int av_get_frame_filename(char *buf, int buf_size, const char *path, int number)
{
    const char *p;
    char *q, buf1[20], c;
    int nd, len, percentd_found;

    q = buf;
    p = path;
    percentd_found = 0;
    for (;;) {
        c = *p++;
        if (c == '\0')
            break;
        if (c == '%') {
            do {
                nd = 0;
                while (av_isdigit(*p))
                    nd = nd * 10 + *p++ - '0';
                c = *p++;
            } while (av_isdigit(c));

            switch (c) {
            case '%':
                goto addchar;
            case 'd':
                if (percentd_found)
                    goto fail;
                percentd_found = 1;
                snprintf(buf1, sizeof(buf1), "%0*d", nd, number);
                len = strlen(buf1);
                if ((q - buf + len) > buf_size - 1)
                    goto fail;
                memcpy(q, buf1, len);
                q += len;
                break;
            default:
                goto fail;
            }
        } else {
addchar:
            if ((q - buf) < buf_size - 1)
                *q++ = c;
        }
    }
    if (!percentd_found)
        goto fail;
    *q = '\0';
    return 0;
fail:
    *q = '\0';
    return -1;
}