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Contents

Architectural Overview

The PlaylistManager service provides the ability to create and maintain playlists.

The PlaylistManager service provides access to a list of playlists, which in turn, contain a list of tracks.

Using the PlaylistManager service you can read, insert and delete playlists as well as read, insert and delete tracks from an individual playlist. Each playlist and track within a playlist is given a unique id.

To insert a playlist, provide the id of the playlist you wish to insert 'after' and the associated metadata, (name, description and image id). An empty playlist is inserted into the correct position and the id of the new playlist is returned. To insert in the first position, insert after the special id of 0.

To insert a track, provide the id of the playlist and the id of the track you wish to insert 'after' and the associated udn and metadata id. The track is inserted and the id of the new track is returned. To insert in the first position. insert after the special id of 0. If the track originated from a media server the udn should contain the udn of the media server and the metadata id contain the id contained in the DidlLite of the track. Otherwise the udn should be empty and the metadata id contain DidlLite describing of the track.

There are two ways to read the list of playlists or the list of tracks in a playlist. The first reads a single entry and the second reads a list of entries.

There are two ways to delete the playlists or the the tracks in a playlist. The first deletes a single entry and the second deletes a list of entries.

IdArray and TokenIdArray

The PlaylistManager service has two eventide state variable called IdArray and TokenArray. Both arrays are base64 encoded arrays of 32 bit, big endian unsigned integers. Each Id and Token represents a playlist in the list of playlists. An empty array indicates an empty list if playlists. A Change in Token for a playlist indicates that the playlist contents has changed.

Whether you acquire the IdArray and TokenArray via events or polling, you immediately know the number and order of the ids of the playlists, as well as whether an individual playlist has changed. What you don't necessarily know is the metadata for those ids.

As the metadata for a large number of playlists can easily be several megabytes of xml, blindly fetching all the metadata every time the playlists change is inefficient and will give a poor user experience. In order to quickly display playlists updates and ensure interoperability with other control points on the network, it is strongly recommended that you maintain the following two data structures:

  • A copy of the latest IdArray and TokenArray
  • A cache mapping id's to their associated metadata.

With this decoupled approach, you only need to fetch the metadata for the ids added to the playlists. Changes to the order of ids in the playlists require no action.

As a further enhancement, when an insert completes successfully, you know both the metadata (as you supplied it), and the new id (returned by the PlaylistManager on completion of the insert action). This information can be directly inserted into the cache, saving subsequent unnecessary retrieval.

Playlist IdArray

The obtain a playlist's IdArray, provide the id of the playlist to the action PlaylistReadArray. The IdArray returned is a base64 encoded array of 32 bit, big endian unsigned integers. Each Id represents a track in the playlist. An empty IdArray indicates an empty playlist.

When you acquire the IdArray, through the action PlaylistReadArray, you immediately know the number and order of the ids in the playlist. What you don't necessarily know is the metadata for those ids.

As the metadata for a large number of playlists can easily be several megabytes of xml, blindly fetching all the metadata every time the playlist changes is inefficient and will give a poor user experience. In order to quickly display playlist updates and ensure interoperability with other control points on the network, it is strongly recommended that you maintain the following two data structures:

  • A copy of the latest IdArray
  • A cache mapping id's to their associated metadata.

With this decoupled approach, you only need to fetch the metadata for the ids added to the playlist. Changes to the order of ids in the playlist require no action.

As a further enhancement, when an insert completes successfully, you know both the metadata (as you supplied it), and the new id (returned by the PlaylistManager on completion of the insert action). This information can be directly inserted into the cache, saving subsequent unnecessary retrieval.

Events

A short while (approx 300ms) after any change to the list of playlists, the PlaylistManager will event all subscribers the current IdArray and TokenArray. The eventing of these state variables is moderated to prevent excessive updates.

A short while (approx 300ms) after any changes to a playlist, the PlaylistManager will event all subscribers the current TokenArray. The eventing of this state variable is moderated to prevent excessive updates.

Polling

For control points that can't subscribe to events, two additional actions are provided. The first, PlaylistArrays, reads the IdArray and TokenArray directly. This action also returns an ArraysToken, which should be saved and periodically passed to a second action, PlaylistArraysChanged, which reports whether or not your copy of IdArray and TokenArray are out of date. If they are, calling PlaylistArrays again will ensure you have up to date versions.

Actions

Metadata

Returns the Metadata describing the PlaylistManager.

ImagesXml 

  <ImageList>
    <Entry>
      <Id></Id>
      <Uri></Uri>
    </Entry>
  </ImageList>

PlaylistReadArray

Report the current id array for the specified playlist.

The IdArray is an ordered array of ids that represent each track in the playlist.

PlaylistReadMetadata

Given a playlist id, report its associated Metadata.

PlaylistRead

Given a playlist id, report its associated Name, Description and ImageId.

PlaylistUpdate

Updates the Name, Description and ImageId for the specified playlist.

PlaylistInsert

Inserts an empty playlist with the specified Name, Description and ImageId after the specified playlist id.

PlaylistDeleteId

Delete from the list of playlists the playlist with the specified Id.

PlaylistDeleteAll

Clears all the playlists.

PlaylistsMax

Report the maximum number of playlists in the playlists id array. This remains constant while a particular OpenHome device remains registerted on the network, but may vary between different models of OpenHome device from different manufacturers. A value of 0 indicates no limit.

TracksMax

Report the maximum number of tracks in a playlist id array. This remains constant while a particular OpenHome device remains registerted on the network, but may vary between different models of OpenHome device from different manufacturers. A value of 0 indicates no limit.

PlaylistArrays

Report the current id array and token array.

The IdArray is an ordered array of ids that represent each playlist in the list of playlists.

This action also reports a Token, which can be used to quickly detect if the id array or token array has changed since it was last read (see PlaylistArraysChanged).

PlaylistArraysChanged

Check to see if the id array or token array has changed since gathering the specified Token. This Token must have been previously collected from the PlaylistArrays action.

This mechanism is provided specifically for clients unable to partake in UPnP eventing.

Read

Given a playlist id and a track Id, report its associated Metadata.

ReadList

Given a playlist id and a space separated list of track Id's, report their associated Metadata in the following xml form: 

  <TrackList>
    <Entry>
      <Id></Id>
      <Metadata></Metadata>
    </Entry>
  </TrackList>

Insert

DeleteId

Delete from the specified playlist the track with the specified Id.

DeleteAll

Clears the specified playlist.

Technical Details 

   Domain  : av.openhome.org
   Name    : PlaylistManager
   Version : 1

PlaylistManager Service Description (XML) 

<?xml version="1.0" encoding="utf-8"?>
 
<scpd xmlns="urn:schemas-upnp-org:service-1-0">
 
    <specVersion>
        <major>1</major>
        <minor>0</minor>
    </specVersion>
 
    <actionList>
        <action>
            <name>Metadata</name>
            <argumentList>
                <argument>
                    <name>Metadata</name>
                    <direction>out</direction>
                    <relatedStateVariable>Metadata</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
 
        <action>
            <name>ImagesXml</name>
            <argumentList>
                <argument>
                    <name>ImagesXml</name>
                    <direction>out</direction>
                    <relatedStateVariable>ImagesXml</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
 
        <action>
            <name>PlaylistReadArray</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Array</name>
                    <direction>out</direction>
                    <relatedStateVariable>IdArray</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistReadMetadata</name>
            <argumentList>
                <argument>
                    <name>IdList</name>
                    <direction>in</direction>
                    <relatedStateVariable>IdList</relatedStateVariable>
                </argument>
                <argument>
                    <name>Metadata</name>
                    <direction>out</direction>
                    <relatedStateVariable>Metadata</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistRead</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Name</name>
                    <direction>out</direction>
                    <relatedStateVariable>Name</relatedStateVariable>
                </argument>
                <argument>
                    <name>Description</name>
                    <direction>out</direction>
                    <relatedStateVariable>Description</relatedStateVariable>
                </argument>
                <argument>
                    <name>ImageId</name>
                    <direction>out</direction>
                    <relatedStateVariable>ImageId</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistUpdate</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Name</name>
                    <direction>in</direction>
                    <relatedStateVariable>Name</relatedStateVariable>
                </argument>
                <argument>
                    <name>Description</name>
                    <direction>in</direction>
                    <relatedStateVariable>Description</relatedStateVariable>
                </argument>
                <argument>
                    <name>ImageId</name>
                    <direction>in</direction>
                    <relatedStateVariable>ImageId</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistInsert</name>
            <argumentList>
                <argument>
                    <name>AfterId</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Name</name>
                    <direction>in</direction>
                    <relatedStateVariable>Name</relatedStateVariable>
                </argument>
                <argument>
                    <name>Description</name>
                    <direction>in</direction>
                    <relatedStateVariable>Description</relatedStateVariable>
                </argument>
                <argument>
                    <name>ImageId</name>
                    <direction>in</direction>
                    <relatedStateVariable>ImageId</relatedStateVariable>
                </argument>
                <argument>
                    <name>NewId</name>
                    <direction>out</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistDeleteId</name>
            <argumentList>
                <argument>
                    <name>Value</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistDeleteAll</name>
        </action>
        <action>
            <name>PlaylistsMax</name>
            <argumentList>
                <argument>
                    <name>Value</name>
                    <direction>out</direction>
                    <relatedStateVariable>PlaylistsMax</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>TracksMax</name>
            <argumentList>
                <argument>
                    <name>Value</name>
                    <direction>out</direction>
                    <relatedStateVariable>TracksMax</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistArrays</name>
            <argumentList>
                <argument>
                    <name>Token</name>
                    <direction>out</direction>
                    <relatedStateVariable>ArraysToken</relatedStateVariable>
                </argument>
                <argument>
                    <name>IdArray</name>
                    <direction>out</direction>
                    <relatedStateVariable>IdArray</relatedStateVariable>
                </argument>
                <argument>
                    <name>TokenArray</name>
                    <direction>out</direction>
                    <relatedStateVariable>TokenArray</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>PlaylistArraysChanged</name>
            <argumentList>
                <argument>
                    <name>Token</name>
                    <direction>in</direction>
                    <relatedStateVariable>ArraysToken</relatedStateVariable>
                </argument>
                <argument>
                    <name>Value</name>
                    <direction>out</direction>
                    <relatedStateVariable>IdArrayChanged</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
 
        <action>
            <name>Read</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>TrackId</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Metadata</name>
                    <direction>out</direction>
                    <relatedStateVariable>Metadata</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>ReadList</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>TrackIdList</name>
                    <direction>in</direction>
                    <relatedStateVariable>IdList</relatedStateVariable>
                </argument>
                <argument>
                    <name>TrackList</name>
                    <direction>out</direction>
                    <relatedStateVariable>TrackList</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>Insert</name>
            <argumentList>
                <argument>
                    <name>Id</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>AfterTrackId</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Udn</name>
                    <direction>in</direction>
                    <relatedStateVariable>Udn</relatedStateVariable>
                </argument>
                <argument>
                    <name>MetadataId</name>
                    <direction>in</direction>
                    <relatedStateVariable>MetadataId</relatedStateVariable>
                </argument>
                <argument>
                    <name>NewTrackId</name>
                    <direction>out</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>DeleteId</name>
            <argumentList>
                <argument>
                    <name>TrackId</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
                <argument>
                    <name>Value</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
        <action>
            <name>DeleteAll</name>
            <argumentList>
                <argument>
                    <name>TrackId</name>
                    <direction>in</direction>
                    <relatedStateVariable>Id</relatedStateVariable>
                </argument>
            </argumentList>
        </action>
    </actionList>
 
    <serviceStateTable>
 
        <stateVariable sendEvents="yes">
            <name>Metadata</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="yes">
            <name>ImagesXml</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="yes">
            <name>IdArray</name>
            <dataType>bin.base64</dataType>
        </stateVariable>
        <stateVariable sendEvents="yes">
            <name>TokenArray</name>
            <dataType>bin.base64</dataType>
        </stateVariable>
        <stateVariable sendEvents="yes">
            <name>PlaylistsMax</name>
            <dataType>ui4</dataType>
        </stateVariable>
        <stateVariable sendEvents="yes">
            <name>TracksMax</name>
            <dataType>ui4</dataType>
        </stateVariable>
 
        <stateVariable sendEvents="no">
            <name>PlaylistList</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>Id</name>
            <dataType>ui4</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>IdList</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>Name</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>Description</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>ImageId</name>
            <dataType>ui4</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>TrackList</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>Udn</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>MetadataId</name>
            <dataType>string</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>ArraysToken</name>
            <dataType>ui4</dataType>
        </stateVariable>
        <stateVariable sendEvents="no">
            <name>IdArrayChanged</name>
            <dataType>boolean</dataType>
        </stateVariable>
    </serviceStateTable>
</scpd>
Retrieved from "http://wiki.openhome.org/wiki/Av:Developer:PlaylistManagerService"