Make RTX pt/apt reconfigurable by calling WebRtcVideoChannel2::SetRecvParameters.

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 b0d3b89b8a2115f4b83b576a2f54e125f9d47c04..c8521885bda3ed4c4e7ea0a03c862ba3ee2664dd 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -1242,16 +1242,7 @@ void WebRtcVideoChannel2::ConfigureReceiverRtp(
     flexfec_config->rtp_header_extensions = config->rtp.extensions;
   }
 
-  for (size_t i = 0; i < recv_codecs_.size(); ++i) {
-    uint32_t rtx_ssrc;
-    if (recv_codecs_[i].rtx_payload_type != -1 &&
-        sp.GetFidSsrc(ssrc, &rtx_ssrc)) {

[brandtr, 2017/01/20 14:49:22]

Since |ssrc| is invariant in this loop, sp.GetFidSsrc will always write the same
value to |rtx_ssrc|. Cf. line 1237.

-      webrtc::VideoReceiveStream::Config::Rtp::Rtx& rtx =
-          config->rtp.rtx[recv_codecs_[i].codec.id];
-      rtx.ssrc = rtx_ssrc;

[brandtr, 2017/01/20 14:49:22]

... and therefore all key-value pairs in |rtx| have the same SSRC set.

-      rtx.payload_type = recv_codecs_[i].rtx_payload_type;
-    }
-  }
+  sp.GetFidSsrc(ssrc, &config->rtp.rtx_ssrc);
 
   config->rtp.extensions = recv_rtp_extensions_;
 }
@@ -2198,7 +2189,12 @@ void WebRtcVideoChannel2::WebRtcVideoReceiveStream::ConfigureCodecs(
     config_.decoders.push_back(decoder);
   }
 
-  // TODO(pbos): Reconfigure RTX based on incoming recv_codecs.
+  config_.rtp.rtx_payload_types.clear();
+  for (const VideoCodecSettings& recv_codec : recv_codecs) {
+    config_.rtp.rtx_payload_types[recv_codec.codec.id] =
+        recv_codec.rtx_payload_type;
+  }
+
   config_.rtp.ulpfec = recv_codecs.front().ulpfec;
   flexfec_config_.payload_type = recv_codecs.front().flexfec_payload_type;