static int split_field_copy(Picture *dest, Picture *src,
                            int parity, int id_add){
    int match = !!(src->reference & parity);

    if (match) {
        *dest = *src;
        pic_as_field(dest, parity);
        dest->pic_id *= 2;
        dest->pic_id += id_add;
    }

    return match;
}