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stream_plugin.md

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Stream plugin

A stream plugin is an executable binary or script that is started by the server for a specific stream and offers playback control capabilities and provides information about the stream's state, as well as metadata for the currently playing track. The Snapcast server communicates via stdin/stdout with the plugin and sends newline delimited JSON-RPC-2.0 commands and receives responses and notifications from the plugin, as described below. In upcoming releases shared library plugins might be supported as well.
A stream is connected to a plugin with the controlscript stream source parameter, e.g.

[stream]
source = pipe:///tmp/snapfifo?name=MPD&controlscript=meta_mpd.py

If a relative path is given, Snapserver will search the script in /usr/share/snapserver/plug-ins. An example script meta_mpd.py is shipped with the server installation, that can be used with mpd stream sources.

A Stream plugin must support and handle the following requests, sent by the Snapcast server

The following notifications can be sent by the plugin to notify the server about changes. The Plugin.Stream.Ready should be fired as soon as the plugin is ready to receive commands, upon reception, the server will query the stream's properties

Requests

The following requests will be sent by the Snapserver to the stream plugin. Upon startup Snapserver will wait for the plugin's ready notification to query the supported properties. The controlling capabilities are encoded into these boolean properties: canGoNext, canGoPrevious, canPlay, canPause, canSeek, canControl. If canControl is false, the server will not send any control commands to the plugin.

Plugin.Stream.Player.Control

Used to control the player. The property canControl must be true.

{"id": 1, "jsonrpc": "2.0", "method": "Plugin.Stream.Player.Control", "params": {"command": "<command>", "params": { "<param 1>": <value 1>, "<param 2>": <value 2>}}}

Supported commands

  • play: Start playback (if canPlay is true)
    • params: none
  • pause: Stop playback (if canPause is true)
    • params: none
  • playPause: Toggle play/pause (if canPause is true)
    • params: none
  • stop: Stop playback (if canControl is true)
    • params: none
  • next: Skip to next track (if canGoNext is true)
    • params: none
  • previous: Skip to previous track (if canGoPrevious is true)
    • params: none
  • seek: Seek forward or backward in the current track (if canSeek is true)
    • params:
      • offset: [float] seek offset in seconds
  • setPosition: Set the current track position in seconds (if canSeek is true)
    • params:
      • position: [float] the new track position

Example

{"id": 1, "jsonrpc": "2.0", "method": "Plugin.Stream.Player.Control", "params": {"command": "setPosition", "params": { "position": 17.827 }}}

Expected response

Success:

{"id": 1, "jsonrpc": "2.0", "result": "ok"}

Error:

Any json-rpc 2.0 conformant error with an error message that helps the user to diagnose the error

Plugin.Stream.Player.SetProperty

Snapserver will send the SetProperty command to the plugin, if canControl is true.

{"id": 1, "jsonrpc": "2.0", "method": "Plugin.Stream.Player.SetProperty", "params": {"<property>", <value>}}

Supported propertys

  • loopStatus: [string] the current repeat status, one of:
    • none: the playback will stop when there are no more tracks to play
    • track: the current track will start again from the begining once it has finished playing
    • playlist: the playback loops through a list of tracks
  • shuffle: [bool] play playlist in random order
  • volume: [int] voume in percent, valid range [0..100]
  • rate: [float] The current playback rate, valid range (0..)

Expected response

Success
{"id": 1, "jsonrpc": "2.0", "result": "ok"}
Error

Any json-rpc 2.0 conformant error with an error message that helps the user to diagnose the error

Plugin.Stream.Player.GetProperties

{"id": 1, "jsonrpc": "2.0", "method": "Plugin.Stream.Player.GetProperties"}

Supported propertys

  • playbackStatus: [string] The current playback status, one of:
    • playing
    • paused
    • stopped
  • loopStatus: [string] The current repeat status, one of:
    • none: The playback will stop when there are no more tracks to play
    • track: The current track will start again from the begining once it has finished playing
    • playlist: The playback loops through a list of tracks
  • shuffle: [bool] Traverse through the playlist in random order
  • volume: [int] Voume in percent, valid range [0..100]
  • rate: [float] The current playback rate, valid range (0..)
  • position: [float] Current playback position in seconds
  • canGoNext: [bool] Whether the client can call the next method on this interface and expect the current track to change
  • canGoPrevious: [bool] Whether the client can call the previous method on this interface and expect the current track to change
  • canPlay: [bool] Whether playback can be started using play or playPause
  • canPause: [bool] Whether playback can be paused using pause or playPause
  • canSeek: [bool] Whether the client can control the playback position using seek and setPosition
  • canControl: [bool] Whether the media player may be controlled over this interface
  • metadata: [json] message with the following (optional) fields:
    • trackId: [string] A unique identity for this track within the context of an MPRIS object (eg: tracklist).
    • file: [string] The current song.
    • duration: [float] The duration of the song in seconds; may contain a fractional part.
    • artist: [list of strings] The track artist(s).
    • artistSort: [list of strings] Same as artist, but for sorting. This usually omits prefixes such as “The”.
    • album: [string] The album name.
    • albumSort: [string] Same as album, but for sorting.
    • albumArtist: [list of strings] The album artist(s).
    • albumArtistSort: [list of strings] Same as albumartist, but for sorting.
    • name: [string] A name for this song. This is not the song title. The exact meaning of this tag is not well-defined. It is often used by badly configured internet radio stations with broken tags to squeeze both the artist name and the song title in one tag.
    • date: [string] The song’s release date. This is usually a 4-digit year.
    • originalDate: [string] The song’s original release date.
    • composer: [list of strings] The composer(s) of the track.
    • performer: [string] The artist who performed the song.
    • conductor: [string] The conductor who conducted the song.
    • work: [string] “a work is a distinct intellectual or artistic creation, which can be expressed in the form of one or more audio recordings”
    • grouping: [string] “used if the sound belongs to a larger category of sounds/music” (from the IDv2.4.0 TIT1 description).
    • comment: [list of string] A (list of) freeform comment(s)
    • label: [string] The name of the label or publisher.
    • musicbrainzArtistId: [string] The artist id in the MusicBrainz database.
    • musicbrainzAlbumId: [string] The album id in the MusicBrainz database.
    • musicbrainzAlbumArtistId: [string] The album artist id in the MusicBrainz database.
    • musicbrainzTrackId: [string] The track id in the MusicBrainz database.
    • musicbrainzReleaseTrackId: [string] The release track id in the MusicBrainz database.
    • musicbrainzWorkId: [string] The work id in the MusicBrainz database.
    • lyrics: [list of strings] The lyricist(s) of the track
    • bpm: [integer] The speed of the music, in beats per minute.
    • autoRating: [float] An automatically-generated rating, based on things such as how often it has been played. This should be in the range 0.0 to 1.0.
    • comment: [list of strings] A (list of) freeform comment(s).
    • composer: [list of strings] The composer(s) of the track.
    • contentCreated: [string] Date/Time: When the track was created. Usually only the year component will be useful.
    • discNumber: [integer] The disc number on the album that this track is from.
    • firstUsed: [string] Date/Time: When the track was first played.
    • genre: [list of strings] List of Strings: The genre(s) of the track.
    • lastUsed: [string] Date/Time: When the track was last played.
    • lyricist: [list of strings] List of Strings: The lyricist(s) of the track.
    • title: [string] The track title.
    • trackNumber: [string] The track number on the album disc.
    • url: [string uri] The location of the media file.
    • artUrl: [string uri] The location of an image representing the track or album. Clients should not assume this will continue to exist when the media player stops giving out the URL.
    • artData: [json] Base64 encoded image representing the track or album. if artUrl is not specified, Snapserver will decode and cache the image, and will publish the image via artUrl.
      • data: [string] Base64 encoded image
      • extension: [string] The image file extension (e.g. "png", "jpg", "svg")
    • useCount: [integer] The number of times the track has been played.
    • userRating: [float] A user-specified rating. This should be in the range 0.0 to 1.0.
    • spotifyArtistId: [string] The Spotify Artist ID
    • spotifyTrackId: [string] The Spotify Track ID

Expected response

Success
{"id": 1, "jsonrpc": "2.0", "result": {"canControl":true,"canGoNext":true,"canGoPrevious":true,"canPause":true,"canPlay":true,"canSeek":false,"loopStatus":"none","playbackStatus":"playing","position":93.394,"shuffle":false,"volume":86}}

{"id": 1, "jsonrpc": "2.0", "result": {"canControl":true,"canGoNext":true,"canGoPrevious":true,"canPause":true,"canPlay":true,"canSeek":true,"loopStatus":"none","metadata":{"album":"Doldinger","albumArtist":["Klaus Doldinger's Passport"],"artUrl":"http://coverartarchive.org/release/0d4ff56b-2a2b-43b5-bf99-063cac1599e5/16940576164-250.jpg","artist":["Klaus Doldinger's Passport feat. Nils Landgren"],"contentCreated":"2016","duration":305.2929992675781,"genre":["Jazz"],"musicbrainzAlbumId":"0d4ff56b-2a2b-43b5-bf99-063cac1599e5","title":"Soul Town","trackId":"7","trackNumber":6,"url":"Klaus Doldinger's Passport - Doldinger (2016)/06 - Soul Town.mp3"},"playbackStatus":"playing","position":72.79499816894531,"shuffle":false,"volume":97}}
Error

Any json-rpc 2.0 conformant error with an error message that helps the user to diagnose the error

Notifications

Plugin.Stream.Player.Properties

{"jsonrpc": "2.0", "method": "Plugin.Stream.Player.Properties", "params": {"canControl":true,"canGoNext":true,"canGoPrevious":true,"canPause":true,"canPlay":true,"canSeek":false,"loopStatus":"none","playbackStatus":"playing","position":593.394,"shuffle":false,"volume":86}}

Same format as in GetProperties. If metadata is missing, the last known metadata will be used, so the plugin must not send the complete metadata if one of the properties is updated.

Plugin.Stream.Log

Send a log message

{"jsonrpc": "2.0", "method": "Plugin.Stream.Log", "params": {"severity":"Info","message":"<Log message>"}}

Supported severitys

  • trace verbose debug-level message
  • debug debug-level message
  • info informational message
  • notice normal, but significant, condition
  • warning warning conditions
  • error error conditions
  • fatal critical conditions

Plugin.Stream.Ready

The plugin shall send this notification when it's up and ready to receive commands

{"jsonrpc": "2.0", "method": "Plugin.Stream.Ready"}

Server

TODO: this belongs to doc/json_rpc_api/control.md

Requests

To control the stream state, the following commands can be sent to the Snapcast server and will be forwarded to the respective stream:

{"id": 1, "jsonrpc": "2.0", "method": "Stream.Control", "params": {"id": "Pipe", "command": command, "params": params}}
{"id": 1, "jsonrpc": "2.0", "method": "Stream.SetProperty", "params": {"id": "Pipe", "property": property, "value": value}}

Notifications

{"jsonrpc": "2.0", "method": "Stream.OnProperties", "params": {"id": "Pipe", "properties": {}}}