code: func (c *Page) StartScreencast(format string, quality int, maxWidth int, maxHeight int, everyNthFrame int) (*gcdmessage.ChromeResponse, error) {
  	var v PageStartScreencastParams
  	v.Format = format
  	v.Quality = quality
  	v.MaxWidth = maxWidth
  	v.MaxHeight = maxHeight
  	v.EveryNthFrame = everyNthFrame
  	return c.StartScreencastWithParams(&v)
  }
docs: // StartScreencast - Starts sending each frame using the `screencastFrame` event.
  // format - Image compression format.
  // quality - Compression quality from range [0..100].
  // maxWidth - Maximum screenshot width.
  // maxHeight - Maximum screenshot height.
  // everyNthFrame - Send every n-th frame.