AAC converter (Apple Digital Master)

aac-adm-convert.sh

#!/usr/bin/env bash

set -eu

if [[ $# -eq 0 ]]; then
  echo "Usage: $0 [-d] [-s] [-o output_dir] files..."
  echo "Options:"
  echo "  -d      Delete original files after processing (default: off)"
  echo "  -s      Downsample to 44100 Hz if applicable (default: off)"
  echo "  -o dir  Set output directory (default: aac)"
  exit 1
fi

if ! command -v afconvert &>/dev/null; then
  echo "Error: afconvert not found. This script only works on macOS." >&2
  exit 1
fi

if ! command -v ffprobe &>/dev/null; then
  echo "Error: ffprobe not found. Please install it using 'brew install ffmpeg'." >&2
  exit 1
fi

if ! command -v ffmpeg &>/dev/null; then
  echo "Error: ffmpeg not found. Please install it using 'brew install ffmpeg'." >&2
  exit 1
fi

delete_files=false
downsample=false
output_dir="aac"

while getopts "dso:" opt; do
  case $opt in
  d) delete_files=true ;;
  s) downsample=true ;;
  o) output_dir="$OPTARG" ;;
  *)
    echo "Usage: $0 [-d] [-s] [-o output_dir] files..." >&2
    exit 1
    ;;
  esac
done
shift "$((OPTIND - 1))"

mkdir -p "$output_dir"

for input in "$@"; do
  base_name=$(basename "$input")
  echo "Processing: $base_name"

  output="$output_dir/${base_name%.*}.m4a"
  temp_caf="./.${base_name}.caf"

  sample_rate=$(ffprobe -v error -select_streams a:0 -show_entries stream=sample_rate -of default=noprint_wrappers=1:nokey=1 "$input" || echo "0")

  if [[ $downsample == true && $sample_rate -gt 44100 ]]; then
    temp_args="-d LEI24@44100 --src-complexity bats -r 127"
  elif [[ $downsample == false && $sample_rate -gt 48000 ]]; then
    temp_args="-d LEF32@48000 --src-complexity bats -r 127"
  else
    temp_args="-d 0"
  fi

  afconvert "$input" "$temp_caf" $temp_args -f caff --soundcheck-generate

  afconvert "$temp_caf" "$output" -d aac -f m4af -ue pgcm 2 --soundcheck-read -b 256000 -q 127 -s 2
  rm -f "$temp_caf"

  temp_m4a="./.tmp${base_name}.m4a"
  ffmpeg -hide_banner -v error -i "$output" -i "$input" -map 0:a -map_metadata 1 -c:a copy "$temp_m4a" -y
  mv "$temp_m4a" "$output"

  [[ $delete_files == true ]] && rm -f "$input"
  echo "Processed: $output"
done