Node Web Audio API
=====================
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This library implements the [web audio API specification](http://webaudio.github.io/web-audio-api/) 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 :
```javascript
var AudioContext = require('web-audio-api').AudioContext
, context = new AudioContext
, Speaker = require('speaker')
context.outStream = new Speaker({
channels: context.format.numberOfChannels,
bitDepth: context.format.bitDepth,
sampleRate: context.sampleRate
})
// 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](http://alsa.opensrc.org/Aplay). For this, simply send the generated sound straight to `stdout` like this :
```javascript
var AudioContext = require('web-audio-api').AudioContext
, context = new AudioContext
context.outStream = process.stdout
// 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](http://icecast.org/) is a open-source streaming server. It works great, and is very easy to setup. **icecast** accepts connections from [different source clients](http://icecast.org/apps/) which provide the sound to encode and stream. [ices](http://www.icecast.org/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](http://funktion.fm/#/projects/versificator-rubbish-stream)
Using Gibber
---------------
[Gibber](https://github.com/charlieroberts/Gibber) is a great audiovisual live coding environment for the browser made by [Charlie Roberts](http://charlie-roberts.com). 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:
```javascript
context._kill()
debugger
```
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` and `mathjs` 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**
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