win32: Replace glsinkbin with d3d12convert on Windows

On Windows, we don't want to use GL and let D3D12 do all the work.

But as long as we don't support all formats and implement all the
interfaces GstPlayer expects, we need to have a way to convert.

So we put a d3d12convert for that.

Related: https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/3956

modules/media/gtkgstpaintable.c

@@ -28,6 +28,10 @@
 
 #include <math.h>
 
+#ifdef GDK_WINDOWING_WIN32
+#include <gdk/win32/gdkwin32.h>
+#endif
+
 struct _GtkGstPaintable
 {
   GObject parent_instance;
@@ -164,6 +168,30 @@ gtk_gst_paintable_video_renderer_create_video_sink (GstPlayerVideoRenderer *rend
 
   g_object_get (GTK_GST_SINK (sink), "uses-gl", &uses_gl, NULL);
 
+#ifdef GDK_WINDOWING_WIN32
+  if (GDK_IS_WIN32_DISPLAY (display))
+    {
+      GstElement *bin, *convert;
+      GstPad *pad, *ghostpad;
+      gboolean res = TRUE;
+      
+      convert = gst_element_factory_make ("d3d12convert", NULL);
+      if (convert)
+      {
+        bin = gst_bin_new ("d3d12sinkbin");
+        res &= gst_bin_add (GST_BIN (bin), convert);
+        res &= gst_bin_add (GST_BIN (bin), sink);
+        res &= gst_element_link_pads (convert, "src", sink, "sink");
+        pad = gst_element_get_static_pad (convert, "sink");
+        ghostpad = gst_ghost_pad_new ("sink", pad);
+        gst_element_add_pad (bin, ghostpad);
+        gst_object_unref (pad);
+        g_assert (res);
+        sink = bin;
+      }
+    }
+  else
+#endif
   if (uses_gl)
     {
       GstElement *glsinkbin;