m4a.js

function getData(url){
  return new Promise((resolve, reject) => {
    console.log("download " + url);
    var req = new XMLHttpRequest({mozSystem: true});
    req.open("GET", url, true);
    req.overrideMimeType("audio/mp4");
    req.responseType = "blob";
    req.onload = () => {
      console.log("downloaded");
      resolve(req.response);
    };
    req.onerror = error => {
      console.log("error");
      reject(error);
    };
    req.onprogress = event =>{
      console.log(event.loaded + "/" + event.total);
    };
    req.send();
  });
}

window.addEventListener("load", function() {
  console.log("Hello World!");
  var player = document.querySelector("audio");

  getData("URL of m4a file").then(buffer =>{
    player.src = window.URL.createObjectURL(buffer);
    player.play();
  }, error => { console.log(error); });

});