I think it is safe to say you have to plan on moving media you care about to a different format every couple decades. From the first Edison wax cylinders, to today's latest format, the technology has changed that often, and if you care you have to follow. Sure you can keep older stuff working and some do. You can also say the same about photographs and books: most degrade after a few decades, but there if you spend $$$ you can get archival grade that will last for a century or two (many centuries if you store in a desert, but in human friendly places a century is all you should count on).
I have some archival grade CDs and DVDs that claim they will last longer. However I'm not sure if readers will exist as long as the media.
I've always wondered if you could do something with dot-matrix-on-aluminum-foil. It wouldn't look the prettiest and the information density would be low, but it seems like it would be cheap and last forever.
The scene mentioning the big EMP-reset in Blade Runner 2049 made me wonder just how much would be lost to us in such a scenario. Much that we care about is currently on highly sensitive storage.
What format should I invest in (developing/purchasing/etc) that would A) be easy-ish to read from B) be dense enough to exceed the point I might as well just be using paper/glass slides/microfiche/and so on, and could be ramped back up from pretty crude tech.
Combine "end of civilization", "time-travelling with tech", and other thought-experiment scenarios for fun.
If it is end of civilization you care about then print out survival instructions. Basic low tech things that one person can do in a farm sized area with minimal help.
Don't worry about advanced stuff. How to make a transistor will be lost long before we develop a new civilization capable of needing transistors. So don't waste paper on it.
I bet I could probably put movies and media on a BluRay using whatever format was the most stable over the past ten years and be sure that it would be readable by somebody without too much trouble 20 years from now. After that, however, planned obsolesce gets you.
I guess this is the first time I've faced the fact that unless it is printed out at archival quality in some manner that humans can read, it basically won't exist 200 years from now. The data will perhaps be around in some kind of conglomerated and bowdlerized format, but the "you" part of the data will be lost in obscurity, and that's assuming that some version of the cloud stays intact that long.
I have some archival grade CDs and DVDs that claim they will last longer. However I'm not sure if readers will exist as long as the media.