[primaeval]

Hello I'm trying to get this working on Nvidia Shield and I'm confused on how(downloaded binaries what do I next?), I even think I might have ffmpeg(I had to install it via termux for something else but didn't work I think) its just can't find it.

I'm not sure if you can use the termux ffmpeg without rooting your Shield. You might be able to copy it to a shareable folder.
Find out what architecture your Shield is either by looking at the top of the kodi.log file or using DroidInfo in the play store. It might also just be in the Kodi Settings somewhere. I can't remember.
Then grab the binary of ffmpeg for that architecture from here: https://github.com/Khang-NT/ffmpeg-binary-android
unzip it and point to it in Settings.
It will get copied to the right place to run.
If it doesn't work turn on Settings \ Debug \ Debug menus and run Maintenance \ Delete ffmpeg. Then try a different ffmpeg binary.