Bash script to normalize audio from files using the `ffmpeg` tool

mass-normalize.sh

#!/bin/bash
mp3gain="/cygdrive/a/apps/mp3gain/mp3gain.exe"
id3="/cygdrive/a/apps/id3/id3.exe"
concurrent_jobs=4

if [ -z "${1}" ]; then
 echo "usage: ${0} <directory> [<directory> ...]"
 exit 1
fi

for arg in "${@}"; do
 if [ ! -d "${arg}" ]; then
  echo "not a directory: ${arg}"
  exit 1
 fi
done

_ifs="${IFS}"
IFS=$'\n'
filelist=($(find "${@}" -iname "*.mp3"))
IFS="${_ifs}"
iwd="${PWD}"
logfile="${iwd}/${0%.sh}.log"

if [ ${#filelist[@]} -lt 1 ]; then
 echo "no mp3 files found in: ${1}"
 exit 0
fi

echo "These files will be normalized:"
count=0
for path in "${filelist[@]}"; do
 count=$((10#${count} + 1))
 echo "- ${path}"
 if [ ${count} -ge 10 ]; then
  echo "- (Additional $((10#${#filelist[@]} - 10)) files)"
  break
 fi
done

# In case you want to confirm before starting...
#echo "
#Continue? [yn]"
#read -sn1 resp
#if [ "${resp,}" != "y" ]; then
# echo "no."
# exit 0
#fi
#echo "yes."

echo "Phase 1: normalize in parallel."
for path in "${filelist[@]}"; do
 echo "- ${path}"
 dir="${path%/*}"
 file="${path##*/}"
 if [ "$(jobs -p 2>&1 | wc -l)" -ge ${concurrent_jobs} ]; then
  echo -n "Waiting background jobs: "
  wait -n
  retstat="${?}"
  if [ ${retstat} -ne 0 ]; then
   echo "Error trying to normalize file. aborting."
   cd "${iwd}"
   if [ "$(jobs -p 2>&1 | wc -l)" -gt 0 ]; then
    echo -n "Waiting remaining background jobs: "
    wait
    echo "done."
   fi
   echo "Check '${logfile}' for normalize tool output."
   exit 1
  fi
  echo " done."
 fi
 cd "${dir}"
 "${mp3gain}" /u "${file}"
 retstat="${?}"
 if [ ${retstat} -ne 0 ]; then
  echo "Error running mp3gain. aborting."
  cd "${iwd}"
  exit 1
 fi
 "${iwd}/normalize.sh" "${file}" 2>&1 >> "${logfile}" &
 cd "${iwd}"
done

if [ "$(jobs -p 2>&1 | wc -l)" -gt 0 ]; then
 echo -n "Waiting concurrent jobs: "
 while [ "$(jobs -p 2>&1 | wc -l)" -gt 0 ]; do
  wait -n
  echo -n "."
  retstat="${?}"
  if [ ${retstat} -ne 0 ]; then
   echo "Error trying to normalize file. aborting."
   cd "${iwd}"
   if [ "$(jobs -p 2>&1 | wc -l)" -gt 0 ]; then
    echo -n "Waiting remaining background jobs: "
    wait
    echo "done."
   fi
   echo "Check '${logfile}' for normalize tool output."
   exit 1
  fi   
 done
 echo "done."
fi

echo "
Pahse 2: replace files."
for path in "${filelist[@]}"; do
 echo "- ${path}"
 dir="${path%/*}"
 file="${path##*/}"
 nfile="${file%.mp3}_.mp3"
 cd "${dir}"
 if [ ! -f "${nfile}" ]; then
  echo "Normalize tool didn't output expected file: ${nfile}"
  cd "${iwd}"
  exit 1
 else
  echo -n "Overwriting file with normalized one: "
  output="$("${id3}" --duplicate "${file}" "${nfile}" 2>&1)"
  retstat="${?}"
  if [ ${retstat} -ne 0 ]; then
   if [ "${output::36}" == "id3: note: could not read tags from " ]; then
    echo -n "no id3 info, "
   else
    echo "Failed copying over ID3 tag to file.
--- id3.exe output ---
${output}
---
Aborting."
    cd "${iwd}"
    exit 1
   fi
  fi
  
  mv "${nfile}" "${file}"
  retstat="${?}"
  if [ ${retstat} -ne 0 ]; then
   echo "Failed overwriting file. Aborting."
   cd "${iwd}"
   exit 1
  else
   echo "done."
  fi
 fi
 cd "${iwd}"
done

echo "
All done! Hopefully!"

normalize.sh

#!/bin/bash

# Normalize to -14LUFs (youtube, spotify defaults).
target_lufs=-14 # youtube, spotify and other streaming media
ffmpeg="/cygdrive/a/apps/ffmpeg/bin/ffmpeg.exe"

if [ -z "${1}" ]; then
 echo "usage: ${0} <mp3 file>"
 exit 1
elif [ ! -f "${1}" ]; then
 echo "unable to locate  mp3 file: ${1}"
 exit 1
fi

destfile="${1%.mp3}_.mp3"

echo -n "Analyzing ${1}: "
# infer
output="$("${ffmpeg}" -i "${1}" -af loudnorm=print_format=summary -f null - 2>&1)"
retstat="${?}"

if [ ${retstat} -ne 0 ]; then
 echo "failed.
Unable to analyze file. ffmpeg returned non-zero error status ${retstat}.
--- ffmpeg output ---
${output}
---"
 exit 1
else
 echo "done."
fi

sampleout="Input Integrated:     -9.2 LUFS
Input True Peak:      +0.1 dBTP
Input LRA:             2.2 LU
Input Threshold:     -19.4 LUFS

Output Integrated:   -23.5 LUFS
Output True Peak:    -11.6 dBTP
Output LRA:            1.7 LU
Output Threshold:    -33.6 LUFS

Normalization Type:   Dynamic
Target Offset:        -0.5 LU
"

vals=($(echo "${output}" | egrep "^Input (Integrated|True Peak|LRA|Threshold): " | sed -E "s/:  +/:/;s/^[^:]+://;s/ (LUFS|dBTP|LU)//;s/\r//" | tr '\n' ' '))
input_i="${vals[0]}"
input_tp="${vals[1]}"
input_lra="${vals[2]}"
input_thres="${vals[3]}"

echo "int: ${input_i}
tp: ${input_tp}
lra: ${input_lra}
thres: ${input_thres}

Output file: ${destfile}"

if [[ ! "${input_i}" =~ ^(|\+|-)[0-9]+(|\.[0-9]+)$ || \
      ! "${input_tp}" =~ ^(|\+|-)[0-9]+(|\.[0-9]+)$ || \
      ! "${input_lra}" =~ ^(|\+|-)[0-9]+(|\.[0-9]+)$ || \
      ! "${input_thres}" =~ ^(|\+|-)[0-9]+(|\.[0-9]+)$ ]]; then
 echo "One of the required values were not in the expected format."
 exit 1
fi

if [ -e "${destfile}" ]; then
 dfbak="${destfile//./_}-$(date +%Y%m%d%H%M%S).mp3"
 echo -n "Destination file exists, renaming it to: ${dfbak}"
 output="$(mv "${destfile}" "${dfbak}" 2>&1)"
 retstat="${?}"
 if [ ${retstat} -ne 0 ]; then
  echo ", failed.
Unable to replace file: ${output}"
  exit 1
 else
  echo ", done."
 fi
fi

if [ "${input_i}" == "-inf" -o "${input_tp}" == "-inf" ]; then
 echo -n "
File is either silent or doesn't have enough data to be normalized. Copying over: "
 output="$(cp "${1}" "${1%.mp3}_.mp3" 2>&1)"
 retstat="${?}"

 if [ ${retstat} -ne 0 ]; then
  echo "failed.
ffmpeg failed to copy file over.
--- cp output ---
${output}
---"
  exit 1
 else
  echo "Done.
Saved to: ${1%.mp3}_.mp3"
 fi
else
 echo -n "
Applying ${target_lufs} LUFS normalization: "
# apply
 output="$("${ffmpeg}" -i "${1}" -af loudnorm=I=${target_lufs}:TP=-1:LRA=11:measured_I=${input_i}:measured_TP=${input_tp}:measured_LRA=${input_lra}:measured_thresh=${input_thres} -q:a 0 "${1%.mp3}_.mp3" 2>&1)"
 retstat="${?}"

 if [ ${retstat} -ne 0 ]; then
  echo "failed.
ffmpeg failed to normalize file.
--- ffmpeg output ---
${output}
---"
  exit 1
 else
  echo "Done.
Saved to: ${1%.mp3}_.mp3"
 fi
fi

Am I reinventing the wheel here? I did a lot of research and didn't find any bash script -- or ffmpeg arguments -- for normalizing audio.
I ended up using a set of arguments provided by google search's AI that seemed to do the job just fine. Normalized over 3000 files and the playlist goes out loud well.

I'm using this to normalize old (and new) MP3 files I'm playing in an old Windows 7 machine with WinAmp, also in an old (but loud) stereo. When we're talking about 70+dB of audio intensity on a 50W RMS amplifier, it really matters when some songs are too low or too high.

The above script is meant for individual files' normalization. It won't fit, for instance, when a previous song "connects" to the next, in particular with albums' introductory tracks that are usually some instruments or FX that gets "normalized" really high in respect to their continuation in the actual "track one" of that album.

To automate the normalization of entire discographies, I'm using another script that I'll post and link from here.

Edit: Oops, I've noticed I can just add the second file to the gist itself, so there you go, the "full project" to normalize a whole library of MP3 files. It can probably easily be adjusted to other music/video formats.
Notice the "orchestrator" runs up to concurrent_jobs normalization calls in parallel, helping fill in CPU usage for faster conversion of whole libraries. You may adjust the value according to the host's CPU count for increased speed.