WMA to M4B Converter

How to Convert WMA to M4B Online

1. Upload Your WMA Files: Drag and drop or click "+ Add Files" to load one or many .wma tracks. Batch upload is supported, which matters when an audiobook arrives as 40+ chapter files from an older Windows Media library.
2. Pick a Quality Preset: The default is Highest. For spoken-word audiobooks, Medium or Low (typically around 64 kbps AAC) is usually indistinguishable from the source and shrinks the file ~50%. Switch to Custom Bitrate to type a value like 96k, or use Constant Bitrate with a fixed preset (64, 96, 128, 160, 192 kbps).
3. Set Channels, Sample Rate, and Trim (Optional): Leave Audio Channel on Original for narration; force Mono to halve the size for single-voice content. Audio Sample Rate can stay at Original or drop to 22050 Hz for voice. Use Trim to clip dead air at the start or chop a 10-hour file into chapter-sized pieces.
4. Convert and Download: Click Convert. Files are remuxed into an MP4 container with the .m4b extension and AAC audio, then delivered to your browser — no sign-up, no watermark, no email.

Why Convert WMA to M4B?

Windows Media Audio was released in August 1999 and shipped as the default codec in Windows Media Player throughout the Windows XP and Vista era, so a lot of long-form content — ripped audiobooks, lecture series, recorded sermons, dictation — still exists as .wma. The trouble is that WMA has no native playback on iOS, macOS, or Android, and Apple Books, Plex, Audiobookshelf, and BookPlayer all expect M4B for proper audiobook treatment (chapter markers, position bookmarks, the right library shelf). Converting moves your library from a Microsoft-only silo into the cross-platform audiobook ecosystem.

• Apple Books "Audiobooks" shelf — Files dragged into the macOS Books app are filed as audiobooks only when they carry the .m4b extension; the same AAC audio with an .m4a extension lands in the Music app instead.
• Resume-position bookmarking — M4B is the same MP4 container as M4A, but players (Apple Books, Plex, Audiobookshelf, BookPlayer, Prologue) treat .m4b as long-form and persist your last position automatically; WMA has no equivalent convention.
• iPhone and iPad playback without sideloaded codecs — iOS has never shipped WMA decoders. Converting to M4B lets the file play natively in Apple Books, VLC, or any AAC-capable app — no Flip4Mac, no third-party codec pack.
• Plex and Audiobookshelf libraries — Both home-media servers detect .m4b as audiobook content and parse embedded chapter metadata; WMA shows up as generic "music" or gets skipped.
• Smaller files at speech-friendly bitrates — A 10-hour audiobook re-encoded at 64 kbps AAC lands around 275 MB; the same content as 128 kbps WMA is roughly double, and AAC sounds cleaner at the same bitrate.
• Future-proofing a deprecated codec — Microsoft has not added WMA features since the late 2000s, and Windows 11's Media Player still plays WMA but no longer encourages it. AAC inside MP4 is an ISO standard with decoders everywhere.

WMA vs M4B — Format Comparison

Bitrate Guide for Spoken-Word Audio

Most commercial audiobooks ship at 64 kbps mono or 64 kbps stereo AAC — there's rarely an audible benefit to going higher for narration.

Frequently Asked Questions

Will my chapter markers from the original WMA carry over to the M4B?

In most cases, no. Chapter markers were never a standard part of WMA — most .wma audiobooks rely on separate per-chapter files instead of in-file markers. If your source already had ASF script commands, they don't survive the transcode. To add real chapter atoms to the output, you generally need a dedicated audiobook tool (Audiobook Builder on macOS, AudioBookConverter on Windows, or ffmpeg with a metadata file) after the format conversion is done.

Can I merge several WMA chapter files into a single M4B?

This page converts each input file 1:1, so a 40-chapter WMA set becomes 40 M4B files. To combine them into a single audiobook with chapter breaks, do the WMA-to-M4B conversion first and then concatenate the M4B files using a tool that preserves AAC streams (ffmpeg's concat demuxer is the usual choice, since it stitches without re-encoding).

Will the M4B play in the Audible app?

No. The Audible app on iOS, Android, and the web only plays Audible-issued .aax / .aa files tied to an Audible account; it has no import for outside audio. For self-converted M4B files, use Apple Books, Plex, Audiobookshelf, BookPlayer, Prologue, Voice Audiobook Player, or any general AAC-capable player.

Is converting WMA Lossless to M4B AAC really a downgrade?

Technically yes — you're going from a lossless codec to a lossy one — but for spoken-word content the difference is inaudible, and the file shrinks roughly 5-10x. If the source is music and you want bit-exact output, convert your WMA Lossless to FLAC instead (see WMA to FLAC); M4B is the wrong target for archival music.

Why does my converted M4B show up under "Music" instead of "Audiobooks" in Apple Books?

The .m4b extension is the signal that triggers the audiobook shelf. If a player or sync tool renamed the file to .m4a, drop it back to .m4b. On older iTunes builds you also had to right-click the track and select "Get Info → Options → Media Kind: Audiobook" manually; modern Apple Books on macOS 13+ handles this from the extension alone.

What's the difference between converting to M4B vs M4A?

The audio is identical — both wrap AAC inside an MP4 container. The extension is the only difference, and it changes how players treat the file: .m4a is filed as music, .m4b is filed as an audiobook and gets resume-position bookmarking. If you don't need audiobook behaviour, WMA to M4A produces the same audio with the music-track extension.

Can I batch-convert a whole folder of WMA audiobooks at once?

Yes — drop the entire folder's worth of files into the upload area in one go. Each file is converted with the same settings, which is convenient when you've ripped a 30-disc audiobook set and every chapter needs the same 64 kbps mono treatment.

Does the conversion preserve metadata like title, author, and album art?

Title, artist (often used for "author"), album (often used for "book title"), and embedded cover art from the WMA ASF tags are mapped to the equivalent MP4 atoms during transcode. Fields specific to Windows Media (WM/Composer, WM/Genre subgenre, etc.) may not have a direct iTunes-MP4 equivalent and can be dropped. If you need pristine audiobook metadata, expect to clean it up afterwards in a tag editor like Kid3 or Mp3tag.

Is there a file size limit?

There is a per-file limit shown on the upload screen for the free tier; long audiobooks (5+ hours at high bitrate) sometimes exceed it. The workaround is to trim the file into halves first (use Audio Cutter or the in-page Trim control), convert each piece, then re-join. Most spoken-word WMA files at typical bitrates stay well under any per-file cap.