直播流PTS值异常：FFmpeg接收UDP流时DTS/PTS跳变问题求助

使用FFmpeg源码接收UDP网络视频流时，音视频包的DTS和PTS偶尔会同时跳变——从较大值突然降到相差数十倍的极小值，直接影响音视频同步，导致播放卡顿，需要代码层面的解决方案。

收流写入缓冲区的处理代码 #

//read video package
if(pAvPacket->stream_index == pThis->m_iVideoStreamIndex)
{
    std::cout<<"Video_Packet_DTS: "<<pAvPacket->dts<<"   Video_Packet_PTS: "<<pAvPacket->pts<<std::endl;
    
     //Video frame rate assignment
    if(pThis->m_pVideoTimeBase->num > 0 && pAvPacket->duration > 0)
        pThis->m_iVideoFPS = (pThis->m_pVideoTimeBase->den / pThis->m_pVideoTimeBase->num) / pAvPacket->duration;

    if(pThis->m_iDecodeMode == DECODE_MODE_ONLY_CURRENT_COLLECTION)
        pThis->m_videoDecodeThreadState = THREAD_NEED_STOP;     //stop the thread
    else
        pThis->m_videoDecodeThreadState = THREAD_NEED_RUN;      //make the thread run

    if(pThis->m_iMultiMediaType != MULTI_MEDIA_TYPE_FILE
            && pAvPacket->flags == AV_PKT_FLAG_KEY)
    {
            pThis->m_bIsFindIFrame = YTRUE;
    }

    VideoFramesCount ++;
    pThis->m_iReadVideoPacketCount ++;
    if(pThis->m_iDecodeMode != DECODE_MODE_ONLY_CHECK_NET && pThis->m_iDecodeMode != DECODE_MODE_AUDIO && pThis->m_bIsFindIFrame)
        YGlobCircleBufferWrite<AVPacket *>(pThis->m_videoPacketBuffer, &pAvPacket, 1);
    else
        av_packet_unref(pAvPacket);
    pAvPacket = YNULL;
}

运行时打印的PTS/DTS信息 #

Video_Packet_DTS: 8590470992   Video_Packet_PTS: 8590470992
Video_Packet_DTS: 8590474592   Video_Packet_PTS: 8590474592
Video_Packet_DTS: 8590478192   Video_Packet_PTS: 8590478192
Video_Packet_DTS: 8590481792   Video_Packet_PTS: 8590481792
Video_Packet_DTS: 550800   Video_Packet_PTS: 550800
Video_Packet_DTS: 554400   Video_Packet_PTS: 554400
Video_Packet_DTS: 558000   Video_Packet_PTS: 558000
Video_Packet_DTS: 561600   Video_Packet_PTS: 561600
Video_Packet_DTS: 565200   Video_Packet_PTS: 565200

错误日志信息 #

[h264 @ 04fea380] non-existing PPS 0 referenced
[h264 @ 04fea380] decode_slice_header error
[h264 @ 04fea380] no frame!
[swscaler @ 19b04600] Warning: data is not aligned! This can lead to a speed loss
[mp3float @ 04feadc0] overread, skip -6 enddists: -2 -2
[mpegts @ 04fcbf40] DTS 550800 < 8590481792 out of order
[mp3float @ 04feadc0] overread, skip -7 enddists: -6 -6
[mp3float @ 04feadc0] overread, skip -5 enddists: -2 -2

代码层面解决方案 #

• 检测并修正时间戳跳变
  维护全局时间戳偏移量timestamp_offset，初始为0。每次收到包时：

  1. 记录上一个有效包的PTS值（仅记录关键帧的PTS，避免非关键帧干扰）
  2. 计算当前包PTS与上一个有效PTS的差值，若差值为负且绝对值超过10倍单帧时长，判定为跳变
  3. 更新偏移量：timestamp_offset = 上一个有效PTS - 当前PTS + timestamp_offset
  4. 对后续所有包的PTS/DTS加上该偏移量，保证时间戳连续
     注意：必须在收到关键帧后再应用修正，避免非关键帧依赖旧时间戳导致解码失败。

• 重置解码上下文
  检测到时间戳跳变时，调用avcodec_flush_buffers()清空解码器缓存，丢弃缓冲区中未解码的旧包，等待新关键帧到来后重新启动解码流程，避免旧数据干扰新流解析。

• 增强UDP流容错性
  如果是MPEG-TS封装的UDP流，在打开流时设置mpegts_flags=resync，让FFmpeg的TS解析器自动处理流重新同步；如果是RTP封装流，设置reorder_queue_size参数开启包序重组，减少无序包导致的时间戳异常。

• 修正FPS计算逻辑
  当前整数除法会导致FPS精度丢失，改为浮点计算更准确：

  if(pThis->m_pVideoTimeBase->num > 0 && pAvPacket->duration > 0) {
      double frame_duration = av_q2d(*pThis->m_pVideoTimeBase) * pAvPacket->duration;
      pThis->m_iVideoFPS = 1.0 / frame_duration;
  }
  

  准确的单帧时长能更精准地判断时间戳跳变。

内容的提问来源于stack exchange，提问作者watermelon_seven