Implement source timestamp synchronization

renderers/video_renderer_gstreamer.c

@@ -65,7 +65,7 @@ void video_renderer_render_buffer(video_renderer_t *renderer, raop_ntp_t *ntp, u
 
     buffer = gst_buffer_new_and_alloc(data_len);
     assert(buffer != NULL);
-
+    GST_BUFFER_DTS(buffer) = (GstClockTime)pts;
     gst_buffer_fill(buffer, 0, data, data_len);
     gst_app_src_push_buffer (GST_APP_SRC(renderer->appsrc), buffer);
 }