The audioprocess event of the ScriptProcessorNode interface is fired when an input buffer of a script processor is ready to be processed.

This event is not cancelable and does not bubble.

An AudioProcessingEvent. Inherits from Event.

Also implements the properties inherited from its parent, Event.

playbackTime Read only

A double representing the time when the audio will be played, as defined by the time of AudioContext.currentTime.

inputBuffer Read only

An AudioBuffer that is the buffer containing the input audio data to be processed. The number of channels is defined as a parameter numberOfInputChannels, of the factory method AudioContext.createScriptProcessor(). Note that the returned AudioBuffer is only valid in the scope of the event handler.

outputBuffer Read only

An AudioBuffer that is the buffer where the output audio data should be written. The number of channels is defined as a parameter, numberOfOutputChannels, of the factory method AudioContext.createScriptProcessor(). Note that the returned AudioBuffer is only valid in the scope of the event handler.

scriptNode.addEventListener("audioprocess", (audioProcessingEvent) => {
  // The input buffer is a song we loaded earlier
  const inputBuffer = audioProcessingEvent.inputBuffer;

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

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

    // Loop through the 4096 samples
    for (let 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;
    }
  }
});

You could also set up the event handler using the onaudioprocess property:

scriptNode.onaudioprocess = (audioProcessingEvent) => {
  // ...
};

Since the August 29, 2014, Web Audio API specification publication, this feature has been deprecated. It is no longer on track to become a standard.

It was replaced by AudioWorklets and the AudioWorkletNode interface.

• Web Audio API