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

Dart in 2016: The fastest growing programming language at Google, 2nd fastest growing in TIOBE Index

Dart was the fastest growing programming language at Google in 2016 with millions of lines of code written. It also made it to TIOBE Index Top 20 this month (see TIOBE's methodology).

It takes time to build something as ambitious as Dart and, in some ways, Dart is still in its infancy. But we're glad the hard work is starting to pay off.

Many thanks to our amazing community!

We're going to celebrate by ... releasing 1.22 next week (as per our usual 6 week release schedule).

The new Google AdSense user interface: built with AngularDart

AdSense is a free, simple way to earn money by placing ads on your website. The team just launched a completely new version of their app for publishers. Read all about it here. We asked Daniel White, the tech lead for the project, some questions because the new UI happens to be built with Dart and Angular2.


AdSense launched way back in 2003. How long is it since the last big redesign?
Last big redesign was called ‘AdSense 3’ and launched about 6 years ago. It was written in Google Web Toolkit (GWT) and the UI has evolved through several iterations - but this is the first ground-up redesign in 6 years. There are a number of long-standing UX issues that we’ve taken the opportunity to solve. A big shout-out to our UX team who’ve been 100% behind this project. We couldn’t have done it without them!

How many software engineers worked on the project?
Purely on the AdSense applications, we have a team of close to 100. Around 25% of them write Dart.

How many lines of code?
We have around 160K LO…

A stronger Dart for everyone

We are constantly asking ourselves:
How do we make developers even more productive when writing Dart apps? We believe that a critical part of the answer to this question is to make strongmode – a sound static type system for Dart – the standard for all Dart developers.

Teams that use Dart to build apps like Soundtrap, AdWords, AdSense, and Greentea say they really enjoy using strong mode features, such as early error detection. In fact, teams that have switched completely to strong mode cite not only early error detection but also better code readability and maintainability as major benefits. We hear this both from small teams and Рeven more so Рfrom large teams with hundreds of developers writing and maintaining millions of lines of Dart code. As Björn Sperber from Soundtrap says,
Strong mode and the smooth integration with IntelliJ is a joy to use and a huge improvement. If you’ve tried out Flutter, you’ve already used strong mode checks from the Dart analyzer.

Given the benefits …