Quote:
Originally Posted by GeoffR
The kepub file itself is not always much bigger than the epub, but a lot more data gets stored in the database for a kepub than for an epub. I don't know what it all is for, but some is probably to do with the Kobo DRM scheme, and some to do with the bookstore (links to similar books, etc.), and more detailed statistics. Also there is BeyondTheBook data such as author photographs, etc. that epubs don't have.
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Encrypted kepubs are a lot bigger than unencrypted kepubs/epubs.
I just compared a book from my ~/Library/Application Support/Kobo/Kobo Desktop Edition/kepub/ directory after I "liberated" it. The original is 631KB, the liberated one is 303KB.
If Kobo's DRM is any good, it
ought to be turning each file into data that's incompressible (Shannon's theory?) and that kind of bears out looking at the zip files. Using "unzip -lv":
Code:
Length Method Size Ratio Date Time CRC-32 Name
80880 Defl:N 68738 15% 11-02-12 15:23 3ec01420 OEBPS/html/009_chap3.html [original]
80872 Defl:N 25283 69% 08-16-14 09:49 2c067dd2 OEBPS/html/009_chap3.html [liberated]
All the content that's encrypted can be compressed much better after liberation.
I haven't looked much at what goes in the DB, aside from there being one row in it for each encrypted file in each protected book.