code: func (t *Track) Tempo() int {
  	if t == nil {
  		return 0
  	}
  	tempoEvType := MetaByteMap["Tempo"]
  	for _, ev := range t.Events {
  		if ev.Cmd == tempoEvType {
  			return int(ev.Bpm)
  		}
  	}
  	return 0
  }
docs: // Tempo returns the tempo of the track if set, 0 otherwise