#!/bin/sh
#
# 2mp3 - convert MP4 video, various audio formats, and MIDI, to MP3 audio
#
# $Id$

# not guaranteed to be perfect for every occasion

# source: https://askubuntu.com/questions/84584/converting-mp4-to-mp3

Die()
{
  echo $0: fatal error: $@ 1>&2
  exit 1
}

DieIfMissing()
{
  for f in "$@"
  do
    type "$f" >/dev/null 2>&1 || Die missing required executable: $f
  done
}

Usage()
{
  Die Usage: $0 [-c|-v] mp4file1 > mp3file
}

In2MP3()
{
  ffmpeg -i "$1" \
    -vn -acodec libmp3lame -ac 2 $mp3type -ar 48000 -f mp3 -y /dev/stdout
}

File2MP3()
# argument: $1, a filename
{
  if file -bi "$1" | grep -q ^audio/midi
  then
    DieIfMissing timidity
    timidity "$1" -Ow -o - | In2MP3 -
  else
    In2MP3 "$1"
  fi
}

DieIfMissing ffmpeg
DieIfMissing file

variable=0

while :
do
  case "$1" in
  -v) variable=1;;
  -c) variable=0;;
  -*) Usage;;
  *) break;;
  esac
  shift
done

if [ $variable = 1 ]
then
  mp3type='-qscale:a 4'
else
  mp3type='-ab 160k'
fi

if [ $# -eq 0 ]
then
  set -- -
fi

for i in "$@"
do
  if [ "$i" = - ]
  then
    DieIfMissing tempfile
		t=`tempfile -p 2pm3`
    trap "rm $t" INT QUIT EXIT
    cat "$i" > $t
    File2MP3 "$t"
  else
    File2MP3 "$i"
  fi
done