Can't extract CC from ATSC dvr-ms recording

This is a registered copy of SA and I have no problem calling it from DTB. And I do select output CC as SRT in UTF8(or UTF16), and the file was processed, I got correct xml file, except the srt file. It did create at the end of the processing but its just empty. Same if I select smi/sub format, all I get is some empty file.

Did I miss sth? can anyone give me some suggestion?

Thanks!