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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _poster_frame_rId(self):
 """Return the rId of relationship to poster frame image. The poster frame is the image used to represent the video before it's played. """

        _, poster_frame_rId = self._slide_part.get_or_add_image_part(
            self._poster_frame_image_file
        )
        return poster_frame_rId