remove audio

ffmpeg -i $input_file -c copy -an $output_file

analyze volume

ffmpeg -i video.webm -filter:a volumedetect -f null /dev/null
[Parsed_volumedetect_0 @ 0x55e432de4900] n_samples: 540692480
[Parsed_volumedetect_0 @ 0x55e432de4900] mean_volume: -22.3 dB
[Parsed_volumedetect_0 @ 0x55e432de4900] max_volume: 0.0 dB
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_0db: 848
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_1db: 2410
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_2db: 16381
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_3db: 76821
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_4db: 162412
[Parsed_volumedetect_0 @ 0x55e432de4900] histogram_5db: 295138

change volume

ffmpeg -i input.wav -filter:a "volume=10dB" output.wav
or
ffmpeg -i input.wav -filter:a "volume=0.5" output.wav

opus

for i in *.mp3; do ffmpeg -i "$i" -c:a opus "${i%.*}.opus"; done