static int mov_write_track_metadata(AVIOContext *pb, AVStream *st,
                                    const char *tag, const char *str)
{
    int64_t pos = avio_tell(pb);
    AVDictionaryEntry *t = av_dict_get(st->metadata, str, NULL, 0);
    if (!t || !utf8len(t->value))
        return 0;

    avio_wb32(pb, 0);   /* size */
    ffio_wfourcc(pb, tag); /* type */
    avio_write(pb, t->value, strlen(t->value)); /* UTF8 string value */
    return update_size(pb, pos);
}

The product divides a value by zero.