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• How can I manually pass a SoundCloud track duration to HTML5 audio ?

  30 janvier 2016, par thebaer

  I’m currently using a stripped-down version of Canvas.fm to convert SoundCloud mp3 streams into ogg streams using Node and ffmpeg, to support the audio element in ogg-playing browsers like Firefox. My problem is : while the duration is correctly set for SoundCloud’s mp3 streams, the ogg stream gives an indefinite duration in the player ; I want the actual duration to show up.

  I noticed when requesting a SoundCloud mp3 stream, I get a canceled request, a pending one, and then a 206 Partial Content response. My Node app does similar redirects, without as many headers, since I’m sending them myself.

  Should I be trying to calculate/forge the Content-Length or Content-Range headers ? Or does HTML5 audio get the duration from mp3 metadata/ID3 information ? If I can get the duration from SoundCloud’s API (which I can), how can I pass this to the client in my ogg stream ?

• How can I manually pass a SoundCloud track duration to HTML5 audio ?

  19 juin 2013, par thebaer

  I'm currently using a stripped-down version of Canvas.fm to convert SoundCloud mp3 streams into ogg streams using Node and ffmpeg, to support the audio element in ogg-playing browsers like Firefox. My problem is : while the duration is correctly set for SoundCloud's mp3 streams, the ogg stream gives an indefinite duration in the player ; I want the actual duration to show up.

  I noticed when requesting a SoundCloud mp3 stream, I get a canceled request, a pending one, and then a 206 Partial Content response. My Node app does similar redirects, without as many headers, since I'm sending them myself.

  Should I be trying to calculate/forge the Content-Length or Content-Range headers ? Or does HTML5 audio get the duration from mp3 metadata/ID3 information ? If I can get the duration from SoundCloud's API (which I can), how can I pass this to the client in my ogg stream ?

• How to pipe rgba data using Node.js to ffmpeg ?

  7 juillet 2015, par Swoth

  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

  Problem
  Everything except the transfer of stored rgba-array-data to ffmpeg works. I don’t seem to manage the transport using Node.js. How do I pass my frames to ffmpeg using Node.js and what did I do wrong ?

  What I do
  The code below renders and saves each frame as rgba data to an array. The renderScene-function renders each animation frame.

  console.log("Rendering getImageData, length:"+ videoLength);
  
  var dataArray = [];
  
  function imageDataCallback() {
  
      dataArray.push(context.getImageData(0, 0, 1280, 720).data);
  
  }
  
  rekapi.on('afterUpdate', imageDataCallback);
  
  
  
  var time = Date.now();
  
  renderScene(rekapi);
  
  console.log('Time used: ' + (Date.now() - time) + 'ms;');
  
  rekapi.off('afterUpdate', imageDataCallback);

  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']);

  I also tried using -i pipe:0, which is the same as -i -, just to be sure.
  After process creation i registered for various events to know what happens :

   child.on('error', function(error){
  
      console.log(error);
  
  });
  
  child.stdin.on('data', function (data) {
  
      console.log('data retrieved')
  
  });
  
  child.on('exit', function (code) {
  
      console.log('child exit with code:' + code)
  
  });

  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 and as it seems no definded child-callback (like data) except error has been called. I am not 100% sure about the lifecycle but, as I understood, data should be called each time I write something.

  I am very new to Node.js, thus I might not understand the big picture of it’s child processes.

  Since my reputation is too low I am not allowed to post more than 2 links (first question) and I don’t feel comfortable using non-typed languages like JavaScript.