MIDI output driver support for setting master volume

[joncampbell123]

• ALSA: That's just a port to a MIDI device and may be software or hardware, so all we can hope is the MIDI device/synth downstream supports GS master volume SysEx
• Apple CoreAudio: Use Apple's CoreAudio midi synth. Great. Now how do you control the output volume of the AuGraph? Apple's developer site is terrible at answering this question. Often if you find anything it's just a list of constants or structs and it doesn't say anything about it. So let's say you somehow found out about a property to set audio volume. Great. What do I put in it? What's the valid range? What do I do with this? Where do I put it? What function do I call with it? Does it even have anything to do with an AuGraph? For fuck's sake Apple, Microsoft documents shit better than you do, and they've traditionally been terrible at documentation in the past!
• Apple CoreMIDI: Just a MIDI port, probably to hardware or the synth. Hope the device recognizes GS master volume control.
• MT32: Does the MT-32 support any kind of volume control or do we need to render the emulation and then apply the volume before going to the mixer, like we did with Fluidsynth?
• Synth: Fluidsynth. This one has already been done.
• Timidity: MIDI data port. If Timidity supports GS volume, great. If not, not much we can do.
• Win32: Holy crap, Microsoft gets it. Use the midi* Win32 functions to identify if we're talking to Microsoft's software GS synth and whether volume control is supported, and if so, use this function to control volume: https://learn.microsoft.com/en-us/windows/win32/api/mmeapi/nf-mmeapi-midioutsetvolume. However, if Microsoft is using stuff licensed from Roland GS, it might already support the GS master volume SysEx and we don't need to apply translation.

[joncampbell123]

Apple also says that CoreAudio functions are deprecated now, and they'd rather you use https://developer.apple.com/documentation/avfaudio/avaudioengine/

If there's a way to call their MIDI synth with that and control audio volume, or even route it into DOSBox-X's audio mixer code, that would be great.