- moved the sound system's sound stream for the music out of the song objects.

It is now being handled by the controlling code.
While of no benefit for GZDoom itself, this finally allows to separate the entire music code into a separate, engine independent project that merely provides streamed music data when not playing on a hardware device (WinMM Midi or CD Audio.)
The tight coupling of the music code with the sound backend made this nearly impossible before

libraries/zmusic/mididevices/music_softsynth_mididevice.cpp

@@ -99,7 +99,7 @@ SoundStreamInfo SoftSynthMIDIDevice::GetStreamInfo() const
 	{
 		chunksize *= 2;
 	}
-	return { chunksize, SampleRate, isMono };
+	return { chunksize, SampleRate, isMono? 1:2 };
 }
 
 //==========================================================================