showspatial

Watch on youtube.com
doc

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

This filter is not available on ffmpeg 4.1.

The description in the official documentation:

Convert stereo input audio to a video output, representing the spatial relationship between two channels.

The commandline in uploaded video was:

[me@host: ~]$ ffmpeg421="/c/Program Files/ffmpeg-4.2.1-win64-shared/bin/ffmpeg"
[me@host: ~]$ for f in "" ",aphaser" ",apulsator" ; do \
> for i in *.mp4 *.wav ; do (
> set -x ; "${ffmpeg421}" -filter_complex "
> amovie=$i,atrim=0:4
> ${f}
> ,asplit=3[out1][a1][a2];
> [a1]showfreqs=s=$((16*60/5*2))x$((9*60)):fscale=log:cmode=separate[v1];
> [a2]showspatial=s=$((16*60/5*3))x$((9*60))[v2];
> [v2][v1]hstack,format=yuv420p[out0]" \
> -map '[out0]' -map '[out1]' -f matroska - 2>/dev/null) | (
> ffplay - -autoexit 2>/dev/null) ; done ; done