Command-Line – How to Mute from the Command Line

Go to

System Preferences then Keyboard and click Shortcuts then Custom Shortcuts:

Click on Add

Fill in:

Toggle microphone

and

amixer set Capture toggle

For usb webcams you need to chose device (-c 1), or maybe another number.

amixer -c 1 sset Mic toggle

Click Apply and then associate a new key with this command (e.g. the Pause/Break key).

You can control PulseAudio thoroughly through the command line using pacmd and pactl commands. For options see man pages or the wiki at PulseAudio:

pacmd list-sinks (or pactl list short sinks) for name or index number of possible sinks

pacmd set-default-sink "SINKNAME" to set the default output sink

pacmd set-default-source "SOURCENAME" to set the default input

pacmd set-sink-volume index volume

pacmd set-source-volume index volume for volume control (65536 = 100 %, 0 = mute; or a bit more intuitive 0x10000 = 100 %, 0x7500 = 75 %, 0x0 = 0 %)

and many many more CLI options.

Note: Changing the output sink through the command line interface can only take effect if stream target device reading is disabled. This can be done by editing the corresponding line in /etc/pulse/default.pa to:

load-module module-stream-restore restore_device=false

Restart PulseAudio for changes to take effect:

pulseaudio -k

For a more elaborate tutorial on how to do this, and for instructions on how to change the sink during playback see this answer.