music.js

var music = new Music(data);

setInterval(function() {
  var res = music.next();
  if (res.bars.length + res.beats.length + res.tatums.length + res.sections.length + res.segments.length) {
    console.log(res);
  }
});

function Music(data) {
  this.data = data;
}

Music.prototype.next = function() {
  if (!this.start) {
    this.start = new Date();
  }
  var now = new Date();
  var time = (now - this.start) / 1000;

  var res = {};

  ['bars', 'beats', 'tatums', 'sections', 'segments'].forEach(function(key) {
    res[key] = [];
    this.data[key] = this.data[key].filter(function(el, i) {
      if (el.start <= time) {
        res[key].push(el);
        return false;
      }
      return true;
    });
  }, this);

  return res;
};