I was testing something out the other day and I enabled RD mode, I noticed the keyboard flickers on the left and right side to indicate system activity.
Then I got the idea, why not use this as a VU meter/pulser.
I'm not sure if this is possible since:
1. The media player is closed source so I'm not sure how the sound can be detected (unless routed from pulseaudio)
2. Can the LEDs be controlled by the user/program? Sure an echo command would work but that wouldn't be the ideal way to do it.

So what I'm asking, is this possible?

KB backlight leds are controlled by engine3, you need to stop this engine,
using echo disabled > engine3_mode.
Then you can control the brightness of each led by echoing brightness values into /sys/class/leds/lp5523\:kb1/brightness, (replace 1 by any digit 1-5).

Of course, you need to worry about mce restarting the engine or writing values to the brightness file.