Hi,
First time poster here - please be gentle on me :-).
I have decrypted and ripped all of my DVDs into individual VIDEO_TS structures
for just the main movie or an individual TV episode. Each move or TV episode
consists of a VIDEO_TS folder containing the original uncompressed
VIDEO_TS.IFO, VTS_01_0.IFO and VTS_01_[1->N].VOB files.
The time has finally come for me to COMPRESS everything into MKV files and I
want to do that using a script calling ffmpeg. My intention is to toss all
audio streams except English 5.1 (where possible) and only keep one subtitle
track containing forced English subtitles IF forced subtitles exist. However,
dealing with forced subtitles has proven to be too much for me :-(.
I know that forced English subtitles can be authored a couple different ways -
either as a separate subtitle track or as part of the regular English subtitle
track in which the forced bits are tagged so they can be identified and
displayed separately if requested. Irrespective of which technique is employed,
my DVD player always just works when displaying only forced subtitles.
Likewise, Apple's DVD Player app also just works (although it won't play MKV
files). Annoyingly, I haven't found ANY other playing software that will
reliably play my ripped movies/episodes and only display forced subtitles as
needed (i.e. AUTOMATICALLY select the right forced subtitle track or
AUTOMATICALLY only display the forced subtitles within the English subtitle
track).
I'd like to start with movies containing forced subtitles are not in their own
subtitle track but rather tagged within the regular English subtitle track.
Here's something that works. Using MakeMKV, I first convert the VIDEO_TS
structure into an MKV file called "uncompressed.mkv". I don't know yet how to
instruct ffmpeg to specifically pick out only the subtitle track containing the
embedded forced subtitles, so for now I'll pick it manually and run the
following ffmpeg command (notably utilizing the "-forced_subs_only 1" option
and the "dvdsub" codec:
ffmpeg -forced_subs_only 1 \
-i uncompressed.mkv \
-vsync cfr \
-map 0:0 -c:v hevc_videotoolbox -disposition:v default \
-map 0:1 -c:a:0 copy -disposition:a:0 default \
-map 0:5 -c:s:0 dvdsub -disposition:s:0 default \
-default_mode passthrough \
compressed.mkv
That works i.e. when I play "compressed.mkv" I only see English subtitles when
the non-English stuff is spoken :-).
However, for reliability reasons I'd like to avoid for now, I don't want to
first convert my movie to MKV i.e. I'd like to have ffmpeg directly operate on
the original VOB structure. I understand that (to my IMMENSE displeasure) in
2022 FFmpeg is unable to treat a DVD structure as a single movie - it can only
deal with ONE VOB file. So I did:
cat *.VOB > combined.vob
and used that as the input to the same ffmpeg command i.e.:
(Please ignore the different stream numbers - MakeMKV removes the VOB's stream
0:0 <dvd_nav_packet> and subtracts 1 from each of them)
ffmpeg -forced_subs_only 1 \
-i combined.vob \
-vsync cfr \
-map 0:1 -c:v hevc_videotoolbox -disposition:v default \
-map 0:2 -c:a:0 copy -disposition:a:0 default \
-map 0:6 -c:s:0 dvdsub -disposition:s:0 default \
-default_mode passthrough \
compressed.mkv
That did NOT work because the resultant subtitle track was completely empty! I
also tried another trick for defining the ffmpeg input using:
-i concat:"$(ls -1 VIDEO_TS/*.VOB | sort | xargs echo | sed 's/ /|/g')"
but it still yielded an empty subtitle track. Same thing when I also tried:
cat VTS_01_0.IFO *.VOB > combined.vob
I've been able to confirm the VOB files contain all of the subtitles, and that
VIDEO_TS.IFO is irrelevant, but I haven't been able to prove if VTS_01_0.IFO
contains the tags for the specific forced subtitles (I suspect not, but I don't
know).
Anybody know what's going on here? How come ffmpeg respects "-forced_subs_only
1" for an MKV but not for a VOB?
Sorry for the lengthy email - if you've made it this far I'm already thankful!
Regards,
Mick
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