The DPLA Exchange can, or will soon, deliver audiobooks as Readium audiobook manifests. These manifests will be of two types:

• Open-access audiobooks served as-is without obfuscation or encryption
• Commercially licensed audiobooks, for which access to individual audio files is mediated through an access restriction API. The access restriction API is described in protection.md

The DPLA Exchange's responsibility is to distinguish between these two types of audiobooks in the ODL feeds it serves to library middleware.

The circulation manager's responsibility is to understand this distinction and to preserve it in the OPDS feeds that tell a client what books are available.

The client's responsibility is to negotiate the access restriction API when necessary, using a secret key.

Ahead of time, NYPL and DPLA will establish this secret key. NYPL will compile the key into the mobile app called "SimplyE".