bin/video-transcode at master · nilsboy/bin · GitHub

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#!/usr/bin/env bash-with-comments

# Transcode a media file to x264 preserving all video, audio and subtitle tracks
#
# For deinterlacing set DEINTERLACE env var.

# NOTE: for libfdk_aac on Ubuntu 18.04 use snap:
# sudo snap install ffmpeg --devmode

source bash-helpers

# fix aspect "flag" - make 4:3 to display as 16:9 for NTSC:
# mkvpropedit *.mkv --edit track:v1 --set display-width=853

infile="$*"
INFO "Encoding $infile..."

# video quality - crf:
# A change of ±6 should result in about half/double the file size, although your results might vary.
# lower values would result in better quality (at the expense of higher file sizes).
# http://slhck.info/articles/crf
# default crf: 23
# less is better
# DVD needs 23? / the lower the res the higher quality neede?
crf=29

# Even though apparently all dvds are interlaced - usually results seem to be better without deinterlacing.
# deinterlace
if [[ $DEINTERLACE ]] ; then
  deinterlacer="-vf yadif"
  deinterlaced_name="-deinterlaced"
  WARN '#################################### Deinterlacing!'
fi

## AUDIO
# -cutoff: default is 14000Hz for audio
#
# 224 kbit 6-ch AAC seems to be the current standard (2020-06-28).
audio="-c:a libfdk_aac -b:a 224k -cutoff 20000"

if [[ $STEREO ]] ; then
  audio="-c:a libfdk_aac -vbr 5 -cutoff 20000 -ac 2"
  stereo_name="-stereo"
  WARN '#################################### Forcing stereo!'
fi

# Audio "hi-fi transparency demands data rates of at least 128 kbit/s CBR. The
# MPEG-2 audio tests showed that AAC meets the requirements referred to as
# "transparent" for the ITU at 128 kbit/s for stereo, and 320 kbit/s for 5.1 audio."
# (https://en.wikipedia.org/wiki/Advanced_Audio_Coding)
#
# Audio codec options:
# https://www.ffmpeg.org/ffmpeg-codecs.html
# ac3 is the best quality audio encoder directly included in libav - see:
# https://trac.ffmpeg.org/wiki/Encode/HighQualityAudio
# libfdk_aac is the best aac encoder.

# outfile=$(basename "$infile").crf${crf}-aac${deinterlaced_name}${stereo_name}.mkv
outfile="$infile".tmp.mkv
nfoDir=$(dirname "$infile")/nfo
nfo="$nfoDir/recode.nfo"

if [[ -e $outfile ]] ; then
  DIE "Outfile: $outfile exists."
fi

# prevent ffmpeg from reading stdin (problem with bash-with-comments)
< /dev/null \
ffmpeg \
  # shows -vf option like yadif etc.
  -loglevel verbose \
  #
  -i "$infile" \
  #
  # include all video streams
  -map 0:v \
  #
  -c:v libx264 \
  -crf $crf \
  $deinterlacer \
  #
  # May prevent "Too many packets buffered for output stream":
  # Had this problem with a DVD ISO.
  -max_muxing_queue_size 9999 \
  #
  # TODO: Only reencode if not aac etc already.
  #
  # NOTE: -vbr reports an error but that message is supposably wrong (http://www.ffmpeg-archive.org/FDK-AAC-OUTPUTS-CBR-AUDIO-STREAM-ONLY-td4670348.html)
  # The bitrate does seam to fluctuate.
  # "the VBR setting is unsupported and only works with some parameter combinations"
  #
  # include all audio streams
  -map 0:a \
  #
  $audio \
  #
  # passthrou
  # -c:a copy \
  #
  # downmix to 2 channels (ignores the subwoofer channel)
  $stereo \
  #
  # include all subtitle streams
  -map 0:s? \
  # copy subtitles as is
  -c:s copy \
  #
  $outfile

INFO "Done: $infile"

mkdir -p "$nfoDir"
echo "$infile reencoded with crf: ${crf}" >> "$nfo"

mv "$outfile" "$infile"
mv "$infile" "$infile.reenc_x264.mkv"

if [[ $DEINTERLACE ]] ; then
  WARN '#################################### Deinterlacing!'
fi

if [[ $STEREO ]] ; then
  WARN '#################################### Forcing stereo!'
fi