I just asked this question in the Computer Graphics SE but I also kind of want to ask it in the Video Production SE which may have a different view on the topic. What are the SE rules and how to best do this if allowed at all?
The policy is that cross-posting is not allowed.
That is not to question your motives for asking a question across multiple sites, but unfortunately the most common scenario for cross-posting is that folks will shotgun questions across every site that even remotely match what they're asking for. Unfortunately, that typically means they're disregarding norms of each community while their content is spread too far and wide to be attentive to any followup questions or edits each community may have.
Essentially, we don't really like to question the motives of why someone is asking a question, so sometimes it is best to have these broad policies in place so we can keep the system simple and help the most people possible.
The best practice here is to ask your question on one site… and then bring what you have learned to ask again elsewhere if necessary. You might even be able add some of those experiences into subsequent questions to share what you have learned. That would stay within the spirit of the policy while avoiding the problems asking a lot of questions all at once.
Generally it is frowned upon to post the exact same question on multiple sites, however if you have distinct things you are looking for about the same situation, it may be possible to ask different but similar questions to different communities.
The idea behind this is that we want questions to be at the best place for them to be found so that we don't split up good answers to the question, but for example, if you were trying to setup an online billing site, you might ask about legal aspects of it on law and programming aspects on stack overflow.
Your question involves upscaling a video so looks on-topic - the Signal Processing SE is another candidate.