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• Writing data to a Node.js child process's stdin fails due to ECONNRESET

  8 juillet 2015, par Swoth

  Problem
  Passing data to a child process’s stdin seems to fail. It fails due to an ECONNRESET after writing the data.

  Context
  I am developing a small programm that is supposed to render a video, as fast as possible, based on frames captured from a canvas. The animation is rendered to a headless canvas implementation using Rekapi (JavaScript animation framework). The headless canvas is a Node.js module called node-canvas by Automattic. The animation frames are rendered one after another, after each rendering the frame is retrieved using canvas.getImageData().data (Uint8ClampedArray - rgba, faster than canvas.toDataUrl) and put into an array. Every frame is supposed to be send to ffmpeg to create a video.

  Rekapi -> canvas -> getImageData -> array -> ffmpeg

  What I do
  I already tried various possibilities to pipe that data to ffmpeg. In general I created a child process in Node.js executing ffmpeg :

  var spawn = require('child_process').spawn;    
  
  var child = spawn('ffmpeg', [
  
          '-pix_fmt', 'rgba',
  
          '-s','1280x720',
  
          '-r', 25,
  
          '-f', 'rawvideo',
  
          '-vcodec', 'rawvideo',
  
          '-i', '-', // read frames from stdin
  
          '-threads', 0, // use all cores
  
          'test.mpg']);

  Now I write my array data to the child’s stdin :

  for(var i = 0; i < dataArray.length; ++i){
  
      var buffer = new Buffer(dataArray[i]);
  
      child.stdin.write(buffer);
  
      console.log('wrote: ' + i);
  
  }

  I wrote 25 frames this way. The console displays the following :

  wrote: 24
  
  wrote: 25
  
  events.js:85
  
        throw er; // Unhandled 'error' event
  
              ^
  
  Error: read ECONNRESET
  
      at exports._errnoException (util.js:746:11)
  
      at Pipe.onread (net.js:559:26)

  ffmpeg generated a 0 byte test.mpg.
  I am very new to Node.js, thus I might not understand the big picture of it’s child processes.

• how to convert an rstp ffmpeg mp4 buffer into ImageData inside nodejs (nestjs)

  23 décembre 2022, par distante

  I am reading an rtsp stream using ffmpeg in this way :

  


    const ffmpegArgs = [
    '-rtsp_transport',
    'tcp',
    '-i',
    this.rtspStreamPath,
    '-vcodec',
    'copy',
    '-f',
    'mp4',
    '-movflags',
    'frag_keyframe+empty_moov',
    '-reset_timestamps',
    '1',
    '-vsync',
    '1',
    '-flags',
    'global_header',
    '-bsf:v',
    'dump_extra',
    '-y',
    '-', // output to stdout
  ];
    const liveffmpeg = spawn(ffmpegPath, ffmpegArgs, {
      detached: false,
    });

    liveffmpeg.stdout.on('data', (data) => {
      console.log('data here!', data.toString());
    });


  


  Later I pipe the liveffmpeg.stdout to the response object of my NestJS controller so it can be consumed by the frontend in a video HTML Element.

  


  In the frontend I calculate this by doing a snapshot of the video element into a canvas, getting the ImageData from the canvasContext and doing my calculations after I get two or more updates.

  


  Now I need to do the exact same thing on the backend but I am not able to convert the data value from liveffmpeg.stdout.on('data', ) into an ImageData so I can use the same average function I use in the frontend.

  


  I already installed node-canvas to try to reproduce the frontend steps but to be able to draw something inside the canvas context I need an Image and no Video object can be constructed in nodejs.

  


  So, is there a way to convert the stdout data of the FFmpeg process into ImageData objects ? Or, to extract the images of each data update so I can manually draw them on the node-canvas element and get the ImageData ?

  


  Thanks !

  


  PDd : I think convert them into Uint8ClampedArray could also work since node-canvas has a function that uses that : createImageData(data: Uint8ClampedArray, width: number, height?: number) => ImageData

  


• How to impose PNG stream over exist video using ffmpeg and image2pipe ?

  16 avril 2019, par Михаил Магомедов

  I reproduce the steps of this article with nodeJs :

  https://blog.scwu.io/rendering-canvas-to-mp4-using-nodejs/

  I not need to generate a new video from the stream of png pictures, me need impose png stream over exist video, please tell me how to do it ?

  var recorder = spawn("ffmpeg", [
  
      "-y", "-f", "image2pipe",
  
      "-vcodec", "png", "-r", "60",
  
      "-i", "-", "-vcodec", "h264",
  
      "-r", "60", "output.mp4"
  
  ]);
  
  
  
  for(var i = 0; i<100; i++){
  
      ...some ctx processing
  
      let url = canvas.toDataURL(),
  
          data = atob( url.substring(url.indexOf("base64") + 7) );
  
  
  
      recorder.stdin.write(data, "binary");
  
  }
  
  
  
  recorder.stdin.end();