`ebur128=video=1’, and `ebur128=video=1:gauge=shortterm’

Watch on youtube.com
doc

https://ffmpeg.org/ffmpeg-filters.html#ebur128

video=1 (left side of uploaded video)

#! /bin/sh
ifn="Air on the G String (from Orchestral Suite no. 3, BWV 1068).mp3"
ifnb="`basename \"${ifn}\" .mp3`"
pref="`basename $0 .sh`"

#
ffmpeg -y -i "${ifn}" -filter_complex "
[0:a]ebur128=size=1920x1080:video=1[v][a]
" -map '[v]' -map '[a]' \
  "${pref}_${ifnb}.mp4"

video=1:gauge=shortterm (right side of uploaded video)

#! /bin/sh
ifn="Air on the G String (from Orchestral Suite no. 3, BWV 1068).mp3"
ifnb="`basename \"${ifn}\" .mp3`"
pref="`basename $0 .sh`"

#
"/c/Program Files/ffmpeg-4.1-win64-shared/bin/ffmpeg" -y \
    -i "${ifn}" -filter_complex "
[0:a]ebur128=size=1920x1080:video=1:gauge=shortterm[v][a]
" -map '[v]' -map '[a]' \
  "${pref}_${ifnb}.mp4"