web-audio-engine


> Pure JS implementation of the Web Audio API

Installation

``
npm install --save web-audio-engine
`

##### download
- web-audio-engine.js

API


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

$3

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
:construction_worker: _TODO: WRITE DESCRIPTION_

`js
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);
`

$3


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_

`js
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));
});
`

$3

:construction_worker: _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_

`html


`

$3


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

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

// composeWith(context);

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

$3

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

$3


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

`js
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);
});
`

$3


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

`js
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

`js
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.

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

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.

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

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