Generate audiobooks from E-books with Kokoro-82M
254 comments
·January 15, 2025laserbeam
stavros
> On the other, some of my favorite audio books all stood out because the narrator was interpreting the text really well
This (and everything else with AI) isn't saying "you don't need good actors any more". It's saying "if you don't have an audiobook, you can make a mediocre one automatically".
AI (text, images, videos, whatever) doesn't replace the top end, it replaces the entire bottom-to-middle end.
j4coh
RIP to future top-enders that would normally have started out on the bottom to middle end.
aredox
Bingo. AI is going to destroy any pathway for training and accruing experience.
An embalming tech for our dying civilization.
sam_lowry_
> RIP to future top-enders that would normally have started out on the bottom to middle end.
This stance always reminds me of the Profession, a 1957 novella by Isaac Asimov that depicts pretty much the future where there are only top performers and the ignorant crowd.
anothermathbozo
Virtually every book I want this for has been around for 70+ years and still no high or low quality audiobook has been produced. How long do I have to wait for those aspiring top-enders before an audiobook can be made available?
gosub100
I'm super opposed to AI, but I see this as a rare positive. As someone already said, the win here is to have a audiobook where one doesn't yet exist. hell, maybe the tables will turn and the scrubs will do the hard work of discovering which titles are popular with an audience, then the ebook industry can capitalize on AI by hiring voice actors to produce proper titles?
null
CuriouslyC
It's common for shows to use big name actors as voices because they draw an audience, nothing will change. Just means a smaller pool of voice actors and they'll mostly be good looking.
cmdtab
The value of distribution is increasing while the value of content and product is decreasing for all but the top end.
Der_Einzige
Not RIP at all. "Meritocracy" was coined in a book literally warning us about how terrible such a society would be: https://en.wikipedia.org/wiki/The_Rise_of_the_Meritocracy
The "top-enders" are the privileged who need to have some of their gains for their intelligence redistributed to others. The alternative is "survival of the smartest", which is de-facto what we have today and what Young was trying to warn us about.
numpad0
AI TTS has been available for quite some time. Tacotron V1 is about 8 years old. I don't think we saw much bottom end replacement.
IMGO(gut opinion), generative AI is a consumption aid, like a strong antacid. It lets us be done with $content quicker, for content = {book, art, noisy_email, coding_task}. There's obvious preconceptions forming among us all from "generative" nomenclature, but lots of surviving usages are rather reductive in relevant useful manners.
sam_lowry_
Yeah, let us not blame AI. Audible damaged the quality of audiobooks than AI.
no_wizard
Bottom end really, Middle end is still superior to this AI drivel.
felixhummel
I wholeheartedly agree. https://en.m.wikipedia.org/wiki/Stephen_Briggs got me hooked on Terry Pratchett's Discworld series. I loved "Going Postal".
IndrekR
I know someone who listened Terry Pratchett's "Wachen! Wachen!" audiobook on Spotify while living in Germany for few years. It was so well narrated that he also acquired some peculiarities of local dialects used by specific characters in the book. Locals in Bavaria were quite surprised of a foreigner speaking such language.
dmazin
Absolutely.
Even on the non-fiction side, the narration for Gleick's The Information adds something.
While I want this tool for all the stuff with no narration, NYT/New Yorker/etc replacing human narrators with AI ones has been so shitty. The human narrators sound good, not just average. They add something. The AI narrators are simply bad.
ldoughty
I agree with you, but also want to point out:
New authors, self-publishers, can't afford tens of thousands of dollars to get an audiobook recorded professionally... This can limit their distribution.
Authors might even choose not to make such version (or lack confidence to record themselves), so AI capable of making a decently passable version would be nice -- something more than reading text blandly. AI in theory could attempt to track the scene and adjust.
plorg
By observation the current approach is for authors to narrate the book themselves of they think their readers will want it and if they feel reasonably confident in their own narration.
DidYaWipe
You can get narrators to work on a royalty basis.
WillAdams
Yes, but if the alternative is not having a book, or having to listen to one poorly read (I love Librivox, but there are some books which I just haven't been able to finish because of readers, and many more which were nixed for family vacation travel listening on that account), this may be workable.
micw
With this technology, one could produce high quality audio books without having access to high quality narrators by annotating the books with the voice, speed and such things.
I wonder if a standardized markup exists to do so.
albert_e
There is SSML for speech markup to indicate various characters of speech like whispers, pronunciation, pace, emphasis, etc.
With LLMs proving to be very good at generating code, it may be reasonable to assume they can get good at generating SSML as well.
Not sure if there is a more direct way to channel the interpretation of the tone/context/emotion etc from prose into generated voice qualities.
If we train some models on ebooks along with their professionally produced human-narrated audiobooks, with enough variety and volume of training data, the models might capture the essence of that human-interpretation of written text? Just maybe?
Amazon with its huge collection of Audible + Kindle library -- if it can do this without violating any rights -- has a huge corpus for this. They already have "whispersync" which is a feature that syncs text in a kindle ebook with words in corresponding audible audiobook.
micw
Good points, thank you! I just tested it. While ChatGPT was very good in adding generic (textual) annotations, the result for generating SSML where very poor (lack of voice names, lack of distinction between narrator and character etc).
Probably the results with a model trained for this plus human audit could lead to very good results.
pegasus
They still wouldn't be high quality. It's just not possible to capture the precise tone of voice in an annotation, and that precision I believe really makes a difference. My experience is that the deeper the narrator understands the text and conveys that understanding, the easier it becomes for me to absorb that information.
vasco
Have you tried those "podcast from a paper" models? They do some of the things you are saying they don't, although it's not 100% it's also miles ahead of for example human Polish TV lectors, or other monotone style narrations.
KeplerBoy
Don't end to end trained models already do this to some extent? Like raising the pitch towards a question mark, like a human would.
TortoiseTTS has a few examples under prompt engineering on their demo site: https://nonint.com/static/tortoise_v2_examples.html
micw
That's a bit of basic and random. Some models have the features you describe. From the better models you get a slightly different voice for text in quotes.
But the difference to good audio books is that you have * different voices for the narrator and each character * different emotions and/or speed in certain situations.
I guess you could use a LLM to "understand" and annotate an existing book if there's a markup and then use TTS to create an audio book from it and so automate most of the the process.
ahoka
I guess this is still very useful if you are blind.
loktarogar
Yeah, for accessibility purposes on things that aren't already narrated, this is kind of thing is huge.
em-bee
that's the thing. it's not just for accessibility. anything not already narrated is a fair target for TTS. i don't have time to sit down and read books. all reading is done on the go, while getting around or doing daily routines at home. i have a small book that i am reading now, which should take a few hours to finish, but in the time i manage to get done reading it i will probably have listened to two or three audio books.
oh, and it's also a boon for those who can't afford to buy audiobooks.
flir
I was just thinking about automatically slapping an mp3 on every blog post, just an accessibility nicety.
Can someone with low vision tell me if this would be useful to them? It may be that specialist tools already do this better.
taude
Agree with you on this.
My example, I was never a Wheel of Time fan, but the new audio editions done by Rosamund Pike are quite the performance, and make me like the story. She brings all the characters to life in a way thats different than just reading. It's a true performance.
delegate
The quality is great (amazing even), but I can't listen to AI generated voices for more than 1 minute. I don't know why, I just don't like it. I immediately skip the video on youtube if the voice is AI generated.
Might be because our brains try to 'feel' the speaker, the emotion, the pauses, the invisible smile, etc.
No doubt models will improve and will be harder to identify as AI generated, but for now, as with diffusion images, I still notice it and react by just moving on..
rockemsockem
That kinda means the quality isn't great or amazing. Good TTS should be nearly or indistinguishable from a human speaker and should include emoting, natural pauses, etc
CMay
Haven't really been following the latest in TTS ML, but I expected this to be better or at least as good-bad as the stuff you hear on YouTube. Somehow it sounds worse. It really is jarring to listen to any of these ML voices and can't really stand it. Nope out of every video that uses them and can't tell if YouTube never recommends them to me for that reason, or just because the recommendations around what I watch are just so rarely going to be from some low reputation channel.
Take a moment here for a second though and think about it. Even if these voices got to be really good, indistinguishable almost... would I want to listen to it even then? If it was an NPC's generated voice and generated dialogue in a game to help enrich the world building, maybe in that context. On YouTube or with newscasters? Probably not. Audio books? Think I would still rather have it be a real person, because it's like they're reading a story to me and it feels better if it's coming from someone. There's also the unknown factor, where if it's ML generated it's so sterile that the unknowns are kind of gone.
Think about it like this, in the movie industry we had practical effects that were charming in a way. You could think about the physical things that had to occur to make that happen. Movie magic. Now, everything is so CG it's like the magic is gone. Even though you know people put serious hard work into it, there's a kind of inauthenticity and just lack of relevance to the real world that takes something away from it.
It's like a real magician has interesting tricks, while an artificial magician is most likely just a liar.
Still, I grant that it makes some cool things possible and there is potential if things are done right. Some positive mixture of real humans and machine generated stuff so it isn't devoid of anything connected to real life effort.
_DeadFred_
For new generations/those coming up now this will be the norm and not generate the negative reaction is does for us, it will just be part of how the world is and has always been, and eventually we will be the minority.
Future generations will never know a world where you don't watch a 2 hour AI generated orientation video about the wonders of working for Generic Corp when you start a new job.
xdennis
Among other things, what I don't like is the hallucinated stress. Take the classic example of:
> I never said she stole my money
It can have 7 different meanings based on which word you stress out.
The new AI voices sound very natural at a shallow level, but overall pronounce things in odd ways. Not quite wrong, but subtly unnatural which introduces some cognitive load.
Old TTS systems with their monotonic voices are less confusing, but sound very robotic.
DidYaWipe
erroneous or inappropriate ≠ hallucinated
yjftsjthsd-h
> I immediately skip the video on youtube if the voice is AI generated.
I mean, I do that because it's correlated with the content being garbage. If I'm intentionally using it on content I want to consume I expect it to be different, though I haven't gotten around to trying it properly yet so I guess we'll see. (OTOH I already listen to ebooks via pre-AI TTS, so I'm optimistic)
karmasimida
Yeah same.
Doesn't mean the quality is bad. In fact I think Kokoro's quality is amazing.
But it is not the right tool for narration, the kind of training data they use make the sound too flat, if that makes sense.
swores
Can anyone recommend an open source option that would allow training on a custom voice (my own, so I'd be able to record as many snippets as it needed to train on) to allow me to use it for TTS generation without sharing it off my machine?
Edit: I'll wait to see if any recommendations get made here, if not I might give this one a go: https://github.com/coqui-ai/TTS
hm64
Coqui is great, but in practice, I found Piper easier to set up, train, and deploy as an ONNX file. Big thanks to the Sherpa development team for their helpful resources: https://k2-fsa.github.io/sherpa/onnx/tts/piper.html and to the Rhasspy team for their training guide: https://github.com/rhasspy/piper/blob/master/TRAINING.md.
I also found DEMUCS + Whisper + pydub to be a super helpful combo for creating quality datasets.
drewbitt
There is a fork here https://github.com/idiap/coqui-ai-TTS 'coqui-tts'
Though according to the TTS leaderboard, Fish Speech https://github.com/fishaudio/fish-speech and Kokoro are higher.
xnx
AFAIK Kokoro can't be fine tuned
numpad0
I think you can probably generate TTS audio by classical means, and voice2voice that audio through RVC or Beatrice V2. Haven't looked into it in a while but Beatrice is apparently super fast and CPU only.
eamag
F5-TTS, I wrote a post about it https://eamag.me/2025/Voice-Cloning
jsemrau
I wrote this a while ago about xTTSv2 mixed with Nvidia's Nemo. Maybe it kicks off your journey.
https://jdsemrau.substack.com/p/teaching-your-agent-to-speak...
esskay
If I recall Coqui is very much a dead project, just one to be aware of.
pprotas
I would love to have an e-reader that allows me to switch between text and audio at the press of a button. Imagine reading your book on the couch and then switching into audio mode while doing the dishes seamlessly, by connecting bluetooth headphones.
InsideOutSanta
Kindles used to provide this feature, but publishers and/or the Authors Guild stopped it, because audio rights and text rights are handled differently. In other words, when Amazon sells you a text book, it does not have the right to then also do TTS on that text and let you listen to it.
There's some contemporary discussion of what happened here: https://tidbits.com/2009/03/02/why-the-kindle-2-should-speak...
I think there is still integration with Audible, though. If you buy a book on the Kindle and on Audible, the position will sync, and you can switch between listening and reading without losing your place in the book.
albert_e
Yes the feature is called WhisperSync -- I used it many years ago and it was pretty good.
I tried it while on a treadmill so it allowed me to follow the book with more focus without sacrificing much else.
thfuran
Isn't whisper sync the current version that relies on owning both the ebook and audiobook?
hamzakc
I am not sure if this still works, but 2-3 years ago I listened to a kindle book that I bought through my Echo show device. It was pretty good. I listened to it while I was cooking. It even allowed you to carry on where you left off. But I did notice that a few pages were skipped as I had read the book before. I have since packed away my echo show so I can't verify if they have removed this feature or not.
Brybry
I used that TTS feature semi-regularly on a Kindle 2.
It wasn't a good experience but it was nice to be able to keep 'reading' a book while I was exercising.
It worked for me for over a decade, until I broke the device. I don't know if I never updated the firmware or if the fact I used Calibre to convert books bypassed the feature gate.
dsign
It is a supported feature in the epub 3.0 standard. It's possible to distribute an epub with audio, and have the audio sync to the HTML elements that form the ebook's text. And there is an e-reader that actually supports this feature, I can't remember which one now but it should be possible to find it with Google.
It's more of an open problem how to create those epubs. I have some code that can do it using Elevenlabs audio, but I imagine it way harder to have something similar for a human narrator.... who's going to do the sync? Maybe we need a sync AI.
freefaler
You can do it easily with non-DRM books (or DRM stripped books):
For Android:
- Moon+ reader pro - some paid high-quality TTS voices (like Acapella)
For iOS:
- Kybook reader and internal iOS voices (no external TTS voices for the walled garden)
This works well enough to listen to a book while you walk and when you get back home read on the WC from the place you stopped.
Additionally if you buy a tablet or an android ebook reader, you install the app there an you can continue on your bigger/better device seamlessly.
Whisper-sync for the masses! Ahoy...
basedrum
But you need an android phone, and can't use a kobo or similar wink reader?
freefaler
for ios you use Kybook on your iphone and your ipad. It syncs positions between the devices. When you go for a walk, opens Kybook, start TTS. When back home, open your tablet, you'll see the page TTS has stopped reading to.
monkeydust
Literally started doing that this week with Amazon Audible. I gave in an started the three month 99c trial and downloaded the app.
What surprised me a good way was my Kindle app was aware of this and asked if I wanted to download the audible version of the current book I am reading.
Been listening on the way to work and then reading on the way back. Enjoying it so far.
mmahemoff
Some Kindke books also have a checkbox to add the audio (for a fee) when you buy it. Sometimes I’ve seen books discounted to e.g. £0.99, but adding the audio might be £5.99. The upsell seems to be a good hack for adding some revenue when there’s a deep discount being used to drive interest.
llamaimperative
Boox Ultra Tab whatever the fuck (their product naming sucks) + Readwise Reader = amazing for this
Not quite seamless but it works. It has a cursor that follows the words as they’re spoken to, which allows you to read and hear (“immersive reading”) which I find to be extremely helpful for maintaining focus.
leobg
iOS Voice Dream Reader. First app I install on a new iPhone since 2010 I believe. I will even cut and scan physical books just so I can read them in the app. The story of the guy who made it is also interesting!
qurashee
This looks incredible! I’ve had an idea simmering in the back of my mind for a while now: creating an audiobook from an ebook for my commute using the voice of a specific audiobook narrator I really enjoy. The concept struck me after coming across the Infinite Conversation project here on HN. Unfortunately, I just haven’t found the time to bring it to life yet. :(
eamag
For a specific narrator you can try F5-TTS, here's a post how https://eamag.me/2025/Voice-Cloning
leobg
Made this for my kids for Christmas:
- take an ebook in any language - AI translates it to German - AI speaks it using the voice of their fav narrator - a UI showing the text as it is being read
Now they can read Asimov, Kulansky, Bryson, regardless of whether a translation or audio version exists. :)
vinni2
What about the copyright issue? You can’t mimic the voice of a narrator without their consent. OpenAI landed in trouble after using Scarlett Johansson’s voice in a demo.
https://www.theverge.com/2024/5/20/24161253/scarlett-johanss...
notachatbot123
No limitations on this kind of thing if you are in private use.
vinni2
Forgive me for not knowing it was for personal use.
qurashee
Indeed I was thinking about private use only.
benatkin
She only won in that OpenAI decided it wasn’t worth the trouble.
K0balt
Yeah, by my ear it was pretty clearly not SJ’s voice-likeness, although there were some superficial similarities.
But some people could have mistook it due to some regional accent similarities, though it would be akin to interpretation of any light southern drawl with a similar timbre as being SJ.
amrrs
Kokoro really mentions that they used only permissive licensed voice
cwmoore
The word “kokoro” means “heart” in Japanese, which I learned making the (heart shaped and paperback) puzzle books at https://www.kakurokokoro.com/
tkgally
Note that kokoro (心) means “heart” in the sense of “spirit,” “soul,” “mind,” “emotions,” etc. It doesn’t mean “heart” in the sense of “internal organ that pumps blood.” That is shinzō (心臓).
I once heard an American friend with so-so Japanese ability ask a Japanese woman who had recently had a heart operation how her kokoro was doing, and she looked surprised and taken aback.
Side note: After I started reading HN in 2019, I was struck by how many tech products mentioned here have Japanese names. I compiled a list for a few years and eventually posted it:
terhechte
Its also the name of the AI in Terminator Zero https://villains.fandom.com/wiki/Kokoro
I'm not sure if that is related here.
albert_e
I hope a plugin for Calibre ebook management software comes along that makes it easier to convert select titles from your epub library to decent audio versions -- and a decent open source app for tablets and smartphones that can let us seamlessly consume both the ebook and audiobook at will.
Dowwie
2025 may be the year where we can generate a dramatic audiobook with ambient music, sound effects, and theatrical narration using neural networks. Many of the parts already exist.
cess11
I would for sure not want this for fiction, it's too obvious that the voice has no understanding whatsoever of the text, but it's probably pretty nice for converting short news texts or notifications to audio.
vanderZwan
Your point is a valid one, but I want to add to it that it is also a matter of expectations and how one listens.
Years ago, when I was dating someone who spoke Russian as one of her native languages, we had to do a funny compromise when watching films together with her parents: they didn't speak a word of English, so we'd use the Russian dub with English subtitles.
I noticed that the Russian dub was just one man reading a translation in a flat voice over what was happening on the screen, no attempts at voice acting or matching the emotions. Usually the dub would have a split second delay to the actual lines, so you'd still hear the original voices for a moment (and also a little bit in the background).
At first I found it very jarring, but they explained that this flatness was a feature. You'll quickly learn to "filter out" the voice while still hearing the translation, and the faint presence of the original voices was enough to bring the emotional flavor back. The lack of voice acting helped with the filtering.
This turned out to apply to me as well, even though I don't speak Russian! My brain subconsciously would filter out the dub, and extract most of the original performance through the subtitles and faint presence of the original voices. Obviously the original version would have been a better experience for me, but it was still very enjoyable.
Of course a generated audiobook is not a dub, as there is no "original voice" to extract an emotional performance from. But some listeners might still be able do something similar. The lack of understanding in the generated voice and its predictable monotony might allow them to filter out everything but the literal text, and then fill it in with their own emotional interpretations. Still not as great as having proper story teller who does understand the text and knows how to deliver dramatic lines, but perhaps not as bad as expected either.
arafalov
Here is the rest of that story.
When the foreign movies started to filter into the Soviet Union's illegal movie theatres, you would get 3 or 4 movies playing at once in one room. There would be a TV in each corner of the room and 4 or 5 rows of plastic chairs in front of it in an arch.
ALL of the movies were being revoiced by the same person. So, if you were sitting in the back of the 5th row, you were potentially getting the sound from an action movie, a comedy, a horror movie and a romance at the same time. In the same voice.
You learned to filter really well. So, if that's what they were trained on, watching a single movie must have been very relaxing.
vanderZwan
Looking at the modern internet experience it sounds like the Soviet Union's illegial movie theatres were ahead of their time!
aleksiy123
Watching these as russian/english bilingual is very painful, tho I grew up in western world so maybe I'm just not used to it.
To add on a slight tangent. Many books/audiobooks just don't exist in other languages at all. So even getting some monotone is a lot better than getting nothing.
I think this is where these models really shine. Cheaply creating cross language media and unlocking the knowledge/media to underprivileged parts of the world.
vanderZwan
> Watching these as russian/english bilingual is very painful, tho I grew up in western world so maybe I'm just not used to it.
I figured that their opinion probably wasn't universal, hahaha.
And yes, it's at the very least a win for accessibility
em-bee
indeed, audio books come in many forms, some are rather flat, and some include different voices, even by different speakers, or include a few voiced sound effects, laughing, crying, singing, etc. TTS is extra flat, but if the quality is good otherwise then it is like reading with my ears, and i add the emotions myself.
cess11
It's not a "point", I didn't make an argument.
I dislike german and russian style dubs as well, I'd rather learn a bit of the original language.
calgoo
Audible has thousands of books available "for free" with their membership that are all AI generated. I was the same in the start, but after listening to a few, it really comes down to the voice used. I spent 8h on a plane listening to 1 book, and there was maybe 5 occasions where i had an issue with the voice; and i think all where just "AI weirdness", similar to chat LLMs messing up simple sentence structure or image generating LLMs adding an extra finger.
arafalov
The one I tried, had a lot of issues. It was a music theory book and it did not know how to pronounce C# (it kept saying C 'hash'). It also referred to, but did not read out the diagrams, or tables.
So, it was not just the voice, but the quality control pipeline that was missing as well.
Maybe it mostly works for old plain text books, but if nobody is checking.....
cess11
I don't think dominant suppliers like Audible should exist so that matters little to me.
sysworld
Finally! Been trying all the TTS models popping up on here for ages, and they've all been pretty average, or not work on Mac, or only work on really short text, or be reeealy slow.
But this one works pretty quick, is easy to install, has some passible voices. Finally I can start listening to those books that have no audio version.
I'm a slow reader, so don't read many books. If a book doesn't have an audiobook version, chances are I won't read it.
PS, I have used elevenlabs in the past for some small TTS projects, but for a full book, it's price prohibitive for personal use. (elevenlabs has some amazing voices)
Thank you to the dev/s who worked on this!
TypoAtLineZero
I am having a very similar setup locally, which uses Chrome with the 'Read Aloud' plugin. I am capturing the audio stream via QJackCtl/VLC. Voices, speed, pitch can be adjusted. Efficient and quickly set up
lc64
"was trained on <100 hours of audio"
How the hell was it trained on that little data ?
bbminner
I suppose it means per speaker. And it is based on a simplified style tts 2 which from my small dive into the subject seems one of the smaller models achieving great quality.
null
Havoc
Yeah that surprised me as well - seems low vs what is used on text llms . To be fair 100 hours of speaking is a lot of speaking though
On the one hand, this is very convenient. Probably cool for some non-fiction.
On the other, some of my favorite audio books all stood out because the narrator was interpreting the text really well, for example by changing the pacing during chaotic moments. Or those audiobooks with multiple narrators and different voices for each character. Not to mention that sometimes the only cue you get for who's speaking during dialogue is how the voice actor changes their tone. I have mixed feelings about using this and losing some of that quality.
I would totally use this over amateur ebooks or public domain audiobooks like the ones on project guttenberg. As cool as it is/was for someone to contribute to free books... as a listener it was always jarring to switch to a new chapter and hear a completely different voice and microphone quality for no reason.