AIFF to M4B Converter

Turning an AIFF Recording into an Audiobook File

M4B is not a different format from M4A — it is the same MPEG-4 Part 14 container (ISO/IEC 14496-14) carrying the same AAC audio, with an extension that tells audiobook players "treat this as a book". That single signal is what buys you position memory, playback-speed controls and a separate Audiobooks shelf instead of a track lost in a music library. This page covers turning a narration, lecture or interview recorded as AIFF into that file: which bitrate to pick, how big the result will be, and what M4B will and will not do for you.

How to Convert AIFF to M4B

1. Upload Your AIFF File: Drag .aif or .aiff files onto the page or click "+ Add Files". Files convert individually with shared settings — the queue does not join them into one book.
2. Set the Bitrate under File Compression: File Compression opens on the Quality Preset dropdown, the hands-off mode — and the least predictable control here, with nothing actually pre-selected in it. Switch to Constant Bitrate (the dropdown runs from 8 kbps to 384 kbps and opens on 128 kbps), Variable Bitrate and one of its five AAC bands, or Custom Bitrate to name an exact figure. Spoken word rarely needs more than 64 kbps.
3. Fold to Mono and Trim: Narration recorded in stereo carries no stereo information, so set Audio Channel to MONO and halve the file for free. Audio Sample Rate can drop to 24000 HZ for voice, and Trim takes a start time and duration if you are cutting a book into parts.
4. Convert and Download: Click Convert and save the .m4b. No sign-up, no watermark.

Walk-through: Choosing a Bitrate for Spoken Word

The instinct is to protect quality by choosing a high bitrate, but narration is the one kind of audio where that is genuinely wasted. A voice occupies a narrow band, has no stereo image worth preserving, and is listened to on phone speakers and earbuds during commutes. Work from the constraint you actually have:

• You want it to sound like the source: 64 kbps mono AAC is comfortably clean for speech, and is the safe default when the recording has music beds or field noise.
• You want the smallest sane file: 32-48 kbps mono is where commercial audiobooks tend to sit. Compression artefacts on sibilance become audible below about 32 kbps.
• The book has music or dramatised sound design: keep it stereo and use 96-128 kbps; Variable Bitrate's top band, 96k-112k, is the alternative if you would rather let the encoder vary the rate than name a number.
• You need to hit a device or upload limit: use Specific file size and enter the number, then check the result — on a long recording the encoder has plenty of room, on a short one a small target will hurt.

M4B, M4A and MP3 for Audiobooks

Common Errors and How to Fix Them

• The file shows up under Music instead of Audiobooks. The library imported it as a track. In Apple's apps, audiobooks belong to the Books app rather than Music — add the file there, and confirm the extension really is .m4b and not .m4b.m4a after downloading.
• The player forgets where you stopped. Position memory is a player feature, not a file feature. Audiobook-aware apps store the bookmark; a general music player will restart the file from zero no matter what extension it carries.
• There are no chapters. Converting one AIFF produces one continuous track. Chapter markers have to be authored, either by building the book from per-chapter files in a dedicated audiobook tool or by adding a chapter list afterwards with an MP4 utility such as MP4Box or the mp4v2 tools.
• The upload never finishes. AIFF is uncompressed: a 10-hour stereo recording at 44.1 kHz 16-bit is around 6.4 GB before conversion. Convert chapter by chapter, or trim the source into parts first with the audio cutter.
• The voice sounds thin or lispy. The bitrate is too low for the recording. Step up to 64 kbps, and check you have not also dropped Audio Sample Rate to 16000 HZ or lower, which cuts the treble that consonants need.
• An Android app refuses the .m4b. Support varies by app rather than by platform. Either use a player that handles audiobooks, or rename the file to .m4a — the bytes inside are the same MPEG-4 container either way.

When This Doesn't Work

Three jobs sit outside a format converter. Chapter markers, cover art and per-book metadata are authoring tasks: this page hands you a clean single-track M4B, and a dedicated audiobook builder or an MP4 tagging tool is what turns several of those into a chaptered book. Audible's .aax downloads are a separate, DRM-protected format — they are not accepted here and cannot be converted. And if what you actually need is one file that plays on absolutely everything, including old car head units and cheap MP3 players, MP3 remains the safer target, at the cost of the audiobook behaviour the .m4b extension unlocks.

Frequently Asked Questions

What actually makes a file an audiobook — the extension or something inside it?

Almost entirely the extension. M4B and M4A are the same MPEG-4 Part 14 container with the same AAC audio inside; the .m4b name is the convention audiobook players look for before enabling position memory, speed controls and a separate shelf. The container can additionally hold chapter markers, artwork and hyperlinks, which is what distinguishes a fully authored audiobook from a plain long track.

Will this converter create chapter markers?

No. One AIFF in produces one continuous M4B, with no chapter list. If you need chapters, either author the book from per-chapter source files in an audiobook builder, or convert here and then add a chapter track with an MP4 utility. Nothing about the file produced here prevents that — the container already supports chapters, it just has none.

What bitrate should I use, and how big will the file be?

For narration, 64 kbps mono is the quality-first answer and 32-48 kbps mono is where most commercial audiobooks live. Our encoder writes a fixed bitrate, so the size is arithmetic you can check: 64,000 ÷ 8 = 8,000 bytes per second, which is 28.8 MB per hour and about 288 MB for a 10-hour book. At the page's 128 kbps default in stereo, that same book would be roughly 576 MB.

Should I convert narration to mono?

Yes, unless the recording genuinely uses the stereo field. A single voice recorded to two channels carries the same signal twice, so Audio Channel set to MONO halves the file with no audible change. Keep stereo for dramatised productions, music beds, or interviews recorded with separated microphones.

Can I just rename an .m4a to .m4b?

Usually, yes — the container and codec are identical, so renaming is enough for most players to reclassify the file. It works in the other direction too, which is the standard workaround when an app refuses .m4b. What renaming cannot do is add chapters or artwork that were never in the file.

Does the AIFF's title and artist information carry over?

Partially at best. AIFF stores text in NAME, AUTH and ANNO chunks, while MPEG-4 keeps metadata in its own atoms, and audiobook fields such as author, narrator, series and cover art have no AIFF equivalent to come from. Plan on tagging the finished M4B in your library app or a tagging tool.

Why is my AIFF source so much larger than the finished book?

Because AIFF is uncompressed linear PCM at a fixed 176,400 bytes per second for 44.1 kHz 16-bit stereo — about 10.6 MB every minute, or 636 MB an hour. AAC at 64 kbps mono runs at 28.8 MB an hour, roughly 22 times smaller. That ratio is also why very long AIFF recordings are awkward to upload: the practical limit here is upload size and time, not anything in the encoder.

Will the M4B play on Windows and Android, or only on Apple devices?

It plays widely. VLC, foobar2000 and mpv open .m4b on any desktop, and several Android audiobook players handle it natively; the extension originated with Apple but the container is a plain ISO standard. The one place you may hit friction is a basic music player that only recognises .m4a — renaming solves it.

Are my files private when I convert them here?

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared or made public.

Need the plain music-library version of the same file instead? AIFF to M4A writes the identical AAC audio under the extension music apps expect.