KFX

KFX is a new Kindle format from Amazon. Very little is known about this format at this time. X seems to be Roman Numeral 10 thereby skipping 9. There is also an extension change to .AZW8 for final products.

Overview

This new format is released with the Kindle paperwhite 3 and others. It includes

• a new enhanced typesetting engine that includes soft-hyphens
• the new Bookerly font.
• a new image format with higher compression called JXR
• Page Flip: A multi-page thumbnail view that reflects the current font and margin settings.
• Table viewer: Data tables in books can be viewed and magnified independently of the other book content.
• Kindle Interactive Edition: These are like Print Replica books, but can have additional reader-activated media.
• Comics: Comics delivered in KFX format support page and panel viewing modes and double-page spreads.
• Kindle in Motion: These books have images and auto-playing video at fixed locations on pages with the main text flowing around them.

This seems to be a binary version of JSON. In this respect it seems to be a follow-on from AZK. KFX seems to be derived from a intermediate form called KDF which can be built using the latest beta version of Kindle Previewer.

Creating KFX

This MobileRead forum discussion describes a Calibre plugin. The following quote comes from the forum. "The purpose of the KFX Conversion Output plugin is to convert e-books into KFX files that can be sideloaded to newer Kindle apps and devices. This allows books obtained from sources other than Amazon to be read with Enhanced Typesetting." This technique makes use of the Amazon Kindle Previewer version 3.

One user has reported that conversion of ePub directly to KFX has errors but converting to RB format from ePub and then converting the RB format to KFX works ok.

KDP

Amazon's Digital Text Platform is now a KDP file that can be built using Kindle Previewer version 3. This is yet another related format for bundling KFX content. See also Kindle Create.

KFX Content

An example of the top level:

 B00UZSTXL4_EBOK/amzn1.drm-voucher.v1.cd614ffd-319f-4b9e-99b7-238c6fe78f1e.voucher (DRM voucher)
 B00UZSTXL4_EBOK/B00UZSTXL4_EBOK.azw (encrypted main container)
 B00UZSTXL4_EBOK/CR!6AS14VN94H79K68RG9EKT09T41N0.azw.res (resource container)
 B00UZSTXL4_EBOK/CR!SNRJN8W7KX07Z8MVGN4AMWXSFR3E.azw.md (metadata container)

KPF

KPF file format is KFX data stored in a SQL database. This is the native format for the new Word based Kindle Create. (Replaces KindleGen).

KFX Manga

The new Manga format used in KFX is designed to manage image files. It has the ability to show two side by side on a page. The menu is different from that on a standard KFX file.

Kindle for PC support

Starting with version 1.19, Kindle for PC will download books in KFX format and display them with enhanced typesetting.

The various files that make up the KFX format are all present, but named differently compared with an e-ink Kindle. Here is the same book after downloading to both platforms.

Kindle Paperwhite 2:

• Perfect State (Kindle Single)_B00UZSTXL4.kfx (encrypted main container)
• Perfect State (Kindle Single)_B00UZSTXL4.sdr/assets/voucher (DRM voucher)
• Perfect State (Kindle Single)_B00UZSTXL4.sdr/assets/metadata.kfx (metadata container)
• Perfect State (Kindle Single)_B00UZSTXL4.sdr/assets/attachables/CR!AX7PNNAM616C90FBFYKZ53GVC0QK.kfx (resource container)

Kindle for PC 1.19:

• B00UZSTXL4_EBOK/amzn1.drm-voucher.v1.cd614ffd-319f-4b9e-99b7-238c6fe78f1e.voucher (DRM voucher)
• B00UZSTXL4_EBOK/B00UZSTXL4_EBOK.azw (encrypted main container)
• B00UZSTXL4_EBOK/CR!6AS14VN94H79K68RG9EKT09T41N0.azw.res (resource container)
• B00UZSTXL4_EBOK/CR!SNRJN8W7KX07Z8MVGN4AMWXSFR3E.azw.md (metadata container)

Dictionary Support

Amazon has released version 8.1 of the Kindle for Android app and one of the new features is "free Kindle dictionaries for five new languages – Hindi, Tamil, Marathi, Gujarati, and Malayalam."

The Hindi dictionary was downloaded in a new variant of KFX format. It is a SQLite database containing content encrypted by KFX DRM.

For more information

• MobileRead Thread
• new self publishing blog
• Amazon ION the predecessor to KFX
• Amazon lab Github reference implementation