FFmpeg has frame interpolation, using the filters minterpolate and tblend (minterpolate for this example because it's "better") which I used back then when I started out trying it. It produced insanely bad frames and was really slow. Take the image below for example. Granted this is a "dark" frame where the AI has difficulty differentiating things, but this effect is less in more advanced models. (This video is in 720p)
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But this isn't the only example. Even in light areas, as long as the frame has mildly complex pixels that it can't understand, it just goes completely south. These are in 1080p, but the same problem arises. These are the shots I took that show it better freeze framed, but in movement there are noticeable things like in the second frame where Dokkaebi's legwear (and sleeves in another animation by Idemi) has major artifacting where any light spot or reflection will "glitch out" and cease to be recognizable.
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Of course on other, better models this doesn't happen, but in FFmpeg the limited capability of the software shows it. Of course it's still industry standard and many (if not all, I'm not a software engineer) interpolation softwares actually base upon it like SVP that does frame interpolation real time.
I don't know why I wrote this thing for a porn forum, but that's what I found.
Edit: I realize that the images look shitty. I'm on a 16:10 monitor that is less than 1920 pixels long.