Audio objects can be file backed and support out of core processing. How can I test if an Audio object is file backed and programmatically extract the file path?
This information is displayed, but I want to get it programmatically.
Note that Audio objects are atomic so First[au] doesn't work. I can convert to a non-atomic form in several ways, but I consider this a nasty hack.

AudioInformation[au], but can be queried explicitly, e.g.AudioInformation[au, "AudioID"]. – Szabolcs Oct 07 '16 at 15:18