Splits OpenAudible decrypted mp3 files to a form suitable for Garmin watch audiobook playback

openaudible_split_for_garmin.sh

#!/bin/bash

# Based on: http://crunchbang.org/forums/viewtopic.php?id=38748#p414992
# m4bronto

# Metadata looks like this:
#     Chapter #0:0: start 0.000000, end 1290.013333
#       first   _     _     start    _     end

while [ $# -gt 0 ]; do

# extract mp3 metadata to tmp.txt
ffmpeg -i "$1" 2> tmp.txt

# extract author name
author=`cat tmp.txt | grep -w artist | head -n 1 | cut -d ' ' -f16-`

# extract book name
book=`cat tmp.txt | grep -w album | head -n 1 | cut -d ' ' -f17- | sed "s/\s*(Unabridged)//"`

# extract last chapter number
max_chapter=`cat tmp.txt | grep -w title | grep -w Chapter | tail -n 1 | cut -d ' ' -f20-`

# figure out the max number of digits in a chapter name (to be able to generate 0 padded file names and titles later)
max_chapter_digits_p1=`echo $max_chapter | wc -c`
max_chapter_digits=$(( $max_chapter_digits_p1 -1 ))

mkdir -p "$author"/"$book"

# extract the book cover to cover.png
rm -f cover.png
ffmpeg -i "$1" -an -vcodec copy cover.png 2>/dev/null
rm -f "$author/$book/cover.png"
cp cover.png "$author"/"$book"

# iterate over the chapters
while read -r first _ _ start _ end; do

  if [[ $first = Chapter ]]; then
    read  # discard line with Metadata:
    read _ _ chapter_w_prefix
    chapter=`echo $chapter_w_prefix | sed "s/Chapter //"`

    # pad the chapter number with 0s
    printf -v padded_chapter "%0${max_chapter_digits}g" $chapter
    
    rm -f in.mp3

    # split the chapter out to its own in.mp3 file, set the title to e.g. Chapter 02/22 - Book Name
    ffmpeg  -vsync 2 \
            -i "$1" \
            -vn \
            -codec copy \
            -ss "${start%?}" -to "$end" \
            -map_metadata 0 -id3v2_version 3 -write_id3v1 1 \
            -metadata title="$chapter_w_prefix/$max_chapter - $book" \
            -metadata track="$chapter/$max_chapter" \
            -f mp3 in.mp3  </dev/null

    rm -f "$author/$book/$padded_chapter.mp3"
    
    # add the cover to the mp3, renaming it from in.mp3 to <chapter with 0 padding>.mp3, e.g. 02.mp3
    ffmpeg -i in.mp3 -i cover.png -map 0:0 -map 1:0 -c copy -id3v2_version 3 \
          -metadata:s:v title="Album cover" -metadata:s:v comment="Cover (front)"  \
           "$author/$book/$padded_chapter.mp3" </dev/null

    # rm in.mp3
  fi
done <tmp.txt

rm tmp.txt
rm cover.png

shift
done