I generally think that for storage/archiving you should use CPU encoding and only use GPU for things like transcoding where real-time results are crucial.
GPU encoding is a lot worse quality than CPU, and you can’t change the settings to what you want. Better to just accept the extra time requirement to get a better result.
I would try making one video into the format you want and see if it plays where you want it.
I like the interface of Airsonic, but it looks like it hasn’t been updated in 4 years, and Airsonic-advanced hasn’t had any action since February of last year for the experimental branch or 2020 for the stable branch.
What do people use? I tried Navidrome a while back and wasn’t happy for some reason. Should I try it again?
I personally would not use it for anything that is being saved on your drive. Using cpu encoder is slower but I just let it run over night or whatever and it will be done later.
Save GPU encoding for when you need it smaller right now like when you are transcoding on the fly.