FFMPEG script to convert two image sequences. To Use: `bash convert.sh` and answer it's questions

convert.sh

#!/bin/bash
function join_by { local IFS="$1"; shift; echo "$*"; }


read -r -p $'\e[;1;4mInput path with %d format:\e[0m ' INPUT_PATH; 
read -r -p $'\e[;1;4mOutput directory:\e[0m ' OUTPUT_DIR;

read -r -p $'\e[;1;4mWould you like to convert the filetype? [y/N]\e[0m ' convertType
if [[ "$convertType" =~ ^([yY][eE][sS]|[yY])+$ ]]
then
  read -r -p $'\e[;1;4mEnter destination filetype:\e[0m ' outputFileType;
else
  outputFileType=(${INPUT_PATH//./ }[-1])
fi

read -r -p $'\e[;1;4mWould you like to scale the image? [y/N]\e[0m ' scaleImage
if [[ "$scaleImage" =~ ^([yY][eE][sS]|[yY])+$ ]]
then
  read -r -p $'\e[;1;4mEnter output size eg 300x300:\e[0m ' outputSize;
  scaleParam="-vf scale=$outputSize ";
else
  scaleParam="";
fi

_INPUT_PARTS=(${INPUT_PATH//./ });
# echo "_INPUT_PARTS: ${join_by "|" $_INPUT_PARTS}";
_INPUT_BASE=`join_by "." ${_INPUT_PARTS[@]::${#_INPUT_PARTS[@]}-2}`;
# echo "_INPUT_BASE: $_INPUT_BASE";
_INPUT_EXT=${_INPUT_PARTS[-1]};
# echo "_INPUT_EXT: $_INPUT_EXT";
GLOB_PATH="${_INPUT_BASE}.*.${_INPUT_EXT}";
# echo "GLOB_PATH: $GLOB_PATH";

_frames=($(ls -d $GLOB_PATH));
_sorted=($(sort <<< "${_frames[*]}"));

# echo "_sorted: $_sorted";

_first_filename=${_sorted[0]};
_last_filename=${_sorted[-1]};
# echo "First Frame: $_first_filename";
# echo "Last Frame: $_last_filename";

_first_frame_number_parts=(${_first_filename//./ });
_first_frame_number=(${_first_frame_number_parts[-2]});
# echo "First Frame Num: $_first_frame_number";
_last_parts=(${_last_filename//./ });
_last_frame_number=(${_last_parts[-2]});
# echo "Last Frame Num: $_last_frame_number";

INPUT_FILENAME="${INPUT_PATH##*/}";
# echo "INPUT_FILENAME: $INPUT_FILENAME";
INPUT_FILENAME_PARTS=(${INPUT_FILENAME//./ });
INPUT_FILENAME_NO_EXT=`join_by "." ${INPUT_FILENAME_PARTS[@]::${#INPUT_FILENAME_PARTS[@]}-1}`;
# echo "INPUT_FILENAME_NO_EXT: $INPUT_FILENAME_NO_EXT";
OUTPUT_FILENAME="${INPUT_FILENAME_NO_EXT}.${outputFileType}";
OUTPUT_PATTERN="$OUTPUT_DIR/$OUTPUT_FILENAME";


echo -e "\e[;1mffmpeg -f image2 -start_number $_first_frame_number -i $INPUT_PATH $scaleParam $OUTPUT_PATTERN \e[0;31m\e[90m";
ffmpeg -f image2 -start_number $_first_frame_number -i $INPUT_PATH $scaleParam $OUTPUT_PATTERN;
echo -e "\e[0m";