A simple file LUFS meter using FFmpeg, and inspired by rsgain and iZotope RX Waveform Statistics.

lufsmeter.sh

#!/usr/bin/env bash

# ==================================================================
# LUFS Meter
#   Analyzes audio files and extracts loudness metrics based on the
#   ITU-R BS.1770-4 (EBU R128) standard.
#
# AUTHOR:
#   gustavomdsantos@pm.me
# ==================================================================

show_help() {
  cat << EOF
Usage: $(basename "$0") [OPTIONS] FILE...

Analyze audio files and report loudness statistics.

Options:
  -h, --help    Show this help message and exit

Metrics:
  Integrated          Overall loudness of the file (LUFS).
  Short-Term Max      Maximum loudness of the file (LUFS).
  SIR                 Short-to-Integrated Ratio, measures the
                      dynamic lift above the average loudness (LU).
  Perceived Loudness  A linear scale based on human perception (%).
  True-Peak           The maximum absolute level of the signal (dBTP).
  Peak                The maximum sample value (dBFS).

Requires: ffmpeg, ffprobe, bc
EOF
}

# Process options
case "$1" in
  -h|--help)
    show_help
    exit 0
    ;;
  "")
    show_help
    exit 1
    ;;
esac

for cmd in ffmpeg ffprobe bc; do
  if ! command -v "$cmd" &> /dev/null; then
    echo "Error: Tool '$cmd' not found. Please install it to continue."
    exit 1
  fi
done

if [ "$#" -eq 0 ]; then
  echo "Usage: $0 file1 [file2 ...]"
  exit 1
fi

for file in "$@"; do
  echo -ne "Analyzing: \"$(basename "$file")\"...\r"

  output=""
  diff=""
  sample_peak=""
  perceived_loudness=""
  
  channels=$(ffprobe -v error -select_streams a:0 -show_entries stream=channels -of default=noprint_wrappers=1:nokey=1 "$file")

  if [ "$channels" -eq 1 ]; then
    audio_filter="pan=stereo|c0=c0|c1=c0,ebur128=peak=true,astats=measure_overall=1:reset=0"
  else
    audio_filter="ebur128=peak=true,astats=measure_overall=1:reset=0"
  fi

  log=$(ffmpeg -hide_banner -nostats -i "$file" -filter_complex "[0:a]$audio_filter" -f null - 2>&1)

  integrated=$(echo "$log" | grep "I:" | tail -n1 | sed -n 's/.*I:\s*\([-0-9.]*\).*/\1/p' | tr -d ' ')
  short_term=$(echo "$log" | grep "S:" | sed -n 's/.*S:\s*\([-0-9.]*\).*/\1/p' | sort -n | tail -n1 | tr -d ' ')
  true_peak=$(echo "$log" | grep -A2 "True peak:" | grep "Peak:" | sed -n 's/.*Peak:\s*\([-0-9.]*\).*/\1/p' | tr -d ' ')
  peak=$(echo "$log" | grep -i "Peak level dB" | head -n1 | sed -E 's/.*: (.*)/\1/' | tr -d ' ')

  # SIR (Short-to-Integrated Ratio), inspired by the PAPR (Peak-to-Average Power Ratio).
  # Formula: SIR = Short-Term Max - Integrated
  if [[ -n "$integrated" && -n "$short_term" ]]; then
    sir_raw=$(echo "scale=2; $short_term - $integrated" | LC_ALL=C bc)
    sir=$(LC_ALL=C printf "%.1f" "$sir_raw")
  fi

  # Perceived Loudness (PL), a simple linear interpolation of LUFS-I scale.
  # Formula: PL = (IL + 17) * (100 / 11)
  # Eg.: -17 LUFS = 0% | -11.5 LUFS = 50% | -6 LUFS = 100%
  if [[ -n "$integrated" ]]; then
    pl_raw=$(echo "scale=4; ($integrated + 17) * 100 / 11" | LC_ALL=C bc)
    pl=$(LC_ALL=C printf "%.1f" "$pl_raw")
  fi

  if [[ -n "$peak" && "$peak" != "inf" ]]; then
    sample_peak=$(LC_ALL=C printf "%.1f" "$peak")
  fi

  echo -ne "\033[K"
  output="Track: \"$(basename "$file")\"\n\n"
  output+="          Integrated: ${integrated:-N/A} LUFS\n"
  output+="      Short-Term Max: ${short_term:-N/A} LUFS\n"
  output+="                 SIR: ${sir:-N/A} LU\n"
  output+="  Perceived Loudness: ${pl:-N/A} %\n"
  output+="           True-Peak: ${true_peak:-N/A} dBTP\n"
  output+="                Peak: ${sample_peak:-N/A} dBFS"
  
  echo -e "\n$output\n"
done