Namo PubtreeViewer App for Android, The Holy Grail of reading apps?
I admit, it doesn't offer the most intuitive interface, nor is it abundant with features (to say the least) but, at least it does what it says on "the box" unlike many reading apps I have tried over the past few days.
You could say I've tried them all, I have created an RTL-Fixed-Layout-Audio-Embedded monster, yes. A Validated, Standard-Compliant EPUB3 With double spread pages, RTL'ed and Audio files (mp3/m4a) embedded into it.
This unknown app with around ~1,000 downloads is just starting it's way into the ePub reading apps store and is already showing great promise, I highly recommend it!

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For those of you who are curious to know of the necessary meta data and encodings needed for this sort of EPUB, look at the following details. Please note that these settings should work for iBooks and most of the Android Reading apps, all of the apps would have bugs like displaying audio controls or displaying 1 page instead of 2 page spread etc, Namo app works best, there they are:
- MP3/m4a files: both of them should work just fine for Android (*Sidenote: mp3 for Kindle and m4a for iBooks), make sure to encode with Stereo and AAC encoder, 256kbps (recommended) and 48kHz
- CSS Reset: Make sure to include the cssreset-min.css from http://yuilibrary.com/
- File Structure: 1 Image (and possible audio file embedded) per HTML file, a toc.html (a must for epub3) and com.apple.ibooks.display-options.xml include..
- A little bit more CSS:
- This is where the magic happens:
content.opf:
sample html file:
Cheers