Monitoring volume level in Maemo 5 using MAFW

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Created: divanov (19 Mar 2010)

Last edited: lpvalente (21 Apr 2013)

This article presents a code snippet to monitor volume level with the Media Application Framewoek (MAFW).

The Media Application Framework (MAFW) provides an open, flexible and extensible layer that eases the development of multimedia applications for the Maemo platform. MAFW API

You normally start with obtaining MafwRegistry object and loading plugin(s):

/* gcc mafw.c -o mafw -g --std=gnu99 -Wall $(pkg-config --libs --cflags mafw glib-2.0) */
 
#include <glib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libmafw/mafw.h>
 
int main(int agrc, char** argv)
{
    g_type_init();
 
    MafwRegistry *registry = mafw_registry_get_instance();
 
    GError *error = NULL;
    if(!mafw_registry_load_plugin(registry, "mafw-gst-renderer", &error)) {
        if(error) {
            printf("%s\n", error->message);
            g_error_free(error);
        }
        printf("Cannot load mafw_gst_renderer plugin\n");
        exit(1);
    }
 
    GList *renderers = mafw_registry_get_renderers(registry);
    print_extensions(renderers);
    GList *sources = mafw_registry_get_sources(registry);
    print_extensions(sources);
 
    GMainLoop *loop = g_main_loop_new (NULL, FALSE);
    g_main_loop_run (loop);
 
    exit(EXIT_SUCCESS);
}

The next step is to browse properties provided by an extension and listening for "property-changed" signal (note that you can connect to "property-changed::volume" if you want to monitor only "volume" property):

static void print_extensions(GList *extensions)
{
    for(GList *iter = extensions; iter; iter = iter->next) {
        MafwExtension* extension = (MafwExtension*)iter->data;
        g_signal_connect(extension, "property-changed",
                         G_CALLBACK(property_changed_cb), NULL);
        const gchar *name = mafw_extension_get_name(extension);
        const gchar *uuid = mafw_extension_get_uuid(extension);
        const gchar *plugin = mafw_extension_get_plugin(extension);
        printf("%s[%s]:%s\n", name, uuid, plugin);
        const GPtrArray *properties = mafw_extension_list_properties(extension);
        for(int i = 0; i < properties->len; i++) {
            MafwExtensionProperty *property = properties->pdata[i];
            mafw_extension_get_property(extension, property->name,
                                        property_get_cb, NULL);
        }
    }
}

Callbacks are defined like this:

static void property_get_cb(MafwExtension *self, const gchar *name,
                            GValue *value, gpointer udata, const GError *error)
{
    if(error) {
        printf("%s\n", error->message);
    } else {
        print_property(name, value);
    }
}
 
static void property_changed_cb(MafwExtension *self, const gchar *name,
                                GValue *value, gpointer udata)
{
    print_property(name, value);
}

Printing a property value (dealing with GValue)

static void print_property(const gchar *name, GValue *value)
{
    switch(G_VALUE_TYPE(value)) {
    case G_TYPE_UINT:
        printf("\t%s[%s] = %u\n", name, G_VALUE_TYPE_NAME(value),
               g_value_get_uint(value));
        break;
    case G_TYPE_INT:
        printf("\t%s[%s] = %i\n", name, G_VALUE_TYPE_NAME(value),
               g_value_get_int(value));
        break;
    case G_TYPE_BOOLEAN:
        printf("\t%s[%s] = %i\n", name, G_VALUE_TYPE_NAME(value),
               g_value_get_boolean(value));
        break;
    case G_TYPE_STRING:
        printf("\t%s[%s] = \"%s\"\n", name, G_VALUE_TYPE_NAME(value),
               g_value_get_string(value));
        break;
    default:
        printf("\t%s[%s]\n", name, G_VALUE_TYPE_NAME(value));
        break;
    }
}

The property of your interest is "volume".