Webcam barcode reading (zbar, emscripten)

<!DOCTYPE html>
<html>
  <head>
    <title>JS in-browser barcode reader</title>
      <style type="text/css">
        body > div {
          position: relative;
          width: 320px; height: 240px;
        }
        video { position: absolute; top: 0; left: 0; width: 320px; height: 240px; }
        div#inner {
          position: absolute;
          margin: 0 auto;
          top: 0; left: 0;
          width: 260px; height: 180px;
          border: 30px solid rgba(64,64,64, 0.5);
          zindex: 1000;
        }
        div#redline {
          position: absolute;
          top: 120px;
          width: 320px;
          height: 2px;
          background-color: rgba(255, 0, 0, 0.3);
          zindex: 1001;
        }
      </style>
    </head>
    <body>
      <h1>Barcode scanner</h1>
      <p>Based on <a href="https://github.com/yurydelendik/zbarjs">zbarjs</a> - Code: <a href="https://gist.github.com/jazzido/9435670">https://gist.github.com/jazzido/9435670</a></p>
      <div>
        <video autoplay></video>
        <div id="inner"></div>
        <div id="redline">
        </div>
      </div>
      <ul id="decoded">
      </ul>
      <canvas style="display:none;"></canvas>

var worker = new Worker('zbar-processor.js');
        worker.onmessage = function(event) {
            if (event.data.length == 0) return;
            var d = event.data[0];
            var entry = document.createElement('li');
            entry.appendChild(document.createTextNode(d[2] + ' (' + d[0] + ')'));
            list.appendChild(entry);
        };

function snapshot() {
            if (localMediaStream === null) return;
            var k = (320 + 240) / (video.videoWidth + video.videoHeight);
            canvas.width = Math.ceil(video.videoWidth * k);
            canvas.height = Math.ceil(video.videoHeight * k);
            var ctx = canvas.getContext('2d');
            ctx.drawImage(video, 0, 0, video.videoWidth, video.videoHeight,
                          0, 0, canvas.width, canvas.height);

var data = ctx.getImageData(0, 0, canvas.width, canvas.height);
            worker.postMessage(data);
        }

setInterval(snapshot, 500);

navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;
        window.URL = window.URL || window.webkitURL || window.mozURL || window.msURL;

if (navigator.getUserMedia) {
            navigator.getUserMedia({video: true},
                                   function(stream) { // success callback
                                       if (video.mozSrcObject !== undefined) {
                                           video.mozSrcObject = stream;
                                       } else {
                                           video.src = (window.URL && window.URL.createObjectURL(stream)) || stream;
                                       }
                                       localMediaStream = true;
                                   },
                                   function(error) {
                                       console.error(error);
                                   });
        }
        else {
        }
      </script>
    </body>
</html>