def find_video_details_by_ids(self, video_ids, ext=None):
        """doc: http://open.youku.com/docs/doc?id=47
        """
        url = 'https://openapi.youku.com/v2/videos/show_batch.json'
        params = {
            'client_id': self.client_id,
            'video_ids': video_ids
        }
        if ext:
            params['ext'] = ext
        r = requests.get(url, params=params)
        check_error(r)
        return r.json()
doc: http://open.youku.com/docs/doc?id=47