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.
Here is an answer from KDP support:
Thanks for writing to us. We are sorry for the trouble you had.
Yes. As mentioned earlier,
Books created with Kindle Textbook Creator can be read on:
Free Kindle reading apps for iPad, iPhone, Android phones, Android tablets, PC and Mac.
But, Interactive features like audio, video, hyperlinks and image pop-ups are currently only available on 3rd generation or newer Fire tablets.
Please note, at present, these features are not supported/present in iOS and Android devices.
Books created with Kindle Textbook Creator are not made available on Kindle eInk readers.
However the support's answer is wrong. Fire 5th generation can't play audio either. He then added that 4th and 6th generation can, but 5th generation kindle fire can't. That is a total mess. It seems Amazon deprived e-textbooks and that is pity.