code: func (f FFmpegThumbnailer) Command(uri *url.URL) (string, []string) {
  	return "ffmpeg", []string{
  		"-seekable", "1",
  		"-i", uri.String(),
  		"-vf", "thumbnail",
  		"-frames:v", "1",
  		"-f", "image2pipe",
  		"-c:v", "png",
  		"pipe:1",
  	}
  }
docs: // Command implements the Command method for the Thumbnailer interface.