#!/bin/bash -e

# Many DVDs released in Australia are sped up from 24fps to 25fps.
# This script reverses the procedure, correcting the audio pitch.
# The video framerate is adjusted without re-encoding. The audio is slowed and
# volume normalised then re-encoded as mp3.

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

FORCEFPS="24"
SLOWDOWN="0.96"

destdir="$1"
shift

for infile in "$@"; do
    outfile="$destdir/$(basename "$infile")"

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

    set -x
    tmpdir="$(mktemp -d "${TMPDIR:-/var/tmp}/pal-XXXXXXXX")"
    mplayer -novideo -ao pcm:file="${tmpdir}/audio.wav" -vo null "$infile"
    sox "${tmpdir}/audio.wav" "${tmpdir}/audio-fixed.wav" speed "${SLOWDOWN}" gain -n
    lame --preset standard "${tmpdir}/audio-fixed.wav" "${tmpdir}/audio.mp3"
    trackid="$(mkvmerge -i "$infile" | grep video | sed 's/^Track ID \(.\):.*$/\1/')"
    mkvmerge -o "${outfile}" --default-duration "${trackid}:${FORCEFPS}fps" --no-audio "$infile" "${tmpdir}/audio.mp3"

    rm -rf "$tmpdir"
done