format timelapse video from synology.sh

#!/bin/bash

do_work() {
  local dir=$1
  local start_time=$2
  local duration_to_keep=$3
  cd $dir
  rm -v trimmed_*.mp4 *.txt
  for file in *.mp4; do
    output_file="trimmed_$file"
    ffmpeg -y -i "$file" -ss $start_time -t $duration_to_keep -c copy "$output_file"
  done
  # delete small files that are probably invalid
  find . -type f -name "trimmed_*.mp4" -size -40M -delete

  # Create lists based on the variable part of the file names
  for file in trimmed_*.mp4; do
    # Extract the variable part of the filename
    var_part=$(echo "$file" | sed -E 's/^trimmed_([^_]+-[0-9]{8}-[0-9]{6}-[0-9]{13}\.mp4)$/\1/' | sed 's/-[0-9]\{8\}-[0-9]\{6\}-[0-9]\{13\}\.mp4$//')
    # Add the file to the corresponding list
    echo "file '$file'" >> "$var_part.txt"
  done

  # Concatenate files based on the lists
  for list in *.txt; do
    var_part=$(basename "$list" .txt)
    output_file="${var_part}.mp4"
    ffmpeg -y -f concat -safe 0 -i "$list" -c copy "$output_file"
    mv "$output_file" "../${1}_${output_file}"
  done
}

do_work am 19 14
do_work pm 11 16