InAudible can use chapter information embedded in the .aa(x) file, but the below is when you start with an MP3 audiobook in arbitrary chunks, like CD or tape sides, or 5-hour or so lumps as Audible delivers.
I do this in
MP3DirectCut.
The very important feature this editor has is that it edits MP3 without reencoding the audio. So there is no quality loss as you get when using editors like Audacity.
If the book is divided into arbitrary pieces (not chapters), eg. CD tracks or cassette tape sides, edit out any "This is Audible", "End of side 3", etc. Edit each individually, then "Save complete audio" using Control-W, to make a trimmed MP3.
Now join all these trimmed MP3s into one file, using File/Batch/Join to file
Open the combined file in the editor.
Special menu, "
Pause detection"
It has four parameters, and these are my current settings:
Level: default -31.3 dB -- this defines "silence"
Min duration: 3.4 sec -- how long the silence has to be to be marked -- this is the one you need to experiment with for each book.
Cue offset: -25 frames -- where the cue point will be placed (25 frames before end of silence)
After pause detection skip: 1 second -- min gap between pauses. Need this small as sometimes you have 2 or 3 pauses at the beginning and you want to find them all.
First I just let it find a half dozen "pauses" and then stop it and check them.
MP3DC is a bit idiosyncratic in its interface, but has nice shortcuts once you learn them; they are all in the manual, you won't work it out just playing with it.
You'll need to know how to navigate the track, and how to set ("DEL") and clear ("E") cue points.
Then go to the start (Home key) and skip to the cue points you've just found: ctrl-right goes to the next one, ctrl-left to the previous.
Press space to play and see if it's a chapter break.
Just skip through them all and see what you've found. If you found a real chapter break and lots of non-chapter breaks, look at the chapter break and see how long the pause was before it.
I've had durations between 1.6 and 4 seconds, depending on the book.
Then use a bit less than that in your "duration" setting and ctrl-Z a few times to clear all the cues you set, and try again.
When you have a setting that finds all the chapters and not too much else, let it complete.
Then rewind and check them all. You can drag the cue points with the mouse to reposition them and delete the cues you don't want ("E").
Then
File/Save split and it will split the file at the cues.
It sounds complex, but once you've done it a few times it's usually quick and reliable.
Some are a pain, when the pause between chapters is no longer than between paragraphs. Or there is music between chapters, not silence.
Then I might refer to the ebook version to track them down.
Library Genesis is a very good archive of ebooks.
After the split, move the original file away and open
MP3tag on the folder.
You can use that to rename and tag the new files quickly and consistently.
At least use Tools/autonumbering.
For naming the chapters, find the table of contents, e.g. by getting the ebook from Library Genesis, though if it's just "Chapter 1,2,3" it's not necessary, then use that with MP3tag to add title tags and usually rename the segments.
Then dig up a nice cover image, crop and maybe filter it in Irfanview or Photoshop, save to 500x500 pixels 40-50 kB jpeg and add that.
All of this cutting and joining is lossless, no reencoding, so no quality loss, and very fast.
However, if I do want to downsample it, I use fre:ac on the folder.
For just
cutting into chunks of approx equal time, say 20 minutes, using MP3DirectCut pause detection again, put the pause duration down to 1 second. That will find break points of that length or larger, so not the middle of a word. Then set "After pause detection skip" to the chunk size in seconds; i.e. 1200 for 20 minutes. Now it will mark a cue at 1-second pause (hopefully between sentences); then skip 20 minutes and look for the next pause and mark it, etc.
'Pops' at beginning of cut tracksThe great advantage of MP3DC is that it operates directly on MP3 frames without de/re-encoding, but it means that cuts can sometimes be abrupt and give you a "pop" at the beginning of a cut track.
You can manually fix that by zooming in at the start, select about 0.1 second and fade in (control F). Then control-W to save the file.
Or you can do it by using its batch processing:
Select the files, "Simple fade", 0.1 seconds (from start) and then select the destination folder and "Start".
Once you have a folder of MP3 chapters, you can compile them into an M4B:
See
this guide.