convert HH:MM:SS to SS

echo "0:25:30" | awk -F: '{ print ($1 * 3600) + ($2 * 60) + $3 }'

add chapters:

Chapter data and other metadatda in id3tags.txt

ffmpeg -i in.mp3 -i id3tags.txt -map_metadata 1 -c:a copy -id3v2_version 3 -write_id3v1 1 out.mp3

use script chptr:

Put chapter data in a file (in the example below file is named chapters):

0:0:14  0:2:15  глава едно
0:2:16  0:4:10  глава две
0:4:11  0:6:40  глава три

Format is:

start_time   end_time    chapter_title

Values are tab delimited. Run script as below:

./chptr title="my podcast" artist="the artist formerly known as Prince" \
pubdate="2019" copyright="cc-by" \
track="02" mp3=myfile.mp3 meta=chapters

Arguments:

title - episode tile
artist - podcast name
copyright - copyright notice 
track - episode number
pubdate - publication date
mp3 - audio file to be chaptered
meta - name of the file containing chapter data

Order of the arguments does not matter. Look for output file with_chapters.mp3