static int mov_open_dref(AVFormatContext *s, AVIOContext **pb, char *src,
                         MOVDref *ref)
{
    /* try relative path, we do not try the absolute because it can leak information about our
       system to an attacker */
    if (ref->nlvl_to > 0 && ref->nlvl_from > 0) {
        char filename[1024];
        char *src_path;
        int i, l;

        /* find a source dir */
        src_path = strrchr(src, '/');
        if (src_path)
            src_path++;
        else
            src_path = src;

        /* find a next level down to target */
        for (i = 0, l = strlen(ref->path) - 1; l >= 0; l--)
            if (ref->path[l] == '/') {
                if (i == ref->nlvl_to - 1)
                    break;
                else
                    i++;
            }

        /* compose filename if next level down to target was found */
        if (i == ref->nlvl_to - 1 && src_path - src  < sizeof(filename)) {
            memcpy(filename, src, src_path - src);
            filename[src_path - src] = 0;

            for (i = 1; i < ref->nlvl_from; i++)
                av_strlcat(filename, "../", 1024);

            av_strlcat(filename, ref->path + l + 1, 1024);

            if (!s->io_open(s, pb, filename, AVIO_FLAG_READ, NULL))
                return 0;
        }
    }

    return AVERROR(ENOENT);
}