ScriptProcessorNode
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 ScriptProcessorNode
interface allows the generation, processing, or analyzing of audio using JavaScript. It is an AudioNode
audio-processing module that is linked to two buffers, one containing the input audio data, one containing the processed output audio data. An event, implementing the AudioProcessingEvent
interface, is sent to the object each time the input buffer contains new data, and the event handler terminates when it has filled the output buffer with data.
The size of the input and output buffer are defined at the creation time, when the AudioContext.createScriptProcessor()
method is called (both are defined by AudioContext.createScriptProcessor()
's bufferSize
parameter). The buffer size must be a power of 2 between 256
and 16384
, that is 256
, 512
, 1024
, 2048
, 4096
, 8192
or 16384
. Small numbers lower the latency, but large number may be necessary to avoid audio breakup and glitches.
If the buffer size is not defined, which is recommended, the browser will pick one that its heuristic deems appropriate.
Number of inputs | 1 |
---|---|
Number of outputs | 1 |
Channel count mode | "max" |
Channel count | 2 (not used in the default count mode) |
Channel interpretation | "speakers" |
Properties
Inherits properties from its parent, AudioNode
.
ScriptProcessorNode.bufferSize
Read only- Returns an integer representing both the input and output buffer size. Its value can be a power of 2 value in the range
256
–16384
.
Event handlers
ScriptProcessorNode.onaudioprocess
- Represents the
EventHandler
to be called.
Methods
No specific methods; inherits methods from its parent, AudioNode
.
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 'ScriptProcessorNode' in that specification. |
Working Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 14 webkit | 25 (25) | 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 | 25.0 (25) | 1.2 | Not supported | Not supported | 6 webkit |
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/scriptprocessornode