[JQZ*]

Good its working. I thought I'd dealt with the ffmpeg overwriting issue. Obviously I was dreaming.

Newer Android versions have increasingly restrictive permissions on where you can write to which is probably why your second sd card is causing problems.
ffmpeg is also run in a limited shell within Kodi as the Kodi process's user.
I'm not sure if adding the card as Adopted Storage solves the problem. It becomes more trusted then.
Be careful: I think that might wipe the card if you change it to Adopted Storage.

Yes. It will wipe the data, but it's pretty new with just some video files I added that I can replace. I've asked the folks at xda-developers about that. I was thinking of moving some apps over to the bigger card. But I came to agree with all the replies that flash drives will develop write/rewrite issues over time. Still if I don't move any apps to the card, and use it only for data storage, I wonder if I'd be okay. I did get the Android SDK setup on my PC and am able to run adb shell, which was one way I read about setting the 64 GB card as internal/adopted storage.
 

You might have to put a different path in the "ffmpeg recording path" setting to deal with ffmpeg's point of view.
I don't know what that is though.

Hah! Me neither
 

You might be able to change the permissions of a folder in the sdcard to the same as Kodi so it is writeable.
I expect you need a rooted phone.

I rooted an older phone back in 2012. I've been reviewing my notes on what I did and have been searching for solutions for this phone.
 

Theoretically I could try to pipe the output of ffmpeg back into Kodi so it could write to the second sdcard but I got scared off doing that as some operating system specific issues cropped up.
It might have just been that it was troublesome within the binary IPTV Simple Client addon.
If I have the energy I'll have another look at it.

I'll keep checking in to see if you come up with anything.
 

Another convoluted and probably tricky way is to find a network path that ffmpeg can write to, maybe an smb or nfs server running on the same device.

I'll look into that. It's been a pretty intensive crash course in dealing with the android OS the past few days. I set up a Linux Mint flash drive 3-4 years ago, but it seems I'm forgotten a lot about linux. Thanks for getting things this far though primaeval.