code: func (s FrameSize) GetString() string {
  	if s.StepWidth == 0 && s.StepHeight == 0 {
  		return fmt.Sprintf("%dx%d", s.MaxWidth, s.MaxHeight)
  	} else {
  		return fmt.Sprintf("[%d-%d;%d]x[%d-%d;%d]", s.MinWidth, s.MaxWidth, s.StepWidth, s.MinHeight, s.MaxHeight, s.StepHeight)
  	}
  }
docs: // Returns string representation of frame size, e.g.
  // 1280x720 for fixed-size frames and
  // [320-640;160]x[240-480;160] for stepwise-sized frames