libalac

libalac

Bindings to the official Apple Lossless (ALAC) encoder and decoder.

WARNING: This module is rather broken. I wrote it with poor understanding of how the codec works. Use at your own risk!

Installing

$ npm install libalac

Encoder usage

The encoder is a regular stream:

var alac = require('libalac');
var enc = alac.encoder({
  sampleRate: 44100,
  channels: 2,
  bitDepth: 16
});
input.pipe(enc).pipe(output);

alac.encoder() must have an object argument, which can contain regular readable and writable stream options, along with the following:

• sampleRate (in Hz) required
• channels, required
• bitDepth, required
• framesPerPacket, defaults to 4096 (usually no need to modify this)

The encoder object also has the following properties:

• cookie, a buffer containing the ALAC magic cookie. These are parameters for the decoder, and is what you'd place in e.g. the kuki chunk of a CAF-file.

• packets, array of sizes of packets in the stream. This array is only ever pushed to, and can be modified, or even replaced with an array-like object, as long as it has a push method.

• sampleRate, channels, bitDepth, and framesPerPacket containing the final parameters used in the encoder.

Note that the encoder always reads input in native byte order!

Decoder usage

The decoder is a regular stream:

var alac = require('libalac');
var dec = alac.decoder({
  cookie: cookie,
  channels: 2,
  bitDepth: 16,
  framesPerPacket: 4096,
  packets: packets
});
input.pipe(dec).pipe(output);

alac.decoder() must have an object argument, which can contain regular readable and writable stream options, along with the following:

• cookie, required, a buffer as generated by the encoder
• channels, required
• bitDepth, required
• framesPerPacket, required
• packets, an array of packet sizes

Instead of providing packets up front, it can also be provided (or extended) during streaming by calling packets(arr) one or more times.

Usually, these parameters can all be extracted from the container format. For example, in a CAF-file, they live in the desc, kuki and pakt chunks.

Note that the decoder always outputs in native byte order!

Hacking the code

git clone https://github.com/stephank/libalac.git
cd libalac
npm install
npm test