Which audiobook formats play on iPhone with Audiobookshelf

MP3 files, and M4B or M4A files with AAC audio inside, are formats the iPhone plays on its own. They’re the safe choice for any Audiobookshelf app, streamed or downloaded.

Other formats can work when you stream, because Audiobookshelf converts them on the fly. They can fail once downloaded, because a download is always the original file and your iPhone has to play it as it is.

How Audiobookshelf sends audio to your phone

When an app starts a book, it tells the server which file types it can play.

• The app can play the file - the server sends the file exactly as it is stored. This is called direct play.
• The app can’t play it - the server turns the book into a stream of short pieces while you listen. MP3 and AAC audio go into the stream as they are. The other formats in the table below are re-encoded to AAC.
• Downloads - the server hands over the original files. Nothing is converted, so the phone needs to play the format itself.

The check uses the file type, such as MP3 or M4B, not the codec inside it (the kind of audio encoding the file holds). That’s why an M4B with unusual audio inside can slip through as direct play and then not play.

Which formats can I stream or download?

Format	Streaming	Downloaded
MP3	Plays	Plays (see the note on seeking below)
M4B or M4A with AAC	Plays	Plays
M4B with MP3 audio inside	Can play without sound on iPhone	Can play without sound on iPhone
M4B with xHE-AAC (some Libation downloads)	The server has to read the file first; see the xHE-AAC page	Depends on the app and iOS
FLAC, Opus, Ogg, WMA, AIFF, WebM, CAF	Re-encoded to AAC when the server converts	Depends on what iOS can play; convert to be safe
M4B with ALAC, AC-3 or E-AC-3 (Dolby)	Re-encoded to AAC when the server converts	Depends on what iOS can play

Whether a format in the bottom two rows is converted depends on the app. If the app says it can play the file, the server sends it as it is.

Why does my M4B play without sound on iPhone?

A likely cause is MP3 audio inside the M4B file instead of AAC. The player shows the book moving along, but there’s no sound. The person who reported it saw this in Safari and in an iPhone app. Audiobookshelf contributors put it down to iOS not playing MP3 inside that kind of file, and the issue was closed as not planned.

You can check in the Audiobookshelf web page: open the book, and the audio files list shows the codec for each file. If it says mp3 for an .m4b file, re-encode it:

1. As an admin, open the book, click the edit (pencil) button and go to the Tools tab.
2. Next to Make M4B Audiobook File, click Open Manager.
3. Keep the codec on AAC. For MP3 books it starts on AAC; Copy keeps the MP3 audio and gives you the same silent file.
4. Click Start M4B Encode.

The tool backs up the original files to the server’s metadata folder first.

Why won’t AC-3 or E-AC-3 books stream?

Before v2.31.0, books with AC-3 or E-AC-3 (Dolby) audio failed when the server had to convert them, mostly in web browsers and on some Android phones. v2.31.0 fixed the conversion. Update the server if you’re on an older version.

Why does seeking jump back to the start?

One likely cause is a variable bitrate (VBR) MP3 without a proper header, so the player can’t work out where a time sits in the file. If that’s the cause, re-encoding the file fixes it. Seeking jumps back to the start walks through how to confirm it and the fix.

Which audiobook formats does SoundLeaf play?

SoundLeaf asks Audiobookshelf for the original file when it’s MP3 or M4B, M4A or MP4. For other file types, it asks for a stream, and the server converts the audio where needed.

Downloads in SoundLeaf are the original files, played by Apple’s own audio player. So if a book streams fine but won’t play after you download it, the format is the first thing to check. Converting it to M4B with AAC, as above, usually fixes that. Download the book again after converting. The downloads guide covers how SoundLeaf stores books for offline listening.