Skip to main content

Web Audio API and Dart

Posted by Seth Ladd

UPDATE: 2012/05/12 - remove dart:dom and use dart:html

It's possible to use Frog to compile Dart code that uses Web Audio API. This means Dart can now access a high performance, positional, low latency audio.

The following example code loads up a MP3 over XHR and controls the volume through a slider.


#import('dart:html');


main() {
  AudioContext audioContext = new AudioContext();
  AudioGainNode gainNode = audioContext.createGainNode();


  XMLHttpRequest xhr = new XMLHttpRequest();
  xhr.open("GET", "button-3.mp3", true);
  xhr.responseType = "arraybuffer";
  xhr.on.load.add((e) {


    // asynchronous decoding
    audioContext.decodeAudioData(xhr.response, (buffer) {
      playSound() {
        AudioBufferSourceNode source = audioContext.createBufferSource();
        source.connect(gainNode, 0, 0);
        gainNode.connect(audioContext.destination, 0, 0);
        source.buffer = buffer;
        source.noteOn(0);
      }


      var button = document.query("#play");
      button.disabled = false;
      button.on.click.add((_) {
        playSound();
      });
    }, (error) {
      print('Error decoding MP3 file');
    });


  });  


  xhr.send();


  document.query("#volume").on.change.add((e) {
    var volume = Math.parseInt(e.target.value);
    var max = Math.parseInt(e.target.max);
    var fraction = volume / max;
    gainNode.gain.value = fraction * fraction;
  });


}



Here's the simple HTML page:


<!DOCTYPE html>


<html>
  <head>
    <meta charset="utf-8">
    <title>Hello World</title>
  </head>


  <body>
    <h1>Hello World!</h1>
    <button id="play" disabled>Play</button>
    <label for="volume">Volume: <input type="range" min="0" max="100" id="volume" value="100"></label>
<script type="application/dart" src="app.dart"></script>
    <script src="http://dart.googlecode.com/svn/branches/bleeding_edge/dart/client/dart.js"></script>
  </body>
</html>


NOTE: Dartium, like Chromium, does not play MP3 files. Use an OGG or WAV file with the above sample in Dartium.

To learn more about Web Audio API, I can recommend Getting Started with Web Audio API.

This fix is only in bleeding_edge, so you'll have to compile the project but it will show up in an SDK build very soon. Please do give it a try and let us know how it works.

Enjoy!

Popular posts from this blog

AngularDart 4

AngularDart v4 is now available. We've been busy since the release angular2 v3.1.0 in May. Not only did we "drop the 2", but we also improved the compiler and tightened up the framework to give you smaller code, we updated the package structure to improve usability, and we added several new features. Check out the updated documentation to get started.
Just angular Upgrading to v4 will require more than updating your version constraint. The package has changed names (back) to angular – dropping the 2. You'll need to update your pubspec.yaml and the corresponding imports in your code. In most instances, find-and-replace should do the trick. Going forward, the package will be called package:angular. We'll just update the version number.
Smaller code The updated compiler in 4.0 allows type-based optimizations that not only improve runtime performance but generate better code because we are able to strongly type templates. A big result of the update is that many ap…

The new AdWords UI uses Dart — we asked why

Google just announced a re-designed AdWords experience. In case you’re not familiar with AdWords: businesses use it to advertise on google.com and partner websites. Advertising makes up majority of Google’s revenue, so when Google decides to completely redo the customer-facing front end to it, it’s a big deal. The Dart team is proud to say that this new front end is built with Dart and Angular 2. Whenever you asked us whether Google is ‘even using Dart for anything,’ this is what we had in mind but couldn’t say aloud. Until now. We asked Joshy Joseph, the primary technical lead on the project, some questions. Joshy is focusing on things like infrastructure, application latency and development velocity, so he’s the right person to ask about Dart.Q: What exactly did we launch on Monday?It’s a complete redesign of the AdWords customer experience that is rolling out slowly as a test to a small initial set of advertisers. The most noticeable thing is probably the Material Design look and f…

Const, Static, Final, Oh my!

Posted by Seth Ladd

(This is an "oldie but a goodie" misc@dartlang.org post originally written by Bob Nystrom. It is being posted here as the explanations still ring true.)

Bob writes:


"static", "final", and "const" mean entirely distinct things in Dart:

"static" means a member is available on the class itself instead of on instances of the class. That's all it means, and it isn't used for anything else. static modifies *members*.

"final" means single-assignment: a final variable or field *must* have an initializer. Once assigned a value, a final variable's value cannot be changed. final modifies *variables*.

"const" has a meaning that's a bit more complex and subtle in Dart. const modifies *values*. You can use it when creating collections, like const [1, 2, 3], and when constructing objects (instead of new) like const Point(2, 3). Here, const means that the object's entire deep state can be determ…