From OpenHome

Transport PlayAs Options

The Transport service’s PlayAs action takes arguments for mode (source or group of related sources) and a mode-specific command. Some standard modes and commands are listed below; other manufacturer-specific options are possible.

Playlist

The "playlist" mode supports the following commands:

• id=[track_id] - Halt playback of any current track and switch to the track with the specified id. Returns a 800 fault code if [track_id] is not valid.
• index=[playlist_index] - Halt playback of the current track and switch to the track with the specified index. Returns a 802 fault code if the index is beyond the end of the playlist.

Radio

The "radio" mode supports the following command:

• id=[preset_id] – Start playing the specified preset. Returns a 800 fault code if [preset_id] does not match a current preset

Receiver

The "receiver" mode supports the following command:

   {
       "url": "[sender_url]",
       "metadata": "[openhome_sender_metadata]"
   }

and will start playing the same content as the device that either hosts the ohu or ohm sender or matches the zone in the ohz url.

Single

The "single" mode supports the following command

   {
       "url": "[track_url]",
       "metadata": "[openhome_metadata]"
   }

and will start playing [track_url], reporting the specified metadata. When the track completes, it will be queued again then TransportState will change to Stopped.

External

The "external" mode supports the following command:

• [system_name] – activate the source with whose system name matches [system_name] and start playing.

UpnpAv

The "upnpav" mode supports the following command:

• [blank] – Start playing the last uri set via AVTransport.SetAVTransportUri. Activates the source but leaves transport state as STOPPED if no uri is set.