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Getting Started with Web Audio API

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@mozillaMozilla

Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape.

The Web Audio API provides a powerful and versatile system for
controlling audio on the Web, allowing developers to choose audio sources, add effects to audio, create audio visualizations, apply
spatial effects (such as panning) and much more.

Web audio concepts and usage

The Web Audio API involves handling audio operations inside an audio context, and has been designed to allow modular routing. Basic audio operations are performed with audio nodes, which are linked together to form an audio routing graph. Several sources — with different types of channel layout — are supported even within a single context. This modular design provides the flexibility to create complex audio functions with dynamic effects.
Audio nodes are linked into chains and simple webs by their inputs and outputs. They typically start with one or more sources. Sources provide arrays of sound intensities (samples) at very small timeslices, often tens of thousands of them per second. These could be either computed mathematically (such as
OscillatorNode
), or they can be recordings from sound/video files (like
AudioBufferSourceNode
and
MediaElementAudioSourceNode
) and audio streams (
MediaStreamAudioSourceNode
).
In fact, sound files are just recordings of sound intensities themselves, which come in from microphones or electric instruments, and get mixed down into a single, complicated wave.
Outputs of these nodes could be linked to inputs of others, which mix or modify these streams of sound samples into different streams. A common modification is multiplying the samples by a value to make them louder or quieter (as is the case with
GainNode
).
Once the sound has been sufficiently processed for the intended effect, it can be linked to the input of a destination (
AudioContext.destination
), which sends the sound to the speakers or headphones. This last connection is only necessary if the user is supposed to hear the audio.
A simple, typical workflow for web audio would look something like this:
  1. Create audio context
  2. Inside the context, create sources — such as
    <audio>
    , oscillator, stream
  3. Create effects nodes, such as reverb, biquad filter, panner, compressor
  4. Choose final destination of audio, for example your system speakers
  5. Connect the sources up to the effects, and the effects to the destination.
Timing is controlled with high precision and low latency, allowing
developers to write code that responds accurately to events and is able to target specific samples, even at a high sample rate. So applications such as drum machines and sequencers are well within reach.
The Web Audio API also allows us to control how audio is spatialized. Using a system based on a source-listener model, it allows control of the panning model and deals with distance-induced attenuation or doppler shift induced by a moving source (or moving listener).
You can read about the theory of the Web Audio API in a lot more detail in our article Basic concepts behind Web Audio API.

Web Audio API target audience

The Web Audio API can seem intimidating to those that aren't familiar with audio or music terms, and as it incorporates a great deal of functionality it can prove difficult to get started if you are a developer.
It can be used to simply incorporate audio into your website or application, by providing atmosphere like futurelibrary.no, or auditory feedback on forms. However, it can also be used to create advanced interactive instruments. With that in mind, it is suitable for both developers and musicians alike.
We have a simple introductory tutorial for those that are familiar with programming but need a good introduction to some of the terms and structure of the API.
There's also a Basic Concepts Behind Web Audio API article, to help you understand the way digital audio works, specifically in the realm of the API. This also includes a good introduction to some of the concepts the API is built upon.
Learning coding is like playing cards — you learn the rules, then you play, then you go back and learn the rules again, then you play again. So if some of the theory doesn't quite fit after the first tutorial and article, there's an advanced tutorial which extends the first one to help you practise what you've learnt, and apply some more advanced techniques to build up a step sequencer.
We also have other tutorials and comprehensive reference material
available that covers all features of the API. See the sidebar on this
page for more.
If you are more familiar with the musical side of things, are familiar with music theory concepts, want to start building instruments, then you can go ahead and start building things with the advance tutorial and others as a guide (the above linked tutorial covers scheduling notes, creating bespoke oscillators and envelopes, as well as an LFO among other things.)
If you aren't familiar with the programming basics, you might want to consult some beginner's JavaScript tutorials first and then come back here — see our Beginner's JavaScript learning module for a great place to begin.

Web Audio API Interfaces

The Web Audio API has a number of interfaces and associated events,
which we have split up into nine categories of functionality.
General audio graph definition
General containers and definitions that shape audio graphs in Web Audio API usage.
The
AudioContext
interface represents an audio-processing graph built from audio modules linked together, each represented by an
AudioNode
. An audio context controls the creation of the nodes it contains and the execution of the audio processing, or decoding. You need to create an
AudioContext
before you do anything else, as everything happens inside a context.

AudioContextOptions
The
AudioContextOptions
dictionary is used to provide options when instantiating a new
AudioContext
.
The
AudioNode
interface represents an audio-processing module like an audio source (e.g. an HTML
<audio>
or
<video>
element), audio destination, intermediate processing module (e.g. a filter like
BiquadFilterNode
, or volume control like
GainNode
).
The
AudioParam
interface represents an audio-related parameter, like one of an
AudioNode
. It can be set to a specific value or a change in value, and can be scheduled to happen at a specific time and following a specific pattern.
Provides a maplike interface to a group of 
AudioParam
interfaces, which means it provides the methods 
forEach()
,
get()
,
has()
,
keys()
, and 
values()
, as well as a
size
property.
The
BaseAudioContext
interface acts as a base definition for online and offline audio-processing graphs, as represented by
AudioContext
and
OfflineAudioContext
respectively. You wouldn't use
BaseAudioContext
directly — you'd use its features via one of these two inheriting interfaces.
The
ended
event
The
ended
event is fired when playback has stopped because the end of the media was reached.
Defining audio sources

Interfaces that define audio sources for use in the Web Audio API.
The
AudioScheduledSourceNode
is a parent interface for several types of audio source node interfaces. It is an
AudioNode
.

OscillatorNode
The 
OscillatorNode
 interface represents a periodic waveform, such as a sine or triangle wave. It is an
AudioNode
audio-processing module that causes a given frequency of wave to be created.
The
AudioBuffer
interface represents a short audio asset residing in memory, created from an audio file using the
AudioContext.decodeAudioData()
method, or created with raw data using
AudioContext.createBuffer()
. Once decoded into this form, the audio can then be put into an
AudioBufferSourceNode
.
The
AudioBufferSourceNode
interface represents an audio source consisting of in-memory audio data, stored in an
AudioBuffer
. It is an
AudioNode
that acts as an audio source.
The
MediaElementAudioSourceNode
interface represents an audio source consisting of an HTML5
<audio>
or
<video>
element. It is an
AudioNode
that acts as an audio source.
The
MediaStreamAudioSourceNode
interface represents an audio source consisting of a
MediaStream
(such as a webcam, microphone, or a stream being sent from a remote computer). If multiple audio tracks are present on the stream, the track whose
id
comes first lexicographically (alphabetically) is used. It is an
AudioNode
that acts as an audio source.
A node of type
MediaStreamTrackAudioSourceNode
represents an audio source whose data comes from a
MediaStreamTrack
. When creating the node using the
createMediaStreamTrackSource()
method to create the node, you specify which track to use. This provides more control than
MediaStreamAudioSourceNode
.
Defining audio effects filters
Interfaces for defining effects that you want to apply to your audio sources.
The
BiquadFilterNode
interface represents a simple low-order filter. It is an
AudioNode
that can represent different kinds of filters, tone control devices, or graphic equalizers. A
BiquadFilterNode
always has exactly one input and one output.
The
ConvolverNode
interface is an 
AudioNode
that performs a Linear Convolution on a given
AudioBuffer
, and is often used to achieve a reverb effect.
The
DelayNode
interface represents a delay-line; an
AudioNode
 
audio-processing module that causes a delay between the arrival of an input data and its propagation to the output.
The
DynamicsCompressorNode
interface provides a compression effect, which lowers the volume of the loudest parts of the signal in order to help prevent clipping and distortion that can occur when multiple sounds are played and multiplexed together at once.
The
GainNode
interface represents a change in volume. It is an
AudioNode
audio-processing module that causes a given gain to be applied to the input data before its propagation to the output.
The
WaveShaperNode
interface represents a non-linear distorter. It is an
AudioNode
that use a curve to apply a waveshaping distortion to the signal. Beside obvious distortion effects, it is often used to add a warm feeling to the signal.
Describes a periodic waveform that can be used to shape the output of an OscillatorNode.
Implements a general infinite impulse response (IIR)  filter; this type of filter can be used to implement tone control devices and graphic equalizers as well.
Defining audio destinations

Once you are done processing your audio, these interfaces define where to output it.
The
AudioDestinationNode
interface represents the end destination of an audio source in a given context — usually the speakers of your device.
The
MediaStreamAudioDestinationNode
interface represents an audio destination consisting of a WebRTC
MediaStream
with a single AudioMediaStreamTrack, which can be used in a similar way to a
MediaStream
obtained from
getUserMedia()
. It is an
AudioNode
that acts as an audio destination.
Data analysis and visualization

If you want to extract time, frequency, and other data from your audio, the AnalyserNode is what you need.
The
AnalyserNode
interface represents a node able to provide real-time frequency and time-domain analysis information, for the purposes of data analysis and visualization.
Splitting and merging audio channels

To split and merge audio channels, you'll use these interfaces.
The
ChannelSplitterNode 
interface separates the different channels of an audio source out into a set of mono outputs.
The
ChannelMergerNode
interface reunites different mono inputs into a single output. Each input will be used to fill a channel of the output.
Audio spatialization
These interfaces allow you to add audio spatialization panning effects to your audio sources.
The
AudioListener
interface represents the position and orientation of the unique person listening to the audio scene used in audio spatialization.
The
PannerNode
interface represents the position and behavior of an audio source signal in 3D space, allowing you to create complex panning effects.
The
StereoPannerNode
interface represents a simple stereo panner node that can be used to pan an audio stream left or right.
Audio processing in JavaScript

Using audio worklets, you can define custom audio nodes written in JavaScript or WebAssembly. Audio worklets implement the
Worklet
interface, a lightweight version of the
Worker
interface. Audio worklets are enabled by default for Chrome 66 or later.
The AudioWorklet interface is available via
BaseAudioContext.audioWorklet
, and allows you to add new modules to the audio worklet.
The
AudioWorkletNode
interface represents an
AudioNode
that is embedded into an audio graph and can pass messages to the corresponding
AudioWorkletProcessor
.
The
AudioWorkletProcessor
interface represents audio processing code running in a
AudioWorkletGlobalScope
that generates, processes, or analyses audio directly, and can pass messages to the corresponding
AudioWorkletNode
.
The
AudioWorkletGlobalScope
interface is a
WorkletGlobalScope 
-derived object representing a worker context in which an audio processing script is run; it is designed to enable the generation, processing, and analysis of audio data directly using JavaScript in a worklet thread.

Obsolete: script processor nodes

Before audio worklets were defined, the Web Audio API used the
ScriptProcessorNode
  for JavaScript-based audio processing. Because the code runs in the main thread, they have bad performance. The
ScriptProcessorNode
is kept for historic reasons but is marked as deprecated and will be removed in a future version of the specification.
The ScriptProcessorNode interface allows the generation, processing, or analyzing of audio using JavaScript. It is an
AudioNode
audio-processing module that is linked to two buffers, one containing the current input, one containing the output. An event, implementing the
AudioProcessingEvent
interface, is sent to the object each time the input buffer contains new data, and the event handler terminates when it has filled the output buffer with data.
audioprocess
(event)
The
audioprocess
event is fired when an input buffer of a Web Audio API
ScriptProcessorNode
is ready to be processed.
The
Web Audio API
AudioProcessingEvent
represents events that occur when a
ScriptProcessorNode
input buffer is ready to be processed.
Offline/background audio processing

It is possible to process/render an audio graph very quickly in the background — rendering it to an
AudioBuffer
rather than to the device's speakers — with the following.
The
OfflineAudioContext
interface is an
AudioContext
interface representing an audio-processing graph built from linked together
AudioNode
s. In contrast with a standard AudioContext, an OfflineAudioContext doesn't really render the audio but rather generates it, as fast as it can, in a buffer.
complete
(event)
The
complete 
event is fired when the rendering of an
OfflineAudioContext
is terminated.
The
OfflineAudioCompletionEvent
represents events that occur when the processing of an
OfflineAudioContext
is terminated. The
complete
event implements this interface.

Obsolete interfaces

The following interfaces were defined in old versions of the Web Audio API spec, but are now obsolete and have been replaced by other interfaces.
Used for direct audio processing via JavaScript. This interface is obsolete, and has been replaced by
ScriptProcessorNode
.
Used to define a periodic waveform. This interface is obsolete, and has been replaced by
PeriodicWave
.

Examples

You can find a number of examples at our webaudio-example repo on GitHub.

Specifications

Browser compatibility

    AudioContext

See also

Tutorials/guides
Libraries
  • Tones: a simple library for playing specific tones/notes using the Web Audio API.
  • Tone.js: a framework for creating interactive music in the browser.
  • howler.js: a JS audio library that defaults to Web Audio API and falls back to HTML5 Audio, as well as providing other useful features.
  • Mooog: jQuery-style chaining of AudioNodes, mixer-style sends/returns, and more.
  • XSound: Web Audio API Library for Synthesizer, Effects, Visualization, Recording ... etc
  • OpenLang: HTML5 video language lab web application using the Web Audio API to record and combine video and audio from different sources into a single file (source on GitHub)
  • Pts.js: Simplifies web audio visualization (guide)
Related topics

See also

Credits

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Mozilla (stylized as moz://a) is a free software community founded in 1998 by members of Netscape.

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