Only return stats for the most recent unsignaled audio stream.

webrtc/media/engine/webrtcvoiceengine.cc

 /*
  *  Copyright (c) 2004 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 2249 matching lines @@
     sinfo.residual_echo_likelihood_recent_max =
         stats.residual_echo_likelihood_recent_max;
     sinfo.typing_noise_detected = (send_ ? stats.typing_noise_detected : false);
     sinfo.ana_statistics = stats.ana_statistics;
     info->senders.push_back(sinfo);
   }
 
   // Get SSRC and stats for each receiver.
   RTC_DCHECK_EQ(info->receivers.size(), 0U);
   for (const auto& stream : recv_streams_) {
+    uint32_t ssrc = stream.first;
+    // When SSRCs are unsignaled, there's only one audio MediaStreamTrack, but
+    // multiple RTP streams can be received over time (if the SSRC changes for
+    // whatever reason). We only want the RTCMediaStreamTrackStats to represent
+    // the stats for the most recent stream (the one whose audio is actually
+    // routed to the MediaStreamTrack), so here we ignore any unsignaled SSRCs
+    // except for the most recent one (last in the vector). This is somewhat of
+    // a hack, and means you don't get *any* stats for these inactive streams,
+    // but it's slightly better than the previous behavior, which was "highest
+    // SSRC wins".
+    // See: https://bugs.chromium.org/p/webrtc/issues/detail?id=8158
+    if (!unsignaled_recv_ssrcs_.empty() &&
+        std::find(unsignaled_recv_ssrcs_.begin(),
+                  --unsignaled_recv_ssrcs_.end(),

[the sun, 2017/09/18 18:59:35]

nit: I would've done it

auto end_it = --unsignaled_recv_ssrcs_.end();
if (std::find(unsignaled_recv_ssrcs.begin(), endit, ssrc) != end_it) {
  continue;
}

which is as many lines but easier to read

[Taylor Brandstetter, 2017/09/20 00:19:45]

Can't quite do that since if the list is empty end() == begin() and decrementing
it is technically undefined behavior. But I'll do something similar.

+                  ssrc) != --unsignaled_recv_ssrcs_.end()) {
+      continue;
+    }
     webrtc::AudioReceiveStream::Stats stats = stream.second->GetStats();
     VoiceReceiverInfo rinfo;
     rinfo.add_ssrc(stats.remote_ssrc);
     rinfo.bytes_rcvd = stats.bytes_rcvd;
     rinfo.packets_rcvd = stats.packets_rcvd;
     rinfo.packets_lost = stats.packets_lost;
     rinfo.fraction_lost = stats.fraction_lost;
     rinfo.codec_name = stats.codec_name;
     rinfo.codec_payload_type = stats.codec_payload_type;
     rinfo.ext_seqnum = stats.ext_seqnum;
@@ skipping 97 matching lines @@
                       ssrc);
   if (it != unsignaled_recv_ssrcs_.end()) {
     unsignaled_recv_ssrcs_.erase(it);
     return true;
   }
   return false;
 }
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VOICE