Free online FB2 to AAC converter

An FB2 ebook contains structured text, not recorded sound, so creating an AAC file requires text-to-speech (TTS), not ordinary audio transcoding. This is useful when a phone, car player, or audio workflow accepts AAC but cannot read ebooks.

What the FB2 format is

FB2 (FictionBook 2) is an XML-based ebook format that stores a book’s text and structure, including chapters, titles, and metadata. It is used for digital books, especially fiction, and can be opened or created with ebook software such as Calibre and FBReader. An FB2 file contains no narration track.

What the AAC format is

AAC (Advanced Audio Coding) is a lossy audio codec used for spoken audio, music, and streaming. AAC audio is commonly stored in an .m4a container; some devices also accept raw AAC files with the .aac extension. To make an AAC audiobook from FB2, TTS first turns the book’s text into speech, then an encoder saves that speech as AAC.

How to convert FB2 to AAC

Online on 101convert.com

1. Open the FB2-to-AAC converter page on 101convert.com and upload an FB2 file, or add several files for batch conversion. The page shows the per-file size limit.
2. Before converting, select the voice language and reading speed.
3. Start the conversion, then download the resulting audio file.

Offline with desktop software

Calibre, Piper, and FFmpeg provide an offline workflow on Windows, macOS, and Linux. Calibre extracts the book text, Piper synthesizes speech, and FFmpeg encodes it as AAC. Install Calibre and FFmpeg, install Piper, and download a Piper voice model that matches the book’s language. Then run these commands in a terminal:

1. Convert the FB2 book to plain text with Calibre: ebook-convert "book.fb2" "book.txt".
2. Synthesize the text using the downloaded voice model: piper --model "en_US-lessac-medium.onnx" --output_file "book.wav" < "book.txt". Replace the model filename with the voice model you installed.
3. Encode the WAV speech as mono AAC in an M4A container: ffmpeg -i "book.wav" -ac 1 -c:a aac -b:a 96k "book.m4a".

For a long book, process it chapter by chapter if you want separate audio files and chapter boundaries.

Quality and compatibility

This conversion creates synthetic narration; it does not preserve an author’s recorded performance, and pronunciation depends on the selected voice and TTS engine. AAC bitrate affects compression artifacts, not pronunciation. An M4A file is often accepted by players that support AAC, but check the target device’s required container and extension.