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ScriptProcessorNode

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Note: As of the August 29 2014 Web Audio API spec publication, this feature has been marked as deprecated, and is soon to be replaced by Audio Workers.

ScriptProcessorNode 接口允许使用javaScript生成、处理、分析音频. 它是一个 AudioNode, 连接着两个缓冲区音频处理模块, 其中一个缓冲区包含输入音频数据,另外一个包含处理后的输出音频数据. 实现了 AudioProcessingEvent 接口的一个事件,每当输入缓冲区有新的数据时,事件将被发送到该对象,并且事件将在数据填充到输出缓冲区后结束.

The ScriptProcessorNode stores the input in a buffer, send the audioprocess event. The EventHandler takes the input buffer and fill the output buffer which is sent to the output by the ScriptProcessorNode.

The size of the input and output buffer are defined at the creation time, when the AudioContext.createScriptProcessor() method is called (both are defined by AudioContext.createScriptProcessor()'s bufferSize parameter). The buffer size must be a power of 2 between 256 and 16384, that is 256, 512, 1024, 2048, 4096, 8192 or 16384. Small numbers lower the latency, but large number may be necessary to avoid audio breakup and glitches.

If the buffer size is not defined, which is recommended, the browser will pick one that its heuristic deems appropriate.

Number of inputs 1
Number of outputs 1
Channel count mode "max"
Channel count 2 (not used in the default count mode)
Channel interpretation "speakers"

Properties

Inherits properties from its parent, AudioNode.

ScriptProcessorNode.bufferSize 只读
Returns an integer representing both the input and output buffer size. Its value can be a power of 2 value in the range 25616384.

Event handlers

ScriptProcessorNode.onaudioprocess
Represents the EventHandler to be called.

Methods

No specific methods; inherits methods from its parent, AudioNode.

Example

The following example shows basic usage of a ScriptProcessorNode to take a track loaded via AudioContext.decodeAudioData, process it, adding a bit of white noise to each audio sample of the input track (buffer) and play it through the AudioDestinationNode. For each channel and each sample frame, the scriptNode.onaudioprocess function takes the associated audioProcessingEvent and uses it to loop through each channel of the input buffer, and each sample in each channel, and add a small amount of white noise, before setting that result to be the output sample in each case.

Note: For a full working example, see our script-processor-node github repo (also view the source code.)

var myScript = document.querySelector('script');
var myPre = document.querySelector('pre');
var playButton = document.querySelector('button');
      
// Create AudioContext and buffer source
var audioCtx = new AudioContext();
source = audioCtx.createBufferSource();

// Create a ScriptProcessorNode with a bufferSize of 4096 and a single input and output channel
var scriptNode = audioCtx.createScriptProcessor(4096, 1, 1);
console.log(scriptNode.bufferSize);

// load in an audio track via XHR and decodeAudioData

function getData() {
  request = new XMLHttpRequest();
  request.open('GET', 'viper.ogg', true);
  request.responseType = 'arraybuffer';
  request.onload = function() {
    var audioData = request.response;

    audioCtx.decodeAudioData(audioData, function(buffer) {
    myBuffer = buffer;   
    source.buffer = myBuffer;
  },
    function(e){"Error with decoding audio data" + e.err});
  }
  request.send();
}

// Give the node a function to process audio events
scriptNode.onaudioprocess = function(audioProcessingEvent) {
  // The input buffer is the song we loaded earlier
  var inputBuffer = audioProcessingEvent.inputBuffer;

  // The output buffer contains the samples that will be modified and played
  var outputBuffer = audioProcessingEvent.outputBuffer;

  // Loop through the output channels (in this case there is only one)
  for (var channel = 0; channel < outputBuffer.numberOfChannels; channel++) {
    var inputData = inputBuffer.getChannelData(channel);
    var outputData = outputBuffer.getChannelData(channel);

    // Loop through the 4096 samples
    for (var sample = 0; sample < inputBuffer.length; sample++) {
      // make output equal to the same as the input
      outputData[sample] = inputData[sample];

      // add noise to each output sample
      outputData[sample] += ((Math.random() * 2) - 1) * 0.2;         
    }
  }
}

getData();

// wire up play button
playButton.onclick = function() {
  source.connect(scriptNode);
  scriptNode.connect(audioCtx.destination);
  source.start();
}
      
// When the buffer source stops playing, disconnect everything
source.onended = function() {
  source.disconnect(scriptNode);
  scriptNode.disconnect(audioCtx.destination);
}

Specifications

Specification Status Comment
Web Audio API
ScriptProcessorNode
Working Draft  

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 14 webkit (Yes) 25 (25) 未实现 15 webkit
22 (unprefixed)
6 webkit
Feature Android Chrome Edge Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
Basic support 未实现 28 webkit (Yes) 25.0 (25) 1.2 未实现 未实现 webkit

See also

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