Architecture and concepts

The overall architecture of Mopidy is organized around multiple frontends and backends. The frontends use the core API. The core actor makes multiple backends work as one. The backends connect to various music sources. Both the core actor and the backends use the audio actor to play audio and control audio volume.

digraph overall_architecture {
"Multiple frontends" -> Core
Core -> "Multiple backends"
Core -> Audio
"Multiple backends" -> Audio
}

Frontends

Frontends expose Mopidy to the external world. They can implement servers for protocols like MPD and MPRIS, and they can be used to update other services when something happens in Mopidy, like the Last.fm scrobbler frontend does. See Frontend API for more details.

digraph frontend_architecture {
"MPD\nfrontend" -> Core
"MPRIS\nfrontend" -> Core
"Last.fm\nfrontend" -> Core
}

Core

The core is organized as a set of controllers with responsiblity for separate sets of functionality.

The core is the single actor that the frontends send their requests to. For every request from a frontend it calls out to one or more backends which does the real work, and when the backends respond, the core actor is responsible for combining the responses into a single response to the requesting frontend.

The core actor also keeps track of the tracklist, since it doesn’t belong to a specific backend.

See Core API for more details.

digraph core_architecture {
Core -> "Tracklist\ncontroller"
Core -> "Library\ncontroller"
Core -> "Playback\ncontroller"
Core -> "Playlists\ncontroller"

"Library\ncontroller" -> "Local backend"
"Library\ncontroller" -> "Spotify backend"

"Playback\ncontroller" -> "Local backend"
"Playback\ncontroller" -> "Spotify backend"
"Playback\ncontroller" -> Audio

"Playlists\ncontroller" -> "Local backend"
"Playlists\ncontroller" -> "Spotify backend"
}

Backends

The backends are organized as a set of providers with responsiblity for separate sets of functionality, similar to the core actor.

Anything specific to i.e. Spotify integration or local storage is contained in the backends. To integrate with new music sources, you just add a new backend. See Backend API for more details.

digraph backend_architecture {
"Local backend" -> "Local\nlibrary\nprovider" -> "Local disk"
"Local backend" -> "Local\nplayback\nprovider" -> "Local disk"
"Local backend" -> "Local\nplaylists\nprovider" -> "Local disk"
"Local\nplayback\nprovider" -> Audio

"Spotify backend" -> "Spotify\nlibrary\nprovider" -> "Spotify service"
"Spotify backend" -> "Spotify\nplayback\nprovider" -> "Spotify service"
"Spotify backend" -> "Spotify\nplaylists\nprovider" -> "Spotify service"
"Spotify\nplayback\nprovider" -> Audio
}

Audio

The audio actor is a thin wrapper around the parts of the GStreamer library we use. In addition to playback, it’s responsible for volume control through both GStreamer’s own volume mixers, and mixers we’ve created ourselves. If you implement an advanced backend, you may need to implement your own playback provider using the Audio API.