FFmpeg loudnorm filter - dual pass loudness normalization example - http://k.ylo.ph/2016/04/04/loudnorm.html

loudness.rb

#!/usr/bin/env ruby

require 'open3'
require 'json'

ffmpeg_bin = '/usr/local/bin/ffmpeg'
target_il  = -24.0
target_lra = +11.0
target_tp  = -2.0
samplerate = '48k'

if ARGF.argv.count != 2
  puts "Usage: #{$PROGRAM_NAME} input.wav output.wav"
  exit 1
end

ff_string  = "#{ffmpeg_bin} -hide_banner "
ff_string += "-i #{ARGF.argv[0]} "
ff_string += '-af loudnorm='
ff_string += "I=#{target_il}:"
ff_string += "LRA=#{target_lra}:"
ff_string += "tp=#{target_tp}:"
ff_string += 'print_format=json '
ff_string += '-f null -'

_stdin, _stdout, stderr, wait_thr = Open3.popen3(ff_string)

if wait_thr.value.success?
  stats = JSON.parse(stderr.read.lines[-12, 12].join)
  loudnorm_string  = '-af loudnorm='
  loudnorm_string += 'print_format=summary:'
  loudnorm_string += 'linear=true:'
  loudnorm_string += "I=#{target_il}:"
  loudnorm_string += "LRA=#{target_lra}:"
  loudnorm_string += "tp=#{target_tp}:"
  loudnorm_string += "measured_I=#{stats['input_i']}:"
  loudnorm_string += "measured_LRA=#{stats['input_lra']}:"
  loudnorm_string += "measured_tp=#{stats['input_tp']}:"
  loudnorm_string += "measured_thresh=#{stats['input_thresh']}:"
  loudnorm_string += "offset=#{stats['target_offset']}"
else
  puts stderr.read
  exit 1
end

ff_string  = "#{ffmpeg_bin} -y -hide_banner "
ff_string += "-i #{ARGF.argv[0]} "
ff_string += "#{loudnorm_string} "
ff_string += "-ar #{samplerate} "
ff_string += ARGF.argv[1].to_s

_stdin, _stdout, stderr, wait_thr = Open3.popen3(ff_string)

if wait_thr.value.success?
  puts stderr.read.lines[-12, 12].join
  exit 0
else
  puts stderr.read
  exit 1
end

Hi, thank you very much for the great loudnorm filter!

1. Is it possible to switch the LRA-Leveler off in order to get a static normalizion processing, that works with fixed gain and limiting?
2. Would it be possible to get MaxMomentary and MaxShortTerm Loudness into the json log file?

Thank you for your help - Wolfgang

I cannot get print_format=json to be accepted by ffmpeg. Are you somehow using ffprobe? I see it has the print_format option.

Input filenames are truncated when using escaped spaces?

Note: loudness2.rb is merely my edit of loudness.rb to use the actual location for installed ffmpeg (EndeavourOS, Arch); namely /usr/bin/ffmpeg

[mmmmna@home Sia Furler]$ ~/Refile\ OUT/loudness2.rb Sia-[KCRW\ studio]-Breathe\ Me-Downtempo2.flac Sia-[KCRW\ studio]-Breathe\ Me-Downtempo3.flac
Sia-[KCRW: No such file or directory
[mmmmna@home Sia Furler]$

cd to ~\Refile\ OUT\ and running from there makes no difference to failure.

Possibly not an error of your script?