Explicitly only add transport-cc RTCP feedback param to default FlexFEC codec.

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index 335ee3a691aed1f66d1f4bc0e628d07e2618fca3..48830714e543edc86b1df61c4c6a67fb7f6e31d1 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -148,7 +148,7 @@ class WebRtcSimulcastEncoderFactory
   std::vector<webrtc::VideoEncoder*> non_simulcast_encoders_;
 };
 
-void AddDefaultFeedbackParams(VideoCodec* codec) {
+void AddDefaultMediaFeedbackParams(VideoCodec* codec) {
   codec->AddFeedbackParam(FeedbackParam(kRtcpFbParamCcm, kRtcpFbCcmParamFir));
   codec->AddFeedbackParam(FeedbackParam(kRtcpFbParamNack, kParamValueEmpty));
   codec->AddFeedbackParam(FeedbackParam(kRtcpFbParamNack, kRtcpFbNackParamPli));
@@ -157,6 +157,11 @@ void AddDefaultFeedbackParams(VideoCodec* codec) {
       FeedbackParam(kRtcpFbParamTransportCc, kParamValueEmpty));
 }
 
+void AddDefaultFlexfecFeedbackParams(VideoCodec* codec) {
+  codec->AddFeedbackParam(
+      FeedbackParam(kRtcpFbParamTransportCc, kParamValueEmpty));

[stefan-webrtc, 2017/01/10 11:38:56]

I think you'd want to add remb here as well in case of receive-side bwe.

[brandtr, 2017/01/10 12:33:51]

That's right. Done.

+}
+
 static std::string CodecVectorToString(const std::vector<VideoCodec>& codecs) {
   std::stringstream out;
   out << '{';
@@ -570,7 +575,7 @@ static rtc::Optional<int> NextFreePayloadType(
 // This is a helper function for GetSupportedCodecs below. It will append new
 // unique codecs from |input_codecs| to |unified_codecs|. It will add default
 // feedback params to the codecs and will also add an associated RTX codec for
-// recognized codecs (VP8, VP9, H264, and Red).
+// recognized codecs (VP8, VP9, H264, and RED).
 static void AppendVideoCodecs(const std::vector<VideoCodec>& input_codecs,
                               std::vector<VideoCodec>* unified_codecs) {
   for (VideoCodec codec : input_codecs) {
@@ -581,8 +586,12 @@ static void AppendVideoCodecs(const std::vector<VideoCodec>& input_codecs,
     codec.id = *payload_type;
     // TODO(magjed): Move the responsibility of setting these parameters to the
     // encoder factories instead.
-    if (codec.name != kRedCodecName && codec.name != kUlpfecCodecName)
-      AddDefaultFeedbackParams(&codec);
+    if (codec.name != kRedCodecName && codec.name != kUlpfecCodecName &&
+        codec.name != kFlexfecCodecName) {
+      AddDefaultMediaFeedbackParams(&codec);
+    } else if (codec.name == kFlexfecCodecName) {
+      AddDefaultFlexfecFeedbackParams(&codec);

[magjed_webrtc, 2017/01/10 10:46:57]

Like the TODO above says, we eventually want this moved into the codec factories
instead. So I would prefer if you move the flexfec feedback params to the
InternalEncoderFactory instead, and only add 'codec.name != kFlexfecCodecName'
to the if-statement here.

[brandtr, 2017/01/10 12:33:51]

Right, should have looked more carefully. Done.

+    }
     // Don't add same codec twice.
     if (FindMatchingCodec(*unified_codecs, codec))
       continue;