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Web Audio API for Angular

Part of <img src="projects/demo/src/assets/web-api.svg" align="top"> Web APIs for Angular

This is a library for declarative use of Web Audio API with Angular 7+. It is a complete conversion to declarative Angular directives, if you find any inconsistencies or errors, please file an issue. Watch out for 💡 emoji in this README for additional features and special use cases.

How to use

After you installed the package, you must add @ng-web-apis/audio/polyfill to your polyfills.ts. It is required to normalize things like webkitAudioContext, otherwise your code would fail.

You can build audio graph with directives. For example, here's a typical echo feedback loop:

<audio src="/demo.wav" waMediaElementAudioSourceNode>
    <ng-container #node="AudioNode" waDelayNode [delayTime]="delayTime">
        <ng-container waGainNode [gain]="gain">
            <ng-container [waOutput]="node"></ng-container>
            <ng-container waAudioDestinationNode></ng-container>
        </ng-container>
    </ng-container>
    <ng-container waAudioDestinationNode></ng-container>
</audio>

💡 AudioBufferService

This library has AudioBufferService with fetch method, returning Promise which allows you to easily turn your hosted audio file into AudioBuffer through GET requests. Result is stored in service's cache so same file is not requested again while application is running.

This service is also used within directives that have AudioBuffer inputs (such as AudioBufferSourceNode or ConvolverNode) so you can just pass string URL, as well as an actual AudioBuffer. For example:

<button
    #source="AudioNode"
    buffer="/demo.wav"
    waAudioBufferSourceNode
    (click)="source.start()"
>
    Play
    <ng-container waAudioDestinationNode></ng-container>
</button>

Supported nodes

You can use following audio nodes through directives of the same name (prefixed with wa standing for Web API):

Terminal nodes

• AudioContext

  💡 Not required if you only need one, global context will be created when needed

  💡 Also gives you access to AudioListener parameters such as positionX

• OfflineAudioContext

  💡 Additionally supports empty autoplay attribute similar to audio tag so it would start rendering immediately

  💡 Also gives you access to AudioListener parameters such as positionX

• AudioDestinationNode

  💡 Use it to terminate branch of your graph

  💡 can be used multiple times inside single BaseAudioContext referencing the same BaseAudioContext.destination

  💡 Has (quiet) output to watch for particular graph branch going almost silent for 5 seconds straight so you can remove branch after all effects played out to silence to free up resources

• MediaStreamAudioDestinationNode

Sources

• AudioBufferSourceNode

  💡 Additionally supports setting URL to media file as buffer so it will be fetched and turned into AudioBuffer

  💡 Additionally supports empty autoplay attribute similar to audio tag so it would start playing immediately

• ConstantSourceNode

  💡 Additionally supports empty autoplay attribute similar to audio tag so it would start playing immediately

• MediaElementAudioSourceNode

• MediaStreamAudioSourceNode

• MediaStreamTrackAudioSourceNode

• OscillatorNode

  💡 Additionally supports empty autoplay attribute similar to audio tag so it would start playing immediately

Processors

• BiquadFilterNode

• ChannelMergerNode

  💡 Use Channel directive to merge channels, see example in Special cases section

• ChannelSplitterNode

• ConvolverNode

  💡 Additionally supports setting URL to media file as buffer so it will be fetched and turned into AudioBuffer

• DelayNode

• GainNode

• IIRFilterNode

• PannerNode

• ScriptProcessorNode

• StereoPannerNode

• WaveShaperNode

AudioWorkletNode

You can use AudioWorkletNode in supporting browsers. To register your AudioWorkletProcessors in a global default AudioContext you can use tokens:

@NgModule({
    bootstrap: [AppComponent],
    declarations: [AppComponent],
    providers: [
        {
            provide: AUDIO_WORKLET_PROCESSORS,
            useValue: 'assets/my-processor.js',
            multi: true,
        },
    ],
})
export class AppModule {}

@Component({
    selector: 'app',
    templateUrl: './app.component.html',
})
export class AppComponent {
    constructor(
        @Inject(AUDIO_WORKLET_PROCESSORS_READY) readonly processorsReady: Promise<boolean>,
    ) {}

    // ...
}

You can then instantiate your AudioWorkletNode:

<ng-container *ngIf="processorsReady | async" waAudioWorkletNode name="my-processor">
    <ng-container waAudioDestinationNode></ng-container>
</ng-container>

If you need to create your own node with custom AudioParam and control it declaratively you can extend WebAudioWorklet class and add audioParam decorator to new component's inputs:

@Directive({
    selector: '[my-worklet-node]',
    exportAs: 'AudioNode',
    providers: [
        {
            provide: AUDIO_NODE,
            useExisting: forwardRef(() => MyWorklet),
        },
    ],
})
export class MyWorklet extends WebAudioWorklet {
    @Input()
    @audioParam()
    customParam?: AudioParamInput;

    constructor(
        @Inject(AUDIO_CONTEXT) context: BaseAudioContext,
        @SkipSelf() @Inject(AUDIO_NODE) node: AudioNode | null,
    ) {
        super(context, node, 'my-processor');
    }
}

💡 AudioParam

Since work with AudioParam is imperative in its nature, there are difference to native API when working with declarative inputs and directives.

NOTE: You can always access directives through template reference variables / @ViewChild and since they extend native nodes work with AudioParam in traditional Web Audio fashion

AudioParam inputs for directives accept following arguments:

• number to set in instantly, equivalent to setting AudioParam.value

• AudioParamCurve to set array of values over given duration, equivalent to AudioParam.setValueCurveAtTime called with AudioContext.currentTime

  export type AudioParamCurve = {
      readonly value: number[];
      readonly duration: number;
  }
  

• AudioParamAutomation to linearly or exponentially ramp to given value starting from AudioContext.currentTime

  export type AudioParamAutomation = {
      readonly value: number;
      readonly duration: number;
      readonly mode: 'instant' | 'linear' | 'exponential';
  };
  

• AudioParamAutomation[] to schedule multiple changes in value, stacking one after another

You can use waAudioParam pipe to turn your number values into AudioParamAutomation (default mode is exponential, so last argument can be omitted) or number arrays to AudioParamCurve (second argument duration is in seconds):

<ng-container
    waGainNode
    gain="0"
    [gain]="gain | waAudioParam : 0.1 : 'linear'"
></ng-container>

This way values would change smoothly rather than abruptly, causing audio artifacts.

NOTE: You can set initial value for AudioParam through argument binding combined with dynamic property binding as seen above.

To schedule an audio envelope looking something like this:

You would need to pass the following array of AudioParamAutomation items:

envelope = [
    {
        value: 0,
        duration: 0,
        mode: 'instant',
    },
    {
        value: 1,
        duration: ATTACK_TIME,
        mode: 'linear',
    },
    {
        value: SUS,
        duration: DECAY_TIME,
        mode: 'linear',
    },
    {
        value: SUS,
        duration: SUSTAIN_TIME,
        mode: 'instant',
    },
    {
        value: 0,
        duration: RELEASE_TIME,
        mode: 'exponential',
    },
];

💡 Special cases

• Use waOutput directive when you need non-linear graph (see feedback loop example above) or to manually connect AudioNode to AudioNode or AudioParam
• Use waPeriodicWave pipe to create PeriodicWave for OscillatorNode
• All node directives are exported as AudioNode so you can use them with template reference variables (see feedback loop example above)
• Use waChannel directive within ChannelMergerNode and direct waOutput directive to it in order to perform channel merging:

<!-- Inverting left and right channel -->
<audio src="/demo.wav" waMediaElementAudioSourceNode>
    <ng-container waChannelSplitterNode>
        <ng-container [waOutput]="right"></ng-container>
        <ng-container [waOutput]="left"></ng-container>
    </ng-container>
    <ng-container waChannelMergerNode>
        <ng-container #left="AudioNode" waChannel></ng-container>
        <ng-container #right="AudioNode" waChannel></ng-container>
        <ng-container waAudioDestinationNode></ng-container>
    </ng-container>
</audio>

💡 Tokens

• You can check Web Audio API support in current browser by injecting WEB_AUDIO_SUPPORT token
• You can check AudioWorklet support in current browser by injecting AUDIO_WORKLET_SUPPORT token
• You can inject BaseAudioContext through AUDIO_CONTEXT token
• AudioContext is created by default with default options when token is requested
• You can also provide custom BaseAudioContext through that token
• Provide FEEDBACK_COEFFICIENTS and FEEDFORWARD_COEFFICIENTS tokens to be able to create IIRFilterNode
• Provide MEDIA_STREAM token to be able to create MediaStreamAudioSourceNode
• Provide MEDIA_STREAM_TRACK token to be able to create MediaStreamTrackAudioSourceNode
• All node directives provide underlying AudioNode as AUDIO_NODE token
• Use AUDIO_WORKLET_PROCESSORS token to declare array of AudioWorkletProcessors to be added to default AudioContext
• Inject AUDIO_WORKLET_PROCESSORS_READY token to initialize provided AudioWorkletProcessors loading and watch for Promise resolution before instantiating dependent AudioWorkletNodes

Browser support

Note that some features (AudioWorklet etc.) were added later and are supported only by more recent versions

IMPORTANT: You must add @ng-web-apis/audio/polyfill to your polyfills.ts, otherwise you will get ReferenceError: X is not defined in browsers for entities they do not support

💡 StereoPannerNode is emulated with PannerNode in browsers that do not support it yet

💡 positionX (orientationX) and other similar properties of AudioListener and PannerNode fall back to setPosition (setOrientation) method if browser does not support it

Angular Universal

If you want to use this package with SSR, you need to mock native Web Audio API classes on the server. You can use our Universal package for this, see this example.

Demo

You can try online demo here

See also

Other Web APIs for Angular by @ng-web-apis

Open-source

Do you also want to open-source something, but hate the collateral work? Check out this Angular Open-source Library Starter we’ve created for our projects. It got you covered on continuous integration, pre-commit checks, linting, versioning + changelog, code coverage and all that jazz.