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Purpose

For linux users, the ability to at runtime switch between alsa and jack audio+midi driver.

Changes

• Make both jack and alsa(linuxdriver) more similar to osx-driver
• Make jack and alsa drivers "subdrivers" of linuxdriver (AudioDriverState).

class design changes

Before:

AudioModule
│
├── LinuxAudioDriver
│   │
│   Alsa
│   └──> device: "default"
│
├── OSXAudioDriver
│   ...
│
└── WasapiAudioDriver
    ...

MidiModule
│
├── LinuxAudioDriver
│   │
│   ├────> AlsaMidiOutPort
│   └────> AlsaMidiInPort
│   
:

After:

AudioModule
│
|         MidiModule
│             |
├── AudioMidiManager (was LinuxAudioDriver)
│        |      │
│        |      ├─── JackDriverState
│        |      │    │
│        |      │    (jack-code)
│        |      │    └──> jack client open
│        |      └──> AlsaDriverState
│        |                      │
│        |              (alsa-code)
│        |                      └──> device: "default"
│        │
│        + LinuxMidiOutPort
│        │
│        ├────> JackMidiOutPort
│        ├────> AlsaMidiOutPort
│        + LinuxMidiInPort
|          :
│
├── OSXAudioDriver
│   ...
│
└── WasapiAudioDriver
    ...

MidiModule
│
├── AudioMidiManager (was LinuxAudioDriver)
│   │
│   + LinuxMidiOutPort
│   │
│   ├────> JackMidiOutPort
│   ├────> AlsaMidiOutPort
│   + LinuxMidiInPort
:

Audio Tests

• start with jack, play and hear audio OK
• start with alsa, play and hear audio OK
• start with jack, switch to alsa, then play OK
• start with alsa, switch to jack, then play OK
• switch from jack to alsa during play OK
• switch from alsa to jack during play OK

Midi tests

• start fluidsynth in verbose mode, musescore and qjackctl (to midi-connect them), verify midi-events are logged by fluidsynth.

Optional cleanups / redesign

Remove LinuxAudioDriver and keep only AlsaAudioDriver and JackAudioDriver as two independent implementations. To switch between them, you need to add another class, something like IAudioDriverProvider. This is what you need to add to IoC (and remove the drivers from IoC). Access the driver through this class, like:

class IAudioDriverProvider ...
{
...

        std::shared_ptr<IAudioDriver> driver() const;
  
        void swithDriver(const std::string& name); 
        async::Chanel<std::string /*name*/> dirverChanged() const;
}


class SomeClass
    Inject<IAudioDriverProvider > audioDriverProvider;


...

     audioDriverProvider()->driver();

This greatly simplifies everything, each class becomes simple and does one thing.
Moreover, such a system is easily scalable; we can easily add other drivers, cross-platform or platform-specific.

Not in scope for this PR

• MIDI-channel-per-instrument

Known cleanups & fixes before merge

• send foreign commits upstream:
  Misc. needed for jack #22373
• cleanup: avoid global in app
• If possible do mutual dependency Injection between module Audio and Midi.
  Testing confirmed, can't inject modules.
  Injection is used, but not at modul level.
• de-pollute any interfaces that got sprinkled with data members
• ensure no public data members begins with m_ (those should be private)
• remove sample-rate dropdown OR make it work,
  No 'requires restart' added
• automatic connection to audio ports upon start
  Not in scope, brings in too much arbitrary heuristics code from Mu3.
• Possible to switch between jack/alsa driver (currently it crashes)
• Possible to switch bufferSize in jack without crash (possible in alsa)
• Possible to disable jack-transport via configuration checkbox