GStreamer 1.10 new API: property_notify_watch

property_notify_watch.c

// gcc -Wall -Wextra property_notify_watch.c `pkg-config --cflags --libs gstreamer-1.0` 
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <gst/gst.h>

#define HIGH (30)
#define SLOW (10)

GstElement *pipeline;
GstElement *videorate;

void sigint_handler(int sig) {
    gint rate = HIGH;
    (void)sig;

    if (videorate) {
        g_object_get (G_OBJECT (videorate), "max-rate", &rate, NULL);

        if (rate <= SLOW) {
            g_print("rate: %d => %d\n", rate, HIGH);
            rate = HIGH;
        } else {
            g_print("rate: %d => %d\n", rate, SLOW);
            rate = SLOW;
        }

        g_object_set (G_OBJECT (videorate), "max-rate", rate, NULL);
    }
}

int main(int argc, char *argv[]) {
    GstBus *bus;
    GstMessage *msg;
    gboolean terminate = FALSE;
    gulong watch_id;
    const gchar*  prop_name;
    const GValue* prop_value;

    /* Initialize GStreamer */
    gst_init (&argc, &argv);

    g_print("%d", getpid());
    signal(SIGINT, sigint_handler);

    /* Build the pipeline */
    pipeline = gst_parse_launch (
		    "gst-launch-1.0 videotestsrc pattern=ball ! "
		    "videorate name=rate max-rate=30 ! "
		    "videoconvert ! ximagesink", NULL);
    videorate = gst_bin_get_by_name ((GstBin *) pipeline, "rate");
    watch_id = gst_element_add_property_notify_watch (videorate, "max-rate", TRUE);

    /* Start playing */
    gst_element_set_state (pipeline, GST_STATE_PLAYING);

    /* Wait until error or EOS */
    bus = gst_element_get_bus (pipeline);
    while (!terminate) {
        msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
                GST_MESSAGE_ERROR | GST_MESSAGE_EOS | GST_MESSAGE_PROPERTY_NOTIFY);

        /* Parse message */
        if (msg != NULL) {
            GError *err;
            gchar *debug_info;

            switch (GST_MESSAGE_TYPE (msg)) {
                case GST_MESSAGE_ERROR:
                    gst_message_parse_error (msg, &err, &debug_info);
                    g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
                    g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
                    g_clear_error (&err);
                    g_free (debug_info);
                    terminate = TRUE;
                    break;
                case GST_MESSAGE_EOS:
                    g_print ("End-Of-Stream reached.\n");
                    terminate = TRUE;
                    break;
                case GST_MESSAGE_PROPERTY_NOTIFY:
                    g_print ("Property notify catched.\n");
                    gst_message_parse_property_notify (msg, NULL, &prop_name, &prop_value);
                    if (G_VALUE_HOLDS_INT(prop_value)) {
                        g_print ("  %s: %d\n", prop_name, g_value_get_int(prop_value));
                    }
                    break;
                default:
                    /* We should not reach here */
                    g_printerr ("Unexpected message received.\n");
                    break;
            }
            gst_message_unref (msg);
        }
    };

    /* Free resources */
    if (msg != NULL)
        gst_message_unref (msg);
    gst_object_unref (bus);
    gst_element_remove_property_notify_watch (videorate, watch_id);
    gst_element_set_state (pipeline, GST_STATE_NULL);
    gst_object_unref (pipeline);
    return 0;
}