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• How can I make ffmpeg output proper SDP data for a data stream

  8 juillet 2021, par Shalom Crown

  I have a program based on the FFMPEG libraries, to add KLV data to a video stream. When I try to sent the output to an RTSP server (rtsp-simple-server), I get a 400 response.

  


  The apparent reason is that the SDP data for the KLV stream is missing the rtpmap.

  


  I would like to add the missing data either by setting the proper parameters in the contexts, or by specifying the data explicitly.

  


  This is the ANNOUNCE captured with Wireshark

  


  ANNOUNCE rtsp://0.0.0.0:8554/test RTSP/1.0
Content-Type: application/sdp
CSeq: 2
User-Agent: Lavf58.29.100
Content-Length: 270

v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 127.0.0.1
t=0 0
a=tool:libavformat 58.29.100
m=video 0 RTP/AVP 96
b=AS:10000
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1
a=control:streamid=0
m=application 0 RTP/AVP 97
b=AS:90
a=control:streamid=1


  


  Code fragment for initializing the data stream :

  


  AVStream* data_track = avformat_new_stream(muxer, nullptr);

if (data_track == nullptr) {
    LOG_ERROR << "failed to open data output stream";
    return nullptr;
}

muxer->oformat->video_codec = AV_CODEC_ID_H264;

AVCodec *klvEncoder = avcodec_find_encoder(AV_CODEC_ID_SMPTE_KLV);

if (klvEncoder == nullptr) {
    klvEncoder = avcodec_find_encoder(AV_CODEC_ID_BIN_DATA);
}

if (klvEncoder == nullptr) {
    klvEncoder = avcodec_find_encoder(AV_CODEC_ID_TEXT);
}

if (klvEncoder != nullptr) {
    klvEncoderContext = avcodec_alloc_context3(encoder);

    avcodec_parameters_from_context(data_track->codecpar, encoderContext);
} else {
    avcodec_parameters_copy(data_track->codecpar, pVideoStream->codecpar);
}

data_track->codecpar->codec_tag =  KLV_ID_TAG;
data_track->codecpar->codec_type = AVMEDIA_TYPE_DATA;
data_track->codecpar->codec_id = AV_CODEC_ID_SMPTE_KLV;
data_track->codecpar->bit_rate = 90000;
data_track->codecpar->format =  AV_SAMPLE_FMT_U8;
data_track->stream_identifier = KLV_ID_TAG;
data_track->id = 0x101;
data_track->time_base = video_track->time_base;
data_track->avg_frame_rate = video_track->time_base;


  


• Can't save process's output stream to file

  10 octobre 2018, par Wahid Masud

  I’m using ffmpeg.exe as a process and output the converted video to memory, then from memory I’m saving the data to a video file (this is the requirement I can’t directly save the converted video to a file). But the conversion is not working for some reason, Here is what I’ve tried,

  var ffmpeg = HttpContext.Current.Server.MapPath("~/FFMpeg/ffmpeg.exe");
  
  var outputDir = HttpContext.Current.Server.MapPath("~/Uploads/converted.mp4");
  
  var inputDir = "https://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_10mb.mp4";
  
  var args = "-i " + inputDir + " -c:v libx264 -preset veryslow -crf 26 " +
  
              "-ar 44100 -ac 2 -c:a aac -strict -2 -b:a 128k -";
  
  
  
  var process = new Process();
  
  process.StartInfo.UseShellExecute = false;
  
  process.StartInfo.FileName = ffmpeg;
  
  process.StartInfo.WorkingDirectory = ffmpeg.Replace("\\ffmpeg.exe", "");
  
  process.StartInfo.Arguments = args;
  
  process.StartInfo.RedirectStandardOutput = true;
  
  process.Start();
  
  process.EnableRaisingEvents = true;
  
  //process.WaitForExit();
  
  Stream output = process.StandardOutput.BaseStream;
  
  process.Exited += (sender, e) =>
  
  {
  
      using (var fileStream = File.Create(outputDir))
  
      {
  
          output.Seek(0, SeekOrigin.Begin);
  
          output.CopyTo(fileStream);
  
      }
  
  };  

  The output file converted.mp4 is created but its 0 kb.

• Using FFMpeg to save an rtsp stream from a certain point in time

  14 août 2013, par Nir

  I would like to use FFMpeg to save a live stream from a certain offset. For example, "from timestamp 00:05 to 00:12".

  I know how to dump the stream to file (ffmpeg -i rtsp ://SRC -r 15 C :/file.mp4), the catch is how to clip it to the givem timestamp, if possible.

  Thanks !