static int parse_key(DBEContext *s)
{
    if (s->key_present) {
        uint8_t *key = s->input;
        int      ret = skip_input(s, 1);
        if (ret < 0)
            return ret;
        return AV_RB24(key) >> 24 - s->word_bits;
    }
    return 0;
}