#!/bin/sh

vertical="$1"
input="$2"
output="$3"
if [ -z "$vertical" ] || [ -z "$input" ]; then
  echo "Usage: $(basename "$0") <vertical-resolution> <input> [<output>]" >&2
  exit 1
fi
if [ -z "$output" ]; then
  d="$(dirname "$input")"
  f="$(basename "$input")"
  ext="${f##*.}"
  noext="${f%.*}"
  output="$d/${noext}_${vertical}p.${ext}"
fi
exec ffmpeg -y \
  -i "$input" -vf "scale=-1:$vertical" -c:v libx264 -c:a copy -vsync 0 "$output"