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    ScriptProcessorNode.onaudioprocess

    This article is in need of a technical review.

    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.

    The onaudioprocess event handler of the ScriptProcessorNode interface represents the EventHandler to be called for the audioprocess event that is dispatched to ScriptProcessorNode node types. An event of type AudioProcessingEvent will be dispatched to the event handler.

    Syntax

    var audioCtx = new AudioContext();
    var scriptNode = audioCtx.createScriptProcessor(4096, 1, 1);
    scriptNode.onaudioprocess = function() { ... }

    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
    The definition of 'onaudioprocess' in that specification.
    Working Draft  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
    Basic support 14 webkit 23 Not supported 15 webkit
    22 (unprefixed)
    6 webkit
    Feature Android Chrome Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile
    Basic support Not supported 28 webkit 25 1.2 Not supported Not supported webkit

    See also

    Document Tags and Contributors

    Contributors to this page: fscholz, chrisdavidmills
    Last updated by: fscholz,