web-audio-api

Node Web Audio API

This library implements the web audio API specification on node.js.

And this is not even alpha. Use this library only if you're the adventurous kind.

What's implemented

• AudioContext(partially)
• AudioParam (almost there)
• AudioBufferSourceNode
• ScriptProcessorNode
• GainNode

Overall view of implementation

Each time you create an AudioNode (like for instance an AudioBufferSourceNode or a GainNode), it inherits from DspObject which is in charge of two things:

• register schedule events with _schedule
• compute the appropriate digital signal processing with _tick

Each time you connect an AudioNode using source.connect(destination, output, input) it connects the relevant AudioOutput instances of source node the the relevant AudioInput instance of the destination node.

To instantiate all of these AudioNode, you needed an overall AudioContext instance. This latter has a destination property (where the sound will flow out), instance of AudioDestinationNode, which inherits from AudioNode. The AudioContext instance keeps track of connections to the destination. When that happens, it triggers the audio loop, calling _tick infinitely on the destination, which will itself call _tick on its input ... and so forth go up on the whole audio graph.

What's left to do

Most of the AudioNodes ... Most of many other things ... :(

Installation

npm install web-audio-api

Demo

Get ready, this is going to blow up your mind :

npm install
gulp default
node test/manual-testing/AudioContext-sound-output.js

Streaming audio

AudioContext just writes PCM data to a node writable stream. The default stream is a stream created with Speaker, which plays the audio back to your soundcard. But you can use any writable stream, file, including the stdin of a child process.

For example, here is an example for streaming audio to an icecast server, using ices :

var spawn = require('child_process').spawn
  , AudioContext = require('web-audio-api').AudioContext
  , context = new AudioContext()

var ices = spawn('ices', ['ices.xml'])
context.outStream = ices.stdin

Cool huh?

Using Gibber

Gibber is a great audiovisual live coding environment for the browser made by Charlie Roberts. For audio, it uses Web Audio API, so you can run it on node-web-audio-api. First install gibber with npm :

npm install gibber.audio.lib

Then to you can run the following test to see that everything works:

npm test gibber.audio.lib

Extensions

Wow! The whole thing is not even half-done that there's already some extensions for it! See the list in the wiki.

Running the debugger

Right now everything runs in one process, so if you set a break point in your code, there's going to be a lot of buffer underflows, and you won't be able to debug anything.

One trick is to kill the AudioContext right before the break point, like this:

context._kill()
debugger

that way the audio loop is stopped, and you can inspect your objects in peace.

Running the tests

Tests are written with mocha. To run them, install mocha with :

npm install -g mocha

And in the root folder run :

npm test

Manual testing

To test the sound output :

npm install
gulp default
node test/manual-testing/AudioContext-sound-output.js

To test AudioParam against AudioParam implemented in a browser, open test/manual-testing/AudioParam-browser-plots.html in that browser.

Contributors

    61	Sébastien Piquemal
    16	ouhouhsami
     4	John Wnek
     2	anprogrammer
     1	Andrew Petersen

Changelog

0.2.0

• refactored to ES6

0.1.5

• AudioNode and AudioContext bug fixes

0.1.4

• audioports : bug fixes

0.1.3

• audioports : implemented channelInterpretation 'speakers'
• AudioContext : added support for mp3 to decodeAudioData

0.1.2

• AudioBufferSourceNode : handler onended implemented
• AudioContext : method decodeAudioData, support only for wav

0.1.1

• ScriptProcessorNode

• AudioBufferSourceNode

  • node is killed once it has finished playing
  • subsequent calls to start have no effect

• AudioContext : method collectNodes

• audioports : bug fixes

0.1.0

• AudioContext (partial implementation)
• AudioParam (missing unschedule)
• AudioBufferSourceNode (missing onended)
• GainNode

Changelog

0.2.0

• refactored to ES6