syncabook VS epubcheck

Amazing! I've made a similar ebooks-audiobooks aligner years ago: https://github.com/r4victor/syncabook. At that time, I chose to synthesize the text and align two audio sequences because I found texts-alignment approaches (including ML-based ones) too compute-intensive and inadequate for long texts. I see Storyteller works by aligning the texts. Could you give some view on how long it takes to sync a book?

Also, my experience was that audio and text versions are often very different (e.g. the audio having an intro missing from the text). It'd very interesting to know how well Storyteller handles such cases. Does it require manual audio/text editing or handle the differences automatically?

Unfortunaly, this audiobook isn't synchorized to the text on Kindle. So, in order to synchronize the epub and audio myself, initially, I tried using syncabook, but the results weren't great for some reason. I then tried using OpenAI's Whisper to generate the text from the audio. This might've given decent results, but ultimately I decided I wanted to keep the book's formatting (paragraphs, emphasis, etc.)

I've tried syncabook, but that didn't help. I've tried whisperX, to get word-level timings, but the results are pretty bad/unusable.

From searching a bit I found https://github.com/r4victor/syncabook this might help anyone intrigued about the idea. I suspect this is the tool you're talking about? Your post is really a long form question, and could have been a lot shorter.

This software can generate epubs with audio completely automatically for a lot of simpler languages. The problem is it doesn't support Japanese.

Others have already mentioned Sigil and Calibre as excellent tools, epubcheck and ACE by DAISY are also useful and open source to verify the files and accessibility.

For ePubs, any editing program (e.g. Calibre, Sigil, etc) will have an ePub check feature. You can also use the W3C's standalone ePub check tool: https://www.w3.org/publishing/epubcheck/

As others have pointed out, this is often caused by books that are either corrupted or incorrectly formatted in some way or another. If the books that cause the freezes are sideloaded this is a likely culprit, and you can try testing them with EPUBcheck or Calibre. If the books are bought via the Kobo store it's less likely the book itself is the issue.

I generally write the HTML and XML files by hand and then use epubcheck to verify if I screwed something up and package the individual source files into a single .epub file (which is basically a .zip file).