Pure JS implementation of the Web Audio API

Fork of mohayonao/web-audio-engine with following changes:

• Use TypeScript and fix some types (#5)
  • Remove BaseAudioContext.suspend() (#6)
• Add new RawDataAudioContext (#5)
• Add support for DynamicsCompressorNode (#1)
• Bug fixes
  • Fixes for BiquadFilterNode and DelayNode (#8)
  • Fix WAVE file decoding (#5)
  • Fix AudioNode.disconnect(x) not disconnecting (#7)

npm install --save web-audio-engine

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

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

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

:constructionworker: _TODO: WRITE DESCRIPTION

import { StreamAudioContext as AudioContext } from 'web-audio-engine';
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);

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

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

Executes rendering process until the provided time.

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

Exports the rendered data as AudioData format.

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

import fs from 'fs';
import { RenderingAudioContext as AudioContext } from 'web-audio-engine';
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));
});

RawDataAudioContext allows you to synchronously step through an AudioContext. This is useful for streaming output at and controlling the rate

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

Renders the next blockSize samples of audio into channelData.

import { RawDataAudioContext } from 'web-audio-engine';
const context = new RawDataAudioContext();
const { blockSize } = context;
const channelData = [
  new Float32Array(blockSize),
  new Float32Array(blockSize),
];

for (let i = 0; i < 100_000; i += blockSize)
  context.process(channelData);
  // Do something with channeLData
}

:constructionworker: _TODO: WRITE DESCRIPTION

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>

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

import { OfflineAudioContext } from 'web-audio-engine';
const context = new OfflineAudioContext(2, 44100 * 10, 44100);

// composeWith(context);

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

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

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.

Returns the function for decoding currently set.

Sets the function for decoding.

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

Executes decoding.

• audioData: ArrayBuffer

import wae from 'web-audio-engine';
import mp3decoder from '/path/to/mp3decoder';
import fs from 'fs';
wae.decoder.set('mp3', mp3decoder);
const AudioContext = wae.RenderingAudioContext;
const context = new AudioContext();
const audioData = fs.readFileSync('amen.mp3');

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

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.

Returns the function for encoding currently set.

Sets the function for encoding.

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

Executes encoding.

• audioData: AudioData
• opts.type: string audio format type - default: "wav"

import wae from 'web-audio-engine';
import mp3encoder from '/path/to/mp3encoder';
import fs from 'fs';
wae.encoder.set('mp3', mp3encoder);
const AudioContext = wae.RenderingAudioContext;
const context = new AudioContext();
const audioData = context.exportAsAudioData();

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

• AnalyserNode
• AudioBuffer
• AudioBufferSourceNode
• AudioContext
• AudioDestinationNode
• AudioNode
• AudioParam
• BiquadFilterNode (audio rate parameter is not supported)
• ChannelMergerNode
• ChannelSplitterNode
• DelayNode (noisy..)
• DynamicsCompressorNode
• 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

import Speaker from 'speaker';
import { StreamAudioContext as AudioContext } from 'web-audio-engine';
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();

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

• https://mohayonao.github.io/web-audio-engine/demo/

$ git clone [email protected]: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

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

• https://mohayonao.github.io/web-audio-engine/benchmark/

$ git clone [email protected]:mohayonao/web-audio-engine.git
$ cd web-audio-engine
$ npm install && npm run build
$ cd benchmark
$ npm install
$ node .

MIT