After lots of trial and error, I finally managed to create a Kindle textbook from a PDF file, to which I added audio buttons linked to MP3 files.
However, when I preview the textbook from Kindle Textbook Creator, I can't hear any sound when I hit the playback button (but the icon does turn into the "pause" button for the length of the audio file).
I tried with videos as well, and they do not play in the preview.
Finally, I tried exporting the textbook and previewing it from Kindle Previewer 3, and I have the same problem (I can see the icon, but it does not produce any sound).
Before you go too far in digital self-publishing, buy a Kindle and a Fire tablet and download the free samples of twenty-five books in your chosen genre, to see how it is usually done. Being unusual is not a good idea in a field like this, with a million self-pubbers trying to climb on your back and push you under the water.
I don't get it ... the very purpose of Kindle Textbook Creator is to create an interactive Kindle book with embedded audio and video. Are you saying that KDP has nothing to do with Kindle Textbook Creator ? Where do all these "textbooks" get published then ?
Those features can be seen only on 3rd Generation Fire Tablets and the Kindle for Android reading application--not by the great majority of customers or the previewers unless they are set to emulate those devices.