#!/bin/sh

ts2sec() {
	IFS=:; set -- $1
  echo $((${1#0}*60*60 + ${2#0}*60 + ${3#0}))
}

SRC="$1"
START="$2"
STOP="$3"

# Calculate the segment time (in seconds)
SPAN="$(($(ts2sec "$STOP") - $(ts2sec "$START")))"

# Generate an output filename
OUT="$(basename "$SRC" .mkv)-cut.mkv"

# Cut exactly the segment requested into $OUT.
ffmpeg -i "$SRC" -ss "$START" -t "$SPAN" -c copy \
  -c:v libx265 -preset slow -crf 23 \
  -c:a libopus -b:a 96k -ac 2 -ar 48000 -y -- "$OUT"

ls -lh "$SRC" "$OUT"