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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
  
  }
  
  //..

• How to convert a Stream on the fly with FFMpegCore ?

  18 octobre 2023, par Adrian

  For a school project, I need to stream videos that I get from torrents while they are downloading on the server.
When the video is a .mp4 file, there's no problem, but I must also be able to stream .mkv files, and for that I need to convert them into .mp4 before sending them to the client, and I can't find a way to convert my Stream that I get from MonoTorrents with FFMpegCore into a Stream that I can send to my client.

  


  Here is the code I wrote to simply download and stream my torrent :

  


  var cEngine = new ClientEngine();

var manager = await cEngine.AddStreamingAsync(GenerateMagnet(torrent), ) ?? throw new Exception("An error occurred while creating the torrent manager");

await manager.StartAsync();
await manager.WaitForMetadataAsync();

var videoFile = manager.Files.OrderByDescending(f => f.Length).FirstOrDefault();
if (videoFile == null)
    return Results.NotFound();

var stream = await manager.StreamProvider!.CreateStreamAsync(videoFile, true);
return Results.File(stream, contentType: "video/mp4", fileDownloadName: manager.Name, enableRangeProcessing: true);


  


  I saw that the most common way to convert videos is by using ffmpeg. .NET has a package called FFMpefCore that is a wrapper for ffmpeg.

  


  To my previous code, I would add right before the return :

  


  if (!videoFile.Path.EndsWith(".mp4"))
{
    var outputStream = new MemoryStream();
    FFMpegArguments
        .FromPipeInput(new StreamPipeSource(stream), options =>
        {
            options.ForceFormat("mp4");
        })
        .OutputToPipe(new StreamPipeSink(outputStream))
        .ProcessAsynchronously();
    return Results.File(outputStream, contentType: "video/mp4", fileDownloadName: manager.Name, enableRangeProcessing: true);
}


  


  I unfortunately can't get a "live" Stream to send to my client.

  


• Find video resolution and video duration of remote mediafile

  22 février 2012, par osgx

  I want to write an program which can find some metainformation of mediafile. I'm interested in popular video formats, such as avi, mkv, mp4, mov (may be other popular too). I want basically to get :

  • Video size (720, 1080, 360 etc)
  • Total runtime of video (may be not very exact)
  • Number of audio streams
  • Name of video codec
  • Name of audio codec

  There is already the mediainfo, but in my program I want to get information about remote file, which may be accessed via ftp, http, samba ; or even torrent (there are some torrent solutions, which allows to read not-yet downloaded file).

  MediaInfo library have no support of samba (smb ://) and mkv format (for runtime).

  Also, I want to know, how much data should be downloaded to get this information. I want not to download full videofile because I have no enough disk space.

  Is this information in the first 1 or 10 or 100 KiloBytes of the file ? Is it at predictable offset if I know the container name and total file size ?

  PS : Platform is Linux, Language is C/C++