I formatted an ePUb in Indesign CC 19. I am ready to put in the audio for the read-along. I researched the viewpoint size to fit more than one IPAD. 2048 x 1536 is what was suggested for my epub because it has a one page landscape spread with no border. I tested it along the way and it looks fantastic in Readium and IBooks. The problem is that when I cracked it open to add the audio. in the page view and the code view both in Dreamweaver and Sigil, the font is too large. It also has put the words vertically. I can't read the words because I can't see the full page. I wonder if I can change the size of the screen so I can add the audio?
I'm inferring a couple assumptions from what you're trying to do. It sound's like a fixed-layout book. Don't worry so much about screen size. Fixed layout books will resize automatically. Just make sure it's still readable on the smaller sizes without zooming.
Then, don't try to edit a fixed layout epub with software, they will never display it properly. You have to add the audio files to the epub package and then edit the .xhtml and .css files manually:
- Unzip the .epub (try a free download called ePub Zip/Unzip)
- Copy the audio files into the OEBPS folder
- Open an .xhtml file with TextEdit (Mac) or other editor
- Insert the code in the header, or wherever it needs to be to accomplish your goal for that particular page in the book.
- Save and repeat for each of the files you need to add. You can test along the way by opening the .xhtml files in your web browser. Don't worry so much about the layout here, just test the audio.
- Once you've linked all the audio files to the correct pages, rezip the epub and open it in iBooks to test.