I like the idea of just recording it, because it is simple.
But, if you are beholden to doing it another way, can you tell us how you ripped the content? Did you use yt-dlp?
Whatever the case, you need separate audio and video streams. They’ll probably both be encrypted.
You’ll need something like mp4decryptor (github.com/axiomatic-systems/Bento4) and and widevine keyguesser thing. I haven’t done this in about 5 years, so forgive me.
There is a specific order of operations that I don’t exactly remember but you’ll need to find up-to-date instructions.