vob2srt.sh

#!/bin/bash

# Create the target dir
mkdir Completed

for mkvFile in *.mkv; do

    # Get the file name without the extension
    filename=$(basename -- "$mkvFile")
    filename="${filename%.*}"

    # Count the vobsub tracks
    numTracks=$(mkvinfo "$mkvFile" | grep -c "S_VOBSUB")
    if [ $numTracks -eq 0 ]; then
        echo "No tracks to convert !"
        continue
    fi

    # Get the vobsub part of the output, and parse to get the track number
    for subTrack in $(mkvinfo "$mkvFile" | grep -B4 "VOBSUB" | grep "mkvextract" | cut -d ":" -f 3 | tr -d -c 0-9); do
        # Try to parse the track language
        trackLang=$(mkvinfo "$mkvFile" | grep -B4 "S_VOBSUB" | grep -C3 "Track UID: $subTrack" | grep "Language:" | cut -d ":" -f 2 | tr -d '\040\011\012\015')
        if [ -z "$trackLang" ]; then
            trackLang="eng"
        fi

        # Extract the vobsub track
        mkvextract tracks "$mkvFile" $subTrack:"$filename"

        # Convert to .srt
        /mnt/c/Program\ Files/Subtitle\ Edit/SubtitleEdit.exe /convert "$filename".sub srt
        if [ $? -ne 0 ]; then
            echo "Failed to convert subtitle to SRT!"
            continue
        fi

        # Merge the .srt into the .mkv
        mkvmerge -o "_$mkvFile" "$mkvFile" --language 0:$trackLang --default-track "0:yes" "$filename.srt"
        if [ $? -ne 0 ]; then
            echo "Failed to merge subtitle to _$mkvFile!"
            continue
        fi

        # Move and cleanup
        mv "_$mkvFile" "Completed/$mkvFile"
        rm "$filename.sub" "$filename.idx" "$filename.srt"
    done
done

Script I've used to add .srt tracks to old DVD rips with vobsub tracks. I'm using WSL to run SubtitleEdit in a bash script (thanks Microsoft !) because I wasn't able to run it on macOS with mono, due to the Winforms 32 bits dependencies (thanks Apple !).

There's room for improvement, the subtitles might not be perfect (SubtitleEdit uses OCR for the conversion), and I can't guarantee that it won't break, but finding this would have saved me a couple of hours.

It requires MKVToolNix.

It's based on a script I found here.