Pure JS implementation of the Web Audio API
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README.md

web-audio-engine

Build Status NPM Version License

Pure JS implementation of the Web Audio API

Installation

npm install --save web-audio-engine
download

API

web-audio-engine provides some AudioContext class for each use-case: audio playback, rendering and simulation.

Class: StreamAudioContext

StreamAudioContext writes raw PCM audio data to a writable node stream. It can be used to playback audio in realtime.

new StreamAudioContext(opts?: object)

Creates new StreamAudioContext instance.

  • opts.sampleRate: number audio sample rate (in Hz) - default: 44100
  • opts.numberOfChannels: number audio channels (e.g. 2: stereo) - default: 2
  • opts.blockSize: number samples each rendering quantum - default: 128
  • opts.bitDepth: number bits per sample - default: 16
  • opts.float: boolean use floating-point values - default: false
context.pipe(destination: stream.Writable): stream.Writable

👷 TODO: WRITE DESCRIPTION

const AudioContext = require("web-audio-engine").StreamAudioContext;
const context = new AudioContext();

// Set the output for audio streaming
context.pipe(process.stdout);

// If you want to playback sound directly in this process, you can use 'node-speaker'.
// const Speaker = require("speaker");
// context.pipe(new Speaker());

// Start to render audio
context.resume();

// composeWith(context);

Class: RenderingAudioContext

RenderingAudioContext records audio data with stepwise processing. It is used to export to a wav file or test a web audio application.

new RenderingAudioContext(opts?: object)

Creates new RenderingAudioContext instance.

  • opts.sampleRate: number audio sample rate (in Hz) - default: 44100
  • opts.numberOfChannels: number audio channels (e.g. 2: stereo) - default: 2
  • opts.blockSize: number samples each rendering quantum - default: 128
context.processTo(time: number|string)

Executes rendering process until the provided time.

  • time: e.g. 10 (10 seconds), "01:30.500" (convert to 90.5 seconds)
context.exportAsAudioData(): AudioData

Exports the rendered data as AudioData format.

context.encodeAudioData(audioData: AudioData, opts?:object): Promise< ArrayBuffer >

Encode audio data to the binary format.

  • audioData: AudioData
  • opts.bitDepth: number bits per sample - default: 16
  • opts.float: boolean use floating-point values - default: false
const fs = require("fs");
const AudioContext = require("web-audio-engine").RenderingAudioContext;
const context = new AudioContext();

// composeWith(context);

context.processTo("00:01:30.000");
// context.currentTime -> 90.00054421768708

context.processTo("00:02:00.000");
// context.currentTime -> 120.00072562358277

const audioData = context.exportAsAudioData();

context.encodeAudioData(audioData).then((arrayBuffer) => {
  fs.writeFile("output.wav", new Buffer(arrayBuffer));
});

Class: WebAudioContext

👷 TODO: WRITE DESCRIPTION

new WebAudioContext(opts?: object)

Creates new WebAudioContext instance.

  • opts.context?: AudioContext the native Web Audio API AudioContext instance
  • opts.destination?: AudioNode - default: opts.context.destination
  • opts.numberOfChannels: number audio channels (e.g. 2: stereo) - default: 2
  • opts.blockSize: number samples each rendering quantum - default: 128
<script src="/path/to/web-audio-engine.js"></script>
<script>
var context = new WebAudioEngine.WebAudioContext({ context: new AudioContext() });

// composeWith(context);

context.resume();
</script>

Class: OfflineAudioContext

This context is compatible with the natvie Web Audio API OfflineAudioContext.

const OfflineAudioContext = require("web-audio-engine").OfflineAudioContext;
const context = new OfflineAudioContext(2, 44100 * 10, 44100);

// composeWith(context);

context.startRendering().then((audioBuffer) => {
  console.log(audioBuffer);
});

Interface: AudioData

interface AudioData {
  numberOfChannels?: number;
  length?: number;
  sampleRate: number;
  channelData: Float32Array[];
}

decoder

The default decoder of web-audio-engine supports "wav" format only. If you need to support other audio format, you are necessary to prepare a decoder yourself.

decoder.get(type: string): function

Returns the function for decoding currently set.

decoder.set(type: string, decodeFn: function)

Sets the function for decoding.

  • decodeFn: (audioData: ArrayBuffer, opts?: object) => Promise< AudioData > The decoding to use.
decoder.decode(audioData: ArrayBuffer, opts?: object): Promise< AudioData >

Executes decoding.

  • audioData: ArrayBuffer
mp3 decoder example
const wae = require("web-audio-engine");
const mp3decoder = require("/path/to/mp3decoder");

wae.decoder.set("mp3", mp3decoder);

const fs = require("fs");
const AudioContext = require("web-audio-engine").RenderingAudioContext;
const context = new AudioContext();
const audioData = fs.readFileSync("amen.mp3");

context.decodeAudioData(audioData).then((audioBuffer) => {
  console.log(audioBuffer);
});

encoder

The default encoder of web-audio-engine supports "wav" format only. If you need to support other audio format, you are necessary to prepare an encoder yourself.

encoder.get(type: string): function

Returns the function for encoding currently set.

encoder.set(type: string, encodeFn: function)

Sets the function for encoding.

  • encodeFn: (audioData: AudioData, opts?: object) => Promise< ArrayBuffer > The encoding to use.
encoder.encode(audioData: AudioData, opts?: object): Promise< ArrayBuffer >

Executes encoding.

  • audioData: AudioData
  • opts.type: string audio format type - default: "wav"
mp3 encoder example
const wae = require("web-audio-engine");
const mp3encoder = require("/path/to/mp3encoder");

wae.encoder.set("mp3", mp3encoder);

const fs = require("fs");
const AudioContext = require("web-audio-engine").RenderingAudioContext;
const context = new AudioContext();
const audioData = context.exportAsAudioData();

context.encodeAudioData(audioData, { type: "mp3" }).then((arrayBuffer) => {
  fs.writeFile("output.mp3", new Buffer(arrayBuffer));
});

Implemented API

  • AnalyserNode
  • AudioBuffer
  • AudioBufferSourceNode
  • AudioContext
  • AudioDestinationNode
  • AudioNode
  • AudioParam
  • BiquadFilterNode (audio rate parameter is not supported)
  • ChannelMergerNode
  • ChannelSplitterNode
  • DelayNode (noisy..)
  • GainNode
  • IIRFIlterNode
  • OscillatorNode (use wave-table synthesis, not use periodic wave)
  • PeriodicWave
  • ScriptProcessorNode
  • StereoPannerNode
  • WaveShaperNode
  • The other not implemented nodes will pass its input to its output without modification.
  • See: Comparison Chart of implemented nodes

Example

const Speaker = require("speaker");
const AudioContext = require("web-audio-engine").StreamAudioContext;
const context = new AudioContext();

const osc = context.createOscillator();
const amp = context.createGain();

osc.type = "square";
osc.frequency.setValueAtTime(987.7666, 0);
osc.frequency.setValueAtTime(1318.5102, 0.075);
osc.start(0);
osc.stop(2);
osc.connect(amp);
osc.onended = () => {
  context.close().then(() => {
    process.exit(0);
  });
};

amp.gain.setValueAtTime(0.25, 0);
amp.gain.setValueAtTime(0.25, 0.075);
amp.gain.linearRampToValueAtTime(0, 2);
amp.connect(context.destination);

context.pipe(new Speaker());
context.resume();

Online Demo

The online demo is here. In this site, you can compare web-audio-engine and the native Web Audio API.

Offline Demo

$ git clone git@github.com:mohayonao/web-audio-engine.git
$ cd web-audio-engine
$ npm install && npm run build
$ cd demo
$ npm install
$ node demo --help

Simplest play demo with node-speaker.

$ node demo sines

Rendering and export to the wav file.

$ node demo -o out.wav sines

Online Benchmark

Currently, this benchmark doesn't work in Chrome or Safari, please use Firefox.

Offline Benchmark

$ git clone git@github.com:mohayonao/web-audio-engine.git
$ cd web-audio-engine
$ npm install && npm run build
$ cd benchmark
$ npm install
$ node .

License

MIT