For all your async streaming MP3 encoding/decoding needs, there's node-lame! This module hooks into libmp3lame, the library that the lame command uses, to provide Encoder and Decoder streams to NodeJS.

node-lame comes bundled with its own copy of libmp3lame and libmpg123, so there's no need to have them installed on your system.

Simply compile and install node-lame using npm:

$ npm install lame

Here's an example of using node-lame to encode some raw PCM data coming from process.stdin to an MP3 file that gets piped to process.stdout:

var lame = require('lame');

// create the Encoder instance
var encoder = new lame.Encoder({
  // input
  channels: 2,        // 2 channels (left and right)
  bitDepth: 16,       // 16-bit samples
  sampleRate: 44100,  // 44,100 Hz sample rate

  // output
  bitRate: 128,
  outSampleRate: 22050,
  mode: lame.STEREO // STEREO (default), JOINTSTEREO, DUALCHANNEL or MONO
});

// raw PCM data from stdin gets piped into the encoder
process.stdin.pipe(encoder);

// the generated MP3 file gets piped to stdout
encoder.pipe(process.stdout);

See the examples directory for some more example code.

The Decoder class is a Stream subclass that accepts MP3 data written to it, and outputs raw PCM data. It also emits a "format" event when the format of the MP3 file is determined (usually right at the beginning).

The Encoder class is a Stream subclass that accepts raw PCM data written to it, and outputs a valid MP3 file. You must specify the PCM data format when creating the encoder instance. Only 16-bit signed samples are currently supported (rescale before passing to the encoder if necessary)...