Comment implémenter des captures d'écran vidéo dans les compétences js HTML5_javascript

<video id="video" controls="controls">
  <source src=".mp4" />
</video>
<button id="capture">Capture</button>
<div id="output"></div>

(function() {
  "use strict";
  var video, $output;
  var scale = 0.25;
  var initialize = function() {
    $output = $("#output");
    video = $("#video").get(0);
    $("#capture").click(captureImage);        
  };
  var captureImage = function() {
    var canvas = document.createElement("canvas");
    canvas.width = video.videoWidth * scale;
    canvas.height = video.videoHeight * scale;
    canvas.getContext('2d')
       .drawImage(video, 0, 0, canvas.width, canvas.height);
    var img = document.createElement("img");
    img.src = canvas.toDataURL();
    $output.prepend(img);
  };
  $(initialize);      
}());