Creating a sideloaded EPUB compatible with Kindle TTS / VoiceView

[skayme]

Hello everyone,

I am trying to understand how Kindle handles TTS (Text-to-Speech) for books.

On recent Kindle devices (for example, the Paperwhite 12th generation), TTS/VoiceView seems to work only with books purchased from the Kindle Store. When I sideload an EPUB (either directly or converted with Calibre), the TTS option does not appear, even though the book content is perfectly readable.

I am wondering if anyone has investigated what metadata, files, or internal structure a Kindle book needs in order to enable TTS.

Is there any known way to:

- convert an EPUB with Calibre into the same format/structure used by Amazon for TTS-enabled books?
- generate the required metadata using another tool?
- modify an EPUB/KFX/AZW3 file with Python or another script to make Kindle recognize it as TTS compatible?

I understand that Amazon may restrict this feature for purchased books, but I am interested in knowing whether the limitation is purely DRM/account related or if there is a technical flag or file structure that enables TTS.

Any information about Kindle book internals, KFX structure, accessibility metadata, or previous research on this topic would be greatly appreciated.

Thanks!

[shamanNS]

Exth header 404 value should control TTS for mobi and azw3 formats.

https://wiki.mobileread.com/wiki/MOBI#EXTH_Header


Editor for modifying those things:

https://github.com/kwkoo/Java-Mobi-Metadata-Editor