From 50c7b99e41ff11dc345680cbda32a1b043f2a3fa Mon Sep 17 00:00:00 2001
From: James Bunton <jamesbunton@delx.net.au>
Date: Mon, 4 Jan 2016 16:26:44 +1100
Subject: [PATCH] fix-pal-speedup now preserves surround sound for movies

---
 fix-pal-speedup | 42 ++++++++++++++----------------------------
 1 file changed, 14 insertions(+), 28 deletions(-)

diff --git a/fix-pal-speedup b/fix-pal-speedup
index 27ddd48..ab49490 100755
--- a/fix-pal-speedup
+++ b/fix-pal-speedup
@@ -3,7 +3,7 @@
 # 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, volume normalised, down-mixed to stereo and encoded as mp3.
+# slowed, and encoded as AAC, preserving surround sound.
 
 if [ -z "$1" -o -z "$2" ]; then
     echo "Usage: $0 destdir infile [infile ...]"
@@ -12,7 +12,7 @@ fi
 
 set -xe
 FORCEFPS="24"
-SLOWDOWN="0.96"
+SLOWFILTER="-filter asetrate=46080,aresample=48000"
 
 function mux_replace_audio {
     local infile="$1"
@@ -30,43 +30,29 @@ function extract_audio {
     mplayer \
         -noconfig all \
         -novideo \
-        -ao "pcm:waveheader:file=${outfile}" \
+        -channels 8 \
+        -dumpaudio \
+        -dumpfile "$outfile" \
         "$infile"
 }
 
-function slow_audio {
-    local infile="$1"
-    local outfile="$2"
-
-    sox \
-        --temp "$tmpdir" \
-        "$infile" \
-        -t wav \
-        "$outfile" \
-        speed "${SLOWDOWN}" \
-        gain -n
-}
-
 function encode_audio {
-    local infile="$1"
-    local outfile="$2"
-
-    lame \
-        --preset standard \
-        "${infile}" "${outfile}"
+    ffmpeg \
+        -i "$1" \
+        $SLOWFILTER \
+        -strict experimental \
+        "$2"
 }
 
 function convert_file {
     local infile="$1"
     local outfile="$2"
-    local audio1="${tmpdir}/audio1.wav"
-    local audio2="${tmpdir}/audio2.wav"
-    local audio3="${tmpdir}/audio3.mp3"
+    local audio1="${tmpdir}/audio1.ac3"
+    local audio2="${tmpdir}/audio2.m4a"
 
     extract_audio "${infile}" "${audio1}"
-    slow_audio "${audio1}" "${audio2}"
-    encode_audio "${audio2}" "${audio3}"
-    mux_replace_audio "${infile}" "${audio3}" "${outfile}"
+    encode_audio "${audio1}" "${audio2}"
+    mux_replace_audio "${infile}" "${audio2}" "${outfile}"
 }
 
 
-- 
2.39.2