Timing issues with playback of the HTML5 Audio API

Posted by pat on Stack Overflow See other posts from Stack Overflow or by pat
Published on 2011-11-22T01:45:09Z Indexed on 2011/11/22 1:51 UTC
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I'm using the following code to try to play a sound clip with the HTML5 Audio API:

HTMLAudioElement.prototype.playClip  = function(startTime, stopTime) { 
  this.stopTime = stopTime;
  this.currentTime = startTime;
  this.play();
  $(this).bind('timeupdate', function(){
    if (this.ended || this.currentTime >= stopTime) {
      this.pause();
      $(this).unbind('timeupdate');
    }
  });

}

I utilize this new playClip method as follows. First I have a link with some data attributes:

<a href=# data-stop=1.051 data-start=0.000>And then I was thinking,</a>

And finally this bit of jQuery which runs on $(document).ready to hook up a click on the link with the playback: $('a').click(function(ev){

  $('a').click(function(ev){

    var start = $(this).data('start'),
        stop = $(this).data('stop'),
        audio = $('audio').get(0),
        $audio = $(audio);

    ev.preventDefault();

    audio.playClip(start,stop);


  })

This approach seems to work, but there's a frustrating bug: sometimes, the playback of a given clip plays beyond the correct data-stop time.

I suspect it could have something to do with the timing of the timeupdate event, but I'm no JS guru and I don't know how to begin debugging the problem. Here are a few clues I've gathered:

  • The same behavior appears to come up in both FF and Chrome.
  • The playback of a given clip actually seems to vary a bit -- if I play the same clip a couple times in a row, it may over-play a different amount of time on each playing.

Is the problem here the inherent accuracy of the Audio API? My app needs milliseconds.

Is there a problem with the way I'm using jQuery to bind and unbind the timeupdate event? I tried using the jQuery-less approach with addEventListener but I couldn't get it to work.

Thanks in advance, I would really love to know what's going wrong.

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