Ref: https://stackoverflow.com/a/16715419/8263383
ffmpeg -f lavfi -i anullsrc=r=44100:cl=mono -t <seconds> -q:a 9 -acodec libmp3lame out.mp3
Ref: https://stackoverflow.com/a/16715419/8263383
ffmpeg -f lavfi -i anullsrc=r=44100:cl=mono -t <seconds> -q:a 9 -acodec libmp3lame out.mp3