Description

Javascript-library for finding out tempo (BPM) of a song and beat tracking. It uses an algorithm “Beatroot” authored by Simon Dixon

Example App

Docs

Instalation

In a browser

<script src="music-tempo.min.js"></script>

Using npm:

$ npm i --save music-tempo

Usage

Pass to the constructor MusicTempo the buffer that contains data in the following format: non-interleaved IEEE754 32-bit linear PCM with a nominal range between -1 and +1, that is, 32bits floating point buffer, with each samples between -1.0 and 1.0. This format is used in the AudioBuffer interface of Web Audio API. The object returned by the constructor contain properties tempo - tempo value in beats per minute and beats - array with beat times in seconds.

Browser

var context = new AudioContext({ sampleRate: 44100 });
var fileInput = document.getElementById("fileInput");

fileInput.onchange = function () {
  var files = fileInput.files;

  if (files.length == 0) return;
  var reader = new FileReader();

  reader.onload = function(fileEvent) {
    context.decodeAudioData(fileEvent.target.result, calcTempo);
  }

  reader.readAsArrayBuffer(files[0]);
}
var calcTempo = function (buffer) {
  var audioData = [];
  // Take the average of the two channels
  if (buffer.numberOfChannels == 2) {
    var channel1Data = buffer.getChannelData(0);
    var channel2Data = buffer.getChannelData(1);
    var length = channel1Data.length;
    for (var i = 0; i < length; i++) {
      audioData[i] = (channel1Data[i] + channel2Data[i]) / 2;
    }
  } else {
    audioData = buffer.getChannelData(0);
  }
  var mt = new MusicTempo(audioData);

  console.log(mt.tempo);
  console.log(mt.beats);
}

Node.js

In Node.js environment can be used node-web-audio-api library

var AudioContext = require("web-audio-api").AudioContext;
var MusicTempo = require("music-tempo");
var fs = require("fs");

var calcTempo = function (buffer) {
  var audioData = [];
  // Take the average of the two channels
  if (buffer.numberOfChannels == 2) {
    var channel1Data = buffer.getChannelData(0);
    var channel2Data = buffer.getChannelData(1);
    var length = channel1Data.length;
    for (var i = 0; i < length; i++) {
      audioData[i] = (channel1Data[i] + channel2Data[i]) / 2;
    }
  } else {
    audioData = buffer.getChannelData(0);
  }
  var mt = new MusicTempo(audioData);

  console.log(mt.tempo);
  console.log(mt.beats);
}

var data = fs.readFileSync("songname.mp3");

var context = new AudioContext();
context.decodeAudioData(data, calcTempo);

Optional parameters

You can pass object with parameters as second argument to the constructor:

var p = { expiryTime: 30, maxBeatInterval: 1.5 };
var mt = new MusicTempo(audioData, p);

Most useful are maxBeatInterval/minBeatInterval and expiryTime. First two used for setting up maximum and minimum BPM. Default value for maxBeatInterval is 1 which means that minimum BPM is 60 (60 / 1 = 60). Default value for minBeatInterval is 0.3 which means that maximum BPM is 200 (60 / 0.3 = 200). Be careful, the more value of maximum BPM, the more probability of 2x-BPM errors (e.g. if max BPM = 210 and real tempo of a song 102 BPM, in the end you can get 204 BPM). expiryTime can be used if audio file have periods of silence or almost silence and because of that beat tracking is failing. Other parameters are listed in documentation.

Other

Tests

Requires mocha and chai

$ npm test

Documentation

Requires esdoc

$ esdoc

Build

Requires gulp and babel. Other dependencies can be found in package.json

$ gulp build

License

MIT License