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• Embedding SMPTE 336M KLV data into video

  8 décembre 2023, par Mateo

  I have a drone video in .MP4 format, and an accompanying log file containing various timecoded data, e.g. GPS location, altitude.

  



  I need to embed the data into the video in the SMPTE 336M (KLV Data Encoding Protocol Using Key-Length-Value) standard format.

  



  I've successfully extracted KLV data from a MPEG2-TS file using FFMPEG and a parser in Node.

  



  Now I need to go the other way : to generate KLV data from my log file and insert it into the relevant video. How this is done ?

  


• C++ RTSP Stream recording timebase wrong ffmpeg

  29 juillet 2021, par Tom Baires

  We fetch a camera stream over RTSP (Axis Q1755 H264). And after a random time we a start recording the stream to a file. I check the video file with ffprobe and realise the start time is not the start time of the recording it is the start time of fetch the stream. My Video has a length of 5 seconds and the start time of the video should be 0. But the real starttime of the Video is at second 20. This leads to a an incorrect timebase. (ffmpeg Version 3.3.3)

  


  I try to repair it, but now i have some time the error timebase 1/180000... i marked my changes with the comment (timebase repair logic)

  


  

  


  ffprobe Output (without timebase repair logic)
The start is higher as the duration, correctly the start is 0 and not 20.080000

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
'C:\testvideo.mp4':  
 Metadata:
     major_brand     : isom
     minor_version   : 512
     compatible_brands: isomiso2avc1mp41
     encoder         : Lavf57.71.100   Duration: 00:00:05.04, start: 20.080000, bitrate: 2675 kb/s
     Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuvj420p(pc, bt709), 800x450 [SAR 1:1 DAR 16:9], 2670 kb/s, 50.20 fps,
 50 tbr, 180k tbn, 360k tbc (default)
     Metadata:
       handler_name    : VideoHandler


  


  Error after the add of timebase repair logic

  


  


  [mpeg4 @ 00000178fcb12b40] timebase 1/180000 not supported by MPEG 4
standard, the maximum admitted value for the timebase denominator is
65535 Could not open codec 'mpeg4' : Unspecified error Cannot start
recording

  


  


  Here some parts of my code

  


  Start Logic

  


  bool RecordingStreamGrabber::start()
{
    CORE_LOG_INFO(m_logger, "Started RecordingStreamGrabber");
    if (m_thread == NULL)
    {
        if (this->prepareInputStream())
        {
            m_run = true;
            m_thread = new std::thread(RecordingStreamGrabber::run, this);
            return true;
        }
        CORE_LOG_ERROR(m_logger, "Error starting RecrodingStreamGrabber");
        return false;
    }
    return false;
}


  


  Prepare Input/Output Stream

  


  bool RecordingStreamGrabber::prepareInputStream()
{
    CORE_LOG_INFO(m_logger, "Preparing Inputstream for recording: " << m_url);

    m_ifmtctx = avformat_alloc_context();
    interrupt_recording_nostop = false;
    interrupt_recording_timeout = m_timeout; // Timeout in milisekunde
    interrupt_recording_starttime = GetTickCount();
    m_ifmtctx->interrupt_callback = interrupt_timeout_cb;

    if (avformat_open_input(&m_ifmtctx, m_url.c_str(), NULL, NULL) != 0)
    {
        m_ifmtctx = NULL;
        CORE_LOG_ERROR(m_logger, "Error opening recording URL: " << m_url);
        return false;
    }

    interrupt_recording_nostop = true;

    if (avformat_find_stream_info(m_ifmtctx, NULL) < 0)
    {
        CORE_LOG_ERROR(m_logger, "Error finding stream in URL: " << m_url);
        avformat_close_input(&m_ifmtctx);
        m_ifmtctx = NULL;
        return false;
    }

    //search for the first video stream
    m_stream_index = -1;
    for (unsigned int i = 0; i < m_ifmtctx->nb_streams && m_stream_index == -1; i++)
    {
        m_iccx = m_ifmtctx->streams[i]->codec;
        if (m_iccx->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            m_istream = m_ifmtctx->streams[i];
            m_stream_index = i;
        }
    }

    if (m_stream_index == -1)
    {
        CORE_LOG_ERROR(m_logger, "Could not find video stream in URL: " << m_url);
        avformat_close_input(&m_ifmtctx);
        m_ifmtctx = NULL;
        return false;
    }

    return true;
}

bool RecordingStreamGrabber::prepareOutputStream()
{
    if (m_ofmtctx)
    {
        CORE_LOG_DEBUG(m_logger, "Close outputfile: " << m_targetfile);
        avformat_free_context(m_ofmtctx);
        m_ofmtctx = NULL;
    }

    m_ofmt = av_guess_format(NULL, m_targetfile.c_str(), NULL);

    m_ofmtctx = avformat_alloc_context();

    m_ofmtctx->oformat = m_ofmt;

    if (avio_open2(&m_ofmtctx->pb, m_targetfile.c_str(), AVIO_FLAG_WRITE, NULL, NULL) != 0)
    {
        avformat_free_context(m_ofmtctx);
        m_ofmtctx = NULL;
        CORE_LOG_ERROR(m_logger, "Error opening outputfile: " << m_targetfile);
        return false;
    }

    m_ostream = avformat_new_stream(m_ofmtctx, NULL);

    avcodec_copy_context(m_ostream->codec, m_iccx);

    m_ostream->sample_aspect_ratio.num = m_iccx->sample_aspect_ratio.num;
    m_ostream->sample_aspect_ratio.den = m_iccx->sample_aspect_ratio.den;

    /* time base: this is the fundamental unit of time (in seconds) in terms
    of which frame timestamps are represented. for fixed-fps content,
    timebase should be 1/framerate and timestamp increments should be
    identically 1. */
    m_ostream->time_base.num = m_iccx->time_base.num;
    m_ostream->time_base.den = m_iccx->time_base.den;

    avformat_write_header(m_ofmtctx, NULL);

#ifdef WIN32
    sprintf_s(m_ofmtctx->filename, sizeof(m_ofmtctx->filename), "%s", m_targetfile.c_str());
#else
    snprintf(m_ofmtctx->filename, sizeof(m_ofmtctx->filename), "%s", m_targetfile.c_str());
#endif
    return true;
}


  


  Recording Logic

  


  void RecordingStreamGrabber::run(RecordingStreamGrabber *_this)
{
    AVPacket packet;
    av_init_packet(&packet);
    int i = 0;
    bool startFrame = true;
    bool keyFrame = false;
    int64_t pts, dts;
    _this->m_tailWritten = true;
    while (_this->m_run)
    {
        if (av_read_frame(_this->m_ifmtctx, &packet) >= 0)
        {
            if ((packet.flags & AV_PKT_FLAG_KEY) == AV_PKT_FLAG_KEY)
            {
                keyFrame = true;
                CORE_LOG_DEBUG(_this->m_logger, "Detected key frame: " << i << "");
            }

            if (_this->m_record)
            {
                if (packet.stream_index == _this->m_stream_index)
                {
                    packet.stream_index = _this->m_ostream->id;

                    if (_this->m_tailWritten == false || keyFrame == true)
                    {
                        //#####################################
                        //timebase repair logic (my changes)
                        //#####################################
                        AVStream *in_stream;
                        AVStream *out_stream;

                        in_stream = _this->m_ifmtctx->streams[packet.stream_index];
                        out_stream = _this->m_ofmtctx->streams[packet.stream_index];

                        if (startFrame)
                        {
                            pts = packet.pts;
                            dts = packet.dts;
                            startFrame = false;
                        }
                        packet.pts -= pts;
                        packet.dts -= dts;

                        packet.pts = av_rescale_q_rnd(packet.pts, in_stream->time_base, out_stream->time_base, (AVRounding)((int)AV_ROUND_NEAR_INF | (int)AV_ROUND_PASS_MINMAX));
                        packet.dts = av_rescale_q_rnd(packet.dts, in_stream->time_base, out_stream->time_base, (AVRounding)((int)AV_ROUND_NEAR_INF | (int)AV_ROUND_PASS_MINMAX));

                        packet.duration = av_rescale_q(packet.duration, in_stream->time_base, out_stream->time_base);
                        //end of my changes
                        
                        av_interleaved_write_frame(_this->m_ofmtctx, &packet);
                        _this->m_tailWritten = false;
                    }
                }
            }
            else if (_this->m_ofmtctx)
            {
                if (_this->m_tailWritten == false)
                {
                    av_write_trailer(_this->m_ofmtctx);
                    avio_close(_this->m_ofmtctx->pb);
                }
                avformat_free_context(_this->m_ofmtctx);
                _this->m_tailWritten = true;
                _this->m_ofmtctx = NULL;
                startFrame = true;
            }
            i++;
            keyFrame = false;
        }
        av_free_packet(&packet);
        av_init_packet(&packet);
    }
    if (_this->m_record)
    {
        av_write_trailer(_this->m_ofmtctx);
        avio_close(_this->m_ofmtctx->pb);
    }
    if (_this->m_ofmtctx)
    {
        avformat_free_context(_this->m_ofmtctx);
        _this->m_ofmtctx = NULL;
    }
    _this->m_record = false;

    avformat_close_input(&_this->m_ifmtctx);
    _this->m_ifmtctx = NULL;
}


  


  Other question
How can I check whether my project uses the deprecated api (answer of @berak) ?

  


• How to play sequentially received video clips

  21 novembre 2017, par Ye Li

  I’m working on a prototype project in which some small video clips are sequentially sent over a network. These clips are chunked (using ffmpeg) from a complete video file. Each of the clips is separately playable (containing exactly one GOP). At the destination, I need to smoothly play the sequentially received files as if I were streaming the video, i.e., play the files at the receiver side one by one in one process. May I know whether this is doable ? And if yes, what is the best practice to do this task ?

  The network transmission/receiving parts are written in Python, but I’m open to use any other languages/tools for doing the task.