#!/bin/bash -e

# Many DVDs released in Australia are sped up from 23.976fps to 25fps.
# This script reverses the procedure, correcting the audio pitch.
# Input files are assumed to be mkv files with track 2 audio.
# The video framerate is adjusted without re-encoding. The audio is slowed and
# normalised then re-encoded as mp3.

if [ -z "$1" -o -z "$2" ]; then
	echo "Usage: $0 destdir infile"
	exit 1
fi

FORCEFPS="24"
SLOWDOWN="0.96"

destdir="$1"
infile="$2"
outfile="$destdir/$(basename "$infile")"
tmpdir="$(tempfile -p 'pal-')"
rm "$tmpdir"

if [ -f "$outfile" ]; then
	echo "Not overwriting $outfile"
	exit 0
fi

set -x
mkdir "$tmpdir"
mkvextract tracks "$infile" 2:"${tmpdir}/audio"
mplayer -ao pcm:file="${tmpdir}/audio.wav" -vo null "${tmpdir}/audio"
sox "${tmpdir}/audio.wav" "${tmpdir}/audio-fixed.wav" speed "${SLOWDOWN}" gain -n
lame --preset standard "${tmpdir}/audio-fixed.wav" "${tmpdir}/audio.mp3"
mkvmerge -o "${outfile}" --default-duration "1:${FORCEFPS}fps" --no-audio "$infile" "${tmpdir}/audio.mp3"

rm -rf "$tmpdir"