winegstreamer: Allow videoconvert to parallelize in the parser.

dlls/winegstreamer/wg_parser.c

@@ -870,6 +870,9 @@ static bool stream_create_post_processing_elements(GstPad *pad, struct wg_parser
                 || !append_element(parser->container, element, &first, &last))
             return false;
 
+        /* Let GStreamer choose a default number of threads. */
+        gst_util_set_object_arg(G_OBJECT(element), "n-threads", "0");
+
         /* GStreamer outputs RGB video top-down, but DirectShow expects bottom-up. */
         if (!(element = create_element("videoflip", "good"))
                 || !append_element(parser->container, element, &first, &last))
@@ -882,6 +885,9 @@ static bool stream_create_post_processing_elements(GstPad *pad, struct wg_parser
                 || !append_element(parser->container, element, &first, &last))
             return false;
 
+        /* Let GStreamer choose a default number of threads. */
+        gst_util_set_object_arg(G_OBJECT(element), "n-threads", "0");
+
         if (!link_src_to_element(pad, first) || !link_element_to_sink(last, stream->my_sink))
             return false;
     }