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AudioWorkletGlobalScope

The AudioWorkletGlobalScope interface of the Web Audio API represents a global execution context for user-supplied code, which defines custom AudioWorkletProcessor-derived classes.

Each BaseAudioContext has a single AudioWorklet available under the audioWorklet property, which runs its code in a single AudioWorkletGlobalScope.

As the global execution context is shared across the current BaseAudioContext, it's possible to define any other variables and perform any actions allowed in worklets — apart from defining AudioWorkletProcessor derived classes.

WorkletGlobalScope AudioWorkletGlobalScope

Instance properties

This interface also inherits properties defined on its parent interface, WorkletGlobalScope.

currentFrame Read only

Returns an integer that represents the ever-increasing current sample-frame of the audio block being processed. It is incremented by 128 (the size of a render quantum) after the processing of each audio block.

currentTime Read only

Returns a double that represents the ever-increasing context time of the audio block being processed. It is equal to the currentTime property of the BaseAudioContext the worklet belongs to.

sampleRate Read only

Returns a float that represents the sample rate of the associated BaseAudioContext.

Instance methods

This interface also inherits methods defined on its parent interface, WorkletGlobalScope.

registerProcessor()

Registers a class derived from the AudioWorkletProcessor interface. The class can then be used by creating an AudioWorkletNode, providing its registered name.

Examples

In this example we output all global properties into the console in the constructor of a custom AudioWorkletProcessor.

First we need to define the processor, and register it. Note that this should be done in a separate file.

// AudioWorkletProcessor defined in : test-processor.js
class TestProcessor extends AudioWorkletProcessor {
  constructor() {
    super();

    // Logs the current sample-frame and time at the moment of instantiation.
    // They are accessible from the AudioWorkletGlobalScope.
    console.log(currentFrame);
    console.log(currentTime);
  }

  // The process method is required - output silence,
  // which the outputs are already filled with.
  process(inputs, outputs, parameters) {
    return true;
  }
}

// Logs the sample rate, that is not going to change ever,
// because it's a read-only property of a BaseAudioContext
// and is set only during its instantiation.
console.log(sampleRate);

// You can declare any variables and use them in your processors
// for example it may be an ArrayBuffer with a wavetable
const usefulVariable = 42;
console.log(usefulVariable);

registerProcessor("test-processor", TestProcessor);

Next, in our main scripts file we'll load the processor, create an instance of AudioWorkletNode — passing the name of the processor to it — and connect the node to an audio graph. We should see the output of console.log() calls in the console:

const audioContext = new AudioContext();
await audioContext.audioWorklet.addModule("test-processor.js");
const testNode = new AudioWorkletNode(audioContext, "test-processor");
testNode.connect(audioContext.destination);

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
AudioWorkletGlobalScope 66 79 76 No 53 14.1 66 66 No 47 14.5 9.0
currentFrame 66 79 76 No 53 14.1 66 66 No 47 14.5 9.0
currentTime 66 79 76 No 53 14.1 66 66 No 47 14.5 9.0
registerProcessor 66 79 76 No 53 14.1 66 66 No 47 14.5 9.0
sampleRate 66 79 76 No 53 14.1 66 66 No 47 14.5 9.0

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/AudioWorkletGlobalScope