Remove the tracks that match certain criteria from MKV files (using jq)

remove-mkv-tracks.sh

#!/usr/bin/env bash
set -Eeuo pipefail

if [[ $# -lt 2 ]]; then
  echo "Usage: $(basename "$0") <preset or jq condition> <files or directories...>"
  echo 'Presets: subrip_only, anime'
  exit 1
fi

JQ_COND="$1"
shift

case "$JQ_COND" in
  subrip_only)
    JQ_COND='.type == "subtitles" and .properties.codec_id != "S_TEXT/UTF8"'
    ;;
  anime)
    JQ_COND='(.type == "audio" and .properties.language == "eng") or (.type == "subtitles" and .properties.codec_id != "S_TEXT/UTF8")'
    ;;
esac

find "$@" -type f -iname '*.mkv' -print | while read -r F; do
  echo "$F"
  JSON="$(mkvmerge -J "$F")"
  NUM_TRACKS="$(echo "$JSON" | jq ".tracks | length")"
  if [[ $NUM_TRACKS -le 2 ]]; then
    echo '> Too few tracks in the file'
    continue
  fi
  TRACKS_TO_KEEP=()
  TRACKS_TO_REMOVE=()
  for T in $(echo "$JSON" | jq ".tracks[] | select($JQ_COND) | .id"); do
    TRACKS_TO_REMOVE+=($T)
  done

  if [[ "${#TRACKS_TO_REMOVE[@]}" -le 0 ]]; then
    echo '> No tracks to remove'
    continue
  fi

  for ((I=0; I<$NUM_TRACKS; I++)); do
    KEEP=1
    for TTR in "${TRACKS_TO_REMOVE[@]}"; do
      if [[ $I -eq $TTR ]]; then
        KEEP=0
      fi
    done
    if [[ $KEEP -ne 0 ]]; then
      TRACKS_TO_KEEP+=($I)
    fi
  done

  if [[ "${#TRACKS_TO_KEEP[@]}" -le 1 ]]; then
    echo '> Refusing to remove too many tracks'
    continue
  fi

  echo "> Keeping ${TRACKS_TO_KEEP[@]} out of $NUM_TRACKS tracks"
  TTK="$(IFS=,; echo "${TRACKS_TO_KEEP[*]}")"
  NEW_F="$F.clean.tmp"
  mkvmerge -o "$NEW_F" --video-tracks "$TTK" --audio-tracks "$TTK" --subtitle-tracks "$TTK" "$F"
  mv "$NEW_F" "$F"
  chmod 644 "$F"
  echo
done

A few examples:

• Remove subtitles that are not SubRip:

  remove-mkv-tracks.sh \
    '.type == "subtitles" and .properties.codec_id != "S_TEXT/UTF8"' \
    *.mkv
  

• Remove all English audio:

  remove-mkv-tracks.sh \
    '.type == "audio" and .properties.language == "eng"' \
    *.mkv