AudioProcessingEvent - Web APIs 编辑

Deprecated

This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

The Web Audio API AudioProcessingEvent represents events that occur when a ScriptProcessorNode input buffer is ready to be processed.

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 AudioWorklet.

Properties

The list below includes the properties inherited from its parent, Event.

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);
}

Browser compatibility

BCD tables only load in the browser

See also

• Using the Web Audio API