flexfec_receiver_add_received_packet

// TODO(eladalon): Consider using packet.recovered() to avoid processing
// recovered packets here.
std::unique_ptr<ForwardErrorCorrection::ReceivedPacket>
FlexfecReceiver::AddReceivedPacket(const RtpPacketReceived& packet) {
  RTC_DCHECK_RUN_ON(&sequence_checker_);

  // RTP packets with a full base header (12 bytes), but without payload,
  // could conceivably be useful in the decoding. Therefore we check
  // with a non-strict inequality here.
  RTC_DCHECK_GE(packet.size(), kRtpHeaderSize);

  // Demultiplex based on SSRC, and insert into erasure code decoder.
  std::unique_ptr<ForwardErrorCorrection::ReceivedPacket> received_packet(
      new ForwardErrorCorrection::ReceivedPacket());
  received_packet->seq_num = packet.SequenceNumber();
  received_packet->ssrc = packet.Ssrc();
  received_packet->extensions = packet.extension_manager();
  if (received_packet->ssrc == ssrc_) {
    // This is a FlexFEC packet.
    if (packet.payload_size() < kMinFlexfecHeaderSize) {
      RTC_LOG(LS_WARNING) << "Truncated FlexFEC packet, discarding.";
      return nullptr;
    }
    received_packet->is_fec = true;
    ++packet_counter_.num_fec_packets;

    // Insert packet payload into erasure code.
    received_packet->pkt = scoped_refptr<ForwardErrorCorrection::Packet>(
        new ForwardErrorCorrection::Packet());
    received_packet->pkt->data =
        packet.Buffer().Slice(packet.headers_size(), packet.payload_size());
  } else {
    // This is a media packet, or a FlexFEC packet belonging to some
    // other FlexFEC stream.
    if (received_packet->ssrc != protected_media_ssrc_) {
      return nullptr;
    }
    received_packet->is_fec = false;

    // Insert entire packet into erasure code.
    // Create a copy and fill with zeros all mutable extensions.
    received_packet->pkt = scoped_refptr<ForwardErrorCorrection::Packet>(
        new ForwardErrorCorrection::Packet());
    RtpPacketReceived packet_copy(packet);
    packet_copy.ZeroMutableExtensions();
    received_packet->pkt->data = packet_copy.Buffer();
  }

  ++packet_counter_.num_packets;

  return received_packet;
}