I use RetroArch for pretty much everything, as it has some of the best and most high-quality cores ported for use with it, has the best audio/video sync I've ever seen, and its shader support is the best, period. It also works amazingly well with a CRT monitor.
How do you get the overscan option to work? I have it enabled and it doesn't overscan.
For example, Sega CD Snatcher uses a 256 horizontal resolution, but the Sega CD bios uses 320. If I set a proper horizontal resolution for 256, it looks fine. However, then the Sega CD bios has distorted text and Sonic looks crooked while the game loads. The Sega CD bios should be missing 64 pixels horizontally since 320 pixels overscans 256, but it's not; it's clearly stretching (crushing) to 256 pixels. I'm not sure if 256 horizontal pixels are used through the entire Snatcher game, but if not then this is a problem. Same problem happens the other way around (Snatcher gets distorted with 320 horizontal pixels)
Couldn't find any option to keep things centered either (like 256x240 centered in 320x240). This option is available in most emulators btw.
Retroarch really is one of the best programs (or frontend ?) for emulation IMO. But this is a problem, especially for games that use multiple resolutions.
Genplus-gx is a true blessing. This is the best Sega CD emulator bar-none! I think the author is EkeEke... Don't know the actual author, but whoever it is, I wouldn't mind giving him $1000.00 if I had it to blow-away 😐 . Really hope it gets integrated into Mednafen (don't really want to screw around myself hehe), or Mess, or independently with proper resolution support.
Kega Fusion is one of my favorites, but the Sega CD is so so. Its SegaCD emulation still has broken sync after all these years (Heart of the Alien tracks are always out of sync; doesn't matter if you make clonecd, bin-cue, or use real disc). Kega-fusion does have 32X emulation which does make it one of the best IMO. Genplus-gx Sega CD has no problems amazingly, but no 32X IIRC. Gens/gs still has to be ported to 64-bit assembly, but it's very similar to Kega Fusion; and it's open source so that is great.
Great emulators, and great authors as usual!
I forgot I was using video_xscale and video_yscale in Retroarch; but they don't' work as mentioned above! Tried every combination custom_viewport, video_aspect_ratio, and video_force_aspect.