Sure it’s old but the stats I posted in a lower comment show that at YouTube’s scale, it makes sense to store.

Are you suggesting they don’t store different versions? This (speculative ik) suggests they do.

I believe they store and that’s why it processes lowest res first and works up

Are you wondering if one instance can be spread across multiple machines? I don’t think that’s possible and seems unnecessary. I say that because spreading users onto more instances creates less load on the larger instances, not more. Edit: I guess you can scale instances across machines!