[FFmpeg-user] sound recording input selection and mix

[pop]

I would like to assign a pair of Ubuntu "HotKey" commands in the 
terminal to switch between sound sources (1) microphone and (2) monitor 
for recording screencasts.  Right now, while recording with microphone I 
must open  "Sound Preferences/input/" window, then reassign from 
"Logitech USB Headset Analog Stereo" to "Internal Audio Analog Stereo" 
in order to record a playing video's audio.  This is an Either/Or kind 
of sound recording.  Ideally, I would like to "mix" monitor audio with 
microphone audio.  I have tried using the Loopback feature, but that 
does not allow adjusting sound levels of microphone versus monitor audio 
on the fly.    I am making YouTube FFMPEG tutorials "Ubuntu Basics rjwse"
Thanks, in advance.  Pop