I'm posting this in case anyone needs this information in the future. It may save someone else some work.
I've been helping someone to listen to librivox books on a talking book player; they're commonly used by people who are blind or partially sighted.
The device plays files stored on a USB memory stick. In the UK, the main talking book service distributes books by sending the memory sticks out in the mail.
I assumed that one could simply copy some LV books on to a USB stick, put them in separate folders, and it would just work. That turns out to be hugely optimistic! The files do play, but in the wrong order. By examining one of the official audiobooks, I established that it expects DAISY format files, which is essentially MP3 files but with a lot of extra metadata files (mostly .smil files) and a few other files.
The DAISY format is maintained and enforced by this group. It does far more than simple audiobooks which makes it seem very complicated if you just want to play a few mp3 files. The format has been mentioned on this forum in the past but not for a very long time, see here.
I didn't bother with the official software - it's needlessly complicated. Instead I found that another user with similar requirements has kindly created a program to process Librivox books in to the required format. The software is available here. It's a command line program, and you may need to compile some source code. That's not as daunting as it sounds, though you may need a friendly techie to help you if that's not your thing.
It's then a case of using one command line to convert the LV files in to a DAISY format book. I found I had to use a couple of command line switches to put the chapters in the correct order, eg:
makedaisy -it -sf Source Daisy
where:
Source is the source folder that contains the LV files
Daisy is the target folder where you want the output files
The program uses LAME to transcode the MP3 files - it seems to convert them to 56kbps.
Hopefully that provides a few hints for anyone else who's trying to do the same thing.
-Ian