利用 HTML5 的 audio 元件測得 audio 檔案的秒數

var audio = document.createElement("audio");
document.querySelector("input").addEventListener( "change", function( event ){
  var file = event.target.files[0];     
  var fileURL = URL.createObjectURL(file);
  audio.addEventListener("loadedmetadata", function(){
    alert( audio.duration + " sec" );   
  });                     
  audio.src = fileURL;    
});