youtube_chapter.sh

#!/bin/sh
set -x

#Download media + metadata
youtube-dl --write-info-json -x --audio-format mp3 -o "tmp_out.%(ext)s" $1

# Maybe a way to get the file name from previous function
INFO="tmp_out.info.json"
AUDIO="tmp_out.mp3"
echo :: $INFO $AUDIO ::
# Fetch the title
TITLE=$(cat "$INFO" | jq -r .title | sed -e 's/[^A-Za-z0-9._-]/_/g' )
                                                #  ^--- Remove all weird character as we want to use it as filename
# We will put all chapter into a directory
mkdir "$TITLE"

# Chapterization
cat "$INFO" |\
jq -r '.chapters[] | .start_time,.end_time-.start_time,.title ' |\
sed -e 's/[^A-Za-z0-9._-]/_/g' |\
xargs -n3 -t -d'\n' sh -c "ffmpeg -y -ss \$0 -i \"$AUDIO\" -to \$1 -codec:a copy  -f mp3  \"$TITLE/\$2.mp3\""

#Remove tmp file
rm tmp_out*

Thank you for this script @totetmatt!

@MilesTEG1, on macOS, you can get GNU xargs by installing:

brew install findutils

Then in the script, use gxargs instead of xargs.
It should work.