"instantiationPhysical is used to identify the format of a particular instantiation as it exists in a physical form that occupies physical space (e.g. a tape on a shelf). This includes physical digital media, such as a DV tape, audio CD, or authored DVD, as well as analog media.
Best practice: PBCore provides a controlled vocabulary for media objects, though any controlled vocabulary can be used so long as it is referenced. For digital storage carriers that contain file-based media, such as data CDs, LTO tapes or hard drives, use instantiationDigital to convey the mime type of the file instead of describing the carrier."