Convert MPEG-4 Audiobook (.m4b) to Advanced Audio Coding (.aac) online for free. Fast, secure audio conversion with no watermarks or registration.
Upload your .m4b file by dragging it into the upload area or clicking to browse.
Choose your output settings. The default settings work great for most files.
Click Convert and download your .aac file when it's ready.
Converting M4B to raw AAC extracts the audio bitstream from the audiobook container, stripping away chapters, bookmarks, and metadata. The result is a bare AAC (ADTS) file containing only the audio data. Since M4B internally uses AAC encoding (typically at 32-64 kbps for spoken word), this conversion can be a lossless stream copy — the same AAC frames are simply unwrapped from the M4B container into a raw ADTS stream.
Some audio processing pipelines, streaming ingest systems, and broadcast multiplexers require raw AAC elementary streams rather than containerized audio. If you need to feed audiobook audio into an HLS segmenter, MPEG-TS multiplexer, or an audio analysis tool that works at the bitstream level, extracting raw AAC from M4B is the necessary first step.
FFmpeg performs a stream copy (-c:a copy) from the M4B container to a raw .aac file in ADTS format. Since M4B stores AAC audio internally, this operation is instant and lossless — the AAC frames are extracted without re-encoding. Chapter markers, bookmark data, and iTunes metadata are discarded (raw ADTS has no metadata support). Each AAC frame in the output has a 7-byte ADTS header with sync word, profile, sample rate, and channel info.
Zero quality change when using stream copy. The AAC audio data is bit-identical to what was inside the M4B container. The only loss is metadata and chapter information.
| Device | M4B | AAC |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Native |
| iPhone/iPad | Partial | Native |
| Android | Partial | Partial |
| Linux | Partial | Partial |
| Web Browser | No |
Resolution: N/A
Bitrate: 320 kbps
OGG Vorbis preferred
Resolution: N/A
Bitrate: 256 kbps
AAC format required
Resolution: N/A
Bitrate: 128 kbps
Lossless FLAC/WAV for best quality
Resolution: N/A
Bitrate: 128 kbps
MP3 mono for spoken word
M4B to raw AAC is a demuxing operation that strips the audiobook container to expose the elementary bitstream. It is instant and lossless but discards all audiobook-specific features.
安全な転送
HTTPS暗号化アップロード
プライバシー優先
処理後にファイルを自動削除
登録不要
すぐに変換を開始
どこでも動作
あらゆるブラウザ、あらゆるデバイス
| No |
| 特徴 | M4B | AAC |
|---|---|---|
| 正式名称 | MPEG-4 Audiobook | Advanced Audio Coding |
| 拡張子 | .m4b | .aac |
| 最適な用途 | Chapter support | Superior to MP3 |