OPDS feed shows two identical "Add epub" buttons for the same book (readaloud vs plain EPUB indistinguishable)

Adding a book from the Storyteller OPDS feed in an OPDS client gives three buttons labeled "Add epub", "Add epub", "Add audiobook" for a book that has all three formats. The feed emits acquisition links with ?format=readaloud, ?format=ebook and ?format=audiobook-rpf, but the first two both carry type="application/epub+zip".

Resolution: This is a limitation of EPUB and OPDS 1.x, not a Storyteller bug: application/epub+zip is the only media type available, and it carries no way to say whether the publication is reflowable, fixed-layout, or contains media overlays, so a client presented with two acquisition links cannot tell the readaloud from the plain EPUB. The format query parameter in the href is Storyteller's own, not something OPDS clients interpret. Storyteller has since added a server setting that controls which formats are published in the OPDS feed, so you can suppress the readaloud (common when consuming the feed on a device that cannot use it, and it is by far the biggest file) or suppress the plain EPUB, whichever you do not want to see. Longer-term fixes live on the client and spec side — link titles, size information, and dedicated properties in OPDS 2.0 — so if the duplicate buttons bother you, report it to your OPDS reader's maintainers as well.