ffmpeg -fflags +genpts -i *.iso -acodec copy -vcodec copy out.mkv
cat *.VOB > output.vob // merge
ffmpeg -i output.vob // check inside
ffmpeg -fflags +genpts -i output.vob -acodec copy -vcodec copy out.mkv // convert
source: https://www.internalpointers.com/post/convert-vob-files-mkv-ffmpeg