Finding books whose metadata differs between Calibre and the book file

[Xenophon]

I'd like to find books that would change if I told Calibre to embed metadata in the book. Or, equivalently, I'd like to find all books that would NOT change if Calibre embedded the current metadata. I don't care about any kind of metadata not held in Calibre; I'm concerned only with mismatches between what Calibre has and what the book file has.

I hope to use this search to track down books where I fat-fingered bulk changes via the tag browser.

Is there an existing way to do this, perhaps via a plugin?

[kovidgoyal]

I doubt it, as most book formats arent even capable of storing all calibre metadata. Mayeb the quality check plugin.

[Quoth]

The only ereader I know that even can use all (or most?) of Calibre's Metadata is Kobo, yet the Kobo doesn't use all possible metadata of epub 2 in the GUI for sort / filters.

As Kovid says the actual book files don't.

Even for epub2 and epub3 they are different. Some formats are very limited. Some have only Author and Title.

[Xenophon]

My fall-back approach would be to try the following:

1. Duplicate the library and all the books to a new location
2. Select all books
3. Embed Meta-data in all books
4. Use a find command to find book files updated since step one.

That's a bit clunky, but it should work OK... as long as the embed metadata command doesn't touch book files when there's nothing to update. Am I in luck on that front?

In any case, for your time and advice!

[kovidgoyal]

No update metadata always updates it doesnt do so only if something changed. And given that ebook file formats are really containers contianing individual files, it's extremely unlikely that even if nothing actually changed the file will remain byte identical.