I have an EPUB file converted from FB2 by my own programmatically. I need to convert exactly programmatically because I'm going to develop an iOS app which should take an FB2 file, convert it to EPUB and then display to the user as EPUB.

The validator http://validator.idpf.org tells me that all is good with my converted EPUB file except the version.

Detected version: Could not determine version.

Results: Congratulations! No problems were found in Dontsova.epub.zip.

Validated using EPUBCheck version 4.1.1.

Unfortunately I'm not able to open the converted file neither by iBooks nor by my own sample ePub reading application which is using SkyEPUB library.

My package consists of the files "mimetype", "content.opf", "book.html", "toc.ncx" and the folder "META-INF" containing the file "container.xml".

The file "mimetype" contains the following line required by the specification:


The file "container.xml" also contains the required xml as shown here: https://www.edrlab.org/epub/anatomy-of-an-epub-3-file/.

The question is: how could I know what is wrong with the converted file which is successfully checked by the IDPF validator, but rejected by iBooks? How could I know the required changes to be able to open the file at least via iBooks?



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