Don't process frames from NDI if source not showing (DistroAV#1404)

Author: BitRate27

src/ndi-source.cpp

@@ -642,6 +642,17 @@ void *ndi_source_thread(void *data)
 			ndiLib->recv_set_tally(ndi_receiver, &tally);
 		}
 
+		//
+		// If this source isn't showing in OBS then don't receive any frames from NDI. This occurs when multiple
+		// scenes have NDI sources that are not being shown and behavior is set to Keep Active. Without this check,
+		// the fps of OBS can decrease dramatically, especially with multiple 4K 60 sources.
+		//
+		if (!obs_source_showing(s->obs_source)) {
+			// Avoid busy-waiting when the source is hidden but kept active.
+			std::this_thread::sleep_for(std::chrono::milliseconds(5));
+			continue;
+		}
+
 		if (ndi_frame_sync) {
 			//
 			// ndi_frame_sync