#!/bin/sh

usage() {
  echo "Usage: $(basename "$0") [ --accurate ] <start> <end> <input> [<output>]"
}

accurate=
while true; do
  case "$1" in
    --accurate) accurate=1 && shift ;;
    -h|--help)
      usage
      exit 0
      ;;
    -*)
      usage >&2
      exit 1
      ;;
    *) break ;;
  esac
done

start="$1"
end="$2"
input="$3"
output="$4"
if [ -z "$start" ] || [ -z "$end" ] || [ -z "$input" ]; then
  usage >&2
  exit 1
fi
if [ -z "$output" ]; then
  d="$(dirname "$input")"
  f="$(basename "$input")"
  ext="${f##*.}"
  noext="${f%.*}"
  output="$d/${noext}_${start}-${end}.${ext}"
fi

# See: https://stackoverflow.com/a/52916510/619216
# See: https://news.ycombinator.com/item?id=22777179
if [ -n "$accurate" ]; then
  exec ffmpeg -ss "$start" -to "$end" -i "$input" "$output"
else
  exec ffmpeg -ss "$start" -to "$end" -i "$input" -c copy -map 0 "$output"
fi