M4B to FLAC Converter

Convert M4B to FLAC online for free. Fast, secure, and high-quality conversion with no sign-up or software required.

Free to useNo file stored beyond 1 hourEncrypted over TLS 1.2/1.3No watermarks

or drag and drop files here

Maximum file size is 1GB

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How it works

Three steps to your converted file

Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.

Upload your file

Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.

Choose an output format

Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.

Convert & download

Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.

What is an M4B file?

M4B is an MPEG-4 audio container file specifically structured for audiobooks and podcasts, functionally identical to M4A but supporting digital rights management (DRM) via Apple's FairPlay protection. Its distinguishing feature is the support for bookmarking metadata, allowing players to resume playback from the last stopping point, and chapter markers for navigation. The format typically utilizes AAC encoding within the ISO/IEC 14496-12 base media file format.

How to open an M4B file

Apple Books (formerly iTunes) is the primary software for opening DRM-protected M4B files on macOS and iOS. Unprotected M4B files can be played on VLC Media Player, Windows Media Player, and specialized audiobook readers like Smart Audiobook Player for Android. Attempting to play DRM-encrypted files on unauthorized non-Apple software will result in decryption errors.

M4B Technical Info

Full Name: MPEG-4 Audiobook
Developed By: Apple Inc.
Initial Release: 2003
MIME Type: audio/m4b

What is a FLAC file?

The Free Lossless Audio Codec (FLAC) is an open-source audio coding format developed by the Xiph.Org Foundation that compresses digital audio without any loss of data (bit-perfect preservation). It employs linear prediction and Rice coding (Golomb-Rice) rather than the perceptual psychoacoustic modeling used in MP3 or AAC. The format structure consists of the 'fLaC' stream marker, metadata blocks (Streaminfo, Vorbis comments for tags, Seekpoints), and audio frames, typically achieving compression ratios of 50-70% compared to raw PCM WAV files.

How to open a FLAC file

FLAC enjoys extensive native support on modern platforms, including Windows 10/11, Android, and macOS (starting with macOS High Sierra). For older systems or advanced playback control, software such as Foobar2000 (Windows) or Vox (macOS) is recommended. The VLC media player is a universal solution for all operating systems, handling FLAC streams and associated metadata seamlessly.

FLAC Technical Info

Full Name: Free Lossless Audio Codec
Developed By: Josh Coalson / Xiph.Org Foundation
Initial Release: 2001
MIME Type: audio/flac

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Why RunConvert

The fastest way to convert any file

Purpose-built for speed, privacy, and breadth of format support.

Convert M4B to FLAC in seconds

Every M4B to FLAC conversion runs on our servers, so your device stays fast and the output quality stays intact.

Fast, cloud-powered

No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.

Secure & private

Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.

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Developer API

Convert M4B to FLAC via API

Automate M4B to FLAC conversions in three steps: create a job, upload your file, then poll for the result.

# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tag": "m4b-to-flac",
    "tasks": {
      "upload-file": {
        "operation": "import/upload"
      },
      "convert": {
        "operation": "convert",
        "input": "upload-file",
        "output_format": "flac"
      },
      "export-result": {
        "operation": "export/url",
        "input": "convert"
      }
    }
  }'

# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.m4b

# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
  -H "Authorization: Bearer YOUR_API_KEY"

Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.