Any thing related to Media Player Remote Interfacing Specification (MPRIS2), which is a standard D-Bus interface which aims to provide a common programmatic API for controlling media players. (Used by Unity sound indicator)
About
The Media Player Remote Interfacing Specification (MPRIS) is a standard D-Bus interface which aims to provide a common programmatic API for controlling media players.
It provides a mechanism for discovery, querying and basic playback control of compliant media players, as well as a tracklist interface which is used to add context to the active media item.
Use
It is the back end API used by Unity sound indicator to detect, query and control music/video players.