Node Web Audio API
This library implements the web audio API specification on node.js.
And this is not even alpha. Use this library only if you're the adventurous kind.
What's implemented
- AudioContext(partially)
- AudioParam (almost there)
- AudioBufferSourceNode
- ScriptProcessorNode
- GainNode
- OscillatorNode (coming soon)
- DelayNode (coming soon)
Installation
npm install web-audio-api
Demo
Get ready, this is going to blow up your mind :
npm install
gulp default
node test/manual-testing/AudioContext-sound-output.js
Audio output
By default, node-web-audio-api doesn't play back the sound it generates. In fact, an AudioContext
has no default output, and you need to give it a writable node stream to which it can write raw PCM audio. After creating an AudioContext
, set its output stream like this : audioContext.outStream = writableStream
.
Example : playing back sound with node-speaker
This is probably the simplest way to play back audio. Install node-speaker with npm install speaker
, then do something like this :
var AudioContext = AudioContext context = Speaker = contextoutStream = channels: contextformatnumberOfChannels bitDepth: contextformatbitDepth sampleRate: contextsampleRate // Create some audio nodes here to make some noise ...
Example : playing back sound with aplay
Linux users can play back sound from node-web-audio-api by piping its output to aplay. For this, simply send the generated sound straight to stdout
like this :
var AudioContext = AudioContext context = contextoutStream = processstdout // Create some audio nodes here to make some noise ...
Then start your script, piping it to aplay like so :
node myScript.js | aplay -f cd
Example : creating an audio stream with icecast2
icecast is a open-source streaming server. It works great, and is very easy to setup. icecast accepts connections from different source clients which provide the sound to encode and stream. ices is a client for icecast which accepts raw PCM audio from its standard input, and you can send sound from node-web-audio-api to ices (which will send it to icecast) by simply doing :
var spawn = require('child_process').spawn
, AudioContext = require('web-audio-api').AudioContext
, context = new AudioContext()
var ices = spawn('ices', ['ices.xml'])
context.outStream = ices.stdin
A live example is available on Sébastien's website
Using Gibber
Gibber is a great audiovisual live coding environment for the browser made by Charlie Roberts. For audio, it uses Web Audio API, so you can run it on node-web-audio-api. First install gibber with npm :
npm install gibber.audio.lib
Then to you can run the following test to see that everything works:
npm test gibber.audio.lib
Overall view of implementation
Each time you create an AudioNode
(like for instance an AudioBufferSourceNode
or a GainNode
), it inherits from DspObject
which is in charge of two things:
- register schedule events with
_schedule
- compute the appropriate digital signal processing with
_tick
Each time you connect an AudioNode
using source.connect(destination, output, input)
it connects the relevant AudioOutput
instances of source
node the the relevant AudioInput
instance of the destination
node.
To instantiate all of these AudioNode
, you needed an overall AudioContext
instance. This latter has a destination
property (where the sound will flow out), instance of AudioDestinationNode
, which inherits from AudioNode
. The AudioContext
instance keeps track of connections to the destination
. When that happens, it triggers the audio loop, calling _tick
infinitely on the destination
, which will itself call _tick
on its input ... and so forth go up on the whole audio graph.
Running the debugger
Right now everything runs in one process, so if you set a break point in your code, there's going to be a lot of buffer underflows, and you won't be able to debug anything.
One trick is to kill the AudioContext
right before the break point, like this:
contextdebugger
that way the audio loop is stopped, and you can inspect your objects in peace.
Running the tests
Tests are written with mocha. To run them, install mocha with :
npm install -g mocha
And in the root folder run :
npm test
Manual testing
To test the sound output, we need to install node-speaker
(in addition of all the other dependencies), and build the library :
npm install
npm install speaker
gulp default
node test/manual-testing/AudioContext-sound-output.js
To test AudioParam
against AudioParam
implemented in a browser, open test/manual-testing/AudioParam-browser-plots.html
in that browser.
Contributors
61 Sébastien Piquemal
16 ouhouhsami
4 John Wnek
2 anprogrammer
1 Andrew Petersen
Changelog
0.2.2
- removed
node-speaker
andmathjs
dependencies
0.2.1
- now use aurora installed from npm instead of distributing a built version of it.
0.2.0
- refactored to ES6
0.1.5
- AudioNode and AudioContext bug fixes
0.1.4
- audioports : bug fixes
0.1.3
- audioports : implemented
channelInterpretation
'speakers' - AudioContext : added support for mp3 to
decodeAudioData
0.1.2
- AudioBufferSourceNode : handler
onended
implemented - AudioContext : method
decodeAudioData
, support only for wav
0.1.1
-
ScriptProcessorNode
-
AudioBufferSourceNode
- node is killed once it has finished playing
- subsequent calls to
start
have no effect
-
AudioContext : method
collectNodes
-
audioports : bug fixes
0.1.0
- AudioContext (partial implementation)
- AudioParam (missing unschedule)
- AudioBufferSourceNode (missing onended)
- GainNode