alac2pcm

A Node.js streaming libary and command line tool that converts Apple Lossless (ALAC) audio to raw PCM audio.

CLI usage

Install as a global module:

npm install -g alac2pcm

Pipe binary ALAC bytes into STDIN and, alac2pcm will output raw PCM audio bytes on STDOUT:

cat audio.alac | alac2pcm > audio.pcm

For a list of available configuration options, write:

alac2pcm --help

Programmatic usage

Install as a local module:

npm install --save alac2pcm

Then you can just use it as a regular node stream:

var Alac2Pcm = require('alac2pcm')

var options = {
  bitDepth: 8
}
var alac2pcm = new Alac2Pcm(options)

sourceAlacStream.pipe(alac2pcm).pipe(pcmPlayer)

Configuration

When instantiating the Alac2Pcm object an optional options object can be provided:

• frameLength - (default: 352) Indicating the frames per packet when no explicit frames per packet setting is present in the packet header. The encoder frames per packet can be explicitly set but for maximum compatibility, the default encoder setting of 4096 should be used
• bitDepth - (default: 16) Describes the bit depth of the source PCM data (maximum value = 32)
• channels - (default: 2) Describes the channel count (1 = mono, 2 = stereo, etc...). When channel layout info is not provided in the 'magic cookie', a channel count > 2 describes a set of discreet channels with no specific ordering
• maxFrameBytes - (default: 0) The maximum size of an Apple Lossless packet within the encoded stream. Value of 0 indicates unknown
• avgBitRate - (default: 0) The average bit rate in bits per second of the Apple Lossless stream. Value of 0 indicates unknown
• sampleRate - (default: 44100) Sample rate of the encoded stream

Aditional, but currently unused options:

• compatibleVersion - (default: 0) Indicating compatible version. Value must be set to 0
• pb - (default: 40) Currently unused tuning parameter. Value should be set to 40
• mb - (default: 10) Currently unused tuning parameter. Value should be set to 10
• kb - (default: 14) Currently unused tuning parameter. Value should be set to 14
• maxRun - (default: 255) Currently unused. Value should be set to 255

Todo's

• Support for Node.js 0.12 and 4

License

MIT