Gstreamer video in GTK Window

UPDATE 2018.03.12: The code has been updated and now runs as expected

I am struggeling a bit with creating a GTK+ Window equivalent to the following gst-launch command gst-launch-1.0 udpsrc port=6000 caps="application/x-rtp" ! rtph264depay ! h264parse ! omxh264dec ! autovideosink

My code is as following:

int main (int argc, char **argv)
{
  GdkWindow *video_window_xwindow;
  GtkWidget *window, *video_window;
  gulong embed_xid;
  GstStateChangeReturn sret;

  gst_init (&argc, &argv);
  gtk_init (&argc, &argv);

  GstElement *pipeline, *udpsrc, *appxrtp, *depay, *parse, *omxh264dec, *videoConvert, *sink;

  pipeline = gst_pipeline_new ("xvoverlay");
  udpsrc = gst_element_factory_make ("udpsrc", NULL); g_assert(udpsrc);

  //Set CAPS
  g_object_set (G_OBJECT (udpsrc), "port", 6000, NULL);
  GstCaps * xrtpcaps = gst_caps_from_string("application/x-rtp,encoding-name=H264");
  g_object_set (udpsrc, "caps", xrtpcaps, NULL);

  depay = gst_element_factory_make ("rtph264depay", NULL); g_assert(depay);
  parse = gst_element_factory_make ("h264parse", NULL); g_assert(parse);
  omxh264dec = gst_element_factory_make ("omxh264dec", NULL); g_assert(omxh264dec);
  videoConvert = gst_element_factory_make ("videoconvert", NULL); g_assert(videoConvert);
  sink = gst_element_factory_make ("xvimagesink", NULL); g_assert(sink);

  //ADD
  gst_bin_add_many (GST_BIN (pipeline), udpsrc, depay, parse, omxh264dec, videoConvert, sink, NULL);

  //LINK
  g_assert(gst_element_link (udpsrc, depay));
  g_assert(gst_element_link (depay, parse));
  g_assert(gst_element_link (parse, omxh264dec));
  g_assert(gst_element_link (omxh264dec, videoConvert));
  g_assert(gst_element_link (videoConvert, sink));

  /* prepare the ui */
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);   

  g_signal_connect (G_OBJECT (window), "delete-event", G_CALLBACK (window_closed), (gpointer) pipeline);
  gtk_window_set_default_size (GTK_WINDOW (window), 600, 400);
  gtk_window_set_title (GTK_WINDOW (window), "GstVideoOverlay Gtk+ demo");

  video_window = gtk_drawing_area_new ();
  gtk_container_add (GTK_CONTAINER (window), video_window);
  gtk_container_set_border_width (GTK_CONTAINER (window), 2);

  gtk_widget_show_all (window);

  video_window_xwindow = gtk_widget_get_window (video_window);
  embed_xid = GDK_WINDOW_XID (video_window_xwindow);
  gst_video_overlay_set_window_handle (GST_VIDEO_OVERLAY (sink), embed_xid);

  /* run the pipeline */
  sret = gst_element_set_state (pipeline, GST_STATE_PLAYING);
  if (sret == GST_STATE_CHANGE_FAILURE)
    gst_element_set_state (pipeline, GST_STATE_NULL);
  else
    gtk_main ();

  gst_object_unref (pipeline);
  return 0;
}

When running it I get a black/empty GTK Window.

Console output is:

NvMMLiteOpen : Block : BlockType = 261 
TVMR: NvMMLiteTVMRDecBlockOpen: 7907: NvMMLiteBlockOpen 
NvMMLiteBlockCreate : Block : BlockType = 261 
TVMR: cbBeginSequence: 1223: BeginSequence  320x240, bVPR = 0
TVMR: LowCorner Frequency = 100000 
TVMR: cbBeginSequence: 1622: DecodeBuffers = 17, pnvsi->eCodec = 4, codec = 0 
TVMR: cbBeginSequence: 1693: Display Resolution : (320x240) 
TVMR: cbBeginSequence: 1694: Display Aspect Ratio : (320x240) 
TVMR: cbBeginSequence: 1762: ColorFormat : 5 
TVMR: cbBeginSequence:1776 ColorSpace = NvColorSpace_YCbCr601
TVMR: cbBeginSequence: 1904: SurfaceLayout = 3
TVMR: cbBeginSequence: 2005: NumOfSurfaces = 24, InteraceStream = 0, InterlaceEnabled = 0, bSecure = 0, MVC = 0 Semiplanar = 1, bReinit = 1, BitDepthForSurface = 8 LumaBitDepth = 8, ChromaBitDepth = 8, ChromaFormat = 5
TVMR: cbBeginSequence: 2007: BeginSequence  ColorPrimaries = 2, TransferCharacteristics = 2, MatrixCoefficients = 2
Allocating new output: 320x240 (x 24), ThumbnailMode = 0
OPENMAX: HandleNewStreamFormat: 3464: Send OMX_EventPortSettingsChanged : nFrameWidth = 320, nFrameHeight = 240 

I am running this as the video source (which seems fine, I am able to consume this with gst-launch without any issues)

gst-launch-1.0 videotestsrc  ! omxh264enc control-rate=2 bitrate=8000000 ! 'video/x-h264, stream-format=(string)byte-stream' ! h264parse ! rtph264pay mtu=1400 ! udpsink host=127.0.0.1 port=6000

Can anyone give me some pointers? Do I need to link differently (when pads are added)?

Adding videoconvert between omxh264dec and sink fixed the problem. The video is now rendered in the GTK Window. Have updated the original code.