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Topic: What is the best format for audiobook (Read 2261 times) previous topic - next topic
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What is the best format for audiobook

I have an old smartphone (nexus 5, andriod 6) that i want to convert my audiobook that i owned to the lowest size possible so i can put it on that particular phone (only 16GB of storage) and still be audible. 


Please excuse if that is a noob question.

Re: What is the best format for audiobook

Reply #1
opus 6-10 kbps. best? i don't know.

Re: What is the best format for audiobook

Reply #2
I believe this is the top 3 for speech/audiobooks currently:
1. xHE-AAC
2. Opus
3. HE-AAC v2

xHE-AAC is quite new and not many apps can open it. It's also the hardest to decode (=eats more battery). Comparing the other two, on my Android phone in Foobar2000 at least, Opus decodes faster than HE-AAC v2 (on my PC it's the opposite).
Based on this, Opus seems like the best choice, unless you can find a way to play back xHE-AAC and don't mind the higher CPU usage.

There are some even more exotic speech-centric formats out there--like a couple developed by MS and Google and also LC3, part of the new BT spec--but I don't know if there are any encoders available to the public, so I doubt that they can be of any use for this purpose.

Re: What is the best format for audiobook

Reply #3
what about codec2?  i google the format it saids it can contain one hour of audio for just 1MB.

Re: What is the best format for audiobook

Reply #4
what about codec2?  i google the format it saids it can contain one hour of audio for just 1MB.
Which players support it? You have to go that way, not finding the perfect codec and then have no playback support.
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Re: What is the best format for audiobook

Reply #6
Do you really want to listen to a robot/synthesizer speaking to you for hours? At 32 kbit/s and 8 hours, you're looking at 110 MB of disk space. That is well within the budget.

Re: What is the best format for audiobook

Reply #7
Someone looking for respectable speech quality (not perfect, but good enough) at a very low file size I suggest... Opus @ 13kbps  NOTE: for example, Bible in a Year with Fr. Mike Schmitz is only 866MB for 6 days 7hrs 24min 32sec of speech audio at this bit rate setting.

at the very least I would say Opus @ 13kbps is a good start point as I would outright avoid anything lower because the storage space savings are no where near enough to justify the fairly steep sound quality drop off as you start going lower than 13kbps down to 12kbps, to 11kbps and so on. I get opinions vary on where one draws the line, but I feel what I said here is a good ball park figure on balance of maximum storage space savings without sacrificing the sound quality TOO much.

NOTE: I suspect it's possible depending on who's speaking, with their voice tone etc, it may effect quality a bit in which case one might need a bit more bit rate to clean it up. but just in my limited testing I feel 13kbps is a pretty good guideline as a bare minimum for speech on Opus. technically, I can still understand what's said going lower than 13kbps but audio quality starts to get a bit too muffled etc. I based this primarily on my Klipsch Pro-Media speakers which I feel are pretty good reasonably priced speakers for a PC. I am sure they would easily please most people.

but I think with all of that said if one wants to play it a bit safer on speech quality it would not hurt to try 16kbps or 24kbps or 32kbps etc. but I think if you exceed about 32kbps or so with Opus, one is probably better off just using MP3 at a higher bit rate (say V9 (65kbps) etc) for compatibility reasons since MP3 has near universal support. because I think the whole point in using Opus over say MP3 for speech is primarily for storage space savings while maintaining passable sound quality. because as I have said before in the past... with speech, top quality is not as big of a deal as it is with music, so it's easier to make some noticeable sacrifice in sound quality (but still retains a large portion of the higher quality source files overall sound quality) for top notch storage space savings/efficiency.
For music I suggest (using Foobar2000)... MP3 (LAME) @ V5 (130kbps). NOTE: using on AGPTEK-U3 as of Mar 18th 2021. I use 'fatsort' (on Linux) so MP3's are listed in proper order on AGPTEK-U3.

Re: What is the best format for audiobook

Reply #8
I’ve prepared many audio books for my portable players. I recorded them from cassette and extracted them from CD as .wav so I could make improvements to quality as desired. For CD sources this was often no change, for the many from cassettes (which were very inexpensive in thrift stores for some years) I did various processing to get the levels more consistent, to repair dropouts, and to remove tape hiss and background noise.

From 16/44.1 wav I encoded with LAME to VBR 8, 22050 kHz, mono mp3. mp3 plays on almost everything. This gives very satisfactory audio quality, easy to listen to and easy to understand. It might sound slightly different than the original but the difference is so small that I soon gave up comparing. I don’t know how it rates on size with other codecs but it definitely produces files that are much smaller than I started with and also much smaller than some I’ve listen to from commercial sources such as Audible.

Re: What is the best format for audiobook

Reply #9
Opus (if supported) or AAC-HE would be good choices on Android 6.  When 6.0 was new Opus support in Android apps could be spotty (not all knew to parse the files and tags), but probably that is a lot better now.  AAC-HE compatibility should be very good regardless.

Re: What is the best format for audiobook

Reply #10
The compatibility argument does not hold, Lame with the proposed parameters does not generate a compressed file with the Layer 3 of MPEG-1, it will use the Layer 3 of MPEG-2, at this point it will have the same compatibility at the decoder level with the ISO specifications of January 2006, remained unchanged until today.

And if you want to hear the differences, you can provide me a test recording of it and it will be received in all formats at the same bitrate. I use 36kbps because USAC or xHE-AAC, HE-AAC, even AAC at fs / 2 and Opus offer the most similar rendering, obviously MP3 offer too many artifacts.

X X X X X

Re: What is the best format for audiobook

Reply #11
Of course I don't go below 24kbps. I have merged into a flac file the ebu tests compressed in Opus in a page that I use for tests.

See https://www.celona.it/test/ and press play.

 

Re: What is the best format for audiobook

Reply #12
I still use an mp3 player with rockbox, so im avoiding more complex codecs.

I use Qaac (LC) V36 44.1khz mono and Lame 3.97 V9 24khz mono.
To me Lame 3.97 sounds better than newer Lame versions at these low bitrates. It sounds very acceptable at only 30kbps imho.
The bitrate of the aac file is 45kbps which is higher than normal. It is usually around 40kbps. It is a bit higher quality than the mp3 file.

I should test which of the 2 is most battery effective.

Re: What is the best format for audiobook

Reply #13
To me Lame 3.97 sounds better than newer Lame versions at these low bitrates.

Sorry for the delay with which I reply. I used LAME 64bits version 3.100 and actually it seems that, as you write, version 3.97 is more efficient. The last test I did in MP3:
MPEG-2, layer III, 22050 Hz, 42 kb/s, 462 kB.

Ogg Vorbis, 24000 Hz, 43 kb/s, 476 kB
Opus, 48000 Hz, 36 kb/s, 398 kB

LC-AAC, 24000 Hz, 35 kb/s, 405 kB
HE-AAC, 48000 Hz, 36 kb/s, 406 kB

xHE-AAC, 48000 Hz, 26 kb/s, 292 kB
Opus, 48000 Hz, 26 kb/s, 292 kB
FLAC, 48000 Hz, s16, 379 kb/s, 4.1 MB

Try them and see which one you should use but keep in mind that it makes no sense to compare an .mp3 file sampled at 22050 Hz with one at 44100 Hz. As you can see by lowering the sampling frequency and not setting any limit to the compressor, therefore in its ideal conditions of operation (VBR at maximum quality), you get a LC-AAC file at 35 kb/s.

The xHE-AAC file cannot be obtained at this bitrate with Exhale. Even requesting a 36kb/s VBR it stops at 26, a value in which the highest quality speech is obtained. It is my favorite for quality but it does not work on your device, nor with BSD, Linux and Windows without installing additional software, on the other hand it works on all tablets, all (modern) mobile phones and even Apple Watch.

Ogg Vorbis is obsolete (like Speex) and Opus works with all current browsers, in old Android versions you will have to change the file extension, on Rockbox you will let me know what works and how, I haven't tried it for too many years. I don't think it makes sense to consider other encoders because they are less supported than these.

Update: I have heard the xHE-AAC file, created after an update and objectively also in this case it feels worse than the previous version, I will report it to the developer.

Re: What is the best format for audiobook

Reply #14
Might want to fix that second Opus link, it points to the ebu-test.mp4.


Re: What is the best format for audiobook

Reply #16

Update: I have heard the xHE-AAC file, created after an update and objectively also in this case it feels worse than the previous version, I will report it to the developer.

The xHE-AAC file has ReplayGain information embedded, resulting different output in Foobar. I can clearly hear the difference if I delete the ReplayGain tags.

I've attached the same file without ReplayGain tags.


Re: What is the best format for audiobook

Reply #18
Excuse me, try to change extension (or container), I remember at 24kbps with .caf and .webm and 36kbps with .opus but it could be the other way around. Listening them at 24kbps the sound is less smooth (or more distorted).

As soon as I am free I will check and correct.

https://www.celona.it/test/ebu-test.opus or https://www.celona.it/test/ebu-test.webm or https://www.celona.it/test/ebu-test.caf