Indexing of media sources available to media composition applications, such as video editing applications and digital audio workstations, is extended to sources of an arbitrary type, including non-file type sources. Examples of such sources include devices using baseband video and audio protocols, network ports and physical devices connected via USB, Thunderbolt, etc. The sources are discovered and indexed even when not previously known to the application with the result that any available bitstream becomes available to the application. Applications access the sources via feeders, which are addressable portals through which media essence is received. The indexing methods involve the instantiation of a hierarchy of plug-in software modules by a format-handling subsystem of the application or by a media indexing service servicing one or more applications.