Obtain a list of asset ids from a lecture.

def _get_lecture_asset_ids(self, course_id, video_id):
        """
        Obtain a list of asset ids from a lecture.
        """
        dom = get_page(self._session, OPENCOURSE_ONDEMAND_LECTURE_ASSETS_URL,
                       json=True, course_id=course_id, video_id=video_id)
        # Note that we extract here "id", not definition -> assetId, as it
        # be extracted later.
        return [asset['id']
                for asset in dom['linked']['openCourseAssets.v1']]