Convert the audio of MKV videos in a folder into AAC, retaining original audio as well

tvshows.sh

#!/bin/bash
#Example: ~/tvshows.sh (from within the desired folder)
ext=( *.mkv )
for e in "${ext[@]}"
do
    for f in "$e"
    do
        if [ -f "$f" ]; then
            episode=`echo "$f" | grep -oP 'S[0-9]{2}E[0-9]{2}'`
            echo "Processing $episode"
            extension="${f##*.}"
            filename="${f%.*}"
            out="${filename}.mp4"
            out="${out/EAC3/AAC}"
            out="${out/AC3/AAC}"
            echo "${f} --> ${out}"
            ffmpeg -hide_banner -i "$f" -map 0:v -c:v copy -map 0:a -c:a copy -map 0:a:0 -c:a:0 aac -map 0:s -c:s mov_text -map_metadata 0 -movflags +faststart "$out" && \
            rm "$f" && echo "Removed ${f}" && \
            rename -v 's/EAC3/AAC/' *$episode* && \
            rename -v 's/AC3/AAC/' *$episode*
            #read -n 1 -p Continue?
        fi
    done
done