Find all .mp4 files in the current directory and subdirectories and convert them into .mkv files without re-encoding. This does not lose any quality and the resulting files are the same size as the originals. This will also repair any .mp4 files which do not have `ctts atom`, which can cause playback issues in numerous players. It will delete it…

mp4tomkv.sh

#!/bin/bash

if ! [ -x "$(command -v mkvmerge)" ]; then
  echo 'Error: mkvmerge is not installed.' >&2
  exit 1
fi

if ! [ -x "$(command -v ffmpeg)" ]; then
  echo 'Error: ffmpeg is not installed.' >&2
  exit 1
fi

# Save original Input File Separator
SAVEIFS=$IFS
# Set the temporary IFS for this script
IFS=$(echo -en "\n\b")

# Always restore the original IFS regardless of how the script exits
trap 'IFS=$SAVEIFS' EXIT

# Create a variable containing all .mp4 files found recursively
Files=$(find . -name "*.mp4" -type f)
for f in $Files
do
  # Print out name of the file we're working on
  echo $f
  newFileName="${f%.mp4}"
  # Create temp file containing all videos from original .mp4
  mkvmerge -A -S -o temp.video.mkv "${newFileName}".mp4
  # Create temp file containing all audio and subtitles from original
  mkvmerge -D -o temp.audio.mkv "${newFileName}".mp4
  # Recombine them into a new .mp4 file
  ffmpeg -loglevel 0 -hide_banner -stats -y -i temp.video.mkv -i temp.audio.mkv -c copy -c:s srt -map 0 -map 1 "${newFileName}".mkv
  # Delete temp files used
  rm temp.video.mkv temp.audio.mkv
done

exit 0