Files to Merge
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M4A is Apple's standard audio format — used for iTunes purchases, Apple Music exports, Voice Memos, and recordings from any number of Apple apps. If you have an audiobook spread across multiple M4A files, or a recording you want to listen to like an audiobook with chapter navigation, this tool merges them into a single M4B with proper structure that apps like Apple Books, Audiobookshelf, and Prologue can actually navigate.
The source audio is re-encoded to your chosen quality setting, so pick a bitrate that matches or exceeds your original M4A files to keep quality loss minimal.
Drag your M4A files into the drop zone or click to browse. All selected files appear in the tracks table — drag to reorder them into the chapter sequence you want before converting.
Fill in the title and author fields so the audiobook displays correctly in your app. Add a cover image by dropping it into the cover art zone — it gets embedded in the M4B and shows up in library views. Album, year, genre, and comment fields are optional but useful for building a well-organised audiobook library.
Match the output bitrate to your source files where possible. For M4A files from iTunes or Apple Music (typically 256 kbps AAC), choose 256 kbps or higher. For voice recordings or podcasts, 64–128 kbps is plenty.
The tool merges your M4A files into one M4B, one chapter per track, with your metadata and cover art embedded. The finished file downloads directly to your device. Import it into Apple Books, Audiobookshelf, or any M4B-compatible player and chapter navigation works immediately.
For a single file, renaming sometimes works in Apple Books and a handful of other apps. But it won't merge multiple files, won't add chapter markers between tracks, and won't embed cover art. If you have more than one M4A or want proper audiobook navigation, you need to actually convert and merge — which is what this tool does.
The audio is re-encoded, so there's a small quality trade-off if you choose a lower bitrate than the source. To minimise this, match or exceed the original bitrate. For speech content, anything above 96 kbps AAC is already beyond what the human ear can distinguish. If lossless output is the priority and you only have one M4A file, the M4B to M4A reverse conversion uses a stream copy and loses nothing.
Apple Books, Audiobookshelf, Prologue, BookPlayer, and Bound all support M4B natively with full chapter navigation. VLC and most general media players can open M4B files too, though chapter support varies. On Android, Smart AudioBook Player and Voice Audiobook Player both handle M4B well.
No. Everything runs in your browser using WebAssembly. Your M4A files never leave your device at any point during conversion.
We don't impose one. The practical limit is your device's available memory. For large batches, enabling Low-RAM mode streams data to disk and prevents the tab from running out of memory mid-conversion.