WMV to M4B Converter

How to Convert WMV to M4B Online

1. Upload Your WMV File: Drag and drop your .wmv file (or several at once) onto the page, or click "+ Add Files" to browse. Conversion runs on our servers — no account, no watermark, and the file is removed from our server after a short retention window.
2. Set the Bitrate under File Compression: Open Advanced Options. File Compression opens on Quality Preset, whose dropdown preselects "Very High (Recommended)" — that is what is sent if you leave it alone — but it is the least predictable control on the page. Use Constant Bitrate to dial in a target instead (the dropdown opens at 128 kbps and the list runs up to 384 kbps) — 64 kbps AAC mono is the standard for audiobook narration and yields about 29 MB per hour of audio. Variable Bitrate offers five AAC bands (96k-112k down to 20k-32k), and Custom Bitrate accepts an exact typed figure.
3. Set Channels, Sample Rate, and Trim (Optional): Change Audio Channel to Mono for voice-only material (halves the file vs Stereo at the same bitrate), set Audio Sample Rate to 44100 Hz or 24000 Hz for speech, and use Trim if you want to drop intros, outros, or a single chapter from the WMV.
4. Convert and Download: Click "Convert," wait for the queue, and download your .m4b. Drop it into Apple Books, Voice for Android, or any audiobook app and it will be filed under audiobooks with resume-playback enabled.

Why Convert WMV to M4B?

WMV is a Microsoft container (ASF wrapper) that typically pairs Windows Media Video with a Windows Media Audio (WMA) track. M4B is the same MPEG-4 / AAC container as M4A but with the .m4b extension that signals "audiobook" to media players — Apple Books, the macOS Music app, and most third-party audiobook players key off that extension to enable resume-on-reopen and to shelve the file with books instead of music. Pulling the audio out of an old WMV into M4B is the usual path for lecture archives, sermons, conference recordings, and personal narrations that started life on a Windows camcorder or screen recorder.

• Lecture and seminar archives — A 90-minute lecture captured as WMV at 1080p can be 1.5–2 GB; the same audio at 64 kbps AAC mono is roughly 43 MB, which fits comfortably in iCloud's free 5 GB tier and streams fine over cellular.
• Sermons and conference talks — Many churches still record to WMV via Windows Movie Maker or older capture cards; M4B preserves chapter markers if you add them, so a multi-part sermon series becomes a single skip-friendly file.
• Self-published audiobooks — Authors recording into Audacity then mixing video for YouTube often end up with a WMV master; M4B is the right deliverable for Apple Books distribution and for ACX-adjacent personal use (ACX itself requires MP3, but M4B is the playback-side equivalent).
• Language-learning recordings — Long-form Pimsleur-style courses benefit from M4B's bookmark/resume behaviour; M4A would land them in the Music library and lose your position.
• Audio research clips for transcription — Whisper, Otter, and macOS dictation all accept M4B; converting from WMV at 24000 Hz or 16000 Hz mono is enough for accurate speech-to-text and keeps uploads small.
• iPod, iPhone, and CarPlay playback — WMV will not play natively on any Apple device without VLC or a transcoder; M4B is universally supported across the Apple ecosystem since iTunes 4.9 (2005).

WMV vs M4B — Format Comparison

AAC Bitrate Quick Guide for Audiobooks

Apple's own guidance for audiobook authoring sits at 64–128 kbps AAC; Audible's downloadable AAX files are encoded at 64 kbps. Going above 128 kbps for pure speech adds size without audible improvement.

Frequently Asked Questions

Will my WMV's chapter markers carry over to the M4B?

Usually not. Standard WMV/ASF authoring tools (Windows Movie Maker, OBS, most camcorder firmware) do not write chapter atoms into the file, so there is nothing to carry across. If you need chapters in the M4B, the typical workflow is: convert to M4B here, then add chapters with a free chapter editor such as MP3tag or mp4chaps (part of mp4v2). Apple Books and Voice will then display them in the chapter list.

What bitrate should I pick for a multi-hour audiobook?

For solo narration, 64 kbps AAC mono is the sweet spot — it matches Audible's own AAX encoding and produces ~29 MB per hour. A 20-hour audiobook lands near 580 MB. If your source has background music or two narrators, step up to 96 kbps mono or 128 kbps stereo; anything above that wastes space on speech-dominant material.

Why is the output much smaller than my WMV file?

You are dropping the video stream entirely. A typical 1080p WMV at 5–8 Mbps spends most of its bytes on pixels; only ~5% of the file is the WMA audio track. Re-encoding that audio to 64 kbps AAC removes another factor of 2–3, so a 1.5 GB lecture WMV commonly converts to a 40–60 MB M4B with the speech intact.

Will the M4B play on Apple Books, iPhone, and CarPlay?

Yes. iTunes, the macOS Music app, Apple Books, iOS, iPadOS, and CarPlay have recognised .m4b as the audiobook variant of MP4/AAC since iTunes 4.9 in 2005. On import, the file is shelved under "Audiobooks" rather than "Music," and Books will resume from your last position when you reopen it.

What is the difference between M4B and M4A?

The bytes inside are essentially the same — both are AAC audio in an MPEG-4 container — but the extension tells the player how to treat the file. .m4b triggers audiobook behaviour: resume-on-reopen, no shuffle by default, and filing under Books/Audiobooks. .m4a lands the file in the Music library and most players will not remember your position. Rename a music .m4a to .m4b and most apps will start treating it as an audiobook.

Can I trim or split a long WMV before converting?

Yes. The Trim control under Advanced Options lets you set a start time and duration before conversion, so you can drop a leader, isolate a single sermon from a 4-hour service recording, or carve a multi-hour lecture into manageable parts. For more flexible cutting after conversion, the Audio Cutter tool accepts M4B and works the same way.

Will the WMA codec cause any quality loss when transcoded to AAC?

Some, because both WMA and AAC are lossy. The pragmatic answer for speech: it is inaudible at 64 kbps AAC and above. WMA Voice in particular targets 5–20 kbps and is already noticeably compressed, so re-encoding at 64 kbps AAC gives you headroom rather than degradation. For music-heavy WMVs originally encoded at 192 kbps WMA, pick 192 kbps AAC or higher to keep the same perceptual quality.

Are there better-targeted xconvert pages for similar conversions?

Yes. If you only need a standard audio file (not the audiobook extension), use WMV to MP3 for maximum device compatibility. If your source is already audio-only, WMA to M4B skips the video-stream-drop step, and MP3 to M4B is the right page for stitching narration tracks into a single audiobook.

Does the file leave my computer?

The file is uploaded to xconvert's servers so the conversion can run with full ffmpeg-quality codec support; we delete it shortly after the download link expires. There is no sign-up, no watermark, and the resulting M4B contains no DRM — unlike Audible's AAX, which is encrypted to your account.