Adding overlay

#include <gst/gst.h>

static GstPad *videosrc_blockpad;
static GstElement *videosrc, *videosink, *pipeline, *textoverlay;

static GstPadProbeReturn pad_probe_videosrc_cb(GstPad * videosrc_pad, GstPadProbeInfo * info, gpointer user_data){

    /* unlink videotestsrc from ximagesink */
    gst_element_set_state(videosink, GST_STATE_NULL);

    /* adding the textoverlay */
    textoverlay = gst_element_factory_make("textoverlay", NULL);
    g_object_set(G_OBJECT (textoverlay), "text", "Hello World!", NULL);
    gst_bin_add(GST_BIN(pipeline), textoverlay);

    /* inserting the text overlay */
    gst_element_link_many(videosrc, textoverlay, videosink, NULL);

    /* Setting new linked elements to GST_STATE_PLAYING */
    gst_element_set_state(videosink, GST_STATE_PLAYING);
    gst_element_set_state(textoverlay, GST_STATE_PLAYING);

    gst_debug_set_threshold_from_string ("*:5", TRUE);

    /* This removes the blocking probe of videotestsrc:src */
    return GST_PAD_PROBE_REMOVE;
}

static gboolean timeout_cb (gpointer user_data){

    gst_pad_add_probe (videosrc_blockpad, GST_PAD_PROBE_TYPE_BLOCK_DOWNSTREAM, pad_probe_videosrc_cb, user_data, NULL);
    return FALSE;
}

int main (int argc, char **argv){
    GMainLoop *loop;

    /* init GStreamer */
    gst_init (&argc, &argv);
    loop = g_main_loop_new (NULL, FALSE);

    videosrc = gst_element_factory_make("videotestsrc", NULL);
    videosrc_blockpad = gst_element_get_static_pad(videosrc, "src");

    videosink = gst_element_factory_make("ximagesink", NULL);

    pipeline = gst_pipeline_new("pipeline");

    gst_bin_add_many(GST_BIN(pipeline), videosrc, videosink, NULL);

    gst_element_link_many(videosrc, videosink, NULL);

    gst_element_set_state(pipeline, GST_STATE_PLAYING);

    g_timeout_add_seconds (5, timeout_cb, loop);

    g_main_loop_run (loop);

    gst_element_set_state (pipeline, GST_STATE_NULL);

    gst_object_unref (pipeline);

    return 0;
}