#!/bin/bash
#
# requires: *topnm, pnmpad, pnmscale, ppmntsc, ppmtoy4m, mpeg2enc,
#           mktemp, awk, file
#

# video format. pal or ntsc
FORMAT=pal

# target image width/height (taking into account visible screen area)
if [ "$FORMAT" = "ntsc" ]; then
  TW=600
  TH=420
else
  TW=632
  TH=512
fi

TMP=$(mktemp ${TMPDIR:-/tmp}/image_convert.pnm.XXXXXX) || exit 2
IMG=$1
MPG=$2

DIR=$(dirname "$MPG")
if [ ! -d "$DIR" ]; then
  mkdir -p "$DIR" || exit 2
fi

trap cleanup EXIT
cleanup()
{
  [ -z "$TMP" ] || rm -f "$TMP"
}

#
# get the file type and set the according converter to PNM
#
FILE_TYPE=$(file -i -L -b "$IMG" 2>/dev/null | cut -f2 -d/)
case "$FILE_TYPE" in
  jpg | jpeg)
  TO_PNM=jpegtopnm
  ;;
  tiff)
  TO_PNM=tifftopnm
  ;;
  bmp | x-bmp)
  TO_PNM=bmptoppm
  ;;
  png | x-png)
  TO_PNM=pngtopnm
  ;;
  Netpbm | pnm | x-portable-pixmap)
  TO_PNM=cat
  ;;
  gif)
  TO_PNM=giftopnm
  ;;
  *)
  echo "filetype '$FILE_TYPE' is not supported"
  exit 1
  ;;
esac

#
# extract the image size & compute scale value
#
LANG=C # get the decimal point right
$TO_PNM "$IMG" >"$TMP" 2>/dev/null
S=$(pnmfile "$TMP" | awk '{ printf "%d %d ",$4,$6 }')
S=$(echo $S $TW $TH | awk '{ sw=$3/$1; sh=$4/$2; s=(sw<sh)?sw:sh; printf "%.4f\n",(s>1)?1.0:s; }')

#
# now run the conversion
#
if [ "$FORMAT" = "ntsc" ]; then
  pnmscale $S "$TMP" | \
    pnmpad -black -width 704 -height 480 | \
    ppmntsc | \
    ppmtoy4m -v 0 -n 1 -r -S 420mpeg2 -F 30000:1001 | \
    mpeg2enc -f 7 -T 90 -F 4 -nn -a 2 -v 0 -o "$MPG"
else
  pnmscale $S "$TMP" | \
    pnmpad -black -width 704 -height 576 | \
    ppmntsc --pal | \
    ppmtoy4m -v 0 -n 1 -r -S 420mpeg2 -F 25:1 | \
    mpeg2enc -f 7 -T 90 -F 3 -np -a 2 -v 0 -o "$MPG"
fi