Web/API/BaseAudioContext/decodeAudioData

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() or FileReader.
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 an AudioBufferSourceNode, 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 [[../../../../../../../mdn.github.io/webaudio-examples/decode-audio-data/index|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 APIThe definition of 'decodeAudioData()' in that specification.	Working Draft

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`decodeAudioData`	Chrome Full support 10 Prefixed' Full support 10 Prefixed' Prefixed' Implemented with the vendor prefix: webkit	Edge Full support ≤18	Firefox Full support 53 Notes' Full support 53 Notes' Notes' Originally implemented on `AudioContext` in Firefox 25.	IE No support No	Opera Full support 22 Full support 22 Full support 15 Prefixed' Prefixed' Implemented with the vendor prefix: webkit	Safari Full support 6 Prefixed' Full support 6 Prefixed' Prefixed' Implemented with the vendor prefix: webkit	WebView Android Full support Yes	Chrome Android Full support 33	Firefox Android Full support 53 Notes' Full support 53 Notes' Notes' Originally implemented on `AudioContext` in Firefox Android 26.	Opera Android Full support 22 Full support 22 Full support 14 Prefixed' Prefixed' Implemented with the vendor prefix: webkit	Safari iOS Full support 6 Prefixed' Full support 6 Prefixed' Prefixed' Implemented with the vendor prefix: webkit	Samsung Internet Android Full support 2.0
Promise-based syntax	Chrome Full support 49	Edge Full support ≤79	Firefox Full support 53 Notes' Full support 53 Notes' Notes' Originally implemented on `AudioContext` in Firefox 36.	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 Notes' Full support 53 Notes' Notes' Originally implemented on `AudioContext` in Firefox Android 36.	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.