Split an m4b into its chapters. No recoding is done, just splitting

m4b_split.sh

#!/bin/bash
# Description: Split an m4b into its chapters. No recoding is done, just splitting
# Usage: m4b_split.sh $input_file $output_dir/
# Requires: ffmpeg, jq
# Author: Hasan Arous
# License: MIT

in="$1"
out="$2"
splits=""
while read start end title; do
  splits="$splits -c copy -ss $start -to $end $out/$title.m4b"
done <<<$(ffprobe -i "$in" -print_format json -show_chapters \
  | jq -r '.chapters[] | .start_time + " " + .end_time + " " + (.tags.title | sub(" "; "_"))')

ffmpeg -i "$in" $splits

Love this, but can't seem to figure out how to get this working with spaces, in situations when:

• the output folder contains spaces
• with an addition of the original filename in the output name (example $out/$filename$title.mp3) if that filename contains spaces

Thanks!

ffmpeg -i "$in" $(ffprobe -i "$in" -show_chapters -print_format json | jq -r '[.chapters[] | "-c copy -ss " + .start_time + " -to " + .end_time + " " + (.tags.title + ".m4b" | gsub(" "; "_"))] | join(" ")')

One-liner

@michaellammers This version handles spaces and chapters that are not alphabetically sorted, but it requires zsh to run. I did that because zsh handles spaces in variable names and arrays, while bash is tricky. Note that this does not and cannot speed up the audio, because it makes a lossless copy (as in the original version of the gist). Non-m4b formats are also supported, as well as metadata that has the wrong ending timestamp for the last chapter. And the ffprobe commands used above don't work; they need something like -v 0 to avoid outputting a lot of junk for some files.

Note that this technique works for chapterized files, but it will make bad sounding splits if the chapters are random and sometimes fall in the middle of a word.

#!/bin/zsh
# Note: this is only good for CHAPTERIZED files. If the breaks come in the middle of a word,
# the result will sound bad.
#
# Note that other containers are also supported!
if [[ -z $1 || -z $2 ]]; then
    echo "Usage: $0 <in file> <out directory>" >&2
    exit 1
fi

in=$1
extension=$1:e
out=$2
mkdir -p $out
metadata_source=${OVERRIDE_METADATA_SOURCE:-$in}

chapters_str=$(ffprobe -i $metadata_source -print_format json -show_chapters -v 0 | \
    jq -r '.chapters[] | .start_time + " " + .end_time + " " + (.tags.title | sub(" "; "_"))')
chapters_arr=("${(@f)chapters_str}")
chapter_count=$#chapters_arr
# Prefix width, like 3 for "001", "002"...
chapter_width=$#chapter_count
n=0
splits=()
# Skip the end because the last chapter should not have the -to flag, in case
# the metadata is wrong. (It was in one case I saw)
for line in $chapters_arr[1,-2]; do
    ((n++))
    echo $line | read start end title
    splits+=(-c copy -c:a copy -map 0:a -ss $start -to $end "$out/${(l:$chapter_width::0:)n} - $title.$extension")
done
echo $chapters_arr[-1] | read start end title
splits+=(-c copy -c:a copy -map 0:a -ss $start "$out/${(l:$chapter_width::0:)n} - $title.$extension")

ffmpeg -i $in $splits

Great, thanks! 🙏

@michaellammers This version handles spaces and chapters that are not alphabetically sorted, but it requires zsh to run. I did that because zsh handles spaces in variable names and arrays, while bash is tricky. Note that this does not and cannot speed up the audio, because it makes a lossless copy (as in the original version of the gist):

#!/bin/zsh
if [[ -z $1 || -z $2 ]]; then
    echo "Usage: $0 <in file> <out directory>" >&2
    exit 1
fi

in=$1
out=$2
mkdir -p $out

chapters_str=$(ffprobe -i $in -print_format json -show_chapters | \
    jq -r '.chapters[] | .start_time + " " + .end_time + " " + (.tags.title | sub(" "; "_"))')
# Prefix width, like 3 for "001", "002"...
width=$(($(echo $chapters_str | wc -l | wc -c) - 1))
n=0
splits=()
echo $chapters_str | \
while read start end title; do
    ((n++))
    splits+=(-c copy -c:a copy -map 0:a -ss $start -to $end "$out/${(l:$width::0:)n} - $title.m4b")
done

ffmpeg -i $in $splits