get some basic info about the currently playing song */
    /* Note the str_unref(); without it we would be leaking memory */
    char * title = aud_drct_get_title ();
    printf ("Title: %s\n", title);
    str_unref (title);

    /* Example use of a configurable Boolean setting */
    if (aud_get_bool ("example", "print_filenames"))
    {
        char * filename = aud_drct_get_filename ();
        printf ("Filename: %s\n", filename);
        str_unref (filename);
    }

    /* Example use of a configurable string setting */
    char * custom = aud_get_str ("example", "custom_string");
    printf ("Custom string: %s\n", custom);
    str_unref (custom);
}

/* Initialization function, called at plugin startup */
bool_t plugin_init (void)
{
    /* Register the default settings declared earlier */
    aud_config_set_defaults ("example", plugin_defaults);

    /* Connect our song-change function to the "playback begin" event */
    hook_associate ("playback begin", song_changed, NULL);

    /* Signify that the plugin was successfully initialized */
    return TRUE;
}

/* Cleanup function, called at plugin shutdown */
void plugin_cleanup (void)
{
    /* Disconnect our song-change function (this is important) */
    hook_dissociate ("playback begin", song_changed);
}

/* Plugin header with various and sundry information */
AUD_GENERAL_PLUGIN
(
    /* Name to be displayed in list of available plugins */
    .name = "Example Plugin",

    /* Text to be displayed in "About Example Plugin" dialog box */
    .about_text = "This is an example plugin",

    /* Pointer to layout for settings dialog */
    .prefs = & plugin_prefs,

    /* Pointer to initialization function */
    .init = plugin_init,

    /* Pointer to cleanup function */
    .cleanup = plugin_cleanup
)

Compile with something like:

gcc -Wall -O2 -fPIC -shared -z defs `pkg-config --cflags --libs audacious` -o example.so example.c

Then copy example.so to /usr/lib/audacious/General and restart Audacious.

It doesn't compile. It nags that the initializer list is not constant.

/* Also for the settings dialog; mostly uninteresting */
const PluginPreferences plugin_prefs = {
   .widgets = prefs_widgets,
   .n_widgets = ARRAY_LEN (prefs_widgets)
};

I guess it's because of the macro ARRAY_LEN?

I commented it out, changed the .n_widgets to '2' and then it can't link because it doesn't find aud_get_str. It says unknown reference.
Any help on that please? Is it because I am trying with the latest stable version 3.4.3 and not the 3.5 that you mention on the top file comment?
Thank you very much in advance.

John Snow wrote:

Any help on that please? Is it because I am trying with the latest stable version 3.4.3 and not the 3.5 that you mention on the top file comment?

Yes. When I said, "Will not work with earlier Audacious versions," I meant that.

For older versions you can use this:

aud_get_string()
sizeof array / sizeof array[0]