I think I understand how to use about 20 of the command line options for ffmpeg and the companion utilities like ffprobe. Which is to say; I understand about 0.5% of the total options they provide and am likely a world leading expert in it. I'm mostly joking -- as in, overstating how many of them I understand.
Understanding ffmpeg borders on a specialization in itself. No big surprise that so many of the alternatives have fallen away over the years as people realize the absolute scope of that piece of software.
i had media center powered by a few perl script that would transcode all videos into formats that ps3 supported in 2007-ish. Yes ffmpeg had a lot of options, 99% of them does not matter, there really only 3 ways to stream to client: as is, repack streams into something client support (i.e. your source is mkv) or transcode into something client support (clients know which formats they support).
People that run these services don't want "dynamic stream quality selection".
You don’t need to understand much of ffmpeg to build a media centre. Your requirements here are extremely simplified and there are hundreds of guides online on how to use it for very simple transcoding.
But if you don’t want to use ffmpeg directly then use one of the many ffmpeg wrappers. Or a different lib entirely like gstreamer or VLC.
Around 15 years ago I built a media centre for my car and the media playback part turned out to be the easiest part of the project.