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

webrtc/media/engine/webrtcvideoengine2.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 1224 matching lines @@
 
   // TODO(brandtr): Generalize when we add support for multistream protection.
   if (sp.GetFecFrSsrc(ssrc, &flexfec_config->remote_ssrc)) {
     flexfec_config->protected_media_ssrcs = {ssrc};
     flexfec_config->local_ssrc = config->rtp.local_ssrc;
     flexfec_config->rtcp_mode = config->rtp.rtcp_mode;
     flexfec_config->transport_cc = config->rtp.transport_cc;
     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_;
 }
 
 bool WebRtcVideoChannel2::RemoveRecvStream(uint32_t ssrc) {
   LOG(LS_INFO) << "RemoveRecvStream: " << ssrc;
   if (ssrc == 0) {
     LOG(LS_ERROR) << "RemoveRecvStream with 0 ssrc is not supported.";
     return false;
   }
@@ skipping 926 matching lines @@
     allocated_decoders_.push_back(allocated_decoder);
 
     webrtc::VideoReceiveStream::Decoder decoder;
     decoder.decoder = allocated_decoder.decoder;
     decoder.payload_type = recv_codecs[i].codec.id;
     decoder.payload_name = recv_codecs[i].codec.name;
     decoder.codec_params = recv_codecs[i].codec.params;
     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;
 
   config_.rtp.nack.rtp_history_ms =
       HasNack(recv_codecs.begin()->codec) ? kNackHistoryMs : 0;
 }
 
 void WebRtcVideoChannel2::WebRtcVideoReceiveStream::SetLocalSsrc(
     uint32_t local_ssrc) {
   // TODO(pbos): Consider turning this sanity check into a RTC_DCHECK. You
@@ skipping 298 matching lines @@
         rtx_mapping[video_codecs[i].codec.id] !=
             ulpfec_config.red_payload_type) {
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket