What is the easiest way to route an audio output (e.g. a playing song) into the recording input of another application (e.g. discord's microphone input)?
I'm looking for a solution that is independent on the output volume and device.
For example: I want an audio file to play at full volume into discord's microphone input while my output volume is only at 20%. I do not neccessarily need to hear the audio file myself.
I'm self-answering this for Linux, but looking for someone who can provide a Windows and Mac OS solution too for a complete Q&A on this issue.