MP3 file

[DrO]

in general no, as neralex has noted...

but if you are using the current 2.x DNAS (2.4.7 at time of reply) and set a backup file on a stream mountpoint, then it's possible to have that provided when there is no source. the downside of that is it'll loop repeatedly unless you try setting the backup loop option to 1 and ensure you set an applicable streampath.

note: that is somewhat experimental when setting the loop count to 1 and so may not work all that well + it's a bit convoluted to setup + it's not really been tested + it strips out all metadata from any files (as this is a manipulation of the streaming-oriented handling for backup files vs stream integration).