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 theBaseAudioContext
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 anAudioWorkletNode
, 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 API The definition of 'AudioWorkletGlobalScope' in that specification. |
Working Draft |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
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