[FFmpeg-user] ffmpeg fails to detect subtitles in a VOB file

[Dan Hentschel]

First some simple background information. I will try to be brief. Some
years ago, I ripped my entire anime collection and mothballed all the DVDs
in the basement. I have been adding to it over the years, and am starting
to wish that the files would take up less room, so I am contemplating
transcoding all the *.vob files to *.mkv files using the x264 codec. Here's
the catch: I want to maintain the subtitle tracks, but ffmpeg doesn't
always detect the subtitles.

WORKING EXAMPLE:

ffmpeg -i 01\ Child\ High\ School\ Student\ --\ She\'s\ a\ Prodigy\ --\
Scary\ Maybe\ --\ Wildcat\ Tomo-chan\!\ --\ The\ Osakan\ Gal.vob

ffmpeg version git-2012-07-10-9b3f9f4 Copyright (c) 2000-2012 the FFmpeg
developers
  built on Jul 10 2012 21:09:09 with gcc 4.6.3

  ... snip ...

Input #0, mpeg, from '01 Child High School Student -- She's a Prodigy --
Scary Maybe -- Wildcat Tomo-chan! -- The Osakan Gal.vob':
  Duration: 00:24:11.10, start: 0.233567, bitrate: 6400 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 8:9
DAR 4:3], 9000 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x80]: Audio: ac3, 48000 Hz, 5.1(side), s16, 448 kb/s
    Stream #0:2[0x81]: Audio: ac3, 48000 Hz, stereo, s16, 224 kb/s
    Stream #0:3[0x20]: Subtitle: dvd_subtitle
    Stream #0:4[0x21]: Subtitle: dvd_subtitle

----------------------------------------------------------------------------

Notice that ffmpeg sees two subtitle tracks in this vob. I am able to then
create an mkv file that has these subtitle tracks in it. I am happy with
the results.


NONWORKING EXAMPLE:

ffmpeg -i 001\ Enter\ Naruto\ Uzumaki\!.vob

ffmpeg version git-2012-07-10-9b3f9f4 Copyright (c) 2000-2012 the FFmpeg
developers
  built on Jul 10 2012 21:09:09 with gcc 4.6.3

   ... snip ...

Input #0, mpeg, from '001 Enter Naruto Uzumaki!.vob':
  Duration: 00:23:06.84, start: 0.060000, bitrate: 8318 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 8:9
DAR 4:3], 9800 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x81]: Audio: ac3, 48000 Hz, stereo, s16, 192 kb/s
    Stream #0:2[0x80]: Audio: ac3, 48000 Hz, stereo, s16, 192 kb/s

-----------------------------------------------------------------------------------

For this one, ffmpeg doesn't see any subtitle tracks. However, I can play
the video with either MythTV's video player, or with VLC, and both of them
are able to detect and display English subtitles. I am not an expert on the
file format in VOBs, but my observation is that neither of the
aforementioned players detects that there is a subtitle stream present
until about 10-20 seconds into the video, at about the time that the first
subtitle is displayed. Is it possible that ffmpeg is not reading far enough
into the file to see the subtitle stream? Is there some way to increase how
much of the file is parsed? I have tried using both the -probesize and the
-analyzeduration fields, but neither seems to help the situation. Any
recommendations?

-- 
dan B hentschel
dan at hentschels.com