decodeAudioData sample

var catMeowingBuffer = null;
var AudioContext = window.AudioContext || window.webkitAudioContext;
var context = new AudioContext();

function onError(err) {
   console.error(err);
}

function loadCatSound(url) {
  var request = new XMLHttpRequest();
  request.open('GET', url, true);
  request.responseType = 'arraybuffer';

  // Decode asynchronously
  request.onload = function() {
      context.decodeAudioData(request.response, function(buffer) {
      catMeowingBuffer = buffer;
    }, onError);
  }
  request.send();
}

loadCatSound("4513.m4a");

function playCatSound() {
    if (catMeowingBuffer !== null) {
       var src = context.createBufferSource();
       src.buffer = catMeowingBuffer
       src.connect(context.destination);
       src.start(0);
    }
}