I have a persistent but intermittent problem when uploading some EPUB3 ebooks to Google Play books. Sometimes the upload seems to take a long time, then stops and gives an error message "Processing failed". At other times, the upload seems to take the same amount of time as other books of similar size, but the processing takes longer and then the "Processing Failed" message appears.
My most recent purchase from Kobo which fails shows "EPUB 3 (DRM-Free)" under the Download options at Kobo. I imported the book to Calibre, which reports the file size as 2.3 MB, well under the size of other boxed sets that have uploaded correctly.
Apart from a bad connection (so that the upload times out), what might be causing these uploads to fail? Could they be malformed in some way that is causing Google Play books to reject them?
Would it help to run the epubs through a validator, or polish them in Calibre? What features might be causing the processing to fail?
I have tried to find an answer via Google support, but the answers I have found so far such as Processing Failed when uploading Book to Google Play Books refer the user to articles like Fix problems using Google Play Books which talk about how to download epubs from Google Play, but don't address the issue of failed uploads.
The 'fix problems' article says "If that doesn’t work, the file type may not be supported by Google Play Books" but that linked article doesn't say anything about what file types Google Play Books supports.
There is an article for content creators wanting to sell books on the Play Books Store: Files and uploading overview but I don't have enough skill at debugging ebooks yet to see where my purchased ebooks might fall short of Google's specifications. Their article on EPUB files says
Google Play Books accepts both EPUB 3 and EPUB 2, though 3.0.1 is preferred.
As far as I know, none of the ebooks have any of the unsupported features mentioned in the epub article:
- The ability to embed audio is limited to EPUB files and doesn't allow for the submission of standalone audio books.
To clarify: many of these purchases are from Kobo, self-published by the authors, and are marked by Kobo as DRM-free. Some are Smashwords editions. I will try to find a promotional book which I can download from both Kobo and Smashwords to see if it makes any difference.