Glossary & core concepts

New to the OVOS media stack? Read this once and the rest of the docs click into place. It defines every acronym and, more importantly, the handful of concepts people most often mix up.

The 30-second mental model

You say "play some jazz". Four kinds of plugin cooperate to make sound come out:

1. a provider finds candidate tracks (searches catalogs),
2. ovos-media (this daemon) decides what to play and tracks what's playing,
3. a backend plays it (hands the URL to VLC, mpv, a Chromecast, …),
4. an extractor resolves a deferred link (e.g. a youtube//… placeholder) into a real stream URL at the moment of playback.

Each is a separate, swappable plugin. That separation is the whole design.

The four plugin roles (don't mix these up)

Role	Entry-point group	Answers the question	Example
MediaProvider	opm.media.provider	"where can I find this?"	youtube, bandcamp, tunein
Playback backend	opm.media.audio / .video / .web	"how do I play this?"	vlc, mpv, chromecast
Stream extractor	opm.ocp.extractor	"what's the real URL?"	youtube, m3u, rss
MPRIS plugin	(see mpris.md)	"what are other apps playing?"	the mpris watcher

Provider vs. backend is the #1 point of confusion. A provider is a search engine (returns a list of results). A backend is a player (turns one result into sound/video). "youtube" exists as both a provider (searches YouTube) and is played by a backend (vlc/mpv) after the youtube extractor resolves the stream.

Terms

Term	Meaning
OCP	OpenVoiceOS Common Play, the framework/protocol for voice-driven media ("play X"). The OCP pipeline is the ovos-core stage that classifies a "play …" utterance and asks providers to search.
ovos-media	This daemon, the OCP-native player. Manages the queue, now-playing state, and playback backends. Runs alongside ovos-audio (which does TTS).
ovos-audio	The separate daemon that handles TTS (and the legacy audio service). Not a replacement for ovos-media; they coexist.
OPM	ovos-plugin-manager, discovers plugins via Python entry points. The opm.* groups above are OPM groups.
Signals	A mediavocab.Signals object, the parsed request a provider receives: title, artist, medium (a MediaType), content_genres, …
Release	A mediavocab.Release, a typed, playable catalog entry a provider returns. The shared currency between search, playback, and MPRIS metadata.
Work	The creative work a Release manifests (Release.work.title, .media_type, …).
MediaType	What kind of content it is (music, movie, podcast, radio, audiobook, …).
PlaybackType	What surface renders it: AUDIO, VIDEO, WEBVIEW, MPRIS. Determines which backend group plays it.
PlayerState	The player's transport state: PLAYING, PAUSED, STOPPED. (A paused track is still PLAYING_* at the track level, pause lives only in PlayerState.)
MediaState	The media's lifecycle: buffering, loaded, end-of-media, invalid, …
now_playing	The single currently-playing Release the daemon tracks (NowPlaying), mirrored to the bus and MPRIS.
SEI	Stream Extractor Identifier, the prefix in a deferred URI (youtube//…, rss//…) that names which extractor resolves it.
deferred / deferred URI	A Release.uri of the form "{sei}//{realuri}" resolved at playback time by an extractor, not at search time.
MPRIS	The freedesktop D-Bus standard (org.mpris.MediaPlayer2) other Linux media apps speak. ovos-media both exposes itself over it and reacts to other players. See mpris.md.
MessageBus	The OVOS WebSocket event bus. Everything ovos-media does is observable/driveable as ovos.common_play.* messages.
Session	A MessageBus conversation scope identified by session_id. The special id "default" means the local/single device. ovos-media only acts on the "default" session (a HiveMind server ignores satellite sessions); see Sessions.
validate_source	The media config flag (default true) that enables the default-session filter. Set false on a satellite that is not getting default-NAT'd sessions so it acts on every session. See Sessions.
OCP search skill (legacy)	The old way to provide searchable catalog media (OVOSCommonPlaybackSkill + @ocp_search), now replaced by MediaProviders. See ocp-skills.md.
OCP game / interactive skill	A skill that is the experience (interactive fiction, quizzes, "play a game") rather than a searchable catalog. These stay as skills, they are not deprecated and have no MediaProvider equivalent. See ocp-skills.md.

Which doc do I want?

• I just want it running → Getting started
• I want to tune it → Configuration
• I'm writing a search plugin → Media providers
• I'm writing a player plugin → Backends
• I want desktop / playerctl control → MPRIS
• I want to understand the internals → Architecture
• I'm running HiveMind satellites / a server → Sessions
• I'm coming from the old stack → Migration guide

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