The github link in the post (GitHub - SmartThingsUle/DLNA-PLAYER: Generic DLNA Player to Smartthings) has the instructions. I’ve copied them below. You’ll need to set up a developer account if you haven’t already yet. You’ll install the smart app and the device handler. From their, you’ll open the app, and find your player. once you find your player, you should be able to use it to play music or give voice announcements like you could with Sonos.
I haven’t personally used it, but looking through the thread others have found success with it
Generic DLNA Player to Smartthings v 1.9.0
Its necessary to update MediaRenderer Connect and Dlna-Player You must uninstall all your MediaRenderes and install again after update.
Installing The MediaRenderer Connect
Open SmartThings IDE in your web browser and log into your account.
Click on the “My Smart Apps” section in the navigation bar.
On your SmartApps page, click on the “+ New SmartApp” button on the right.
On the “New SmartApp” page, Select the Tab “From Code” , Copy the MediaRenderer_Connect source code from GitHub and paste it into the IDE editor window.
Click the blue “Create” button at the bottom of the page. An IDE editor window containing device handler template should now open.
Click the blue “Save” button above the editor window.
Click the “Publish” button next to it and select “For Me”. You have now self-published your SmartApp.
Installing The Device Type
Open SmartThings IDE in your web browser and log into your account.
Click on the “My Device Types” section in the navigation bar.
On your Device Types page, click on the “+ New Device Type” button on the right.
On the “New Device Type” page, Select the Tab “From Code” , Copy the MediaRenderer_Player source code from GitHub and paste it into the IDE editor window.
Click the blue “Create” button at the bottom of the page. An IDE editor window containing device handler template should now open.
Click the blue “Save” button above the editor window.
Click the “Publish” button next to it and select “For Me”. You have now self-published your SmartApp.
Searching the Media Renderers
Open the SmartThings app in your smartphone.
Select the (+) icon to install new things
Go to My Apps section and select MediaRenderer Connect
The MediaRenderer Connect will start to search Your players.
Once the app will show the quantity of media renderers found, activate all the media renderers found and finish the proccess pressing the “Done Button” in both pages.
Get back to main window and you should have the new players in your things section, refresh the page if no players appears.