For videos in particular, if you don't mind shelling out cash, the current go-to (at least according to various AI discord servers I'm on) for AI animation nerd

For videos in particular, if you don't mind shelling out cash, the current go-to (at least according to various AI discord servers I'm on) for AI animation nerds is currently Topaz upscaler. There are free alternatives but I've yet to see any of them work as well as Topaz, though I'm sure that will change soon. For interpolating frames Flowframes is "free" (new features if you join the Patreon) and is IMO very good. I've seen a number of 80s/90s VHS recordings of concerts being uploaded to YouTube in 4K (using Topaz) and they look like they were recorded that way, truly amazing. I do hear it can be a bit of work though getting the settings right.