add filesrc to videomixer dynamically

#include <gst/gst.h>
#include <glib.h>
#include <unistd.h>
#include <string.h>

static GstElement *pipeline;
static gboolean first_time = TRUE;

/* Handler for the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *pad, GstElement *data);

static GstClockTime get_running_time()
{
    GstClock *clock = gst_element_get_clock(pipeline);
    GstClockTime running_time = gst_clock_get_time(clock) - gst_element_get_base_time(pipeline);
    gst_object_unref(clock);

    return running_time;
}


static GstPadProbeReturn dec_event_probe_CB (
    GstPad * pad,
    GstPadProbeInfo * info,
    gpointer user_data
)
{

    GstEvent *event_pad = NULL;
    GstEvent *new_event = NULL;
    GstSegment *segment = NULL;
    if ((info->type & GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM))
    {
        event_pad = gst_pad_probe_info_get_event(info);
        if (first_time && event_pad->type == GST_EVENT_SEGMENT){
            first_time = FALSE;
            g_print("FIRST SEGMENT EVENT RECEIVED!! REPLACING!!!! \n");
            segment = gst_segment_new();
            segment->format = GST_FORMAT_TIME;
            segment->base = get_running_time();
            segment->start = 0;
            segment->stop = -1;
            new_event = gst_event_new_segment(segment);
            gst_event_unref(GST_EVENT(info->data));
            info->data = new_event;
            return GST_PAD_PROBE_OK;
        } else if (event_pad->type == GST_EVENT_EOS){
            g_print("event_probe: EOS arrived!!!! discarding!! \n");
            return GST_PAD_PROBE_DROP;
        } else if (event_pad->type == GST_EVENT_SEEK){
            g_print("event_probe: SEEK event arrived!!!! discarding!! \n");
            return GST_PAD_PROBE_DROP;
        } else if (event_pad->type == GST_EVENT_SEGMENT){
            g_print("event_probe: SEGMENT event arrived!!!!\n");
            return GST_PAD_PROBE_OK;
        } else {
            return GST_PAD_PROBE_OK;
        }

    }

    return GST_PAD_PROBE_OK;

}

static gpointer thread_1(GstElement *mixer)
{
  /* waits 5 seconds and tries to add a filesrc input to the mixer */
  sleep(5);
  GstPad *mpad = gst_element_get_request_pad(mixer, "sink_1");

  GstElement *src =gst_element_factory_make("filesrc", NULL);
  g_object_set(G_OBJECT(src), "location", "video.mkv",NULL);

  GstElement *decoder = gst_element_factory_make("decodebin", NULL);
  GstElement *convert = gst_element_factory_make("identity", NULL);
  g_signal_connect (decoder, "pad-added", G_CALLBACK (pad_added_handler), convert);

  gst_bin_add_many(GST_BIN(pipeline), src, decoder, convert, NULL);
  gst_element_link(src, decoder);
  GstPad *spad = gst_element_get_static_pad(convert, "src");
  gst_pad_link(spad, mpad);


  //gst_element_set_state(pipeline, GST_STATE_PLAYING);

  gst_element_set_state(src, GST_STATE_PLAYING);
  gst_element_set_state(decoder, GST_STATE_PLAYING);
  gst_element_set_state(convert, GST_STATE_PLAYING);


  gst_object_unref(mpad);
  gst_object_unref(spad);
  return NULL;
}

int main(int argc, char *argv[]) {
  /* Initialize GStreamer */
  gst_init (&argc, &argv);

  /* Create the elements */
  GstElement * source = gst_element_factory_make("videotestsrc", NULL);
  g_object_set(source, "is-live", TRUE, NULL);
  GstElement * filter = gst_element_factory_make("capsfilter", NULL);
  GstCaps * fcaps = gst_caps_from_string("video/x-raw, width=720, height=576");
  g_object_set(G_OBJECT(filter), "caps", fcaps, NULL);
  gst_caps_unref(fcaps);
  GstElement *mixer = gst_element_factory_make("videomixer", NULL);
  GstElement *sink = gst_element_factory_make("autovideosink", NULL);

  /* Create the empty pipeline */
  pipeline = gst_pipeline_new ("test-pipeline");

  /* Build the pipeline. Note that we are NOT linking the source at this
   * point. We will do it later. */
  gst_bin_add_many (GST_BIN (pipeline), source, filter, mixer, sink, NULL);
  gst_element_link_many(source, filter, NULL);
  GstPad *mpad = gst_element_get_request_pad(mixer, "sink_0");
  GstPad *fpad = gst_element_get_static_pad(filter, "src");
  gst_pad_link(fpad, mpad);
  gst_object_unref(mpad);
  gst_object_unref(fpad);
  gst_element_link (mixer, sink);

  /* Start playing */
  GMainContext *main_context = g_main_context_new();
  GMainLoop *loop = g_main_loop_new(main_context, FALSE);
  gst_element_set_state (pipeline, GST_STATE_PLAYING);
  GThread *thread = g_thread_new("thread_1", (GThreadFunc)thread_1, mixer);
  g_main_loop_run(loop);


  /* Free resources */
  g_thread_unref(thread);
  gst_element_set_state (pipeline, GST_STATE_NULL);
  gst_object_unref (pipeline);
  return 0;
}

/* This function will be called by the pad-added signal */
static void pad_added_handler (GstElement *src, GstPad *new_pad, GstElement *data) {
  GstPad *sink_pad = gst_element_get_static_pad (data, "sink");
  GstPadLinkReturn ret;
  GstCaps *new_pad_caps = NULL;
  GstStructure *new_pad_struct = NULL;
  const gchar *new_pad_type = NULL;

  g_print ("Received new pad '%s' from '%s':\n", GST_PAD_NAME (new_pad), GST_ELEMENT_NAME (src));

  /* Check the new pad's type */
  new_pad_caps = gst_pad_get_current_caps (new_pad);
  new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
  new_pad_type = gst_structure_get_name (new_pad_struct);
  if (!g_str_has_prefix (new_pad_type, "video/x-raw")) {
    g_print ("  It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);
    goto exit;
  }

  // adds the pad probe to the new src pad on the decoder
  gst_pad_add_probe(new_pad, (GstPadProbeType) GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM ,
          dec_event_probe_CB, NULL, NULL);
  /* Attempt the link */
  ret = gst_pad_link (new_pad, sink_pad);
  if (GST_PAD_LINK_FAILED (ret)) {
    g_print ("  Type is '%s' but link failed.\n", new_pad_type);
  } else {
    g_print ("  Link succeeded (type '%s').\n", new_pad_type);
  }

exit:
  /* Unreference the new pad's caps, if we got them */
  if (new_pad_caps != NULL)
    gst_caps_unref (new_pad_caps);

  /* Unreference the sink pad */
  gst_object_unref (sink_pad);
}