AudioParamDescriptor

在此页

特性
范例
规范
浏览器兼容性
相关话题

AudioParamDescriptor dictionary of the Web 音频 API specifies properties for an AudioParam 对象。 It is used to create custom AudioParam s on an AudioWorkletNode . If the underlying AudioWorkletProcessor 拥有 parameterDescriptors static getter, then the returned array of objects based on this dictionary is used internally by AudioWorkletNode constructor to populate its 参数 property accordingly.

特性

名称: DOMString which represents the name of the AudioParam . Under this name the AudioParam will be available in the 参数 property of the node, and under this name the AudioWorkletProcessor.process method will acquire the calculated values of this AudioParam .
automationRate 可选: 要么 "a-rate" ，或 "k-rate" string which represents an automation rate of this AudioParam 。默认为 "a-rate" .
minValue 可选: A float which represents minimum value of the AudioParam 。默认为 -3.4028235e38 .
maxValue 可选: A float which represents maximum value of the AudioParam 。默认为 3.4028235e38 .
defaultValue 可选: A float which represents initial value of the AudioParam 。默认为 0 .

范例

To demonstrate creation and usage of custom AudioParam s, we'll expand the example from AudioWorkletNode page. There we've created a simple node which outputs white noise. Here, additionally, we'll create a custom gain parameter, so we can directly change volume of the output (although you could use GainNode to achieve this as well).

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

We expand the processor by adding a static parameterDescriptors getter. It will be used internally by the AudioWorkletNode constructor to populate its 参数 with instantiated AudioParam 对象。

// white-noise-processor.js
class WhiteNoiseProcessor extends AudioWorkletProcessor {
  static get parameterDescriptors () {
    return [{
      name: 'customGain',
      defaultValue: 1,
      minValue: 0,
      maxValue: 1,
      automationRate: 'a-rate'
    }]
  }
  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) *
          (parameters['customGain'].length > 1 ? parameters['customGain'][i] : parameters['customGain'][0])
        // note: a parameter contains an array of 128 values (one value for each of 128 samples),
        // however it may contain a single value which is to be used for all 128 samples
        // if no automation is scheduled for the moment.
      }
    })
    return true
  }
}
registerProcessor('white-noise-processor', WhiteNoiseProcessor)

Next, in our main scripts file we'll load the processor, create an instance of AudioWorkletNode passing it the name of the processor, and 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)

Now we can change the gain on the node like this:

const gainParam = whiteNoiseNode.parameters.get('customGain')
gainParam.setValueAtTime(0, audioContext.currentTime)
gainParam.linearRampToValueAtTime(0.5, audioContext.currentTime + 0.5)

规范

规范	状态	注释
Web 音频 API The definition of 'AudioParamDescriptor' in that specification.	工作草案	初始定义。

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

No compatibility data found. Please contribute data for "api.AudioParamDescriptor" (depth: 1) to the MDN 兼容性数据存储库 .

元数据

最后修改： Jul 5, 2019

在此页

特性

范例

规范

浏览器兼容性

相关话题