Read PCM (WAV) data with node.js

audioExtractor.js

var spawn = require('child_process').spawn;

exports.getPcmData = function(filename, sampleCallback, endCallback) {
  var outputStr = '';
  var oddByte = null;
  var channel = 0;
  var gotData = false;
  
  // Extract signed 16-bit little endian PCM data with ffmpeg and pipe to STDOUT
  var ffmpeg = spawn('ffmpeg', ['-i',filename,'-f','s16le','-ac','2',
    '-acodec','pcm_s16le','-ar','44100','-y','pipe:1']);
  
  ffmpeg.stdout.on('data', function(data) {
    gotData = true;
    
    var i = 0;
    var samples = Math.floor((data.length + (oddByte !== null ? 1 : 0)) / 2);
    
    // If there is a leftover byte from the previous block, combine it with the
    // first byte from this block
    if (oddByte !== null) {
      value = ((data.readInt8(i++) << 8) | oddByte) / 32767;
      sampleCallback(value, channel);
      channel = ++channel % 2;
    }
    
    for (; i < data.length; i += 2) {
      value = data.readInt16LE(i) / 32767;
      sampleCallback(value, channel);
      channel = ++channel % 2;
    }
    
    oddByte = (i < data.length) ? data.readUInt8(i) : null;
  });
  
  ffmpeg.stderr.on('data', function(data) {
    // Text info from ffmpeg is output to stderr
    outputStr += data.toString();
  });
  
  ffmpeg.stderr.on('end', function() {
    if (gotData)
      endCallback(null, outputStr);
    else
      endCallback(outputStr, null);
  });
};