Stereo to multichannel

[Vidas59]

A good option would be add-on off stereo conversion to multi-channel by frequency. This would make it possible to refuse filters of speakers; to bring the bass to a better sounding place; better to use AVR amplifiers...

Currently I am using mpv as backend and Midnight commander custom menu as frontend.

ffmpeg -i "$WAV" -filter_complex \
 "[0:a]highpass=f=80,pan=stereo|c0=FL|c1=FR[a_high_stereo]; \
  [0:a]highpass=f=80,pan=mono|c0=FC[a_center]; \
  [0:a]lowpass=f=80,pan=stereo|c0=SL|c1=SR[a_low_stereo]; \
  [0:a]lowpass=f=80,pan=mono|c0=LFE[a_lfe]; \
  [a_high_stereo][a_low_stereo][a_center][a_lfe]join=inputs=4:channel_layout=5.1[out]" \
-map "[out]" -c:a pcm_s16le -f wav - | mpv --audio-channels=5.1 --ao=alsa --audio-device=alsa/hw:0,3 -

Front channels play frequencies above 80 Hz; surround channels play below 80 Hz in back. Lows are better at the listening position than they would be at the front. The center speaker reproduces mono sound from a height in back too.
After such arrangement, I decided that I do not need the acoustic equipment of the room. Others might benefit from a different arrangement from 2.1 to 7.0-1...