docs: def find_next_video_in_playlist(self, playlist_id, cur_video_id):
          """doc: http://open.youku.com/docs/doc?id=78
          """
          url = 'https://openapi.youku.com/v2/playlists/video/next.json'
          params = {
              'client_id': self.client_id,
              'playlist_id': playlist_id,
              'video_id': cur_video_id
          }
          r = requests.get(url, params=params)
          check_error(r)
          return r.json()