docs: 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()