def current_frame(self):
        """Get the current frame (frame that is just visited).

        Returns:
            ndarray or None: If the video is fresh, return None, otherwise
                return the frame.
        """
        if self._position == 0:
            return None
        return self._cache.get(self._position - 1)
Get the current frame (frame that is just visited).

        Returns:
            ndarray or None: If the video is fresh, return None, otherwise
                return the frame.
        
ControlNet-v1-1-nightly/annotator/uniformer/mmcv/video/io.py