Audio book just becomes silent on iPhone after a few hours, no issue with desktop player I built an Audio Book (an M4B) file from a set of MP3 files. The result lasts 18h30, and was encoded using Free MP3 to Audio Book Converter. The resulting file uses AAC version 4 - LC - SBR.

When reading this file with Windows Media Player, I encounter no issue.  But on the iPhone (a 3GS running iOS 4.0.1), the sound just abruptly stops at after a few hours (approx. 5 hours), always at the same place: the player still plays the file, but it emits no sound. Another file, encoded the same way, gave me the same problem: at some point, the sound just stops.

Previous audio books that I had built had no such issue. They last around 10 hours, which is still more than the time at which the two problematic files stop.

Any idea about what could be going on?  Is it not possible to reliably build large audio books for the iPhone?

[EDIT] I just tried to delete the book from the iPhone, and download it again.  Noticed two things: while the length displayed on the book library is 26h36m43, the length displayed in the player itself is only 13h15m21 (one half)...  Other thing is that now, it stops after only a few minutes...

[EDIT] An audio book I converted with the same program is available here (290MB). On my iPhone, all sounds disappear at 30m57s.  I uploaded it twice, with the same result.
It may have been an issue with that iOS version, or the conversion program itself.

Ultimately, however, now that iOS 14 will be released this year, this question is largely unnecessary in 2020 and beyond.