BaseAudioContext: createScriptProcessor() method
Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
The createScriptProcessor()
method of the BaseAudioContext
interface
creates a ScriptProcessorNode
used for direct audio processing.
Note: This feature was replaced by AudioWorklets and the AudioWorkletNode
interface.
Syntax
js
createScriptProcessor(bufferSize, numberOfInputChannels, numberOfOutputChannels)
Parameters
bufferSize
-
The buffer size in units of sample-frames. If specified, the bufferSize must be one of the following values: 256, 512, 1024, 2048, 4096, 8192, 16384. If it's not passed in, or if the value is 0, then the implementation will choose the best buffer size for the given environment, which will be a constant power of 2 throughout the lifetime of the node.
This value controls how frequently the
audioprocess
event is dispatched and how many sample-frames need to be processed each call. Lower values forbufferSize
will result in a lower (better) latency. Higher values will be necessary to avoid audio breakup and glitches. It is recommended for authors to not specify this buffer size and allow the implementation to pick a good buffer size to balance between latency and audio quality. numberOfInputChannels
-
Integer specifying the number of channels for this node's input, defaults to 2. Values of up to 32 are supported.
numberOfOutputChannels
-
Integer specifying the number of channels for this node's output, defaults to 2. Values of up to 32 are supported.
Warning: Webkit currently (version 31) requires that a valid
bufferSize
be passed when calling this method.
Note: It is invalid for both numberOfInputChannels
and
numberOfOutputChannels
to be zero.
Return value
Examples
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. (You can also access the source code.)
js
const myScript = document.querySelector("script");
const myPre = document.querySelector("pre");
const playButton = document.querySelector("button");
// Create AudioContext and buffer source
const 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);
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 = () => {
const audioData = request.response;
audioCtx.decodeAudioData(
audioData,
(buffer) => {
myBuffer = buffer;
source.buffer = myBuffer;
},
(e) => console.error(`Error with decoding audio data: ${e.err}`)
);
};
request.send();
}
// Give the node a function to process audio events
scriptNode.onaudioprocess = (audioProcessingEvent) => {
// The input buffer is the 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;
}
}
};
getData();
// Wire up the play button
playButton.onclick = () => {
source.connect(scriptNode);
scriptNode.connect(audioCtx.destination);
source.start();
};
// When the buffer source stops playing, disconnect everything
source.onended = () => {
source.disconnect(scriptNode);
scriptNode.disconnect(audioCtx.destination);
};
Specifications
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.
Browser compatibility
BCD tables only load in the browser