code.delx.au - transcoding/blob - fix-pal-speedup

   1 #!/bin/bash
   2
   3 # Many DVDs released in Australia are sped up from 24fps to 25fps.
   4 # This script reverses the procedure, correcting the audio pitch.
   5 # - The video framerate is adjusted without re-encoding.
   6 # - The audio is slowed, and encoded as AAC, preserving surround sound.
   7 # - Chapters and subtitles are also adjusted to match the new timing.
   8
   9 if [ -z "$1" ] || [ -z "$2" ]; then
  10     echo "Usage: $0 infile outfile"
  11     exit 1
  12 fi
  13
  14 set -o pipefail -eux
  15 OLDFPS="25"
  16 NEWFPS="24"
  17 SLOWFILTER=("-filter" "asetrate=46080,aresample=osr=48000:resampler=soxr")
  18
  19 function main {
  20     local infile="$1"
  21     local outfile="$2"
  22
  23     local tmpdir=""
  24     tmpdir="$(mktemp -d "${TMPDIR:-/var/tmp}/pal-XXXXXXXX")"
  25     local audiofile="${tmpdir}/audiofile.m4a"
  26
  27     encode_audio "$infile" "$audiofile"
  28     remux_file "$infile" "$audiofile" "$outfile"
  29
  30     rm -rf "$tmpdir"
  31 }
  32
  33 function encode_audio {
  34     ffmpeg \
  35         -i "$1" \
  36         -vn \
  37         "${SLOWFILTER[@]}" \
  38         -c:a libfdk_aac -vbr 3 \
  39         "$2"
  40 }
  41
  42 function remux_file {
  43     local infile="$1"
  44     local audiofile="$2"
  45     local outfile="$3"
  46
  47     local audiodelay=""
  48     audiodelay="$(get_minimum_timestamp "$infile" "audio")"
  49
  50     local videodelay=""
  51     videodelay="$(get_minimum_timestamp "$infile" "video")"
  52
  53     local videotrackid=""
  54     videotrackid="$(get_track_id "$infile" "video")"
  55
  56     local suboptions=()
  57     local subtitletrackid=""
  58     while read -r subtitletrackid; do
  59         suboptions+=("--sync" "${subtitletrackid}:0,${OLDFPS}/${NEWFPS}")
  60     done < <(get_track_id "$infile" "subtitles")
  61
  62     local chapteroptions=()
  63     if [ "$(get_chapter_count "$infile")" -gt 0 ]; then
  64         chapteroptions=("--chapter-sync" "0,${OLDFPS}/${NEWFPS}")
  65     fi
  66
  67     mkvmerge \
  68         -o "${outfile}" \
  69         --default-duration "${videotrackid}:${NEWFPS}fps" \
  70         --sync "${videotrackid}:$((videodelay / 1000000))" \
  71         "${chapteroptions[@]}" \
  72         "${suboptions[@]}" \
  73         --no-audio "$infile" \
  74         --sync "0:$((audiodelay / 1000000))" \
  75         "$audiofile"
  76 }
  77
  78 function get_track_id {
  79     mkvmerge -i -F json "$1" | jq -r ".tracks[] | select(.type == \"$2\") | .id"
  80 }
  81
  82 function get_minimum_timestamp {
  83     mkvmerge -i -F json "$1" | jq -r ".tracks[] | select(.type == \"$2\") | .properties.minimum_timestamp"
  84 }
  85
  86 function get_chapter_count {
  87     mkvmerge -i -F json "$1" | jq -r ".chapters | length"
  88 }
  89
  90 main "$@"