code: public static WxOutMsg respVideo(String to, String mediaId, String title, String description) {
          WxOutMsg out = new WxOutMsg("video");
          out.setVideo(new WxVideo(mediaId, title, description));
          if (to != null)
              out.setToUserName(to);
          return out;
      }
docs: 创建一个视频响应