How to select the streaming source in the tray menu?

[Aqua1ung]

As far as I can tell, one can select the casting sink in the tray menu, however, I cannot seem to find a menu option to select the source to be cast. On the other hand, if one chooses the source in command line, the sink that has been picked in the tray menu is ignored. Hence what's the reason to have a tray menu in the first place?

[ndom91]

The streaming "source" is any application that is trying to output audio then, right? No need to really select one. Mentally, its like plugging in a set of speakers into the 3.5mm audio jack. You don't select a source then either, but any application outputting audio will go to the default sink, in this case the casting target device.