Allow default video receive channel to receive on any unsignalled SSRC,

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 410 matching lines @@
   }
   return nullptr;
 }
 
 DefaultUnsignalledSsrcHandler::DefaultUnsignalledSsrcHandler()
     : default_recv_ssrc_(0), default_sink_(NULL) {}
 
 UnsignalledSsrcHandler::Action DefaultUnsignalledSsrcHandler::OnUnsignalledSsrc(
     WebRtcVideoChannel2* channel,
     uint32_t ssrc) {
-  if (default_recv_ssrc_ != 0) {  // Already one default stream.
-    LOG(LS_WARNING) << "Unknown SSRC, but default receive stream already set.";
-    return kDropPacket;
+  if (default_recv_ssrc_ != 0) {  // Already one default stream, so replace it.
+    channel->RemoveRecvStream(default_recv_ssrc_);

[pthatcher1, 2017/02/17 18:10:37]

I know default_recv_ssrc_ is set down below, but it would be more robust to
future code changes to add this here:

default_recv_ssrc_ = 0;


Imagine, for example, if there were an early return somewhere down below.  Then
we'd end up in a broken state.  

[mo.zanaty, 2017/02/17 18:29:05]

Agreed. Done.

   }
 
   StreamParams sp;
   sp.ssrcs.push_back(ssrc);
   LOG(LS_INFO) << "Creating default receive stream for SSRC=" << ssrc << ".";
   if (!channel->AddRecvStream(sp, true)) {
     LOG(LS_WARNING) << "Could not create default receive stream.";
   }
 
   channel->SetSink(ssrc, default_sink_);
@@ skipping 2083 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