AudioProcessingEvent

{{APIRef("Web Audio API")}}{{deprecated_header}}

The AudioProcessingEvent interface of the Web Audio API represents events that occur when a {{domxref("ScriptProcessorNode")}} input buffer is ready to be processed.

An audioprocess event with this interface is fired on a {{domxref("ScriptProcessorNode")}} when audio processing is required. During audio processing, the input buffer is read and processed to produce output audio data, which is then written to the output buffer.

[!WARNING] This feature has been deprecated and should be replaced by an AudioWorklet.

{{InheritanceDiagram}}

Constructor

• {{domxref("AudioProcessingEvent.AudioProcessingEvent", "AudioProcessingEvent()")}} {{Deprecated_Inline}}
  • : Creates a new AudioProcessingEvent object.

Instance properties

Also implements the properties inherited from its parent, {{domxref("Event")}}.

• {{domxref("AudioProcessingEvent.playbackTime", "playbackTime")}} {{ReadOnlyInline}} {{Deprecated_Inline}}
  • : A double representing the time when the audio will be played, as defined by the time of {{domxref("BaseAudioContext/currentTime", "AudioContext.currentTime")}}.
• {{domxref("AudioProcessingEvent.inputBuffer", "inputBuffer")}} {{ReadOnlyInline}} {{Deprecated_Inline}}
  • : An {{domxref("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 {{domxref("BaseAudioContext/createScriptProcessor", "AudioContext.createScriptProcessor()")}}. Note that the returned <code>AudioBuffer</code> is only valid in the scope of the event handler.
• {{domxref("AudioProcessingEvent.outputBuffer", "outputBuffer")}} {{ReadOnlyInline}} {{Deprecated_Inline}}
  • : An {{domxref("AudioBuffer")}} that is the buffer where the output audio data should be written. The number of channels is defined as a parameter, <code>numberOfOutputChannels</code>, of the factory method {{domxref("BaseAudioContext/createScriptProcessor", "AudioContext.createScriptProcessor()")}}. Note that the returned <code>AudioBuffer</code> is only valid in the scope of the event handler.

Examples

Adding white noise using a script processor

The following example shows how to use of a ScriptProcessorNode to take a track loaded via {{domxref("BaseAudioContext/decodeAudioData", "AudioContext.decodeAudioData()")}}, process it, adding a bit of white noise to each audio sample of the input track (buffer) and play it through the {{domxref("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. (You can also access the source code.)

const myScript = document.querySelector("script");
const myPre = document.querySelector("pre");
const playButton = document.querySelector("button");

// Create AudioContext and buffer source
let audioCtx;

async function init() {
  audioCtx = new AudioContext();
  const source = audioCtx.createBufferSource();

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

  // Load in an audio track using fetch() and decodeAudioData()
  try {
    const response = await fetch("viper.ogg");
    const arrayBuffer = await response.arrayBuffer();
    source.buffer = await audioCtx.decodeAudioData(arrayBuffer);
  } catch (err) {
    console.error(
      `Unable to fetch the audio file: ${name} Error: ${err.message}`,
    );
  }

  // Give the node a function to process audio events
  scriptNode.addEventListener("audioprocess", (audioProcessingEvent) => {
    // The input buffer is the song we loaded earlier
    let inputBuffer = audioProcessingEvent.inputBuffer;

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

    // Loop through the output channels (in this case there is only one)
    for (let channel = 0; channel < outputBuffer.numberOfChannels; channel++) {
      let inputData = inputBuffer.getChannelData(channel);
      let 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) * 0.1;
      }
    }
  });

  source.connect(scriptNode);
  scriptNode.connect(audioCtx.destination);
  source.start();

  // When the buffer source stops playing, disconnect everything
  source.addEventListener("ended", () => {
    source.disconnect(scriptNode);
    scriptNode.disconnect(audioCtx.destination);
  });
}

// wire up play button
playButton.addEventListener("click", () => {
  if (!audioCtx) {
    init();
  }
});

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• Using the Web Audio API