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• Confusion about PTS in video files and media streams

  11 novembre 2014, par user2452253

  Is it possible that the PTS of a particular frame in a file is different with the PTS of the same frame in the same file while it is being streamed ?

  When I read a frame using av_read_frame I store the video stream in an AVStream. After I decode the frame with avcodec_decode_video2, I store the time stamp of that frame in an int64_t using av_frame_get_best_effort_timestamp. Now if the program is getting its input from a file I get a different timestamp from when I stream the input (from the same file) to the program.

  To change the input type I simply change the argv argument from "/path/to/file.mp4" to something like "udp ://localhost:1234", then I stream the file with ffmpeg in command line : "ffmpeg -re -i /path/to/file.mp4 -f mpegts udp ://localhost:1234". Can it be because the "-f mpegts" arguments change some characteristics of the media ?

  Below is my code (simplified). By reading the ffmpeg mailing list archives I realized that the time_base that I’m looking for is in the AVStream and not the AVCodecContext. Instead of using av_frame_get_best_effort_timestamp I have also tried using the packet.pts but the results don’t change.
  I need the time stamps to have a notion of frame number in a streaming video that is being received.
  I would really appreciate any sort of help.

  //..
  
  //argv[1]="/file.mp4";
  
  argv[1]="udp://localhost:7777";
  
  // define AVFormatContext, AVFrame, etc.
  
  // register av, avcodec, avformat_network_init(), etc.
  
  avformat_open_input(&pFormatCtx, argv, NULL, NULL);
  
  avformat_find_stream_info(pFormatCtx, NULL);
  
  // find the video stream...
  
  // pointer to the codec context...
  
  // open codec...
  
  pFrame=av_frame_alloc();
  
  while(av_read_frame(pFormatCtx, &packet)>=0) {
  
          AVStream *strem = pFormatCtx->streams[videoStream];
  
          if(packet.stream_index==videoStream) {
  
              avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
              if(frameFinished) {
  
                  int64_t perts = av_frame_get_best_effort_timestamp(pFrame);
  
                  if (isMyFrame(pFrame)){
  
                       cout << perts*av_q2d(strem->time_base) << "\n";
  
                  }
  
               }
  
  }
  
  //free allocated space
  
  }
  
  //..

• Install ffmpeg on Heruko

  5 octobre 2020, par islalobo

  I have a little node.js app on heroku and I'm trying to use ffmpeg to convert some audio that has been recorded.

  


  To do that I need to install ffmpeg buildpack.

  


  When I add the build pack and deploy, I don't get any errors in the logs, but the application doesn't load and gives me a non-discript error.

  


  Build packs I've tried

  


  

  • https://elements.heroku.com/buildpacks/jonathanong/heroku-buildpack-ffmpeg-latest

  


  • https://elements.heroku.com/buildpacks/dwnld/heroku-buildpack-ffmpeg

  


  


  Code to convert audio

  


    try {
    let process = new ffmpeg(`./public/messages/${req.body.message}`);
    process.then((audio) => {
      audio.fnExtractSoundToMP3(`/messages/${req.body.message}.mp3`, (error, file) => {
        if (!error) console.log('Audio File: ', file);
        if (error) console.log(error);
      });
    }, (error) => {
      console.log('Error: ', error);
    });
  }
  catch(error) {
    console.log(error.code, error.msg);
  }


  


• How to stream mp4 files over RTSP ?

  21 février 2023, par Ramil Galin

  I wrote an RTSP server and now I want to stream mp4 (H264/AAC) files over it. Using FFMPEG I demux mp4 file into audio and video streams. Then I read AVPacket packets, wrap them into rtp packets and send over RTSP server.

  


  So far I'm just trying to send only video packets. I tried to get my RTSP stream using VLC, unfortunately VLC doesn't play anything. Then I tried to put my RTSP stream into the ffmpeg and save my stream into another mp4 file to see what happens with my packets - ffmpeg showed error no start code is found.

  


  I googled the issue and found that mp4 container unlike raw h264 doesn't put SPS/PPS info into the packets. To test it I tried the following. Instead of mp4 file I tried reading raw h264 files and send them over my RTSP server - it worked nicely, I can play my stream using VLC.

  


  So, my question is how can I get SPS/PPS info from mp4 container files ? How to correctly pack them into rtp packet and send over RTSP ?

  


  So far I tried to get sps and pps data using this code :

  


  AVCodecParameters *codecpar = video_stream->codecpar;
for (int i = 0; i < codecpar->extradata_size - 4; i++)
{

  if (
    codecpar->extradata[i] == 0x00 &&
    codecpar->extradata[i + 1] == 0x00 &&
    codecpar->extradata[i + 2] == 0x00 &&
    codecpar->extradata[i + 3] == 0x01
  )
  {
    if (sps_data_ == nullptr)
    {
      sps_data_ = codecpar->extradata + i;
      sps_size_ = i > 0 ? i : codecpar->extradata_size;
    }
    else
    {
      pps_data_ = codecpar->extradata + i;
      pps_size_ = i > 0 ? i : codecpar->extradata_size - sps_size_;
      break;
    }
  }
}


  


  But codecpar->extradata doesn't contain needed info, so if-condition inside the loop is always false. Any help is appreciated.