The current code that sets the f-fwd / rwnd etc isn't in the tree yet (that's the next thing for me to get onto once I've pushed up some of the changes we've made already)
But it is fairly simple... There are a number of .png files that contain the sequences, there is a default set in /usr/share/kodi/media/ledpatterns and you can create your own and save them to /storage/.config/kodi/media/ledsettings (doing this from memory so think that's right)
The code reads all of those at bootup time and stores them in memory, when it gets a notification from Kodi (fast forward etc) then it writes each line to the WS2812 separated either by 16ms or the value in column 26 of the pattern.
Should have it in the tree soon...
led_tools are already in the source tree
This contains an application led_png which runs the png from the command line (i.e. ssh into your box and type led_png /usr/share/kodi/media/ledpatterns/ffwd.png