message: Fix ExternalOutput with Simulcast
diff: @@ -334,6 +334,10 @@ int ExternalOutput::deliverAudioData_(std::shared_ptr<dataPacket> audio_packet)
  int ExternalOutput::deliverVideoData_(std::shared_ptr<dataPacket> video_packet) {
  std::shared_ptr<dataPacket> copied_packet = std::make_shared<dataPacket>(*video_packet);
  + // TODO(javierc): We should support higher layers, but it requires having an entire pipeline at this point
  + if (!video_packet->belongsToSpatialLayer(0)) {
  + return 0;
  + }
  if (videoSourceSsrc_ == 0) {
  RtpHeader* h = reinterpret_cast<RtpHeader*>(copied_packet->data);
  videoSourceSsrc_ = h->getSSRC();
  