`showvolume’

Watch on youtube.com
doc

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

#! /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 "${ifn}" -filter_complex "
[0:a]showvolume,scale=1920:-1,pad=1920:1080:(ow-iw)/2:(oh-ih)/2[v]
" -map '[v]' -map '0:a' -c:a copy \
  "${pref}_${ifnb}.mp4"

# NOTE: showvolume has an option 's'
#       which means "step size"
#       (not "image size").

If you are concerned about the insufficient transparency of “showvolume”, you can combine it with “colorkey”. Like this:

#! /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 "${ifn}" -filter_complex "
[0:a]showvolume,colorkey=black,scale=1920:-1,pad=1920:1080:(ow-iw)/2:(oh-ih)/2[v]
" -map '[v]' -map '0:a' -c:a copy \
  "${pref}_${ifnb}.mp4"

# NOTE: showvolume has an option 's'
#       which means "step size"
#       (not "image size").