using the api method GetVolume for the current media type always returns 0. See below code example:

Code:
(app is of type StreetDeckApp)

uint cmu = app.GetVolume(enumVolumeTypes.eVTCurrentMedia);
uint muu = app.GetVolume(enumVolumeTypes.eVTMusic);

cmu = 0
muu = 61
SetVolume works however, but is useless if we don't know what the volume is at. an increase/decrease function wold do the trick though..