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• ffmpeg the start time of frame is incorrect with option : -vf fps=1/5 [duplicate]

  13 novembre 2019, par Egbert Ke

  This question already has an answer here :

  • How to Generate accurate thumbnails with FFMPEG
    
    1 answer
    

  i have a 31 second video file(0 second to 30 second, 31 seconds total) named 2.mp4, i want to get one frame every 5 seconds. so i do this : ffmpeg -i 2.mp4 -vf fps=1/5 image-%05d.jpg, then i got 6 frames, i check the time of these frames, found that the time sequence is 2, 7, 12, 17, 22, 27. but what i want is 0, 5, 10, 15, 20, 25, 30.

  I google it and got nothing, but a offset dict from a blog :

  process_offset = {
  
      "1" : 0, "2" : 0,
  
      "3" : 1, "4" : 1,
  
      "5" : 2, "6" : 2,
  
      "7" : 3, "8" : 3,
  
      "9" : 4, "10" : 4
  
  }

  it says if the fps is 1/5, the start time of frame is the 2 second.

  Why this happen and what could i do to got the correct frames ?

• The start timestamp is non zero-when remuxing using libavformat

  14 janvier, par animaonline

  I'm remuxing a live rtmp stream using libavformat's sample remuxing.c my code is almost identical to that sample, but it also decodes the audio and video in order to render a preview using SDL, that works great.

  



  My application has a a button to start recording, and whenever the user presses it, the main loop will remux to a file, in a typical situation a user will wait a couple of seconds before initiating a recording, that is where the problems arise, the resulting video has non-zero start time. (I don't see these problems if I manually initiate the recording right after opening the input stream)

  



  e.g.
The user waits 5 seconds before starting a recording, then records for 5 seconds : The reported duration is 5s, while the start timestamp is at 9s. VLC fails to display the duration/position properly, but it works fine in other players.

  



  Here's an example of my main loop

  



  while (1) {
    ret = av_read_frame(ifmt_ctx, &pkt);

    //decode and preview
    //set pts, dts and duration
    //...

    if(ost->record){
        //remux
        ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
        if (ret < 0) {
            fprintf(stderr, "Error muxing packet\n");
            break;
        }
    }

    av_packet_unref(&pkt);
}


  



  I have tried setting mux_ts_offset of the input stream, but it didn't help.

  


• C# UWP Desktop Bridge start ffmpeg with command

  4 décembre 2019, par iNCEPTiON_

  I have a UWP Application which starts a WPF app and communicates via AppServiceConnection which works well,
  what I want to do is to start FFmpeg / FFplay with the command to play a video.

  The code in the WPF app for starting FFmpeg / FFplay via AppServiceConnection

  private void Connection_RequestReceivedAsync(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
  
          {
  
              var value = args.Request.Message["REQUEST"] as string;
  
              switch (value)
  
              {
  
                  case "StartFFmpeg":
  
                      Test();
  
                      break;
  
              }
  
          }
  
  
  
          private void Test()
  
          {
  
              var process = new Process();
  
              process.StartInfo.RedirectStandardOutput = true;
  
              process.StartInfo.RedirectStandardError = true;
  
              process.StartInfo.FileName = Path.GetDirectoryName(Process.GetCurrentProcess().MainModule.FileName) + @"\ffplay.exe";
  
              process.StartInfo.Arguments = @"-i C:\Users\test\video.mp4";
  
  
  
  
  
              process.StartInfo.UseShellExecute = false;
  
              process.StartInfo.CreateNoWindow = true;
  
              process.Start();
  
          }

  this fails with the following error in the UWP app :

  The target process exited without raising a CoreCLR started event. Ensure that the target process is configured to use .NET Core. This may be expected if the target process did not run on .NET Core.
  
  The program '[16824] FFmpeg.Bridge.exe' has exited with code -532462766 (0xe0434352).

  now my question is, is it possible to start FFmpeg / FFplay with the desktop bridge ? or can we only start .net core processes, the process is running with full privileges so why is that not possible ?

  The UWP App won’t be published on the store, it will only run on a local windows machine.