FR: Stream audiobooks from OPDS catalogs alongside ebooks (e.g. BookOrbit)

What problem would this feature solve?

I use BookOrbit to host ebooks, comics/PDFs, and audiobooks, and Readest on iPhone and Mac. I would like to browse those titles in one catalog and listen to recorded audiobooks inside Readest, without maintaining a second audiobook server or switching to the server’s web player.

BookOrbit exposes audiobook entries through OPDS, but discovering an audio entry is not the same as being able to stream it in Readest. Readest’s documented Audiobookshelf integration covers streaming through that server’s API; this request is specifically for OPDS-based audiobook playback.

Describe the solution you'd like.

Support playable audiobook entries from authenticated OPDS catalogs, reusing Readest’s existing recorded-audio player where appropriate:

• Recognize supported audio acquisition links (for example MP3 and M4B/M4A where supported by the platform) and offer a Play/Stream action.
• Start playback without first importing the whole audio file as an ebook; support seeking where the server provides HTTP range requests.
• Use the catalog’s existing authentication safely for playback requests.
• Allow ebook/comic and audiobook entries to coexist in the catalog and, ideally, on the Readest bookshelf with clear media-type indicators.
• Preserve listening position in Readest. Chapter navigation and multi-file audiobooks would be useful follow-ups where suitable metadata is available.

Writing listening progress back to BookOrbit would be a separate, optional server-specific integration; I am not assuming OPDS itself provides progress sync.

Describe workarounds you may have used to acheive the same results.

Keep Readest’s catalog limited to ebooks/comics/PDFs and use BookOrbit’s web player for audio. Audiobookshelf integration is another supported approach, but requires maintaining a separate server alongside BookOrbit.

Additional Context

A live BookOrbit 2.10.0 feed was inspected. Its MP3 entry currently uses a generic MIME type, for example (sanitized):

<link rel="http://opds-spec.org/acquisition"
      href="/api/v1/opds/123/download?fileId=456"
      type="application/octet-stream"
      title="MP3" />

Correct audio MIME types and any required streaming/manifest metadata may need changes on the BookOrbit side too. This request does not ask Readest to assume every generic binary download is audio.

Source inspection of Readest’s current OPDS page shows acquisition downloads going through the book importer, while its stream handler builds an OPDS-PSE page stream. This is a feed/source review, not a claimed end-to-end iOS audio playback test.

Related but different requests: #3025 (Audiobookshelf integration) and #5775 (web browser as a book source).

Thanks for considering this—one reading/listening app connected to one self-hosted library would be very useful.