A simple bash script changing Video file to GIF using ffmpeg. It keeps aspect ratio of the video

vid-to-gif.sh

#!/bin/bash  
read -p "Input Video: " vid
read -p "Known Dimension(VID_WIDTH): " VID_WIDTH
read -p "Known Dimension(VID_HEIGHT): " VID_HEIGHT
# trim file name
x=${vid##*/}
y=${x%.*}
filename=${y##*/}

# keeps aspect ratio
MAX_WIDTH=640
if [ -z $VID_WIDTH ] || [ -z $VID_HEIGHT ]
then
  echo "dimension(VID_WIDTH, VID_HEIGHT) is empty"
  ffmpeg -ss 00:00:00.000 -i "$vid" -pix_fmt rgb24 -r 10 -vf scale=640:-1 "$filename".gif
else
  VID_HEIGHT=$(echo "$MAX_WIDTH/$VID_WIDTH*$VID_HEIGHT" | bc -l)
  VID_WIDTH=$MAX_WIDTH
  dimension=$VID_WIDTH":"$VID_HEIGHT
  echo $dimension
  ffmpeg -ss 00:00:00.000 -i "$vid" -pix_fmt rgb24 -r 10 -vf scale="$dimension" "$filename".gif
fi