The script will convert files containing the EAC3, DTS, or DTS-HD audio codecs to use the AAC codec through the AudioToolbox encoder specified as aac_at. The converted files will get the suffix -AAC_at.mkv to distinguish them from the original files

convert_incompatible_codecs.sh

#!/bin/bash

# Function to check and convert the file if necessary
check_and_convert() {
  local file=$1
  [ -d "$file" ] && return # Skip directories

  # Use ffprobe to get the codec type for each audio stream
  codec_info=$(ffprobe -v error -select_streams a -show_entries stream=codec_name -of default=noprint_wrappers=1:nokey=1 "$file")

  # Check if the file uses the EAC3 or DTS/DTS-HD codec
  if echo "$codec_info" | grep -E -q '^(eac3|dts|dtshd)$'; then
      # Prepare the output file name
      output_basename=$(basename "$file" "${file##*.}") # Remove file extension
      output="${output_basename}AAC_at.mkv"

      echo "Converting file '$file' to use AAC audio codec with AudioToolbox."
      # Run ffmpeg to convert the file with the incompatible audio codecs to AAC using AudioToolbox
      ffmpeg -i "$file" -map 0 -c:v copy -c:a aac_at -b:a 768k -ac 6 -c:s copy "$output"
  else
      echo "Skipping file '$file' because it does not use EAC3 or DTS/DTS-HD codec."
  fi
}

# Enable nullglob so unmatched patterns are removed from the word list
shopt -s nullglob

# Process .mkv and .mp4 files
for f in *.mkv *.mp4; do
  check_and_convert "$f"
done

# Disable nullglob option if needed
shopt -u nullglob