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.

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 256–16384.

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.

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

Browser compatibility

See also

• Using the Web Audio API