# 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
-# normalised then re-encoded as mp3.
+# The video framerate is adjusted without re-encoding. The audio is
+# slowed, and encoded as AAC, preserving surround sound.
if [ -z "$1" -o -z "$2" ]; then
- echo "Usage: $0 destdir infile"
- exit 1
+ echo "Usage: $0 infile outfile"
+ exit 1
fi
+set -xe
FORCEFPS="24"
-SLOWDOWN="0.96"
+SLOWFILTER="-filter asetrate=46080,aresample=osr=48000:resampler=soxr"
-destdir="$1"
-infile="$2"
-outfile="$destdir/$(basename "$infile")"
-tmpdir="$(tempfile -p 'pal-')"
-rm "$tmpdir"
+function mux_replace_audio {
+ local infile="$1"
+ local audiofile="$2"
+ local outfile="$3"
-if [ -f "$outfile" ]; then
- echo "Not overwriting $outfile"
- exit 0
-fi
+ local audiodelay="$(get_audio_delay "$infile")"
+ local videotrackid="$(get_video_trackid "$infile")"
-set -x
-mkdir "$tmpdir"
-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" "${tmpdir}/audio.mp3"
-mkvmerge -o "${outfile}" --default-duration "1:${FORCEFPS}fps" --no-audio "$infile" "${tmpdir}/audio.mp3"
+ mkvmerge \
+ -o "${outfile}" \
+ --default-duration "${videotrackid}:${FORCEFPS}fps" \
+ --no-audio "$infile" \
+ --sync "0:$((audiodelay / 1000000))" \
+ "$audiofile"
+}
-rm -rf "$tmpdir"
+function get_video_trackid {
+ mkvmerge -i "$1" | sed -n 's/Track ID \([0-9]*\): .*video.*/\1/p'
+}
+
+function get_audio_delay {
+ mkvmerge -F json -i "$1" | \
+ jq -r '.tracks[] | select(.type == "audio") | .properties.minimum_timestamp'
+}
+
+function encode_audio {
+ ffmpeg \
+ -i "$1" \
+ -vn \
+ $SLOWFILTER \
+ -c:a libfdk_aac -vbr 3 \
+ "$2"
+}
+function convert_file {
+ local infile="$1"
+ local outfile="$2"
+ local audiofile="${tmpdir}/audiofile.m4a"
+
+ encode_audio "$infile" "$audiofile"
+ mux_replace_audio "$infile" "$audiofile" "$outfile"
+}
+
+
+infile="$1"
+outfile="$2"
+tmpdir="$(mktemp -d "${TMPDIR:-/var/tmp}/pal-XXXXXXXX")"
+convert_file "$infile" "$outfile"
+rm -rf "$tmpdir"