Converts Naruto Kai .mkv episodes with separate subtitle streams to .mp4 with hardcoded subtitles. Chromecast doesn't like the subtitle streams and displays them with no spacing. The script uses ffmpeg with nvidia hardware acceleration.

naruto-kai-sub-fix.sh

#!/bin/bash
# Converts Naruto Kai .mkv episodes with separate subtitle streams to .mp4 with hardcoded subtitles. 
# Chromecast doesn't like the subtitle streams and displays them with no spacing. 
# The script uses ffmpeg with nvidia hardware acceleration.
#
# Recommend to dryrun first which will echo all commands that it will run. If you're happy with it,
# then run the script without the dryrun flag
# Usage: ./naruto-kai-sub-fix.sh /dir/to/search -dryrun
# Usage: ./naruto-kai-sub-fix.sh /dir/to/search 

DIR=$1

find "$DIR" -type f -name "*.mkv" | while read filename; do
        has_subtitles=$(ffprobe -i "$filename" 2>&1 >/dev/null | grep -E "Stream.+Subtitle")
        if [[ -n "$has_subtitles" ]]; then
                name=$(sed -r 's/(.*)\.mkv/\1/' <<<"$filename")
                if [ -f "${name}.mp4" ]; then
                        echo "$name - already done"
                        continue
                fi
                echo "Starting $name"
                if [[ "$2" == "-dryrun" ]]; then
                        echo ffmpeg -loglevel error -hwaccel_device 0 -hwaccel cuda -i "${name}.mkv" -c:v h264_nvenc -vf subtitles="'${name}.mkv'" "${name}.mp4" 2> >(tee errors.txt)
                else
                        ffmpeg -loglevel error -hwaccel_device 0 -hwaccel cuda -i "${name}.mkv" -c:v h264_nvenc -vf subtitles="'${name}.mkv'" "${name}.mp4" 2> >(tee errors.txt)
                fi
        fi
done