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Deprecated
This feature has been removed from the Web standards. Though some browsers may still support it, it is in the process of being dropped. Do not use it in old or new projects. Pages or Web apps using it may break 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 Audio Workers.
Properties
The list below includes the properties inherited from its parent, Event
.
Property | Type | Description |
---|---|---|
target Read only |
EventTarget |
The event target (the topmost target in the DOM tree). |
type Read only |
DOMString |
The type of event. |
bubbles Read only |
boolean |
Does the event normally bubble? |
cancelable Read only |
boolean |
Is it possible to cancel the event? |
playbackTime Read only |
double |
The time when the audio will be played, as defined by the time of AudioContext.currentTime |
inputBuffer Read only |
AudioBuffer |
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 the the returned AudioBuffer is only valid in the scope of the onaudioprocess function. |
outputBuffer Read only |
AudioBuffer |
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 the the returned AudioBuffer is only valid in the scope of the 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 'AudioProcessingEvent' in that specification. |
Working Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 10.0webkit | 25.0 (25.0) | No support | 15.0webkit 22 (unprefixed) |
6.0webkit |
Feature | Android | Firefox Mobile (Gecko) | Firefox OS | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|
Basic support | ? | 26.0 | 1.2 | ? | ? | ? | 33.0 |