OfflineAudioContext

The OfflineAudioContext interface inherits from BaseAudioContext. In contrast with a standard AudioContext, it doesn't render audio to the device hardware. Instead, it processes the audio as quickly as possible and outputs the result to an AudioBuffer.

Constructor

OfflineAudioContext(options: OfflineAudioContextOptions)

interface OfflineAudioContextOptions {
  numberOfChannels: number;
  length: number; // The length of the rendered AudioBuffer, in sample-frames
  sampleRate: number;
}

Properties

OfflineAudioContext does not define any additional properties. Inherits all properties from BaseAudioContext.

Methods

Inherits all methods from BaseAudioContext.

suspend

Schedules a suspension of the time progression in audio context at the specified time.

Parameter	Type	Description
suspendTime	number	A floating-point number specifying the suspend time, in seconds.

Returns Promise<undefined>.

resume

Resume time progression in audio context when it has been suspended.

Returns Promise<undefined>

startRendering

Starts rendering the audio, taking into account the current connections and the current scheduled changes.

Returns Promise<AudioBuffer>.

Events

Inherits onstatechange from BaseAudioContext. It fires when rendering starts (running), when a scheduled suspend point is reached (suspended), after resume (running), and when rendering finishes (closed).

oncomplete

Sets (or removes, when null is assigned) a callback fired when rendering has finished, in the same task that resolves the startRendering promise. state already reads closed inside the callback; the closed statechange itself arrives in a later task. The callback receives an event object:

Field	Type	Description
type	string	Always 'complete'.
target	OfflineAudioContext	The context that finished rendering.
renderedBuffer	AudioBuffer	The rendered audio.

const offlineContext = new OfflineAudioContext({
  numberOfChannels: 2,
  length: 44100,
  sampleRate: 44100,
});

offlineContext.oncomplete = (event) => {
  console.log(`rendered ${event.renderedBuffer.duration}s of audio`);
};

await offlineContext.startRendering();