def is_contiguous(self):
        """Return offset and size of contiguous data, else None."""
        if self._keyframe is None:
            raise RuntimeError('keyframe not set')
        if self._keyframe.is_contiguous:
            return self._offsetscounts[0][0], self._keyframe.is_contiguous[1]
        return None
Return offset and size of contiguous data, else None.