Window WSL bash script to encode videos to under 8mb for discord sharing. Needs ffmpeg.exe in path

8mb2.bash

#!/usr/bin/env bash

set -o errexit
set -o pipefail
set -o nounset
#set -x  #Debug

#
# Re-encode a video to a target size in MB.
# Example:
#    ./8mb2.bash video.mp4 8
# Currently only supports files from current dir. Script can be where ever.
############
# Credit to Marian Minar 
# https://stackoverflow.com/a/61146975/2001062
# Re written by lord-carlos
# Inspired by djkato https://github.com/djkato/Discord-Media-Compressor-sub-8mb

T_SIZE="$2" # target size in MB
T_FILE="${1%.*}-$2MB.webm" # filename out

target=$(wslpath -w "$1")
null=$(wslpath -w "/dev/null")

main () {
    # Original duration in seconds
    O_DUR=$(\
        ffprobe.exe \
        -v error \
        -show_entries format=duration \
        -of csv=p=0 "${target}")

    # Original audio rate
    O_ARATE=$(\
        ffprobe.exe \
        -v error \
        -select_streams a:0 \
        -show_entries stream=bit_rate \
        -of csv=p=0 "${target}")

    # Original audio rate in KiB/s
    O_ARATE=$(\
        awk \
        -v arate="$O_ARATE" \
        'BEGIN { printf "%.0f", (arate / 1024) }')

    # Target size is required to be less than the size of the original audio stream
    T_MINSIZE=$(\
        awk \
        -v arate="$O_ARATE" \
        -v duration="$O_DUR" \
        'BEGIN { printf "%.2f", ( (arate * duration) / 8192 ) }')

    # Equals 1 if target size is ok, 0 otherwise
    IS_MINSIZE=$(\
        awk \
        -v size="$T_SIZE" \
        -v minsize="$T_MINSIZE" \
        'BEGIN { print (minsize < size) }')

    # Give useful information if size is too small
    if [[ $IS_MINSIZE -eq 0 ]]; then
        printf "%s\n" "Target size ${T_SIZE}MB is too small!" >&2
        printf "%s %s\n" "Try values larger than" "${T_MINSIZE}MB" >&2
        exit 1
    fi

    # Set target audio bitrate
    T_ARATE=$O_ARATE


    # Calculate target video rate - MB -> KiB/s
    T_VRATE=$(\
        awk \
        -v size="$T_SIZE" \
        -v duration="$O_DUR" \
        -v audio_rate="$O_ARATE" \
        'BEGIN { print  ( ( size * 8192.0 ) / ( 1.048576 * duration ) - audio_rate) }')

    # Perform the conversion
    ffmpeg.exe \
        -y \
        -i "${target}" \
        -c:v libvpx-vp9 \
        -c:a libopus \
        -deadline good \
        -quality good \
        -cpu-used 0 \
        -b:v "$T_VRATE"k \
        -row-mt 1 \
        -auto-alt-ref 6 \
        -b:a "$T_ARATE"k \
        -pass 1 \
        -an \
        -f webm \
        NUL \
    && \
    ffmpeg.exe \
        -y \
        -i "${target}" \
        -c:v libvpx-vp9 \
        -c:a libopus \
        -deadline good \
        -quality good \
        -cpu-used 0 \
        -b:v "$T_VRATE"k \
        -row-mt 1 \
        -auto-alt-ref 6 \
        -b:a "$T_ARATE"k \
        -pass 2 \
        $T_FILE
}

function STDERR () {
    printf "error?"
    cat - 1>&2
}

main