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https://github.com/chrisguttandin/standardized-audio-context

A cross-browser wrapper for the Web Audio API which aims to closely follow the standard.
https://github.com/chrisguttandin/standardized-audio-context

audio audio-worklet browser polyfill web-audio

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A cross-browser wrapper for the Web Audio API which aims to closely follow the standard.

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# standardized-audio-context



**A cross-browser wrapper for the Web Audio API which aims to closely follow the standard.**



[![version](https://img.shields.io/npm/v/standardized-audio-context.svg?style=flat-square)](https://www.npmjs.com/package/standardized-audio-context)



This package provides a subset (although it's almost complete) of the [Web Audio API](https://webaudio.github.io/web-audio-api) which works in a reliable and consistent way in every supported browser. In contrast to other popular polyfills `standardized-audio-context` does not patch or modify anything on the global scope. In other words, it does not cause any side effects. It can therefore be used safely inside of libraries. It's what's known as a [ponyfill](https://github.com/sindresorhus/ponyfill).



One of the goals of `standardized-audio-context` is to only implement missing functionality and to

avoid rewriting built-in features whenever possible. Please take a look at the paragraph about the

[browser support](#browser-support) below for more information.



There are some things which cannot be faked in a way that makes them as performant as they could be when implemented natively. The most prominent amongst those things is the [`AudioWorklet`](https://webaudio.github.io/web-audio-api/#audioworklet). Please have a look at the [list of all supported methods](https://github.com/chrisguttandin/standardized-audio-context#api) below for more detailed information.



## Usage



The `standardized-audio-context` is available on

[npm](https://www.npmjs.com/package/standardized-audio-context) and can be installed as usual.



```shell

npm install standardized-audio-context

```



You can then import the `AudioContext` and `OfflineAudioContext` like this:



```js

import { AudioContext, OfflineAudioContext } from 'standardized-audio-context';

```



It is also possible to load `standardized-audio-context` with a service like [jspm](https://jspm.org). The import statement from above would then need to be changed to point to a URL.



```js

import { AudioContext, OfflineAudioContext } from 'https://jspm.dev/standardized-audio-context';

```



Once the `AudioContext` and/or `OfflineAudioContext` are imported they can be used in the same way as their native counterparts. The following snippet will for example produce a nice and clean (as well as annoying) sine wave.



```js

import { AudioContext } from 'standardized-audio-context';



const audioContext = new AudioContext();

const oscillatorNode = audioContext.createOscillator();



oscillatorNode.connect(audioContext.destination);



oscillatorNode.start();

```



An alternative approach would be to use the AudioNode constructors (the OscillatorNode constructor in this case) instead of the factory methods.



```js

import { AudioContext, OscillatorNode } from 'standardized-audio-context';



const audioContext = new AudioContext();

const oscillatorNode = new OscillatorNode(audioContext);



oscillatorNode.connect(audioContext.destination);



oscillatorNode.start();

```



## API



### AudioContext



This is an almost complete implementation of the [`AudioContext`](https://webaudio.github.io/web-audio-api/#audiocontext) interface. It only misses the `createScriptProcessor()` method which is deprecated anyway.



The AudioContext implements the following TypeScript interface.



```typescript

interface IAudioContext extends EventTarget {

    readonly audioWorklet?: IAudioWorklet;

    readonly baseLatency: number;

    readonly currentTime: number;

    readonly destination: IAudioDestinationNode;

    readonly listener: IAudioListener;

    onstatechange: null | TEventHandler;

    readonly sampleRate: number;

    readonly state: TAudioContextState;

    close(): Promise;

    createAnalyser(): IAnalyserNode;

    createBiquadFilter(): IBiquadFilterNode;

    createBuffer(numberOfChannels: number, length: number, sampleRate: number): IAudioBuffer;

    createBufferSource(): IAudioBufferSourceNode;

    createChannelMerger(numberOfInputs?: number): IAudioNode;

    createChannelSplitter(numberOfOutputs?: number): IAudioNode;

    createConstantSource(): IConstantSourceNode;

    createConvolver(): IConvolverNode;

    createDelay(maxDelayTime?: number): IDelayNode;

    createDynamicsCompressor(): IDynamicsCompressorNode;

    createGain(): IGainNode;

    createIIRFilter(feedforward: number[], feedback: number[]): IIIRFilterNode;

    createMediaElementSource(mediaElement: HTMLMediaElement): IMediaElementAudioSourceNode;

    createMediaStreamDestination(): IMediaElementAudioDestinationNode;

    createMediaStreamSource(mediaStream: MediaStream): IMediaStreamAudioSourceNode;

    createMediaStreamTrackSource(mediaStreamTrack: MediaStreamTrack): IMediaStreamTrackAudioSourceNode;

    createOscillator(): IOscillatorNode;

    createPanner(): IPannerNode;

    createPeriodicWave(real: number[], imag: number[], constraints?: Partial): IPeriodicWave;

    createStereoPanner(): IStereoPannerNode;

    createWaveShaper(): IWaveShaperNode;

    decodeAudioData(

        audioData: ArrayBuffer,

        successCallback?: TDecodeSuccessCallback,

        errorCallback?: TDecodeErrorCallback

    ): Promise;

    resume(): Promise;

    suspend(): Promise;

}

```



The properties and methods are described in greater detail below.



### OfflineAudioContext



This is an almost complete implementation of the [`OfflineAudioContext`](https://webaudio.github.io/web-audio-api/#offlineaudiocontext) interface. It only misses the `createScriptProcessor()` method which is deprecated anyway.



It implements the following TypeScript interface.



```typescript

interface IOfflineAudioContext extends EventTarget {

    readonly audioWorklet?: IAudioWorklet;

    readonly baseLatency: number;

    readonly currentTime: number;

    readonly destination: IAudioDestinationNode;

    readonly length: number;

    readonly listener: IAudioListener;

    onstatechange: null | TEventHandler;

    readonly sampleRate: number;

    readonly state: TAudioContextState;

    createAnalyser(): IAnalyserNode;

    createBiquadFilter(): IBiquadFilterNode;

    createBuffer(numberOfChannels: number, length: number, sampleRate: number): IAudioBuffer;

    createBufferSource(): IAudioBufferSourceNode;

    createChannelMerger(numberOfInputs?: number): IAudioNode;

    createChannelSplitter(numberOfOutputs?: number): IAudioNode;

    createConstantSource(): IConstantSourceNode;

    createConvolver(): IConvolverNode;

    createDelay(maxDelayTime?: number): IDelayNode;

    createDynamicsCompressor(): IDynamicsCompressorNode;

    createGain(): IGainNode;

    createIIRFilter(feedforward: number[], feedback: number[]): IIIRFilterNode;

    createOscillator(): IOscillatorNode;

    createPanner(): IPannerNode;

    createPeriodicWave(real: number[], imag: number[], constraints?: Partial): IPeriodicWave;

    createStereoPanner(): IStereoPannerNode;

    createWaveShaper(): IWaveShaperNode;

    decodeAudioData(

        audioData: ArrayBuffer,

        successCallback?: TDecodeSuccessCallback,

        errorCallback?: TDecodeErrorCallback

    ): Promise;

    startRendering(): Promise;

}

```



The properties and methods are described in greater detail below.



#### audioWorklet



The [`audioworklet`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-audioworklet) property is only available in a [`SecureContext`](https://webidl.spec.whatwg.org/#SecureContext).



#### listener



⚠️  Firefox and Safari up to version 14.0.1 do not support modifying the listener via AudioParams. Therefore calling any of the scheduling functions on the AudioParams of a listener of an OfflineAudioContext throws a `NotSupportedError`.



#### createAnalyser() / AnalyserNode



This is an implementation of the [`createAnalyser()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createanalyser) factory method. The [`AnalyserNode`](https://webaudio.github.io/web-audio-api/#analysernode) constructor may be used as an alternative.



#### createBiquadFilter() / BiquadFilterNode



This is an implementation of the [`createBiquadFilter()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createbiquadfilter) factory method. The [`BiquadFilterNode`](https://webaudio.github.io/web-audio-api/#biquadfilternode) constructor may be used as an alternative.



#### createBuffer() / AudioBuffer



This is an implementation of the [`createBuffer()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createbuffer) factory method. The [`AudioBuffer`](https://webaudio.github.io/web-audio-api/#audiobuffer) constructor may be used as an alternative.



#### createBufferSource() / AudioBufferSourceNode



This is an implementation of the [`createBufferSource()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createbuffersource) factory method. The [`AudioBufferSourceNode`](https://webaudio.github.io/web-audio-api/#AudioBufferSourceNode) constructor may be used as an alternative.



#### createChannelMerger() / ChannelMergerNode



This is an implementation of the [`createChannelMerger()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createchannelmerger) factory method. The [`ChannelMergerNode`](https://webaudio.github.io/web-audio-api/#channelmergernode) constructor may be used as an alternative.



#### createChannelSplitter() / ChannelSplitterNode



This is an implementation of the [`createChannelSplitter()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createchannelsplitter) factory method. The [`ChannelSplitterNode`](https://webaudio.github.io/web-audio-api/#channelsplitternode) constructor may be used as an alternative.



#### createConstantSource() / ConstantSourceNode



This is an implementation of the [`createConstantSource()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createconstantsource) factory method. The [`ConstantSourceNode`](https://webaudio.github.io/web-audio-api/#ConstantSourceNode) constructor may be used as an alternative.



#### createConvolver() / ConvolverNode



This is an implementation of the [`createConvolver()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createconvolver) factory method. The [`ConvolverNode`](https://webaudio.github.io/web-audio-api/#ConvolverNode) constructor may be used as an alternative.



#### createDelay() / DelayNode



This is an implementation of the [`createDelay()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createdelay) factory method. The [`DelayNode`](https://webaudio.github.io/web-audio-api/#DelayNode) constructor may be used as an alternative.



⚠️  The [delayTime AudioParam](https://webaudio.github.io/web-audio-api/#dom-delaynode-delaytime) can't be set to very small values in any browser except Firefox.



#### createDynamicsCompressor() / DynamicsCompressorNode



This is an implementation of the [`createDynamicsCompressor()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createdynamicscompressor) factory method. The [`DynamicsCompressorNode`](https://webaudio.github.io/web-audio-api/#dynamicscompressornode) constructor may be used as an alternative.



#### createGain() / GainNode



This is an implementation of the [`createGain()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-creategain) factory method. The [`GainNode`](https://webaudio.github.io/web-audio-api/#gainnode) constructor may be used as an alternative.



#### createIIRFilter() / IIRFilterNode



This is an implementation of the [`createIIRFilter()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createiirfilter) factory method. The [`IIRFilterNode`](https://webaudio.github.io/web-audio-api/#iirfilternode) constructor may be used as an alternative.



#### createMediaElementSource() / MediaElementAudioSourceNode



This is an implementation of the [`createMediaElementSource()`](https://webaudio.github.io/web-audio-api/#dom-audiocontext-createmediaelementsource) factory method. The [`MediaElementAudioSourceNode`](https://webaudio.github.io/web-audio-api/#mediaelementaudiosourcenode) constructor may be used as an alternative.



It does only work with an AudioContext but not with an OfflineAudioContext.



#### createMediaStreamDestination() / MediaStreamAudioDestinationNode



This is an implementation of the [`createMediaStreamDestination()`](https://webaudio.github.io/web-audio-api/#dom-audiocontext-createmediastreamdestination) factory method. The [`MediaStreamAudioDestinationNode`](https://webaudio.github.io/web-audio-api/#mediastreamaudiodestinationnode) constructor may be used as an alternative.



It does only work with an AudioContext but not with an OfflineAudioContext.



#### createMediaStreamSource() / MediaStreamAudioSourceNode



This is an implementation of the [`createMediaStreamSource()`](https://webaudio.github.io/web-audio-api/#dom-audiocontext-createmediastreamsource) factory method. The [`MediaStreamAudioSourceNode`](https://webaudio.github.io/web-audio-api/#mediastreamaudiosourcenode) constructor may be used as an alternative.



It does only work with an AudioContext but not with an OfflineAudioContext.



#### createMediaStreamTrackSource() / MediaStreamTrackAudioSourceNode



This is an implementation of the [`createMediaStreamTrackSource()`](https://webaudio.github.io/web-audio-api/#dom-audiocontext-createmediastreamtracksource) factory method. The [`MediaStreamTrackAudioSourceNode`](https://webaudio.github.io/web-audio-api/#mediastreamtrackaudiosourcenode) constructor may be used as an alternative.



It does only work with an AudioContext but not with an OfflineAudioContext.



#### createOscillator() / OscillatorNode



This is an implementation of the [`createOscillator()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createoscillator) factory method. The [`OscillatorNode`](https://webaudio.github.io/web-audio-api/#oscillatornode) constructor may be used as an alternative.



#### createPanner() / PannerNode



This is an implementation of the [`createPanner()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createpanner) factory method. The [`PannerNode`](https://webaudio.github.io/web-audio-api/#pannernode) constructor may be used as an alternative.



#### createPeriodicWave() / PeriodicWave



This is an implementation of the [`createPeriodicWave()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createperiodicwave) factory method. The [`PeriodicWave`](https://webaudio.github.io/web-audio-api/#periodicwave) constructor may be used as an alternative.



#### createStereoPanner() / StereoPannerNode



This is an implementation of the [`createStereoPanner()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createstereopanner) factory method. The [`StereoPannerNode`](https://webaudio.github.io/web-audio-api/#stereopannernode) constructor may be used as an alternative.



The channelCountMode can only be `'explicit'` unless Safari comes up with a native implementation.



#### createWaveShaper() / WaveShaperNode



This is an implementation of the [`createWaveShaper()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-createwaveshaper) factory method. The [`WaveShaperNode`](https://webaudio.github.io/web-audio-api/#waveshapernode) constructor may be used as an alternative.



#### decodeAudioData()



This is an implementation of the

[`decodeAudioData()`](https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-decodeaudiodata) method. There is also a standalone method with a similar interface described below.



### decodeAudioData()



This is a standalone wrapper which can be used in a similar way as the instance method with the same name. The most notable difference is that it expects an (Offline)AudioContext created with this library as the first parameter. But it can also handle a native (Offline)AudioContext. Another difference is that it only returns a promise. It will not call any callbacks.



```js

import { decodeAudioData } from 'standardized-audio-context';



const nativeAudioContext = new AudioContext();



const response = await fetch('/a-super-cool-audio-file');

const arrayBuffer = await response.arrayBuffer();



const audioBuffer = await decodeAudioData(nativeAudioContext, arrayBuffer);

```



### isAnyAudioContext()



This is a utility function which determines if the given value is an AudioContext or not. It does not differentiate between an AudioContext created by `standardized-audio-context` or a native one. But it will return false for an OfflineAudioContext.



```js

import { AudioContext, isAnyAudioContext } from 'standardized-audio-context';



// This will create an AudioContext from standardized-audio-context.

const audioContext = new AudioContext();



isAnyAudioContext(audioContext); // true



// This will create a native AudioContext.

const nativeAudioContext = new window.AudioContext();



isAnyAudioContext(nativeAudioContext); // true

```



### isAnyAudioNode()



This is a helper function which allows to identify an AudioNode without any custom instanceof or property checks. It returns true if the given value is an AudioNode or false if not. It doesn't matter if the given value is an AudioNode which has been created with `standardized-audio-context` or not.



```js

import { OfflineAudioContext, isAnyAudioNode } from 'standardized-audio-context';



// This will create a native AudioContext.

const nativeAudioContext = new AudioContext();



isAnyAudioNode(nativeAudioContext.createGain()); // true



// This will create an OfflineAudioContext from standardized-audio-context.

const offlineAudioContext = new OfflineAudioContext({ length: 10, sampleRate: 44100 });



isAnyAudioNode(offlineAudioContext.createGain()); // true

```



### isAnyAudioParam()



This is a helper function similiar to `isAnyAudioNode()` but for AudioParams. It returns true if the given value is an AudioParam or false in case it isn't. It doesn't matter if the given value is an AudioParam which has been created with `standardized-audio-context` or not.



```js

import { OfflineAudioContext, isAnyAudioParam } from 'standardized-audio-context';



// This will create a native AudioContext.

const nativeAudioContext = new AudioContext();



isAnyAudioParam(nativeAudioContext.createGain().gain); // true



// This will create an OfflineAudioContext from standardized-audio-context.

const offlineAudioContext = new OfflineAudioContext({ length: 10, sampleRate: 44100 });



isAnyAudioParam(offlineAudioContext.createGain().gain); // true

```



### isAnyOfflineAudioContext()



This is a utility function which determines if the given value is an OfflineAudioContext or not. It does not differentiate between an OfflineAudioContext created by `standardized-audio-context` or a native one.



```js

import { OfflineAudioContext, isAnyOfflineAudioContext } from 'standardized-audio-context';



// This will create an OfflineAudioContext from standardized-audio-context.

const offlineAudioContext = new OfflineAudioContext({ length: 10, sampleRate: 44100 });



isAnyOfflineAudioContext(offlineAudioContext); // true



// This will create a native OfflineAudioContext.

const nativeOfflineAudioContext = new window.OfflineAudioContext(1, 10, 44100);



isAnyOfflineAudioContext(nativeOfflineAudioContext); // true

```



### isSupported()



`standardized-audio-context` is also exporting a promise which can be accessed by calling `isSupported()`. This promise resolves to a boolean which indicates if the functionality is supported within the currently used browser. This is not part of the specification.



```js

import { isSupported } from 'standardized-audio-context';



isSupported().then((isSupported) => {

    if (isSupported) {

        // yeah everything should work

    } else {

        // oh no this browser seems to be outdated

    }

});

```



## Browser Support



The goal of this package is to provide a consistent API. But at the same time this package should

not grow indefinitely until everything works in IE 6. Whenever a feature is implemented in every

supported browser which required a polyfill before to work correctly that polyfill gets removed

from this package. And hopefully at some point in the future this package boils down to a file

which only re-exports built-in objects.



But until then great care is taken to avoid any unnecessary bloat. This means whenever a workaround

for a certain browser is added to this library it will be accompanied by a test which checks that

this particular workaround is still needed. I call those tests expectation tests because they test

if a browser behaves as expected. An expectation test is designed to fail when the browser

eventually ships a fix. Once that happens the workaround and the backing expectation test get

removed. The expectation test however gets recycled and will now be used as part of the browser

check performed when calling `isSupported()`.



The list of currently supported browsers includes Chrome v105+, Firefox v113+ and Safari v16.4+. Please note that the tests only run in the current and upcoming version of each browser.



Supporting a browser only means that it is supported on the feature level. It is absolutely

possible that a transpiler like [Babel](https://babeljs.io) is necessary to use this package in

every supported browser without encountering any syntax errors.



This package doesn't work with Node.js.



## TypeScript



This package is written in [TypeScript](https://www.typescriptlang.org/) which means it can be used seamlessly in any TypeScript project. But that is entirely optional.



In contrast to the Web Audio API types that TypeScript provides out of the box the types exported

by `standardized-audio-context` do actually match the concrete implementation. TypeScript

generates its types from the [Web IDL](https://heycam.github.io/webidl) definition of the Web Audio

API which does not always match the actually available implementations.



## Tests



All implemented methods are covered by a large number of tests which run in all the browsers mentioned above. Many thanks to [BrowserStack](https://www.browserstack.com) and [Sauce Labs](https://saucelabs.com) for allowing this module to be tested with their services.



## Security contact information



To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security). Tidelift will coordinate the fix and disclosure.