I've been looking through forum posts and help files, and I haven't found a definitive answer to these questions.
Metadata, including tags and images, can be drawn from several locations - embedded in media files, stored locally alongside media files ("sidecar"), and from online sources like last.FM, Gracenote, etc.
I'm wondering in what order Emby searches for these, and in what order Emby prioritizes them. I can see in the Library properties that I can prioritize the online sources, but I see no way to tell Emby to prefer local metadata over online, or embedded vs. sidecar. For example (sorry to compare to Plex, but that's my experience) Plex can be configured to search for and use embedded tags if present (except images - more on that later). Only if an embedded tag is missing or improper, it then goes to the online source (Plex doesn't support sidecar tags, like Emby does). They used to prefer embedded images, but, because embedded images tend to be low resolution (so not suitable for large display), they switched to preferring sidecar images, then embedded, then online.
So how does Emby prioritize metadata sources? Also, if I manually edit tags, is there a way to tell Emby not to replace my changes during a refresh?