#!/bin/bash

function extract_audio_mp3() {
  conversion_folder="$1"
  file_extension="$2"
  process_num="$3"
  i=0
  j=0
  cd "$conversion_folder"
  for item in *.$file_extension
  do
   ((i++))
   ((j++))
   counter=$(printf %04d $i)
   cmd=$(echo "ffmpeg -i '$item' '$counter"_"$item.mp3'")
   # echo $cmd
   bash -c "$cmd" &
   if [[ $j = $process_num ]]; then
     wait
     $j = 0
   fi
  done
}

echo "Extracting audio & convert to mp3"

# current directory full path
script_dir=$(dirs -l)
# echo $script_dir
extract_audio_mp3 "$script_dir" mov 3

echo "End of extraction and conversion"