html - Sound effects in JavaScript / HTML5

Question

I'm using HTML5 to program games; the obstacle I've run into now is how to play sound effects.

The specific requirements are few in number:

• Play and mix multiple sounds,
• Play the same sample multiple times, possibly overlapping playbacks,
• Interrupt playback of a sample at any point,
• Preferably play WAV files containing (low quality) raw PCM, but I can convert these, of course.

My first approach was to use the HTML5 <audio> element and define all sound effects in my page. Firefox plays the WAV files just peachy, but calling #play multiple times doesn't really play the sample multiple times. From my understanding of the HTML5 spec, the <audio> element also tracks playback state, so that explains why.

My immediate thought was to clone the audio elements, so I created the following tiny JavaScript library to do that for me (depends on jQuery):

var Snd = {
  init: function() {
    $("audio").each(function() {
      var src = this.getAttribute('src');
      if (src.substring(0, 4) !== "snd/") { return; }
      // Cut out the basename (strip directory and extension)
      var name = src.substring(4, src.length - 4);
      // Create the helper function, which clones the audio object and plays it
      var Constructor = function() {};
      Constructor.prototype = this;
      Snd[name] = function() {
        var clone = new Constructor();
        clone.play();
        // Return the cloned element, so the caller can interrupt the sound effect
        return clone;
      };
    });
  }
};

So now I can do Snd.boom(); from the Firebug console and play snd/boom.wav, but I still can't play the same sample multiple times. It seems that the <audio> element is really more of a streaming feature rather than something to play sound effects with.

Is there a clever way to make this happen that I'm missing, preferably using only HTML5 and JavaScript?

I should also mention that, my test environment is Firefox 3.5 on Ubuntu 9.10. The other browsers I've tried - Opera, Midori, Chromium, Epiphany - produced varying results. Some don't play anything, and some throw exceptions.

Answer 1

HTML5 Audio objects

You don't need to bother with <audio> elements. HTML 5 lets you access Audio objects directly:

var snd = new Audio("file.wav"); // buffers automatically when created
snd.play();

There's no support for mixing in current version of the spec.

To play same sound multiple times, create multiple instances of the Audio object. You could also set snd.currentTime=0 on the object after it finishes playing.

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Since the JS constructor doesn't support fallback <source> elements, you should use

(new Audio()).canPlayType("audio/ogg; codecs=vorbis")

to test whether the browser supports Ogg Vorbis.

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If you're writing a game or a music app (more than just a player), you'll want to use more advanced Web Audio API, which is now supported by most browsers.