ffmpeg two pass loudnorm application

ffmpeg-loudnorm.sh

#!/usr/bin/env bash

declare FFMPEG_OUTPUT INPUT OUTPUT;

while [[ -n "$1" ]]; do
    case "$1" in
        --help|-h)
            echo "ffmpeg-loudnorm.sh [--help|-h] [--version] <INPUT> [OUTPUT]";
            printf "\n";
            echo "=== Arguments ===";
            printf "\tINPUT\tThe file to process.";
            printf "\tOUTPUT\tThe file to write the processed file to.";
            printf "\n\n";
            echo "=== Options ===";
            printf "\t--help|-h\tShow this information and then exit.\n";
            printf "\t--version\tShow the version information and then exit.\n";
            echo "";
            echo "Copyright (c) 2025 G'lek Tarssza, licensed under the MIT License.";
            exit 0;
        ;;
        --version)
            echo "v0.0.1 (2025-06-13)";
            exit 0;
        ;;
        *)
            if [[ -z "${INPUT}" ]]; then
                INPUT="$1";
            elif [[ -z "${OUTPUT}" ]]; then
                OUTPUT="$1";
            else
                printf "[\e[38;5;196mFATAL\e[0m] Too many command line arguments provided!\n";
                exit 128;
            fi
        ;;
    esac
    shift 1;
done

if [[ -z "${OUTPUT}" ]]; then
    OUTPUT="${INPUT%.*}_loudnorm.${INPUT##*.}";
    printf "[\e[38;5;208mWARN\e[0m] No output file given, defaulting to '%s'\n" "${OUTPUT}";
fi

printf "[\e[38;5;105mINFO\e[0m] Extracting loudness levels from '%s'...\n" "${INPUT}";

mkfifo ffmpeg_loudnorm;

ffmpeg -hide_banner -i "${INPUT}" '-filter:a' 'loudnorm=print_format=json' -f null - &> ffmpeg_loudnorm &
FFMPEG_OUTPUT="$(awk 'begin {inJSON=false;} {if ($0 ~ "}" && inJSON == "true") {print $0; inJSON = "false"} if ($0 ~ "{" || inJSON == "true") {print $0; if (inJSON != "true") {inJSON="true";}}}' < ffmpeg_loudnorm)";

rm ffmpeg_loudnorm;

set -e;

printf "[\e[38;5;105mINFO\e[0m] Extracted the following parameters from 'ffmpeg':\n";
echo "${FFMPEG_OUTPUT}" | jq '.';

printf "[\e[38;5;105mINFO\e[0m] Creating '%s_loudnorm.%s'...\n" "${OUTPUT}" "${OUTPUT}";
ffmpeg -hide_banner -i "${INPUT}" '-c:v' copy -pass 2 '-filter:a' "loudnorm=linear=true:measured_I=$(echo "${FFMPEG_OUTPUT}" | jq --raw-output '.input_i'):measured_LRA=$(echo "${FFMPEG_OUTPUT}" | jq --raw-output '.input_lra'):measured_tp=$(echo "${FFMPEG_OUTPUT}" | jq --raw-output '.input_tp'):measured_thresh=$(echo "${FFMPEG_OUTPUT}" | jq --raw-output '.input_thresh')" -c:a aac -b:a 256k "${OUTPUT}";

unset FFMPEG_OUTPUT INPUT OUTPUT;

printf "[\e[38;5;105mINFO\e[0m] Done!\n";