Free online W64 to M4B converter

Source format: W64

W64 is an audio container format developed by Sonic Foundry/Sony as an extension of the standard WAV format. It is designed to store very large audio files and supports 64-bit file sizes, which makes it useful when recordings exceed the 4 GB limit of classic WAV. W64 is most often used in professional audio production, long-form recordings, archiving, and editing workflows where uncompressed or high-quality PCM audio must be preserved.

Target format: M4B

M4B is an AAC-based audiobook container in the MPEG-4 family. It is commonly used by audiobook apps and portable players because it can store chapter markers, metadata, and often bookmarks. Compared with uncompressed audio formats, M4B files are usually much smaller while still offering good sound quality. It is a strong choice for audiobooks, lectures, podcasts, and spoken-word content.

How to perform the conversion

The most reliable way to convert W64 to M4B is with FFmpeg, which can read W64 audio and encode it into an M4B-compatible AAC file. This is especially useful if you want precise control over bitrate, chapters, and metadata.

1. Install FFmpeg on your computer.
2. Open a terminal or command prompt in the folder containing your W64 file.
3. Run a command such as ffmpeg -i input.w64 -c:a aac -b:a 128k output.m4b.
4. If you want higher spoken-word quality, you can use a higher bitrate such as 192k or 256k.
5. If your source contains chapter data or metadata, you may need to copy or recreate it separately, because not all W64 files include audiobook-style chapter structure.

If you prefer a graphical workflow, you can first open the W64 file in an audio editor such as Audacity or Adobe Audition, then export to AAC-compatible audio and package it as M4B if the software supports that container. In many cases, FFmpeg is still the simplest and most dependable option. You can also convert the file on 101convert.com for free, without installing any software.

Quality, compatibility, and limitations

W64 is typically uncompressed PCM audio, so the conversion to M4B is a lossy transcode if AAC is used. That means some audio detail is discarded during encoding, although this is usually acceptable for spoken content. For music or archival material, keep the original W64 file as a master copy.

M4B compatibility is best with audiobook players and Apple devices, but support can vary across media players. If chapter markers are important, verify that your target app recognizes them. Also note that M4B is not ideal for editing; it is mainly a distribution and playback format. If your W64 file is very large, the conversion may take some time and require enough free disk space for both the source and the encoded output.