OBS Studio (video capture tool) adds this strange, unwanted scanline effect right away, which is even more annoying. It might be related to the encoder settings, and I basically have no idea how to get rid of it. The game itself and the CRT shader looked perfect on screen. The curved lines were added after I captured it. This can be seen in the video from my channel.

Switched to pictures only (cover box and screenshot). Turned OMX back on. Thanks for the explanation.
Cheers

I just stumbled upon this post...is this about getting 5200(and 800) carts to auto-launch? I am getting ready to build out an 800 and 5200 section on my build. I started with the 5200 and I spent the better part of this afternoon trying to work through the RetroPie documentation of loading carts, extracting, saving, etc. and I only got three to autoload so far...

Though in fairness, it was a busy day for me building JavaScript rules for online ordering templates for some of our customers, lol....among other things...

@dankcushions Yes I think that is what it looks like. But it's much easier to see in motion.
It's not related to the resolution (I tried several).

Report the issue here:
https://github.com/libretro/snes9x2010

Ok, I tried turning off dithering, and it didn't seem to make any difference.

I'm still getting artifacts, like echo-type sounds, sounds that go on longer than they should etc.

I have listened carefully to games that I am very familiar with on other systems, and this definitely only seems to affect Hatari.