• 继续 VCMJitterBuffer::InsertPacket()

1. 记录收到包数量，并且记录第一个rtp收到的时间蹉

  ++num_packets_;
  if (num_packets_ == 1) {
    time_first_packet_ms_ = clock_->TimeInMilliseconds();
  }

2. 旧包处理

• 这里的旧包，是的是通过时间蹉判断，是当前正在解码的时间前面的rtp包（包括相等的）。
• 如果packet 里数据，累加一下丢弃的包个数和收到旧包个数。并且回调状态
• UpdateOldPacket 当rtp恰是当前带解码的包。更新最后解码的seq_num
  其他下面部分代码FindAndInsertContinuousFramesWithState 还不太理解是什么问题

  // Does this packet belong to an old frame?
  if (last_decoded_state_.IsOldPacket(&packet)) {
    // Account only for media packets.
    if (packet.sizeBytes > 0) {
      num_discarded_packets_++;
      num_consecutive_old_packets_++;
      if (stats_callback_ != NULL)
        stats_callback_->OnDiscardedPacketsUpdated(num_discarded_packets_);
    }
    // Update last decoded sequence number if the packet arrived late and
    // belongs to a frame with a timestamp equal to the last decoded
    // timestamp.
    last_decoded_state_.UpdateOldPacket(&packet);
    DropPacketsFromNackList(last_decoded_state_.sequence_num());

    // Also see if this old packet made more incomplete frames continuous.
    FindAndInsertContinuousFramesWithState(last_decoded_state_);
    
    if (num_consecutive_old_packets_ > kMaxConsecutiveOldPackets) {
      LOG(LS_WARNING)
          << num_consecutive_old_packets_
          << " consecutive old packets received. Flushing the jitter buffer.";
      Flush();
      return kFlushIndicator;
    }
    return kOldPacket;
  }

3. 旧包处理

 VCMFrameBuffer* frame;
  FrameList* frame_list;
  const VCMFrameBufferEnum error = GetFrame(packet, &frame, &frame_list);
  if (error != kNoError)
    return error;

• 二级指针方式，返回frame,frame_list.
• GetFrame()方法通过packet 的时间，找到对应得FrameList frame。这个方法里面的逻辑一会单独讲解

3. 网络延迟记录

 int64_t now_ms = clock_->TimeInMilliseconds();
  // We are keeping track of the first and latest seq numbers, and
  // the number of wraps to be able to calculate how many packets we expect.
  if (first_packet_since_reset_) {
    // Now it's time to start estimating jitter
    // reset the delay estimate.
    inter_frame_delay_.Reset(now_ms);
  }

重置时间后，第一个收到包的时间。

4. 不理解的一段代码

  // Empty packets may bias the jitter estimate (lacking size component),
  // therefore don't let empty packet trigger the following updates:
  if (packet.frameType != kEmptyFrame) {
    if (waiting_for_completion_.timestamp == packet.timestamp) {
      // This can get bad if we have a lot of duplicate packets,
      // we will then count some packet multiple times.
      waiting_for_completion_.frame_size += packet.sizeBytes;
      waiting_for_completion_.latest_packet_time = now_ms;
    } else if (waiting_for_completion_.latest_packet_time >= 0 &&
               waiting_for_completion_.latest_packet_time + 2000 <= now_ms) {
      // A packet should never be more than two seconds late
      UpdateJitterEstimate(waiting_for_completion_, true);
      waiting_for_completion_.latest_packet_time = -1;
      waiting_for_completion_.frame_size = 0;
      waiting_for_completion_.timestamp = 0;
    }
  }

5. packet 插入 frame过程

 VCMFrameBufferStateEnum previous_state = frame->GetState();
  // Insert packet.
  FrameData frame_data;
  frame_data.rtt_ms = rtt_ms_;
  frame_data.rolling_average_packets_per_frame = average_packets_per_frame_;
  VCMFrameBufferEnum buffer_state =
      frame->InsertPacket(packet, now_ms, decode_error_mode_, frame_data);

• 保存frame状态（可解码，完整帧之类的）
• FrameData 类型数据构造。是一个Frame附加信息
• InsertPacket 是具体的插入packet 方法。里面需要再详解