flexfec_sender_GetFecPackets

std::vector<std::unique_ptr<RtpPacketToSend>> FlexfecSender::GetFecPackets() {
  RTC_CHECK_RUNS_SERIALIZED(&ulpfec_generator_.race_checker_);
  std::vector<std::unique_ptr<RtpPacketToSend>> fec_packets_to_send;
  fec_packets_to_send.reserve(ulpfec_generator_.generated_fec_packets_.size());
  size_t total_fec_data_bytes = 0;
  for (const auto* fec_packet : ulpfec_generator_.generated_fec_packets_) {
    std::unique_ptr<RtpPacketToSend> fec_packet_to_send(
        new RtpPacketToSend(&rtp_header_extension_map_));
    fec_packet_to_send->set_packet_type(
        RtpPacketMediaType::kForwardErrorCorrection);
    fec_packet_to_send->set_allow_retransmission(false);

    // RTP header.
    fec_packet_to_send->SetMarker(false);
    fec_packet_to_send->SetPayloadType(payload_type_);
    fec_packet_to_send->SetSequenceNumber(seq_num_++);
    fec_packet_to_send->SetTimestamp(
        timestamp_offset_ +
        static_cast<uint32_t>(kMsToRtpTimestamp *
                              env_.clock().TimeInMilliseconds()));
    // Set "capture time" so that the TransmissionOffset header extension
    // can be set by the RTPSender.
    fec_packet_to_send->set_capture_time(env_.clock().CurrentTime());
    fec_packet_to_send->SetSsrc(ssrc_);
    // Reserve extensions, if registered. These will be set by the RTPSender.
    fec_packet_to_send->ReserveExtension<AbsoluteSendTime>();
    fec_packet_to_send->ReserveExtension<TransmissionOffset>();
    fec_packet_to_send->ReserveExtension<TransportSequenceNumber>();
    // Possibly include the MID header extension.
    if (!mid_.empty()) {
      // This is a no-op if the MID header extension is not registered.
      fec_packet_to_send->SetExtension<RtpMid>(mid_);
    }

    // RTP payload.
    uint8_t* payload =
        fec_packet_to_send->AllocatePayload(fec_packet->data.size());
    memcpy(payload, fec_packet->data.cdata(), fec_packet->data.size());

    total_fec_data_bytes += fec_packet_to_send->size();
    fec_packets_to_send.push_back(std::move(fec_packet_to_send));
  }

  if (!fec_packets_to_send.empty()) {
    ulpfec_generator_.ResetState();
  }

  Timestamp now = env_.clock().CurrentTime();
  if (!fec_packets_to_send.empty() &&
      now - last_generated_packet_ > kPacketLogInterval) {
    RTC_LOG(LS_VERBOSE) << "Generated " << fec_packets_to_send.size()
                        << " FlexFEC packets with payload type: "
                        << payload_type_ << " and SSRC: " << ssrc_ << ".";
    last_generated_packet_ = now;
  }

  MutexLock lock(&mutex_);
  fec_bitrate_.Update(total_fec_data_bytes, now);

  return fec_packets_to_send;
}