I wonder how they encode all the information in the PNG file? Apart from the .zip with the entire ROM I assume they snapshot the current memory state on the beginning of the Quote and all the subsequent inputs.
That said, the basics of making a quote are so simple that it should be pretty easy to add Playable Quote capabilities to other emulators with a minimal amount of code.
A full writeup of how it works is here: https://joel.franusic.com/playable_quotes_for_game_boy
Thanks for reminding me that our site said the post wasn't ready yet, I've just updated it with the link to that blog post!
The Raccoon demo behaves the way I might expect this to work: most potential player inputs allow you to reach the Raccoon, trigger his two text prompts, and cut the grass with Link's sword. But you can't enter any other screen, can't leave the second screen out the bottom, and can't perform most other actions; the moment you do, the game would need to run code that the quote never accessed, which triggers the failsafe. Even performing certain "safe" actions out of order occasionally fails, I'm guessing due to the RNG for stuff like leaf particles and whatnot.
You can see what that looks like in this visualization of the Racoon demo: https://tenmile.quote.games/quote-visualizer.html#drop=https...
Oh, and regarding recorded input playback. That is something we haven't gotten working yet. Some of the details for that are in our blog post. The short version is that button presses can happen in the middle of a scan-line, which can make it really tricky to play back if the emulator wasn't designed with that in mind!
The durability of each quote depends on the actions taken while the quote was being made. In the quote of Metroid II, for example, many of the sprites were not recorded, so unless you do exactly what was done in the recording, you'll get a reset.
Here's a visualization of the Metroid II quote: https://tenmile.quote.games/quote-visualizer.html#drop=https...