I'm wondering what experiences people do have with opus codec for audio books? I'm using it for couple of years and I'm maximally happy with it. I've found that I can have very good quality audio with 32kbps and 12kHz cutoff and highest/slowest complexity ( audible is using aac(LC) with 64kbps , 22050Hz sample rate).
I was so exited about possibilities of opus so I created simple streaming application which I'm now using to listen to my audio books (you can check this article http://zderadicka.eu/audioserve-audiobooks-server-stupidly-simple-or-simply-stupid/).
So I'd like to hear experiences of other people with Opus and audio books, tools they are using etc.
No opus but I've encoded hundreds of audiobooks recorded from cassettes or extracted from CD using LAME mp3. I use a modified VBR V8 setting with the sample rate set at 22050HZ mono. Reported output kbps of course constantly varies but is mostly in the low 30's. According to the graphics in RazorLame, where I encode most of my material, it sometimes briefly exceeds 128kbps -- whatever the VBR settings demand to maintain constant quality. The results have never given me anything to complain about and the storage size reduction is quite large.
Having some curiosity after writing the above, I tried tracks from several audiobook in foobar200, which produces a constant display of kbps as it plays mp3. Normally I listen to books with a Sansa personal player which says nothing about such while Windows Explorer gives one figure per file, which is never true with VBR.
I found that one book mostly read out figures in the 40's and 50's kbps and another was frequently below 30kbps. The VBR encoder setting obviously responds to input audio quality which must vary with the reader's voice, the original recording equipment, the studio characteristics, etc.
I'm playing audiobooks on my Rockboxed Sansa Clip Zip. But I don't like Opus because of the 48khz samplerate which needs to be downsampled to 44.1khz by the player. Also replaygain does not seem to work correctly for Opus files on Rockbox. So unfortunately Opus is not an option for me.
In the past i used an older version of lame (3.97 i believe) with mono and VBR -V9 option. This created 24khz mp3 files which sound "ok" for speech. The bitrate varies a lot and is between 24kbps and 36kbps.
Nowadays i use qaac with mono and tvbr -V36 option. This creates 44.1khz lc-aac files with quite high quality. The bitrate is between 30 and 40kbps.