code: func (w *Webcam) GetFrame() ([]byte, uint32, error) {
  	var index uint32
  	var length uint32
  
  	err := mmapDequeueBuffer(w.fd, &index, &length)
  
  	if err != nil {
  		return nil, 0, err
  	}
  
  	return w.buffers[int(index)][:length], index, nil
  
  }
docs: // Get a single frame from the webcam and return the frame and
  // the buffer index. To return the buffer, ReleaseFrame must be called.
  // If frame cannot be read at the moment
  // function will return empty slice