LibbyRip

Userscript with ~1000 active users and an active community.

A Tampermonkey userscript that intercepts and downloads DRM-protected content from the Libby/OverDrive platforms, supporting both audiobooks (MP3) and eBooks (EPUB). This is done by hooking global functions (JSON.parse and Function.prototype.bind) and passively collecting the results.

Audiobook Pipeline

Step	Detail
URL reconstruction	Combines `BIF.objects.spool.components` paths with intercepted `odreadCmptParams` tokens
Chapter preview	Injects `<audio>` elements with live stream URLs
Bulk MP3 download	Parallel `fetch()` calls, individual blob downloads
Single MP3 export	Fetches all parts → pipes into FFmpeg.wasm for concatenation

FFmpeg.wasm Integration

A ~50MB FFmpeg.wasm bundle is loaded lazily and asynchronously to avoid page slowdown. It is used to:
- Concatenate split MP3 parts via a concat demuxer
- Embed ID3 metadata (title, artist, album)
- Embed cover art
- Inject chapter markers via FFmpeg chapter metadata format (FFMETADATA1)

eBook Pipeline

Step	Detail
Content extraction	Forces all spine components to load via `_loadContent()`, then polls until complete
Decryption	Uses the captured `.bind()` argument (decryption function) to decrypt each chapter's HTML
XHTML normalization	Parses HTML with `DOMParser`, lowercases all tags, adds EPUB namespaces, rewrites asset `src` paths, and re-serializes with `XMLSerializer`
Asset gathering	Scrapes `<img>`, `<image>`, and `<link>` tags from chapter iframes to build an asset manifest, then fetches each
EPUB assembly	Programmatically generates `content.opf` (OPF package), `toc.ncx` (NCX navigation), `META-INF/container.xml`, and `mimetype` using `createDocument`/`createElementNS`

Download / Packaging

client-zip (unpkg.com/client-zip@2.5.0) — streaming ZIP generation in the browser, used for both the audiobook chapter dump and EPUB packaging
File System Access API (showSaveFilePicker) — used for streaming ZIP/EPUB directly to disk, bypassing the need to buffer the entire file in memory
Blob URL fallback — for browsers lacking File System Access API support, the ZIP is buffered into a Blob and downloaded via a synthetic <a> click
client-zip is fetched in the extension context (where CSP does not apply) and injected into the page world via a promise-based handshake (__libregrabClientZipReady)

Technologies & APIs Referenced

Tampermonkey / Greasemonkey userscript API
FFmpeg.wasm (custom bundled build)
client-zip v2.5.0
File System Access API (showSaveFilePicker, createWritable, pipeTo)
Web Crypto / crypto.randomUUID()
DOMParser / XMLSerializer
URL API
Blob / Object URLs
fetch API
setInterval polling
DOM injection via <script> tag serialization