normalize-audio.sh

#!/bin/bash

set -euxo pipefail

# These parameters are taken from:
# https://developers.google.com/assistant/tools/audio-loudness
TARGET_LUFS=-16
TP=-1.5
LRA=11

function analyze_lufs()
{
  ffmpeg -i "$1" \
    -af "
      loudnorm=I=$TARGET_LUFS
      :TP=$TP
      :LRA=$LRA
      :dual_mono=true
      :print_format=json
    " \
    -f null - 2>&1 |
    tee >(cat >&2) |
    sed -n '/^{$/,/^}$/p'
}

json="$(analyze_lufs "$1")"
# Example content:
# {
#   "input_i": "-24.32",
#   "input_tp": "-12.34",
#   "input_lra": "2.20",
#   "input_thresh": "-34.33",
#   "output_i": "-14.27",
#   "output_tp": "-2.19",
#   "output_lra": "2.10",
#   "output_thresh": "-24.28",
#   "normalization_type": "dynamic",
#   "target_offset": "0.27"
# }

measured_i="$(echo "$json" | jq -r .input_i)"
measured_tp="$(echo "$json" | jq -r .input_tp)"
measured_lra="$(echo "$json" | jq -r .input_lra)"
measured_thresh="$(echo "$json" | jq -r .input_thresh)"
offset="$(echo "$json" | jq -r .target_offset)"

dir="$(dirname "$1")"
basename="$(basename "$1")"
ext=".${basename/*./}"
ffmpeg -i "$1" \
  -c:v copy \
  -af "
    loudnorm=I=$TARGET_LUFS
    :TP=$TP
    :LRA=$LRA
    :measured_I=$measured_i
    :measured_TP=$measured_tp
    :measured_LRA=$measured_lra
    :measured_thresh=$measured_thresh
    :offset=$offset
    :linear=true
    :print_format=summary
  " \
  "$dir/,${basename/$ext/}-lufs$TARGET_LUFS$ext"