overlayText.sh

#!/bin/bash

while getopts ":i:o:t:" opt; do
  case $opt in
    i) input="$OPTARG"
    ;;
    o) output="$OPTARG"
    ;;
    t) text="$OPTARG"
    ;;
    \?) echo "Invalid option -$OPTARG" >&2
    exit 1
    ;;
  esac

  case $OPTARG in
    -*) echo "Option $opt needs a valid argument"
    exit 1
    ;;
  esac
done

[[ -z "$input" ]] && echo "Must specify -i for input file" && exit
[[ -z "$output" ]] && echo "Must specify -o for output file" && exit
[[ -z "$text" ]] && echo "Must specify -t for text" && exit


ffmpeg -i $input -vf "drawtext=text=$text:x=(w-text_w)/2:y=(h-text_h)/2:fontsize=30:fontcolor=white:box=1:boxcolor=white@0.5: boxborderw=5'" -codec:a copy $output