Audiobook Formats and File Types: Which One is Best?

The audiobook file you should use most is the MP3, but there are many other types of formats that you should know, such as the FLAC.

Audio is growing faster than ebooks or print books. That means that to increase your audiobook sales, you should have a solid understanding of the technical requirements of audio.

While there are a lot of audio formats out there, used by a wide variety of companies, there’s really only one audiobook file format that you need to master, with a few others that are useful to know. 

And we’ll break each one down in this post.

Audiobook File Types

When discussing audiobooks and audio file types, there are quite a number of formats that exist, but only a few that are relevant to audiobook creators.

We’ll take a look at each type, but know that the only ones you really need to worry about are MP3, WAV, and FLAC.

Lossy Compressed Audio Formats

The term “lossy” means that the audio has undergone a compression process. This significantly decreases the audio file size, but can result in loss of quality.

Still, it’s common to use these as audiobooks, and ACX actually recommends the MP3 as their main file format.

So let’s take a look at each of the compressed lossy audio formats for audiobooks.

MP3

By far the most popular (possibly of any file type) is the MP3 (.mp3). MP3 uses its audio coding compression to remove a lot of superfluous data that most of us don’t hear anyway. It stands for MPEG audio layer 3, with layer 3 being its own unique coding scheme. 

An MP3 file is the most common lossy audio format, and though the quality is slightly diminished, vocals still come through without much loss. This means that audiobooks in MP3 are not going to be much different than higher-quality formats.

AAX

You might see an AAX file if you find the actual files of your Audible audiobooks. AAX was an audiobook format developed by Audible using an MPEG-4 container that also allowed for the file to be encrypted with DRM.

This is not a file type that you will ever have to worry about creating. Audible does the transfer for you, but it’s worth knowing that it exists, and that this is what Audible is using to deliver your audiobook files to readers.

M4A/M4B

The compressed format used by Apple, just as the AAX is used by Audible, is the M4A or M4B. 

This is also the format used for music from the Apple store. M4A is more common for music, and the M4B file is more common for audiobooks and podcasts, since it allows for additional metadata like bookmarking, which M4A does not have.

AAC

The AAC format stands for Advanced Audio Coding, and it’s actually a superior form of compression when compared to the MP3. The sound quality is a lot better.

However, AAC has never really caught on the same way that MP3s have, at least for the majority of us consumers. That said, it is a common format used by a variety of companies, including YouTube, the iTunes library, most smart devices, and consoles.

M4P

M4Ps are merely a version of AAC that have digital rights management included. It was originally built by Apple for the iTunes Music store. Like the AAC, the sound quality is generally better.

OGG

OGG is a sort of digital container that holds Vorbis files. Vorbis files are open source, unlike most of the other file types we discuss. It’s also a superior form of audio quality and compression.

That said, it’s a file type that has had some trouble competing with the MP3s and AACs of the world, so it’s often overlooked.

WMA

WMA stands for Windows Media Audio, and there are both Lossy and Lossless formats for it. 

If you use a Windows machine, you’re likely familiar with it, as it was developed by Microsoft and commonly used on their operating systems. That said, it isn’t widely used in other non-Microsoft devices, and it doesn’t really offer any benefits that aren’t also served with an AAC or OGG.

Lossless Compressed Audio Formats

Whereas Lossy files are compressed to significantly decrease file size, sacrificing some quality in the process, “Lossless” files use a compression method that isn’t quite as effective at reducing the size, but maintains all of the audio quality.

There are one or two of these that you should know about when creating your audiobook. So let’s take a look.

FLAC

 FLAC is largely considered to be the most superior form of lossless compressed audio, and it’s no surprise why.

FLAC stands for Free Lossless Audio Codec. It’s an open-source file, which means that there’s no intellectual property problems, and it’s compression is almost as good as an MP3, but without sacrificing any quality whatsoever.

It is one of the formats accepted by Findaway Voices, and you’ll see it pop up more and more. 

WAV

WAV is one of the most popular files types for audio. It’s an older format, but despite this, it is still widely used and is superior to a lot of formats.

WAV files don’t sacrifice any quality at all, though they are a lot larger than a compressed, lossy file. So must audiobooks, even if they were produced as WAVs, will likely be converted to a lossy format by the time the listener gets their hands on an audiobook.

ALAC

Apple Lossless Audio Codec (ALAC) is Apple’s own file format for high-quality audio.

Though originally exclusive to Apple, it became open source and royalty free in 2011. However, it’s still widely in use by Apple, to the exclusion of some superior files like FLAC.

Like others on this list, it doesn’t sacrifice quality, but the compression is not quite as good as FLAC.

WMA

Wait, didn’t we talk about this already?

Yes, WMA has both a lossless and a lossy format. They both use the same extension.

While this is a common format with Windows, it’s not one you should use for audiobooks. The software is proprietary, and has limited hardware support. It’s also the worst in terms of compression efficiency.

So best to stick to FLAC or WAV for your lossless files.

Which is the Best Format?

When it comes to adapting your Kindle ebook for audiobook listeners, there are really just a few formats that you should use.

For lossy formatting, the best are MP3 and AAC. AAC is the best in terms of quality and compression space savings. However, MP3 is so widely used at this point, that you’ll have a better chance of successfully submitting your MP3 audiobook in this format.

For lossless formatting, your best bets are FLAC and WAV. The latter is far more common, but FLAC is easily the superior file type. And a lot of people are beginning to accept FLAC files to begin with, including Findaway Voices.

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Audible/ACX Submission Requirements

We know all the different formats, but what exactly do we need for submitting our book to ACX?

ACX has a number of different requirements for their audiobooks, but the audiobook format is relatively simple.

According to ACX’s own website, they want an MP3 file with a 192kbps (or higher) Constant Bit Rate at 44.1 kHz.

What does this mean?

Bitrate is a measurement of quality with MP3s. A high bitrate will result in a higher-quality MP3 file, though it will also result in a higher file size.

The range for MP3s tend to run from 96 to 320kbps. ACX/Audible’s requirements put it around the middle of that range. You can go higher, but Audible points out that this will likely not result in an increase of quality that listeners will be able to discern.

In other words, just submit an MP3 at 192kbps, and you will be fine.

You can see more of their audio requirements on their website.

Findaway Voices Audio Requirements

While ACX is largely considered the gold standard when it comes to producing audiobooks, Findaway Voices is another major powerhouse that you should consider.

Findaway Voices works with a wide variety of publishers, so if your audio is good enough for Findaway Voices, it should be good enough for everyone.

Like ACX, Findaway accepts MP3s at 192kbps or higher. They also accept FLAC files, however. The sample rate is likewise at 44.1 kHz.

So if you want to submit the absolute highest quality possible, you can do that with Findaway Voices through FLAC files.

Most of the other audio requirements for Findaway are the same as ACX.

The Bottom Line

Audiobooks have come a long way, but the best formats to use for them are still the most basic: the MP3 format or the FLAC format.

While you might want to work with WAV files when working with your audiobook narrator, those files will eventually need to be converted so they will play on an MP3 player.

Then, once you hand the files off to ACX, Findaway Voices, or wherever you submit your files, they will be converted to all the appropriate files for delivery to the listener. 
We hope this article helped. Let us know if you have anything you would add. We love to hear from our readers.