code: func (t *Track) Add(beatDelta float64, e *Event) {
  	if t.ticksPerBeat == 0 {
  		t.ticksPerBeat = 96
  	}
  	e.TimeDelta = uint32(beatDelta * float64(t.ticksPerBeat))
  	t.Events = append(t.Events, e)
  	t.Size += uint32(len(EncodeVarint(e.TimeDelta))) + e.Size()
  }
docs: // Add schedules the passed event after x beats (relative to the previous event)