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 @@ class Engine {
 	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;
@@ -98,6 +99,9 @@ class Engine {
 	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();

doc/classes/AudioServer.xml

@@ -132,7 +132,7 @@
 		<method name="get_output_latency" qualifiers="const">
 			<return type="float" />
 			<description>
-				Returns the audio driver's output latency.
+				Returns the audio driver's effective output latency. This is based on [member ProjectSettings.audio/driver/output_latency], but the exact returned value will differ depending on the operating system.
 			</description>
 		</method>
 		<method name="get_speaker_mode" qualifiers="const">

doc/classes/ProjectSettings.xml

@@ -374,7 +374,8 @@
 		<member name="audio/driver/output_latency" type="int" setter="" getter="" default="15">
 			Specifies the preferred output latency in milliseconds for audio. Lower values will result in lower audio latency at the cost of increased CPU usage. Low values may result in audible cracking on slower hardware.
 			Audio output latency may be constrained by the host operating system and audio hardware drivers. If the host can not provide the specified audio output latency then Godot will attempt to use the nearest latency allowed by the host. As such you should always use [method AudioServer.get_output_latency] to determine the actual audio output latency.
-			[b]Note:[/b] This setting is ignored on all versions of Windows prior to Windows 10.
+			Audio output latency can be overridden using the [code]--audio-output-latency &lt;ms&gt;[/code] command line argument.
+			[b]Note:[/b] This setting is ignored on Android, and on all versions of Windows prior to Windows 10.
 		</member>
 		<member name="audio/driver/output_latency.web" type="int" setter="" getter="" default="50">
 			Safer override for [member audio/driver/output_latency] in the Web platform, to avoid audio issues especially on mobile devices.

drivers/alsa/audio_driver_alsa.cpp

@@ -111,7 +111,7 @@ Error AudioDriverALSA::init_output_device() {
 	// In ALSA the period size seems to be the one that will determine the actual latency
 	// Ref: https://www.alsa-project.org/main/index.php/FramesPeriods
 	unsigned int periods = 2;
-	int latency = GLOBAL_GET("audio/driver/output_latency");
+	int latency = Engine::get_singleton()->get_audio_output_latency();
 	buffer_frames = closest_power_of_2(latency * mix_rate / 1000);
 	buffer_size = buffer_frames * periods;
 	period_size = buffer_frames;

drivers/coreaudio/audio_driver_coreaudio.cpp

@@ -131,7 +131,7 @@ Error AudioDriverCoreAudio::init() {
 	result = AudioUnitSetProperty(audio_unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, kOutputBus, &strdesc, sizeof(strdesc));
 	ERR_FAIL_COND_V(result != noErr, FAILED);
 
-	int latency = GLOBAL_GET("audio/driver/output_latency");
+	int latency = Engine::get_singleton()->get_audio_output_latency();
 	// Sample rate is independent of channels (ref: https://stackoverflow.com/questions/11048825/audio-sample-frequency-rely-on-channels)
 	buffer_frames = closest_power_of_2(latency * mix_rate / 1000);
 

drivers/pulseaudio/audio_driver_pulseaudio.cpp

@@ -222,7 +222,7 @@ Error AudioDriverPulseAudio::init_output_device() {
 			break;
 	}
 
-	int tmp_latency = GLOBAL_GET("audio/driver/output_latency");
+	int tmp_latency = Engine::get_singleton()->get_audio_output_latency();
 	buffer_frames = closest_power_of_2(tmp_latency * mix_rate / 1000);
 	pa_buffer_size = buffer_frames * pa_map.channels;
 

drivers/wasapi/audio_driver_wasapi.cpp

@@ -555,7 +555,7 @@ Error AudioDriverWASAPI::finish_input_device() {
 Error AudioDriverWASAPI::init() {
 	mix_rate = _get_configured_mix_rate();
 
-	target_latency_ms = GLOBAL_GET("audio/driver/output_latency");
+	target_latency_ms = Engine::get_singleton()->get_audio_output_latency();
 
 	Error err = init_output_device();
 	if (err != OK) {

drivers/xaudio2/audio_driver_xaudio2.cpp

@@ -45,7 +45,7 @@ Error AudioDriverXAudio2::init() {
 	speaker_mode = SPEAKER_MODE_STEREO;
 	channels = 2;
 
-	int latency = GLOBAL_GET("audio/driver/output_latency");
+	int latency = Engine::get_singleton()->get_audio_output_latency();
 	buffer_size = closest_power_of_2(latency * mix_rate / 1000);
 
 	samples_in = memnew_arr(int32_t, buffer_size * channels);

main/main.cpp

@@ -211,6 +211,7 @@ static bool debug_navigation = false;
 static bool debug_avoidance = false;
 #endif
 static int frame_delay = 0;
+static int audio_output_latency = 0;
 static bool disable_render_loop = false;
 static int fixed_fps = -1;
 static MovieWriter *movie_writer = nullptr;
@@ -418,6 +419,8 @@ void Main::print_help(const char *p_binary) {
 		OS::get_singleton()->print(")");
 	}
 	OS::get_singleton()->print("].\n");
+	OS::get_singleton()->print("  --audio-output-latency <ms>       Override audio output latency in milliseconds (default is 15 ms).\n");
+	OS::get_singleton()->print("                                    Lower values make sound playback more reactive but increase CPU usage, and may result in audio cracking if the CPU can't keep up.\n");
 
 	OS::get_singleton()->print("  --rendering-method <renderer>     Renderer name. Requires driver support.\n");
 	OS::get_singleton()->print("  --rendering-driver <driver>       Rendering driver (depends on display driver).\n");
@@ -914,6 +917,14 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 				OS::get_singleton()->print("Missing audio driver argument, aborting.\n");
 				goto error;
 			}
+		} else if (I->get() == "--audio-output-latency") {
+			if (I->next()) {
+				audio_output_latency = I->next()->get().to_int();
+				N = I->next()->next();
+			} else {
+				OS::get_singleton()->print("Missing audio output latency argument, aborting.\n");
+				goto error;
+			}
 		} else if (I->get() == "--text-driver") {
 			if (I->next()) {
 				text_driver = I->next()->get();
@@ -1942,6 +1953,9 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	Engine::get_singleton()->set_max_physics_steps_per_frame(GLOBAL_DEF_BASIC(PropertyInfo(Variant::INT, "physics/common/max_physics_steps_per_frame", PROPERTY_HINT_RANGE, "1,100,1"), 8));
 	Engine::get_singleton()->set_physics_jitter_fix(GLOBAL_DEF("physics/common/physics_jitter_fix", 0.5));
 	Engine::get_singleton()->set_max_fps(GLOBAL_DEF(PropertyInfo(Variant::INT, "application/run/max_fps", PROPERTY_HINT_RANGE, "0,1000,1"), 0));
+	Engine::get_singleton()->set_audio_output_latency(GLOBAL_DEF_RST(PropertyInfo(Variant::INT, "audio/driver/output_latency", PROPERTY_HINT_RANGE, "1,100,1"), 15));
+	// Use a safer default output_latency for web to avoid audio cracking on low-end devices, especially mobile.
+	GLOBAL_DEF_RST("audio/driver/output_latency.web", 50);
 
 	GLOBAL_DEF("debug/settings/stdout/print_fps", false);
 	GLOBAL_DEF("debug/settings/stdout/print_gpu_profile", false);
@@ -1955,6 +1969,10 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 		frame_delay = GLOBAL_DEF(PropertyInfo(Variant::INT, "application/run/frame_delay_msec", PROPERTY_HINT_RANGE, "0,100,1,or_greater"), 0);
 	}
 
+	if (audio_output_latency >= 1) {
+		Engine::get_singleton()->set_audio_output_latency(audio_output_latency);
+	}
+
 	OS::get_singleton()->set_low_processor_usage_mode(GLOBAL_DEF("application/run/low_processor_mode", false));
 	OS::get_singleton()->set_low_processor_usage_mode_sleep_usec(
 			GLOBAL_DEF(PropertyInfo(Variant::INT, "application/run/low_processor_mode_sleep_usec", PROPERTY_HINT_RANGE, "0,33200,1,or_greater"), 6900)); // Roughly 144 FPS

misc/dist/linux/godot.6

@@ -58,6 +58,9 @@ Password for remote filesystem.
 \fB\-\-audio\-driver\fR <driver>
 Audio driver ('PulseAudio', 'ALSA', 'Dummy').
 .TP
+\fB\-\-audio\-output\-latency\fR <ms>
+Override audio output latency in milliseconds (default is 15 ms). Lower values make sound playback more reactive but increase CPU usage, and may result in audio cracking if the CPU can't keep up.
+.TP
 \fB\-\-video\-driver\fR <driver>
 Video driver ('Vulkan', 'GLES2').
 .SS "Display options:"

misc/dist/shell/_godot.zsh-completion

@@ -43,6 +43,7 @@ _arguments \
   '--remote-fs[use a remote filesystem]:remote filesystem address' \
   '--remote-fs-password[password for remote filesystem]:remote filesystem password' \
   '--audio-driver[set the audio driver]:audio driver name' \
+  '--audio-output-latency[override audio output latency in milliseconds (default is 15 ms)]:number of milliseconds' \
   '--display-driver[set the display driver]:display driver name' \
   "--rendering-method[set the renderer]:renderer name:((forward_plus\:'Desktop renderer' mobile\:'Desktop and mobile renderer' gl_compatibility\:'Desktop, mobile and web renderer'))" \
   "--rendering-driver[set the rendering driver]:rendering driver name:((vulkan\:'Vulkan renderer' opengl3\:'OpenGL ES 3.0 renderer' dummy\:'Dummy renderer'))" \

misc/dist/shell/godot.bash-completion

@@ -46,6 +46,7 @@ _complete_godot_options() {
 --remote-fs
 --remote-fs-password
 --audio-driver
+--audio-output-latency
 --display-driver
 --rendering-method
 --rendering-driver

misc/dist/shell/godot.fish

@@ -59,6 +59,7 @@ complete -c godot -l render-thread -d "Set the render thread mode" -x -a "unsafe
 complete -c godot -l remote-fs -d "Use a remote filesystem (<host/IP>[:<port>] address)" -x
 complete -c godot -l remote-fs-password -d "Password for remote filesystem" -x
 complete -c godot -l audio-driver -d "Set the audio driver" -x
+complete -c godot -l audio-output-latency -d "Override audio output latency in milliseconds (default is 15 ms)" -x
 complete -c godot -l display-driver -d "Set the display driver" -x
 complete -c godot -l rendering-method -d "Set the renderer" -x -a "(godot_rendering_method_args)"
 complete -c godot -l rendering-driver -d "Set the rendering driver" -x -a "(godot_rendering_driver_args)"

platform/web/audio_driver_web.cpp

@@ -101,7 +101,7 @@ void AudioDriverWeb::_audio_driver_capture(int p_from, int p_samples) {
 }
 
 Error AudioDriverWeb::init() {
-	int latency = GLOBAL_GET("audio/driver/output_latency");
+	int latency = Engine::get_singleton()->get_audio_output_latency();
 	if (!audio_context.inited) {
 		audio_context.mix_rate = _get_configured_mix_rate();
 		audio_context.channel_count = godot_audio_init(&audio_context.mix_rate, latency, &_state_change_callback, &_latency_update_callback);

servers/audio_server.cpp

@@ -200,8 +200,6 @@ void AudioDriverManager::initialize(int p_driver) {
 	GLOBAL_DEF_RST("audio/driver/enable_input", false);
 	GLOBAL_DEF_RST("audio/driver/mix_rate", DEFAULT_MIX_RATE);
 	GLOBAL_DEF_RST("audio/driver/mix_rate.web", 0); // Safer default output_latency for web (use browser default).
-	GLOBAL_DEF_RST("audio/driver/output_latency", DEFAULT_OUTPUT_LATENCY);
-	GLOBAL_DEF_RST("audio/driver/output_latency.web", 50); // Safer default output_latency for web.
 
 	int failed_driver = -1;
 

servers/audio_server.h

@@ -138,8 +138,6 @@ class AudioDriverManager {
 		MAX_DRIVERS = 10
 	};
 
-	static const int DEFAULT_OUTPUT_LATENCY = 15;
-
 	static AudioDriver *drivers[MAX_DRIVERS];
 	static int driver_count;