[WinLychee]

User/Item/Query embeddings are the most common. That way you can generate per-user recommendations, or search results for a given query (with personalization using side information). Video will be interesting, once we have video embeddings (maybe this exists already). It depends on the use-case but a few of your ideas are certainly possible. Generally I've seen them at a coarse rather than fine level, but I'm sure that's out there too.

This looks like a good overview if you want to read about it: https://recsysml.substack.com/p/two-tower-models-for-retriev...