[FFmpeg-user] How to extract DVD subtitle from this VOB file?

[Farhad Mohammadi Majd]

Hello, I have ffmpeg v3.2.9 on Debian v9.3

I have searched WWW for suitable command but none of them worked for
me, and ffmpeg is complex.

== My file ==
$ ffmpeg -i VTS_01_1.VOB
.....
.....
.....
.....
Input #0, mpeg, from 'VTS_01_1.VOB':
  Duration: 00:24:40.83, start: 0.040033, .....
    Stream #0:0[0x1bf]: Data: dvd_nav_packet
    Stream #0:1[0x1e0]: Video: mpeg2video (Main), .....
    Stream #0:2[0x80]: Audio: .....
    Stream #0:3[0x21]: Subtitle: dvd_subtitle
    Stream #0:4[0x20]: Subtitle: dvd_subtitle

=====

I need to those dvd_subtitle(s). How to extract them?

THANKS