#! /bin/sh

set -e

usage () { cat <<EOD 1>&2; }
Usage: $0 [OPTIONS...] SRC [SRC...]

Re-encodes to h.264, preserving audio and subtitles.
Output will be written to \$SRC.h264.mp4

  -height H   Rescale to no taller than H
  -1080p      Rescale to no bigger than 1080p
  -720p       Rescale to no bigger than 720p
  -480p       Rescale to no bigger than 480p
  -bitrate B  Set average bitrate to B, overriding rescale setting
  -swenc      Software encode instead of hardware
EOD

height=ih
codec=h264_v4l2m2m
bitrate="-b:v 2048k"
while true; do
  case "$1" in
    -height|--height)
      height=$2
      shift 2
      ;;
    -1080p|--1080p)
      height=1080
      bitrate="-b:v 2048k"
      shift
      ;;
    -720p|--720p)
      height=720
      bitrate="-b:v 1200k"
      shift
      ;;
    -480p|--480p)
      height=480
      bitrate="-b:v 512k"
      shift
      ;;
    -bitrate|--bitrate)
      bitrateManual="-b:v $2"
      shift 2
      ;;
    -swenc|--swenc)
      codec=h264
      shift
      ;;
    -*)
      usage
      exit
      ;;
    *)
      break
      ;;
  esac
done

if [ "$codec" = "h264" ]; then
  bitrate="-crf 28"
fi
bitrate=${bitrateManual:-$bitrate}

log () {
  echo "=== $*"
}

cmd () {
  nice "$@"
}

# This got a height of 719 (n%2 must = 0)
#-vf "scale='min($width,iw)':'min($height,ih)':force_original_aspect_ratio=decrease,format=yuv420p" \

for fn in "$@"; do
  base=${fn%.*}
  filename=$(basename "$fn")
  intermediate="$base.nut"
  out="$base.h264.mkv"
  [ -f "$out" ] && continue
  case "$fn" in *.h264.mp4) continue ;; esac

  # ffmpeg has some bizarro thing where the h264_v4l2m2m codec won't write to a mkv file,
  # In addition, some subtitles interfere with it too.
  # Solution: transcode video + audio into an intermediate file,
  # then add back any subtitles.

  log "$filename - Scale/Transcode"
  cmd ffmpeg \
    -hide_banner \
    -loglevel warning \
    -stats \
    -i "$fn" \
    -map 0:v \
    -vf "scale=-2:'min($height,ih)':force_original_aspect_ratio=decrease,format=yuv420p" \
    -c:v $codec \
    $bitrate \
    -map 0:a \
    -c:a copy \
    -num_capture_buffers 16 \
    -num_output_buffers 32 \
    -y \
    "$intermediate"

  log "$filename - Add subtitles"
  cmd ffmpeg \
    -hide_banner \
    -loglevel warning \
    -stats \
    -i "$intermediate" \
    -i "$fn" \
    -map 0:v \
    -map 0:a \
    -map 1:s? \
    -c copy \
    -y \
    "$out"

  rm "$intermediate"
done