[FFmpeg-user] ffmpeg mangling heredoc lines in bash

[Samuel Rakitničan]

Dear list,

I am trying to split a mp3 file into multiple tracks with a bash script
using ffmpeg. Somehow I can't achieve the desired effect due to some weird
behavior when ffmpeg is included. So the script is going line by line and
splitting one big mp3 file into multiple files (tracks) based on input from
heredoc data.

#!/bin/bash

if [ ! -f "$1" ]; then
  echo "Invalid input file"
  exit 1
fi

if [ ! -d "$2" ]; then
  mkdir $2 || exit 1
fi

_count=0
while read -r _line; do
  ((_count++))
#  printf "   %s\n" $_line
  echo $_line
  _end=$(echo "$_line" | cut -f1)
  _title=$(echo "$_line" | cut -f2)
  _trackno=$(printf "%02d\n" $_count)
  echo "Writting -ss "${_start-00:00:00}" -to "${_end}" $_trackno -
$_title.mp3"
#  ffmpeg -y -i "$1" -vn -acodec copy -ss "${_start-00:00:00}" -to "$_end" \
#         "$2/$_trackno - $_title.mp3" &> /dev/null
  _start="${_end}"
  sleep 1
done<<'TrackList'
00:01:56 Track 1
00:07:12 Track 2
00:12:15 Track 3
00:16:44 Track 4
TrackList

Script like this produces desired output:
Writting -ss 00:00:00 -to 00:01:56 01 - Track 1.mp3
00:07:12 Track 2
Writting -ss 00:01:56 -to 00:07:12 02 - Track 2.mp3
00:12:15 Track 3
Writting -ss 00:07:12 -to 00:12:15 03 - Track 3.mp3
00:16:44 Track 4
Writting -ss 00:12:15 -to 00:16:44 04 - Track 4.mp3

As soon as I uncomment ffmpeg line, output gets mangled:

00:01:56 Track 1
Writting -ss 00:00:00 -to 00:01:56 01 - Track 1.mp3
0:07:12 Track 2
Writting -ss 00:01:56 -to 0:07:12 02 - Track 2.mp3
:12:15 Track 3
Writting -ss 0:07:12 -to :12:15 03 - Track 3.mp3
00:16:44 Track 4
Writting -ss :12:15 -to 00:16:44 04 - Track 4.mp3

Anyone have an idea of what is happening?


P.S. I managed to achieve what I wanted with another loop, first loop
processes heredoc input into array, and then I process array into input for
ffmpeg.