The mednafen-psx core I’m using (0.9.32) doesn’t seem to stretch games with 224 lines of vertical resolution (pics related) to 240 lines in the way that an actual playstation does. And similarly, it also doesn’t stretch uncommon horizontal resolutions to the correct resolution. I tested the actual FFVII disc out on a tube tv, and–using the menu as an example–the black bars on the top and bottom were filled out, and the right edge of the menu wasn’t cropped off. I know the likely answer is, “it’s not stretched, it’s just overscan”, but when testing I tried my best to discern the actual proportions of the real system vs. the emulated system, and the real PSX did truly look vertically stretched. A good example of this is on the world map in FFVII. The thumbnail of the map in the lower right corner is more square on an actual playstation.
I know there is an easy workaround for the vertical stretching–using a custom resolution, yet this doesn’t fix the horizontal crop that is applied to the right side of the menu screen (the two attached images show what happens when you shift the image 4 pixels to the left in 640x480: you don’t gain any of those pixels back on the right border of the menu–I made sure those pixels were there on my actual PSX). And also this distorts the screens of the game that are truly 320x240, such as the chocobo race stats and prize menu in the FFVII gold saucer (and probably elsewhere in the gold saucer).
I’ve read that the standalone mednafen has “psx.stretch” modes (http://mednafen.sourceforge.net/documentation/psx.html), but I’m not sure whether these apply to the specific issues I’m observing, or if they just stretch the 4:3 images to fit on displays with other aspect ratios.