Node.js WebM generation with whammy and sharp

nodejs-webm

var Whammy = require('node-whammy'),
    sharp = require('sharp');

function canvasToWebp(canvas, callback) {

  sharp(canvas.toBuffer()).toFormat(sharp.format.webp).toBuffer(function(e, webpbuffer) {
    var webpDataURL = 'data:image/webp;base64,' + webpbuffer.toString('base64');
    callback(webpDataURL);
  });

}

function sendAsWEBP(response, canvas) {

  var encoder = new Whammy.Video(7);

  var currentId = 0,
      time = 0,
      timeout = 20000,
      delay = 20
      addedFrame = -1,
      totalFrames = 3,
      tmpFrames = Array.apply(null, Array(totalFrames));

  var addFrame = function addFrame(context) {
    var id = currentId++;
    canvasToWebp(context.canvas, function(webmData) {
      tmpFrames[id] = webmData;
      for(var i = addedFrame + 1; i < totalFrames; ++i) {
        if(tmpFrames[i] !== undefined) {
          encoder.add(tmpFrames[i]);
          addedFrame = i;
        }
        else {
          break;
        }
      }
    });
  };

  var checkReady = function checkReady() {
    if(totalFrames <= addedFrame + 1) {
      try {
        var output = encoder.compile(true);
        response.type('webm');
        response.send(new Buffer(output));
        console.log('Webm compilation: ' + time + 'ms');
      }
      catch(err) {
        response.send(err.toString());
      }
    }
    else if((time += delay) < timeout) {
      setTimeout(checkReady, delay);
    }
    else {
      response.send('Timeout of ' + timeout + 'ms exceed');
    }
  };

  var context = canvas.getContext("2d");

  // Add 3 frames
  addFrame(context);
  addFrame(context);
  addFrame(context);

  setTimeout(checkReady, delay);

};