Don't create unsignalled receive streams for RTX and ULPFEC packets.

talk/media/webrtc/webrtcvideoengine2.cc

 /*
  * libjingle
  * Copyright 2014 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 1358 matching lines @@
       return;
     case webrtc::PacketReceiver::DELIVERY_UNKNOWN_SSRC:
       break;
   }
 
   uint32 ssrc = 0;
   if (!GetRtpSsrc(packet->data(), packet->size(), &ssrc)) {
     return;
   }
 
-  // TODO(pbos): Ignore unsignalled packets that don't use the video payload
-  // (prevent creating default receivers for RTX configured as if it would
-  // receive media payloads on those SSRCs).
+  int payload_type = 0;
+  if (!GetRtpPayloadType(packet->data(), packet->size(), &payload_type)) {
+    return;
+  }
+
+  // See if this payload_type is registered as one that usually gets its own
+  // SSRC (RTX) or at least is safe to drop either way (ULPFEC). If it is, and
+  // it wasn't handled above by DeliverPacket, that means we don't know what
+  // stream it associates with, and we shouldn't ever create an implicit channel
+  // for these.
+  for (auto& codec : recv_codecs_) {
+    if (payload_type == codec.rtx_payload_type ||
+        payload_type == codec.fec.red_rtx_payload_type ||
+        payload_type == codec.fec.ulpfec_payload_type) {
+      return;
+    }
+  }
+
   switch (unsignalled_ssrc_handler_->OnUnsignalledSsrc(this, ssrc)) {
     case UnsignalledSsrcHandler::kDropPacket:
       return;
     case UnsignalledSsrcHandler::kDeliverPacket:
       break;
   }
 
   if (call_->Receiver()->DeliverPacket(webrtc::MediaType::VIDEO,
           reinterpret_cast<const uint8_t*>(packet->data()), packet->size()) !=
       webrtc::PacketReceiver::DELIVERY_OK) {
@@ skipping 1188 matching lines @@
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VIDEO