webrtc中，H264 添加start code

在早期版本中，如57版本，是通过这个函数实现的：

size_t VCMSessionInfo::Insert(const uint8_t* buffer,
                              size_t length,
                              bool insert_start_code,
                              uint8_t* frame_buffer)

 

 

在后面的的版本中，为：

H264SpsPpsTracker::PacketAction H264SpsPpsTracker::CopyAndFixBitstream(
    VCMPacket* packet)

 

 

//在这里执行完成后，添加到packet_buffer_中；

int32_t RtpVideoStreamReceiver::OnReceivedPayloadData(
    const uint8_t* payload_data,
    size_t payload_size,
    const WebRtcRTPHeader* rtp_header,
    const absl::optional& generic_descriptor,
    bool is_recovered) {

......

  if (packet.codec() == kVideoCodecH264) {
    // Only when we start to receive packets will we know what payload type
    // that will be used. When we know the payload type insert the correct
    // sps/pps into the tracker.
    if (packet.payloadType != last_payload_type_) {
      last_payload_type_ = packet.payloadType;
      InsertSpsPpsIntoTracker(packet.payloadType);
    }

    switch (tracker_.CopyAndFixBitstream(&packet)) {
      case video_coding::H264SpsPpsTracker::kRequestKeyframe:
        keyframe_request_sender_->RequestKeyFrame();
        RTC_FALLTHROUGH();
      case video_coding::H264SpsPpsTracker::kDrop:
        return 0;
      case video_coding::H264SpsPpsTracker::kInsert:
        break;
    }

  } else {
    uint8_t* data = new uint8_t[packet.sizeBytes];
    memcpy(data, packet.dataPtr, packet.sizeBytes);
    packet.dataPtr = data;
  }

  packet_buffer_->InsertPacket(&packet);
  return 0;
}