[FFmpeg-user] Extracting forced subtitles from a DVD.

[Ferdi Scholten]

> Anybody know what's going on here? How come ffmpeg respects "-forced_subs_only 1" for an MKV but not for a VOB?
>
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In the VOB structure the subtitle track may begin at the first time 
where it is needed. When you only have the VOB files, the forced 
subtitles might not be at the beginning of the structure so will not be 
found by ffmpeg when it analyzes the first 5 seconds (default) of the 
VOB file. You can force ffmpeg to analyze a bigger part of the VOB file 
to find additional streams by adding -analyzeduration and -probesize in 
your command. Both default to 5000000 meaning it wil scan the first 
5000000 microseconds of the first 5000000 bytes of the file. Specify 
large values here to analyze a much bigger part of the file for a longer 
duration.
for example:

ffmpeg -analyzeduration 10000000M \
-probesize 10000000M \
-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


Greetings
Ferdi Scholten