Specifies which of the Media Cache Sources that are configured on the system can be
accessed by a VOD edge application. The wildcard (*) character means that all Media Cache
sources configured on the system can be accessed by the application. Selected Media Cache
sources can be specified as a comma-separated list. Media Cache Sources are HTTP-based
servers and network-attached file systems that provide file-based content to the Media
Cache system for re-streaming. For example, a VOD application running on an Amazon EC2
instance could include amazons3 and/or dvrorigin Media Cache Sources.