Shell script that encodes a movie to the free AV1 video codec using the highest possible quality

transcode-av1.sh

#!/bin/sh

# Helper script to transcode to high-quality AV1 clips via ffmpeg
#
# Uses best possible settings with two-pass encode.
# Encoding a full will take months or years!
#

# File from which the video is taken
inputFile=$1

# File to which the final generated output video will be written
outputFile=${inputfile%.*}.av1transcoded.webm

# Whether to encode the video into 2x2 tiles instead of whole
#
# Allows decoders to decode single frames with up to 4 threads
# Might not be necessary for modern decoders (which simply decode
# 4 frames in parallel, thereby achieving the same without tiles.
# Also lowers quality/efficiency a little bit.
#
: ${useFourTiles:=false}

# Bits per second to use for the video and audio streams
#
# Suggested for stereo movies     | Suggested for 5.1 movies
# --------------------------------|--------------------------------
#    768 =  672 video +  96 audio
#   1024 =  928 video +  96 audio
#   1536 = 1408 video + 128 audio   1536 = 1280 video + 256 audio
#   2048 = 1920 video + 128 audio   2048 = 1792 video + 256 audio
#   2560 = 2432 video + 128 audio   2560 = 2152 video + 384 audio
#   3072 = 2944 video + 128 audio   3072 = 2688 video + 384 audio
#   4096 = 3968 video + 128 audio   4096 = 3712 video + 384 audio
#   5120 = 4992 video + 128 audio   5120 = 4736 video + 384 audio
#                                   6144 = 5670 video + 384 audio
: ${videoBitRate:=2432}
: ${audioBitRate:=128}

# After how many frames to force a keyframe
#
# More keyframes worsen overall compression but allow better seeking.
# Many encoders recommend one keyframe per second, but one every two
# seconds is much more sensible imho.
#
: ${keyFrameInterval:=72}

# Whether to do a 10-bit encode
#
# Ten bit encodes are claimed to avoid banding, but I've yet to see
# any of it in a high-quality 8-bit encode.
#
: ${tenBit:=false}

# Set to crop the video
#
# Should be set to "width:height:offsetX:offsetY" if used
# Leave set to false in order to perform no cropping at all
#
: ${cropBoundaries:=false}

# Whether to sharpen the video
#
: ${sharpenVideo:=false}

# ----------------------------------------------------------------------------------------------- #

# Delete intermediate file if already there
if [[ -f ffmpeg2pass-0.log ]]
then
	echo Deleting intermediate files...
	rm ffmpeg2pass-0.log
fi

ffmpegParameters=()

# If the user has specified cropping bounds, set up the respective ffmpeg parameter
if [ "$cropBoundaries" = false ]
then
	echo Cropping disabled.
else
	echo Cropping to $cropBoundaries
	ffmpegParameters+=(-filter:v crop=$cropBoundaries)
fi

# ----------------------------------------------------------------------------------------------- #

# Video encoder settings
#
ffmpegParameters+=(-strict experimental)
ffmpegParameters+=(-c:v libaom-av1)
ffmpegParameters+=(-b:v $videoBitRate)
ffmpegParameters+=(-g $keyFrameInterval)
ffmpegParameters+=(-auto-alt-ref 1)
ffmpegParameters+=(-lag-in-frames 25)
ffmpegParameters+=(-crf 0)
#ffmpegParameters+=(-frame-parallel 1)

if [ "$tenBit" = true ]
then
	echo 10-bit encode
	ffmpegParameters+=(-pix_fmt yuv420p10le)
else
	echo 8-bit encode
	ffmpegParameters+=(-pix_fmt yuv420p)
fi

if [ "$useFourTiles" = true ]
then
	echo Encoding as 2x2 tiles
	ffmpegParameters+=(-tile-columns 2)
	ffmpegParameters+=(-tile-rows 2)
else
	echo Encoding as single tile
fi

# ----------------------------------------------------------------------------------------------- #

# Audio encoder settings
#
ffmpegParameters+=(-c:a libopus)
ffmpegParameters+=(-b:a $audioBitRate)
ffmpegParameters+=(-ar 48000)

# ----------------------------------------------------------------------------------------------- #

# Other settings
#
ffmpegParameters+=(-threads 1)

# ----------------------------------------------------------------------------------------------- #

echo "ffmpeg options: ${ffmpegParameters[@]}"

# ----------------------------------------------------------------------------------------------- #

echo "=============================================================================="
echo ""
echo "Encoding first pass"
echo ""

ffmpeg \
	-hide_banner \
	-i "$inputFile" \
	-shortest \
	"${ffmpegParameters[@]}" \
	-cpu-used 1 \
	-pass 1 \
	-f null \
	/dev/null

echo "=============================================================================="
echo ""
echo "Encoding second pass"
echo ""

ffmpeg \
	-hide_banner \
	-i "$inputFile" \
	-shortest \
	"${ffmpegParameters[@]}" \
	-cpu-used 0 \
	-pass 2 \
	-y \
	$outputFile