Html5 web audio api - Offline rendering

webkitOfflineAudioContext.js

window.onload = init;
  var context;
  var bufferLoader;
  var offline;

  function init() {
    // Fix up prefixing
    window.AudioContext = window.AudioContext || window.webkitAudioContext;
    context = new AudioContext();
    bufferLoader = new BufferLoader(
      context, [
        '/sound/sound1.mp3',
      ],
      finishedLoading
    );

    bufferLoader.load();
  }

  function finishedLoading(bufferList) {
    offline = new webkitOfflineAudioContext(2, 10 * 44100, 44100);

    var source1 = offline.createBufferSource();
    source1.buffer = bufferList[0];

    var lowpass = offline.createBiquadFilter();
    lowpass.type = 0;
    lowpass.frequency.value = 0;

    source1.connect(lowpass);
    lowpass.connect(offline.destination);
    source1.start(0);

    recorder = new Recorder(lowpass);
    recorder.record();

    offline.startRendering();

    offline.oncomplete = function(ev) {
      console.log('oncomplete');
      var source = context.createBufferSource();
      source.buffer = ev.renderedBuffer;
      source.connect(context.destination);
      source.start(0);

      recorder.stop();
      recorder.exportWAV(function(s) {
        sendWaveToPost(s);
      });
    }
  }

  function sendWaveToPost(blob) {
    var data = new FormData();

    data.append("audio", blob, (new Date()).getTime() + ".wav");

    var oReq = new XMLHttpRequest();
    oReq.open("POST", "/audio/save_file");
    oReq.send(data);
    oReq.onload = function(oEvent) {
      if (oReq.status == 200) {
        console.log("Uploaded");

      } else {
        console.log("Error " + oReq.status + " occurred uploading your file.");
      }
    };
  }