Using command line tools you can do the following:

- [Install brew][1]
- Update and doctor brew
- Install portaudio, ffmpeg and all dependencies with brew

        brew install portaudio
        brew install ffmpeg
- Install pip by downloading [get-pip.py][2] (direct link) and executing

        sudo python ~/Downloads/get-pip.py
- Install [soundmeter][3]

        sudo pip install soundmeter

- Run soundmeter. To get help use the -h switch:


        soundmeter -h
		optional arguments:
		  -h, --help            show this help message and exit
		  -c, --collect         collect RMS values to determine thresholds
		  -s SECONDS, --seconds SECONDS
								time in seconds to run the meter (default forever)
		  -a {stop,exec-stop,exec}, --action {stop,exec-stop,exec}
								triggered action
		  -t [+|-]THRESHOLD [NUM ...], --trigger [+|-]THRESHOLD [NUM ...]
								trigger condition (threshold RMS and number of times)
		  -e SCRIPT, --exec SCRIPT
								shell script to execute upon trigger
		  -d, --daemonize       run the meter in the background
		  --log [LOGFILE]       log the meter (default to ~/.soundmeter/log)
		  -v, --verbose         verbose mode
		  --segment SECONDS     audio segment length recorded in seconds (defaults to
								0.5)

Simply running `soundmeter` will output an [RMS value][4]. After defining a threshold you can trigger a shell script action (which may itself trigger an AppleScript script)  with the -e switch.

Entering `soundmeter --segment 0.1 --log` watching online TV (climate change and coffee farming in Colombia - the end of Arabica beans) will show something like:

	2017-01-25 18:16:02,289 24
	2017-01-25 18:16:02,665 24
	2017-01-25 18:16:03,037 31
	2017-01-25 18:16:03,399 3
	2017-01-25 18:16:03,769 15
	2017-01-25 18:16:04,142 11
	2017-01-25 18:16:04,524 9
	2017-01-25 18:16:04,891 7
	2017-01-25 18:16:05,257 7
	2017-01-25 18:16:05,632 0
	2017-01-25 18:16:06,001 7
	2017-01-25 18:16:06,384 0
	2017-01-25 18:16:06,745 2
	2017-01-25 18:16:07,113 10
	2017-01-25 18:16:07,491 14
	2017-01-25 18:16:07,860 6
	2017-01-25 18:16:08,223 0
	2017-01-25 18:16:08,609 13
	2017-01-25 18:16:08,973 16
	2017-01-25 18:16:09,347 7
	2017-01-25 18:16:09,720 26
	2017-01-25 18:16:10,091 1
	2017-01-25 18:16:10,464 38 ← an Arabica bean died here
	2017-01-25 18:16:10,835 13
	2017-01-25 18:16:11,204 Stopped

*Just to confirm: that's the microphone input level and not the sound level of the TV stream because the above installation runs in a VM guest and the TV stream on the hosting Mac - tested but not logged with some clapping which will increase the RMS to values above 200!*


  [1]: http://brew.sh/
  [2]: https://bootstrap.pypa.io/get-pip.py
  [3]: https://pypi.python.org/pypi/soundmeter
  [4]: https://en.wikipedia.org/wiki/Root_mean_square