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The decodeAudioData()
method of the AudioContext
Interface is used to asynchronously decode audio file data contained in an ArrayBuffer
. In this case the ArrayBuffer
is usually loaded from an XMLHttpRequest
's response
attribute after setting the responseType
to arraybuffer
. 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.
Syntax
Older callback syntax:
audioCtx.decodeAudioData(audioData, function(decodedData) { // use the decoded data here });
Newer promise-based syntax:
audioCtx.decodeAudioData(audioData).then(function(decodedData) { // use the decoded data here });
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){"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(compressedBuffer).then(function(decodedData) { // use the decoded data here });
Parameters
- ArrayBuffer
- An ArrayBuffer containing the audio data to be decoded, usually grabbed from an
XMLHttpRequest
'sresponse
attribute after setting theresponseType
toarraybuffer
. - DecodeSuccessCallback
- A callback function to be invoked when the decoding successfully finishes. The single argument to this callback is an AudioBuffer representing 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. - DecodeErrorCallback
- An optional error callback, to be invoked if an error occurs when the audio data is being decoded.
Returns
An AudioBuffer
representing the decoded PCM audio data.
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API Определение 'decodeAudioData()' в этой спецификации. |
Рабочий черновик |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 10.0webkit | 25.0 (25.0) | Нет | 15.0webkit 22 (unprefixed) |
6.0webkit |
Promise-based syntax | 49.0 | (Да) | Нет | (Да) | Нет |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | Firefox OS | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | ? | (Да) | 26.0 | 1.2 | ? | ? | ? | 33.0 |
Promise-based syntax | ? | 49.0 | (Да) | (Да) | Нет | ? | ? | 49.0 |