Prefer external video codecs over internal in SDP

webrtc/media/engine/webrtcvideoengine.cc

Index: webrtc/media/engine/webrtcvideoengine.cc
diff --git a/webrtc/media/engine/webrtcvideoengine.cc b/webrtc/media/engine/webrtcvideoengine.cc
index b6447329e265519da1f19d29f1227006feeff8c0..e1939c35d01e2ddce412c67271eb59272da09982 100644
--- a/webrtc/media/engine/webrtcvideoengine.cc
+++ b/webrtc/media/engine/webrtcvideoengine.cc
@@ -537,8 +537,6 @@ static std::vector<VideoCodec> GetSupportedCodecs(
                << CodecVectorToString(internal_codecs);
 
   std::vector<VideoCodec> unified_codecs;
-  AppendVideoCodecs(internal_codecs, &unified_codecs);
-
   if (external_encoder_factory != nullptr) {
     const std::vector<VideoCodec>& external_codecs =
         external_encoder_factory->supported_codecs();
@@ -547,6 +545,8 @@ static std::vector<VideoCodec> GetSupportedCodecs(
                  << CodecVectorToString(external_codecs);
   }
 
+  AppendVideoCodecs(internal_codecs, &unified_codecs);
+
   return unified_codecs;
 }