static int mov_write_udta_tag(AVIOContext *pb, MOVMuxContext *mov,
                              AVFormatContext *s)
{
    AVIOContext *pb_buf;
    int ret, size;
    uint8_t *buf;

    ret = avio_open_dyn_buf(&pb_buf);
    if (ret < 0)
        return ret;

    if (mov->mode & MODE_3GP) {
        mov_write_3gp_udta_tag(pb_buf, s, "perf", "artist");
        mov_write_3gp_udta_tag(pb_buf, s, "titl", "title");
        mov_write_3gp_udta_tag(pb_buf, s, "auth", "author");
        mov_write_3gp_udta_tag(pb_buf, s, "gnre", "genre");
        mov_write_3gp_udta_tag(pb_buf, s, "dscp", "comment");
        mov_write_3gp_udta_tag(pb_buf, s, "albm", "album");
        mov_write_3gp_udta_tag(pb_buf, s, "cprt", "copyright");
        mov_write_3gp_udta_tag(pb_buf, s, "yrrc", "date");
        mov_write_loci_tag(s, pb_buf);
    } else if (mov->mode == MODE_MOV && !(mov->flags & FF_MOV_FLAG_USE_MDTA)) { // the title field breaks gtkpod with mp4 and my suspicion is that stuff is not valid in mp4
        mov_write_string_metadata(s, pb_buf, "\251ART", "artist",      0);
        mov_write_string_metadata(s, pb_buf, "\251nam", "title",       0);
        mov_write_string_metadata(s, pb_buf, "\251aut", "author",      0);
        mov_write_string_metadata(s, pb_buf, "\251alb", "album",       0);
        mov_write_string_metadata(s, pb_buf, "\251day", "date",        0);
        mov_write_string_metadata(s, pb_buf, "\251swr", "encoder",     0);
        mov_write_string_metadata(s, pb_buf, "\251des", "comment",     0);
        mov_write_string_metadata(s, pb_buf, "\251cmt", "comment",     0);
        mov_write_string_metadata(s, pb_buf, "\251gen", "genre",       0);
        mov_write_string_metadata(s, pb_buf, "\251cpy", "copyright",   0);
        mov_write_string_metadata(s, pb_buf, "\251mak", "make",        0);
        mov_write_string_metadata(s, pb_buf, "\251mod", "model",       0);
        mov_write_string_metadata(s, pb_buf, "\251xyz", "location",    0);
        mov_write_string_metadata(s, pb_buf, "\251key", "keywords",    0);
        mov_write_raw_metadata_tag(s, pb_buf, "XMP_", "xmp");
    } else {
        /* iTunes meta data */
        mov_write_meta_tag(pb_buf, mov, s);
        mov_write_loci_tag(s, pb_buf);
    }

    if (s->nb_chapters && !(mov->flags & FF_MOV_FLAG_DISABLE_CHPL))
        mov_write_chpl_tag(pb_buf, s);

    if ((size = avio_close_dyn_buf(pb_buf, &buf)) > 0) {
        avio_wb32(pb, size + 8);
        ffio_wfourcc(pb, "udta");
        avio_write(pb, buf, size);
    }
    av_free(buf);

    return 0;
}

The product divides a value by zero.