Hi.
Case 1. Play Spotify = no with ST
1.- DLNA its a protocol media to play and control music, vol, etc, and you must to knows how works.
2.- Airplay its a diferrent protocol, Spotify its a close protocol, etc
3.- DLNA basically works with a DLNA server (where media is stored and published) and a media player or a Media Renderer.
4.- Media player can search content in a media server and play the media (movie, music, etc) but can not be controlled externally, basically its a dvd player but you can search the media manually.
5.- Media Renderer can be controlled externally with a control point, but can not search media , bassically its a dumb device who listen orders, the control point commonly its a smartphone who send the orders through a control point app
6.- The media must to be available to be played, the DLNA server alway publish the content to be played, then the control point send a command to control the media renderer,
Example
speaker load the media http://myserver/mysong.mp3
speaker play
seaker stop
etc
7.- Comonlly the control point in a smartphone could create a temporal DLNA server with the media inside the phone, then the media its available to a media renderer, but when the phone close the control point , the temporal server its closed too.
8.- the best way to smartthings to play a song when you arrives it’s the media must to be available always, then you need a DLNA server,
9.- The DLNA server can be local or on line, basically its a web server with all media references,
you can use some hardware dlna servers, or some software dlna servers like PLEX, or some dlna servers in smartphones, to let your music be always available to play.
10.- spotify its a close protocol , you can not play directly the playlist with a DLNA Media Render, its like to have bluetooth and want to connect to a wifi.
11.- some speakers can handle several protocols, airplay, spotify, media renderer, bluetooth but smartthings just can handle natively (for now) dlna commands.
12.- I suggest you to create a DLNA Server with your music, and let ST to play the music you want
13- The old Media Renderers just can handle 1 media, this means it plays just 1 song and then stop
14.- The new Media Renderers can handle containers, this means can load a list and when a song end a new song start. The list its created by the DLNA Server, commonlly a folder
15.- A control point always its asking status to a mediarenderer to play next , but ST can not handle a continuos monitor to a Media Renderer (its not made to be a complex control point), bassically its a very simplistic control point, just load and play.
16.- ST can not be your control point, it just to send messages and continues music after the message its played.
17.- You can not control a play list with ST , just to load and play.
18.- If you speaker support containers, ST just load your container, and the speaker control the list, the speaker its who play the next song until the list finish, no ST.
19.- I have a DLNA server, but my music its very repetitive, then I better use a radio station (genre smooth jazz ) then I create a smart app to load a radio station when I arrive to home, the radio station do not stops each song, then its perfect to me.
20.- You can use the mediarenderer events smart app that I have created to test the radio stations
21.- If you want to play your selected music , I suggest you to read about DLNA Servers.
22.- There are others ways to play spotify when you arrives , but you need something like tasker to start your spotify app in an android phone. you can search something about that