int opt_default(const char *opt, const char *arg)
{
    const AVOption *oc, *of, *os, *oswr = NULL;
    char opt_stripped[128];
    const char *p;
    const AVClass *cc = avcodec_get_class(), *fc = avformat_get_class(), *sc, *swr_class;

    if (!(p = strchr(opt, ':')))
        p = opt + strlen(opt);
    av_strlcpy(opt_stripped, opt, FFMIN(sizeof(opt_stripped), p - opt + 1));

    if ((oc = av_opt_find(&cc, opt_stripped, NULL, 0,
                         AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ)) ||
        ((opt[0] == 'v' || opt[0] == 'a' || opt[0] == 's') &&
         (oc = av_opt_find(&cc, opt + 1, NULL, 0, AV_OPT_SEARCH_FAKE_OBJ))))
        av_dict_set(&codec_opts, opt, arg, FLAGS(oc));
    if ((of = av_opt_find(&fc, opt, NULL, 0,
                          AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ)))
        av_dict_set(&format_opts, opt, arg, FLAGS(of));
#if CONFIG_SWSCALE
    sc = sws_get_class();
    if ((os = av_opt_find(&sc, opt, NULL, 0,
                          AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ))) {
        // XXX we only support sws_flags, not arbitrary sws options
        int ret = av_opt_set(sws_opts, opt, arg, 0);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Error setting option %s.\n", opt);
            return ret;
        }
    }
#endif
    swr_class = swr_get_class();
    if (!oc && !of && !os && (oswr = av_opt_find(&swr_class, opt, NULL, 0,
                          AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ))) {
        int ret = av_opt_set(swr_opts, opt, arg, 0);
        if (ret < 0) {
            av_log(NULL, AV_LOG_ERROR, "Error setting option %s.\n", opt);
            return ret;
        }
    }

    if (oc || of || os || oswr)
        return 0;
    av_log(NULL, AV_LOG_ERROR, "Unrecognized option '%s'\n", opt);
    return AVERROR_OPTION_NOT_FOUND;
}