A mechanism for processing video data is disclosed. A value of an annotated region (AR) object label index of an i-th AR object index (ar_object_label_idx[ar_object_idx[i]]) syntax element is determined. The ar_object_label_idx[ar_object_idx[i]] syntax element is specified to be in a range of N to M, where N and M are integers and N is less than M. A conversion is performed between a visual media data and a bitstream based on the ar_object_label_idx[ar_object_idx[i]] syntax element.