AudioWorkletProcessor

AudioWorkletProcessor interface of the Web 音频 API represents an audio processing code behind a custom AudioWorkletNode . It lives in the AudioWorkletGlobalScope and runs on the Web Audio rendering thread. In turn, an AudioWorkletNode based on it runs on the main thread.

构造函数

AudioWorkletProcessor and classes that derive from it cannot be instantiated directly from a user-supplied code. Instead, they are created only internally by the creation of an associated AudioWorkletNode s. The constructor of the deriving class is getting called with an options object, so you can perform a custom initialization procedures — see constructor page for details.
AudioWorkletProcessor()
Creates a new instance of an AudioWorkletProcessor 对象。

特性

port 只读
返回 MessagePort used for bidirectional communication between the processor and the AudioWorkletNode which it belongs to. The other end is available under the port property of the node.

方法

AudioWorkletProcessor interface does not define any methods of its own. However, you must provide a process() method, which is called in order to process the audio stream.

Events

AudioWorkletProcessor interface doesn't respond to any events.

Usage notes

Deriving classes

To define custom audio processing code you have to derive a class from the AudioWorkletProcessor interface. Although not defined on the interface, the deriving class must have the process method. This method gets called for each block of 128 sample-frames and takes input and output arrays and calculated values of custom AudioParam s (if they are defined) as parameters. You can use inputs and audio parameter values to fill the outputs array, which by default holds silence.

Optionally, if you want custom AudioParam s on your node, you can supply a parameterDescriptors property as a static getter on the processor. The array of AudioParamDescriptor -based objects returned is used internally to create the AudioParam s during the instantiation of the AudioWorkletNode .

结果 AudioParam s reside in the parameters property of the node and can be automated using standard methods such as linearRampToValueAtTime . Their calculated values will be passed into the process() method of the processor for you to shape the node output accordingly.

Processing audio

An example algorithm of creating a custom audio processing mechanism is:

  1. Create a separate file;
  2. In the file:
    1. Extend the AudioWorkletProcessor class (see "Deriving classes" section ) and supply your own process() method in it;
    2. Register the processor using AudioWorkletGlobalScope.registerProcessor() method;
  3. Load the file using addModule() method on your audio context's audioWorklet property;
  4. Create an AudioWorkletNode based on the processor. The processor will be instantiated internally by the AudioWorkletNode 构造函数。
  5. Connect the node to the other nodes.

范例

In the example below we create a custom AudioWorkletNode that outputs white noise.

First, we need to define a custom AudioWorkletProcessor , which will output white noise, and register it. Note that this should be done in a separate file.

// white-noise-processor.js
class WhiteNoiseProcessor extends AudioWorkletProcessor {
  process (inputs, outputs, parameters) {
    const output = outputs[0]
    output.forEach(channel => {
      for (let i = 0; i < channel.length; i++) {
        channel[i] = Math.random() * 2 - 1
      }
    })
    return true
  }
}
registerProcessor('white-noise-processor', WhiteNoiseProcessor)
					

Next, in our main script file we'll load the processor, create an instance of AudioWorkletNode , passing it the name of the processor, then connect the node to an audio graph.

const audioContext = new AudioContext()
await audioContext.audioWorklet.addModule('white-noise-processor.js')
const whiteNoiseNode = new AudioWorkletNode(audioContext, 'white-noise-processor')
whiteNoiseNode.connect(audioContext.destination)
					

规范

规范 状态 Comment
Web 音频 API
The definition of 'AudioWorkletProcessor' in that specification.
工作草案

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