sync/scripts/transcode_m4a.sh

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

# evaluate options through given arguments
file_suffix=
map=
while [[ $# > 0 ]]; do
   case $1 in
      -t | --type) file_suffix=$2; shift 2;;
      -map       ) map='-map 0:0'; shift;;
      *          )                 break ;; # Anything else stops command line processing.
   esac
done

# ensure existence of destination folder
dest=../transcode_m4a
if [[ !(-d $dest) ]]; then
   mkdir $dest
fi

for file in ./*.$file_suffix; do
   echo "ffmpeg -i '$file' -c:a libfdk_aac -profile:a aac_he -b:a 64k $map -movflags +faststart '$dest/${file%$file_suffix}m4a'";
   ffmpeg -i "$file" -c:a libfdk_aac -profile:a aac_he -b:a 64k $map -movflags +faststart "$dest/${file%$file_suffix}m4a";
done