Web/API/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.

Properties

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.

Methods

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.

// test-processor.js
class TestProcessor extends AudioWorkletProcessor {
  constructor () {
    super()
    // current sample-frame and time at the moment of instantiation
    // to see values change, you can put these two lines in process method
    console.log(currentFrame)
    console.log(currentTime)
  }
  // the process method is required - simply output silence,
  // which the outputs are already filled with
  process (inputs, outputs, parameters) {
    return true
  }
}

// the sample rate 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

Specification	Status	Comment
Web Audio APIThe definition of 'AudioWorkletGlobalScope' in that specification.	Working Draft

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`AudioWorkletGlobalScope`	Chrome Full support 66	Edge Full support 79	Firefox Full support 76	IE No support No	Opera Full support 53	Safari No support No	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android No support No	Opera Android Full support 47	Safari iOS No support No	Samsung Internet Android Full support 9.0
`currentFrame`	Chrome Full support 66	Edge Full support 79	Firefox Full support 76	IE No support No	Opera Full support 53	Safari No support No	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android No support No	Opera Android Full support 47	Safari iOS No support No	Samsung Internet Android Full support 9.0
`currentTime`	Chrome Full support 66	Edge Full support 79	Firefox Full support 76	IE No support No	Opera Full support 53	Safari No support No	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android No support No	Opera Android Full support 47	Safari iOS No support No	Samsung Internet Android Full support 9.0
`registerProcessor`	Chrome Full support 66	Edge Full support 79	Firefox Full support 76	IE No support No	Opera Full support 53	Safari No support No	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android No support No	Opera Android Full support 47	Safari iOS No support No	Samsung Internet Android Full support 9.0
`sampleRate`	Chrome Full support 66	Edge Full support 79	Firefox Full support 76	IE No support No	Opera Full support 53	Safari No support No	WebView Android Full support 66	Chrome Android Full support 66	Firefox Android No support No	Opera Android Full support 47	Safari iOS No support No	Samsung Internet Android Full support 9.0

Legend

Full support: Full support
No support: No support