shouldn't implement transform if don't support it. Or    
gst_buffer_copy_into() will print ERROR log.
      } else if (info->transform_func) {
        GstMetaTransformCopy copy_data;

        copy_data.region = region;
        copy_data.offset = offset;
        copy_data.size = size;

        if (!info->transform_func (dest, meta, src,
                _gst_meta_transform_copy, &copy_data)) {
          GST_CAT_ERROR (GST_CAT_BUFFER,
              "failed to copy meta %p of API type %s", meta,
              g_type_name (info->api));
        }
      }