Replaygain for UPnP user, possibly also working from alternative Apps, e.g. Bubble UPNP and HIFI Cast, when my reported bug can be solved.
All files are tagged by replaygain-album and replaygain-track via foobar2000.
Bubble-UPP provides via ffmpeg-converter replay-gain: Off, Album or Track.
The developer of the App Hi-Fi-Cast mentioned, a renderer could read the tags coming from his App.
At GitHub I asked for a solution with gstreamer:
There is a solution, which could be used easily.
Virtual renderes could do it: Off, Album, Track