AAC to M4B Converter
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Supports: AAC
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Need help?How to Convert AAC to M4B
- Upload Your AAC File — Click "Choose Files" or drag and drop your AAC audio file. Only .aac files are accepted.
- Set Audio Quality — Under File Compression, choose from: Quality Preset (Highest through Lowest), File Size Percentage (1-100% slider), Specific File Size (MB/KB), Custom Bitrate (enter any value in kbps), Constant Bitrate (32-384 kbps presets), or Variable Bitrate.
- Adjust Audio Settings (Optional) — Under Audio Codec, the default is AAC. Set Audio Channel to Original, Mono, or Stereo. Change Audio Sample Rate from 8000 Hz through 48000 Hz.
- Trim (Optional) — Under Trim, set a Start Time and Duration in seconds or HH:MM:SS.sss format.
- Convert & Download — Click "Convert" and download your M4B file.
Why Convert AAC to M4B?
M4B (MPEG-4 Audio Book) is Apple's audiobook format. It is essentially an M4A file with a different extension that tells media players to enable audiobook features: chapter markers, bookmarking (resume playback from where you stopped), and metadata for title, author, and narrator. Converting AAC to M4B is useful for creating audiobook files that remember your playback position, organizing spoken-word content in iTunes/Apple Books with proper audiobook metadata, enabling chapter navigation in long audio recordings, and preparing podcast episodes or lectures for audiobook-style playback.
AAC vs M4B Comparison
| Feature | AAC | M4B (Audiobook) |
|---|---|---|
| Audio codec | AAC | AAC (same codec) |
| Container | Raw AAC stream | MPEG-4 (audiobook) |
| Bookmarking | No | Yes (resume playback) |
| Chapter markers | No | Yes |
| iTunes category | Music | Audiobooks |
| Apple Books support | No | Yes (native) |
| Best for | Music, general audio | Audiobooks, podcasts, lectures |
Recommended Bitrates for Audiobooks
| Bitrate | Quality | Best For |
|---|---|---|
| 32 kbps | Acceptable | Single narrator, voice-only |
| 64 kbps | Good | Audiobooks (standard) |
| 96 kbps | High | Audiobooks with music/effects |
| 128 kbps | Very High | Full production audiobooks |
What is the difference between M4B and M4A?
M4B and M4A use the same AAC codec and MPEG-4 container. The only difference is the file extension — M4B tells media players to enable audiobook features (bookmarking, chapter support). iTunes automatically categorizes M4B files under Audiobooks instead of Music.
What bitrate should I use for audiobooks?
64 kbps is the standard for spoken-word audiobooks — it produces clear voice quality at roughly 0.5 MB per minute. Use 32 kbps for maximum compression (acceptable for single-narrator content) or 96-128 kbps if the audiobook includes music or sound effects.
Can I trim the audio during conversion?
Yes. Under Trim, switch to "Trim" and enter a Start Time and Duration. This extracts a specific segment — useful for splitting a long AAC recording into individual chapters.
Does M4B work on Android?
Android does not natively support M4B bookmarking. However, apps like Smart AudioBook Player, Listen Audiobook Player, and VLC can play M4B files with chapter and bookmark support on Android.
Can I merge multiple AAC files into one M4B?
Upload multiple AAC files and they will be processed individually. For merging multiple files into a single chaptered M4B, you would need to combine the AAC files first, then convert the combined file to M4B.