ts_to_string(s_end, sizeof(s_end), ts_start + duration);
len = snprintf(header, sizeof(header), "Dialogue: 0,%s,%s,Default,",
s_start, s_end);
ts_to_string(s_end, sizeof(s_end), ts_start + duration);
len = snprintf(header, sizeof(header), "Dialogue: 0,%s,%s,Default,",
s_start, s_end);