The decodeAudioData()
method of the BaseAudioContext
Interface is used to asynchronously decode audio file data contained in an ArrayBuffer
. In this case the ArrayBuffer
is loaded from XMLHttpRequest
and FileReader
. The decoded AudioBuffer
is resampled to the AudioContext
's sampling rate, then passed to a callback or promise.
This is the preferred method of creating an audio source for Web Audio API from an audio track. This method only works on complete file data, not fragments of audio file data.
Syntax
Older callback syntax:
baseAudioContext.decodeAudioData(ArrayBuffer, successCallback, errorCallback);
Newer promise-based syntax:
Promise<decodedData> baseAudioContext.decodeAudioData(ArrayBuffer);
Parameters
- ArrayBuffer
- An ArrayBuffer containing the audio data to be decoded, usually grabbed from
XMLHttpRequest
,WindowOrWorkerGlobalScope.fetch()
orFileReader
. - successCallback
- A callback function to be invoked when the decoding successfully finishes. The single argument to this callback is an
AudioBuffer
representing the decodedData (the decoded PCM audio data). Usually you'll want to put the decoded data into anAudioBufferSourceNode
, from which it can be played and manipulated how you want. - errorCallback
- An optional error callback, to be invoked if an error occurs when the audio data is being decoded.
Return value
Void, or a Promise
object that fulfills with the decodedData.
Example
In this section we will first cover the older callback-based system and then the newer promise-based syntax.
Older callback syntax
In this example, the getData()
function uses XHR to load an audio track, setting the responseType
of the request to arraybuffer
so that it returns an array buffer as its response
that we then store in the audioData
variable . We then pass this buffer into a decodeAudioData()
function; the success callback takes the successfully decoded PCM data, puts it into an AudioBufferSourceNode
created using AudioContext.createBufferSource()
, connects the source to the AudioContext.destination
and sets it to loop.
The buttons in the example simply run getData()
to load the track and start it playing, and stop it playing, respectively. When the stop()
method is called on the source, the source is cleared out.
Note: You can run the example live (or view the source.)
// define variables var audioCtx = new (window.AudioContext || window.webkitAudioContext)(); var source; var pre = document.querySelector('pre'); var myScript = document.querySelector('script'); var play = document.querySelector('.play'); var stop = document.querySelector('.stop'); // use XHR to load an audio track, and // decodeAudioData to decode it and stick it in a buffer. // Then we put the buffer into the source function getData() { source = audioCtx.createBufferSource(); var request = new XMLHttpRequest(); request.open('GET', 'viper.ogg', true); request.responseType = 'arraybuffer'; request.onload = function() { var audioData = request.response; audioCtx.decodeAudioData(audioData, function(buffer) { source.buffer = buffer; source.connect(audioCtx.destination); source.loop = true; }, function(e){ console.log("Error with decoding audio data" + e.err); }); } request.send(); } // wire up buttons to stop and play audio play.onclick = function() { getData(); source.start(0); play.setAttribute('disabled', 'disabled'); } stop.onclick = function() { source.stop(0); play.removeAttribute('disabled'); } // dump script to pre element pre.innerHTML = myScript.innerHTML;
New promise-based syntax
ctx.decodeAudioData(audioData).then(function(decodedData) { // use the decoded data here });
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'decodeAudioData()' in that specification. |
Working Draft |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
decodeAudioData | Chrome
Full support
10
| Edge Full support ≤18 | Firefox
Full support
53
| IE No support No | Opera
Full support
22
| Safari
Full support
6
| WebView Android Full support Yes | Chrome Android Full support 33 | Firefox Android
Full support
53
| Opera Android
Full support
22
| Safari iOS
Full support
6
| Samsung Internet Android Full support 2.0 |
Promise-based syntax | Chrome Full support 49 | Edge Full support ≤79 | Firefox
Full support
53
| IE No support No | Opera Full support Yes | Safari No support No | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android
Full support
53
| Opera Android ? | Safari iOS No support No | Samsung Internet Android Full support 5.0 |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- See implementation notes.
- See implementation notes.
- Requires a vendor prefix or different name for use.
- Requires a vendor prefix or different name for use.