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The OfflineAudioContext interface is an AudioContext interface representing an audio-processing graph built from linked together AudioNodes. In contrast with a standard AudioContext, an OfflineAudioContext doesn't render the audio to the device hardware; instead, it generates it, as fast as it can, and outputs the result to an AudioBuffer.

Constructor

OfflineAudioContext.OfflineAudioContext()
Creates a new OfflineAudioContext instance.

Properties

Also inherits properties from its parent interface, BaseAudioContext.

OfflineAudioContext.length Read only
An integer representing the size of the buffer in sample-frames.

Event handlers

OfflineAudioContext.oncomplete
Is an EventHandler called when processing is terminated, that is when the complete event (of type OfflineAudioCompletionEvent) is raised, after the event-based version of OfflineAudioContext.startRendering() is used.

Methods

Also inherits methods from its parent interface, BaseAudioContext.

OfflineAudioContext.suspend()
Schedules a suspension of the time progression in the audio context at the specified time and returns a promise.
OfflineAudioContext.startRendering()
Starts rendering the audio, taking into account the current connections and the current scheduled changes. This page covers both the event-based version and the promise-based version.

Deprecated methods

OfflineAudioContext.resume()
Resumes the progression of time in an audio context that has previously been suspended.

Note: The resume() method is still available — it is now defined on the BaseAudioContext interface (see BaseAudioContext.resume()) and thus can be accessed by both the AudioContext and OfflineAudioContext interfaces.

Example

In this simple example, we declare both an AudioContext and an OfflineAudioContext object. We use the AudioContext to load an audio track via XHR (AudioContext.decodeAudioData), then the OfflineAudioContext to render the audio into an AudioBufferSourceNode and play the track through. After the offline audio graph is set up, you need to render it to an AudioBuffer using OfflineAudioContext.startRendering.

When the startRendering() promise resolves, rendering has completed and the output AudioBuffer is returned out of the promise.

At this point we create another audio context, create an AudioBufferSourceNode inside it, and set its buffer to be equal to the promise AudioBuffer. This is then played as part of a simple standard audio graph.

Note: For a working example, see our offline-audio-context-promise Github repo (see the source code too.)

// define online and offline audio context

var audioCtx = new AudioContext();
var offlineCtx = new OfflineAudioContext(2,44100*40,44100);

source = offlineCtx.createBufferSource();

// use XHR to load an audio track, and
// decodeAudioData to decode it and OfflineAudioContext to render it

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;
      source.connect(offlineCtx.destination);
      source.start();
      //source.loop = true;
      offlineCtx.startRendering().then(function(renderedBuffer) {
        console.log('Rendering completed successfully');
        var song = audioCtx.createBufferSource();
        song.buffer = renderedBuffer;

        song.connect(audioCtx.destination);

        play.onclick = function() {
          song.start();
        }
      }).catch(function(err) {
          console.log('Rendering failed: ' + err);
          // Note: The promise should reject when startRendering is called a second time on an OfflineAudioContext
      });
    });
  }

  request.send();
}

// Run getData to start the process off

getData();

Specifications

Specification Status Comment
Web Audio API
The definition of 'OfflineAudioContext' in that specification.
Working Draft Initial definition

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 14Edge Full support YesFirefox Full support 25IE No support NoOpera Full support 15Safari Full support 6WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support 15Safari iOS ? Samsung Internet Android Full support Yes
OfflineAudioContext() constructorChrome Full support 55
Notes
Full support 55
Notes
Notes Before Chrome 59, the default values were not supported.
Edge ? Firefox Full support 53IE No support NoOpera Full support 42Safari ? WebView Android Full support 55
Notes
Full support 55
Notes
Notes Before version 59, the default values were not supported.
Chrome Android Full support 55
Notes
Full support 55
Notes
Notes Before Chrome 59, the default values were not supported.
Edge Mobile ? Firefox Android Full support 53Opera Android Full support 42Safari iOS ? Samsung Internet Android Full support 6.0
lengthChrome Full support 51Edge Full support YesFirefox Full support YesIE No support NoOpera Full support 38Safari No support NoWebView Android Full support 51Chrome Android Full support 51Edge Mobile Full support YesFirefox Android Full support YesOpera Android Full support 38Safari iOS No support NoSamsung Internet Android Full support 5.0
oncompleteChrome Full support 14Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 15Safari Full support 6WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support 15Safari iOS ? Samsung Internet Android Full support Yes
resumeChrome Full support 49Edge Full support YesFirefox No support NoIE No support NoOpera Full support 36Safari No support NoWebView Android Full support 49Chrome Android Full support 49Edge Mobile Full support YesFirefox Android No support NoOpera Android Full support 36Safari iOS No support NoSamsung Internet Android Full support 5.0
suspendChrome Full support 49Edge Full support YesFirefox No support NoIE No support NoOpera Full support 36Safari No support NoWebView Android Full support 49Chrome Android Full support 49Edge Mobile Full support YesFirefox Android No support NoOpera Android Full support 36Safari iOS No support NoSamsung Internet Android Full support 5.0
startRenderingChrome Full support 14Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 15Safari Full support 6WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support 15Safari iOS ? Samsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
See implementation notes.
See implementation notes.

See also

Étiquettes et contributeurs liés au document

Dernière mise à jour par : chrisdavidmills,