Support external audio mixer.

webrtc/api/peerconnection.cc

Index: webrtc/api/peerconnection.cc
diff --git a/webrtc/api/peerconnection.cc b/webrtc/api/peerconnection.cc
index 46bdec594a9c90fcd1630db748921237807902d2..e7ec7d4f426308ac6470ae498d6a88a406006850 100644
--- a/webrtc/api/peerconnection.cc
+++ b/webrtc/api/peerconnection.cc
@@ -1353,6 +1353,15 @@ void PeerConnection::Close() {
   session_->Close();
 }
 
+std::vector<uint32_t> PeerConnection::GetRemoteAudioTrackSsrcs() {

[aleloi, 2016/12/05 14:03:08]

See comment at declaration.

+  std::vector<uint32_t> ssrcs;
+  TrackInfos* infos = GetRemoteTracks(cricket::MEDIA_TYPE_AUDIO);
+  for (const auto& info : *infos)
+    ssrcs.push_back(info.ssrc);
+
+  return ssrcs;
+}
+
 void PeerConnection::OnSessionStateChange(WebRtcSession* /*session*/,
                                           WebRtcSession::State state) {
   switch (state) {