OfflineAudioContext: OfflineAudioContext() constructor
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2021.
The
OfflineAudioContext() constructor—part of the Web Audio API—creates and returns a new
OfflineAudioContext object instance, which can then be used to render
audio to an AudioBuffer rather than to an audio output device.
Syntax
new OfflineAudioContext(options)
new OfflineAudioContext(numberOfChannels, length, sampleRate)
Parameters
You can specify the parameters for the OfflineAudioContext() constructor
as either the same set of parameters as are inputs into the
BaseAudioContext.createBuffer method, or by passing those parameters in an
options object. Either way, the individual parameters are the same.
numberOfChannels-
An integer specifying the number of channels the resulting
AudioBuffershould have. length-
An integer specifying the size of the buffer to create for the audio context, in sample-frames, where one sample-frame is a unit that can contain a single sample of audio data for every channel in the audio data. For example, a 5-second buffer with a
sampleRateof 48000Hz would have a length of5 * 48000 = 240000sample-frames. sampleRate-
The sample-rate of the linear audio data in sample-frames per second. All user agents are required to support a range of 8000Hz to 96000Hz, and may support a wider range than that. The most commonly-used rate is 44100Hz, which is the sample rate used by CD audio.
It is important to note that, whereas you can create a new AudioContext
using the AudioContext() constructor
with no arguments, the OfflineAudioContext() constructor requires three
arguments, since it needs to create an AudioBuffer. This works in exactly
the same way as when you create a new AudioBuffer with the
BaseAudioContext.createBuffer method. For more detail, read Audio buffers: frames, samples and channels from our Basic concepts guide.
Return value
A new OfflineAudioContext object whose associated
AudioBuffer is configured as requested.
Like a regular AudioContext, an
OfflineAudioContext can be the target of events, therefore it implements
the EventTarget interface.
Examples
const offlineCtx = new OfflineAudioContext({
numberOfChannels: 2,
length: 44100 * 40,
sampleRate: 44100,
});
const source = offlineCtx.createBufferSource();
// …
For a full working example, see our offline-audio-context-promise GitHub repo (see the source code too.)
Specifications
| Specification |
|---|
| Web Audio API # dom-offlineaudiocontext-offlineaudiocontext |
Browser compatibility
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