#!/bin/bash
set -euo pipefail

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 <original-video> <new-video>"
  echo "Example: $0 input.mp4 output.webm"
  exit 1
fi

INPUT="$1"
OUTPUT="$2"

if [ ! -f "$INPUT" ]; then
  echo "Error: input file not found: $INPUT"
  exit 1
fi

if [ "$INPUT" = "$OUTPUT" ]; then
  echo "Error: input and output must be different files"
  exit 1
fi

EXT=$(printf '%s' "${OUTPUT##*.}" | tr '[:upper:]' '[:lower:]')

case "$EXT" in
  mp4)
    ffmpeg -i "$INPUT" \
      -c:v libx265 -crf 24 -preset medium \
      -c:a aac -b:a 128k \
      -movflags +faststart \
      "$OUTPUT"
    ;;
  webm)
    ffmpeg -i "$INPUT" \
      -c:v libvpx-vp9 -crf 32 -b:v 0 -deadline good -cpu-used 2 \
      -c:a libopus -b:a 128k \
      "$OUTPUT"
    ;;
  *)
    echo "Error: unsupported output format '.$EXT'"
    echo "Use output extension: .mp4 or .webm"
    exit 1
    ;;
esac