Add a --audio-output-latency command-line argument

This allows optimizing the audio output latency on higher-end CPUs,
especially in projects that do not expose a way to override this setting.

core/config/engine.cpp

@@ -74,6 +74,14 @@ int Engine::get_max_fps() const {
 	return _max_fps;
 }
 
+void Engine::set_audio_output_latency(int p_msec) {
+	_audio_output_latency = p_msec > 1 ? p_msec : 1;
+}
+
+int Engine::get_audio_output_latency() const {
+	return _audio_output_latency;
+}
+
 uint64_t Engine::get_frames_drawn() {
 	return frames_drawn;
 }

core/config/engine.h

@@ -61,6 +61,7 @@ private:
 	double physics_jitter_fix = 0.5;
 	double _fps = 1;
 	int _max_fps = 0;
+	int _audio_output_latency = 0;
 	double _time_scale = 1.0;
 	uint64_t _physics_frames = 0;
 	int max_physics_steps_per_frame = 8;
@@ -99,6 +100,9 @@ public:
 	virtual void set_max_fps(int p_fps);
 	virtual int get_max_fps() const;
 
+	virtual void set_audio_output_latency(int p_msec);
+	virtual int get_audio_output_latency() const;
+
 	virtual double get_frames_per_second() const { return _fps; }
 
 	uint64_t get_frames_drawn();