Awesome

mp3-concat

A transform stream that you write several mp3 files to and transforms them into one single mp3 file.

Just make sure, that you've got mp3cat installed and available in your PATH

example

var fs = require('fs');
var async = require('async');
var concatstream = require('mp3-concat');

// Create the concat stream
var concatenater = concatstream();

// Pipe the output to a 'concat.mp3' file
concatenater.pipe(fs.createWriteStream('concat.mp3'));

// Loop through the files in series
async.eachSeries(['file1.mp3', 'file2.mp3'], function(file, cb) {
  // ... and pipe them into the concatenater
  fs
    .createReadStream(file)
    .on('end', cb)
    .pipe(concatenater, { end: false });
}, function() {
  // Finally, when all files have been read, close the stream
  concatenater.end();  
});

events

.on('offset', cb({ duration: [Number], offset: [Number] }))

This event is emitted per input stream. duration is the calculated duration of the file/stream resource, while offset is its position in the concatenated file. Both numbers are in seconds.

.on('error', cb({ rawError: [Error], reason: [String] })

This event is fired when there's trouble spawning mp3cat. This is most probably because you forgot to install it and add it to your PATH.