Transcode an OGG Vorbis audio file to an MP3 using node-ogg, node-vorbis and node-lame

transcode.js

/**
 * Module dependencies.
 */

var fs = require('fs');
var ogg = require('ogg');
var lame = require('lame');
var vorbis = require('vorbis');

var od = new ogg.Decoder();

od.on('stream', function (stream) {
  var vd = new vorbis.Decoder();

  // the "format" event contains the raw PCM format
  vd.on('format', function (format) {
    var bytesPerSample = format.bitDepth / 8;
    var encoder = new lame.Encoder();
    var out = fs.createWriteStream(new Date().getTime() + '.mp3');
    encoder.pipe(out);

    var leftover;
    vd.on('data', function (b) {

      // first we have to make sure that the Buffer we got is a multiple of
      // "float" sized, so that it will fit nicely into a Float32Array
      if (leftover) {
        b = Buffer.concat([ leftover, b ]);
      }
      var len = (b.length / bytesPerSample | 0) * bytesPerSample;
      if (len != b.length) {
        console.error('resizing Buffer from %d to %d', b.length, len);
        leftover = b.slice(len);
        b = b.slice(0, len);
      }

      // now that we know "b" is aligned to "float" sized, create a TypedArray
      // from it, and create an output Buffer where the "int" samples will go
      var floatSamples = new Float32Array(b);
      var o = new Buffer(floatSamples.length * 2);
      var intSamples = new Int16Array(o);

      // we need to convert all the float samples into short int samples
      // and populate the "intSamples" array
      for (var i = 0; i < floatSamples.length; i++) {
        var f = floatSamples[i];
        var val = Math.floor(f * 32767.0 + 0.5);

        // might as well guard against clipping
        if (val > 32767) {
          console.error('clipping detected: %d -> %d', val, 32767);
          val = 32767;
        }
        if (val < -32768) {
          console.error('clipping detected: %d -> %d', val, -32768);
          val = -32768;
        }
        intSamples[i] = val;
      }

      // write the populated "intSamples" Buffer to the lame encoder
      encoder.write(o);
    });
  });

  // an "error" event will get emitted if the stream is not a Vorbis stream
  // (i.e. it could be a Theora video stream instead)
  vd.on('error', function (err) {
    console.log(err);
    // maybe try another decoder...
  });

  stream.pipe(vd);
});

fs.createReadStream(process.argv[2]).pipe(od);