[HTML5] AudioWorklet API implementation.

Rewrote AudioDriverJavaScript to support multiple processor nodes.
The old (and deprecated) ScriptProcessorNode when threads are not
available, and the new AudioWorklet API when threads are enabled.

The new implementation uses two ring buffers and a shared state to
communicated with the AudioWorklet thread.

The audio.worklet.js JavaScript file is always added to the export
template, but only really used (and downloaded) in the thread build.

8 files changed, 717 insertions, 202 deletions

diff --git a/platform/javascript/SCsub b/platform/javascript/SCsub
index f26b314a51..a0e6fa0e18 100644
--- a/platform/javascript/SCsub
+++ b/platform/javascript/SCsub
@@ -56,9 +56,10 @@ out_files = [
     zip_dir.File(binary_name + ".js"),
     zip_dir.File(binary_name + ".wasm"),
     zip_dir.File(binary_name + ".html"),
+    zip_dir.File(binary_name + ".audio.worklet.js"),
 ]
 html_file = "#misc/dist/html/editor.html" if env["tools"] else "#misc/dist/html/full-size.html"
-in_files = [js_wrapped, build[1], html_file]
+in_files = [js_wrapped, build[1], html_file, "#platform/javascript/native/audio.worklet.js"]
 if env["threads_enabled"]:
     in_files.append(build[2])
     out_files.append(zip_dir.File(binary_name + ".worker.js"))
diff --git a/platform/javascript/audio_driver_javascript.cpp b/platform/javascript/audio_driver_javascript.cpp
index 2535ad1812..dd982bc3a8 100644
--- a/platform/javascript/audio_driver_javascript.cpp
+++ b/platform/javascript/audio_driver_javascript.cpp
@@ -31,7 +31,6 @@
 #include "audio_driver_javascript.h"
 
 #include "core/config/project_settings.h"
-#include "godot_audio.h"
 
 #include <emscripten.h>
 
@@ -45,92 +44,109 @@ const char *AudioDriverJavaScript::get_name() const {
 	return "JavaScript";
 }
 
-#ifndef NO_THREADS
-void AudioDriverJavaScript::_audio_thread_func(void *p_data) {
-	AudioDriverJavaScript *obj = static_cast<AudioDriverJavaScript *>(p_data);
-	while (!obj->quit) {
-		obj->lock();
-		if (!obj->needs_process) {
-			obj->unlock();
-			OS::get_singleton()->delay_usec(1000); // Give the browser some slack.
-			continue;
-		}
-		obj->_audio_driver_process();
-		obj->needs_process = false;
-		obj->unlock();
-	}
+void AudioDriverJavaScript::_state_change_callback(int p_state) {
+	singleton->state = p_state;
 }
-#endif
 
-void AudioDriverJavaScript::_audio_driver_process_start() {
-#ifndef NO_THREADS
-	singleton->lock();
-#else
-	singleton->_audio_driver_process();
-#endif
+void AudioDriverJavaScript::_latency_update_callback(float p_latency) {
+	singleton->output_latency = p_latency;
 }
 
-void AudioDriverJavaScript::_audio_driver_process_end() {
-#ifndef NO_THREADS
-	singleton->needs_process = true;
-	singleton->unlock();
-#endif
-}
+void AudioDriverJavaScript::_audio_driver_process(int p_from, int p_samples) {
+	int32_t *stream_buffer = reinterpret_cast<int32_t *>(output_rb);
+	const int max_samples = memarr_len(output_rb);
 
-void AudioDriverJavaScript::_audio_driver_process_capture(float p_sample) {
-	singleton->process_capture(p_sample);
+	int write_pos = p_from;
+	int to_write = p_samples;
+	if (to_write == 0) {
+		to_write = max_samples;
+	}
+	// High part
+	if (write_pos + to_write > max_samples) {
+		const int samples_high = max_samples - write_pos;
+		audio_server_process(samples_high / channel_count, &stream_buffer[write_pos]);
+		for (int i = write_pos; i < max_samples; i++) {
+			output_rb[i] = float(stream_buffer[i] >> 16) / 32768.f;
+		}
+		to_write -= samples_high;
+		write_pos = 0;
+	}
+	// Leftover
+	audio_server_process(to_write / channel_count, &stream_buffer[write_pos]);
+	for (int i = write_pos; i < write_pos + to_write; i++) {
+		output_rb[i] = float(stream_buffer[i] >> 16) / 32768.f;
+	}
 }
 
-void AudioDriverJavaScript::_audio_driver_process() {
-	int sample_count = memarr_len(internal_buffer) / channel_count;
-	int32_t *stream_buffer = reinterpret_cast<int32_t *>(internal_buffer);
-	audio_server_process(sample_count, stream_buffer);
-	for (int i = 0; i < sample_count * channel_count; i++) {
-		internal_buffer[i] = float(stream_buffer[i] >> 16) / 32768.f;
+void AudioDriverJavaScript::_audio_driver_capture(int p_from, int p_samples) {
+	if (get_input_buffer().size() == 0) {
+		return; // Input capture stopped.
 	}
-}
+	const int max_samples = memarr_len(input_rb);
 
-void AudioDriverJavaScript::process_capture(float sample) {
-	int32_t sample32 = int32_t(sample * 32768.f) * (1U << 16);
-	input_buffer_write(sample32);
+	int read_pos = p_from;
+	int to_read = p_samples;
+	if (to_read == 0) {
+		to_read = max_samples;
+	}
+	// High part
+	if (read_pos + to_read > max_samples) {
+		const int samples_high = max_samples - read_pos;
+		for (int i = read_pos; i < max_samples; i++) {
+			input_buffer_write(int32_t(input_rb[i] * 32768.f) * (1U << 16));
+		}
+		to_read -= samples_high;
+		read_pos = 0;
+	}
+	// Leftover
+	for (int i = read_pos; i < read_pos + to_read; i++) {
+		input_buffer_write(int32_t(input_rb[i] * 32768.f) * (1U << 16));
+	}
 }
 
 Error AudioDriverJavaScript::init() {
 	mix_rate = GLOBAL_GET("audio/mix_rate");
 	int latency = GLOBAL_GET("audio/output_latency");
 
-	channel_count = godot_audio_init(mix_rate, latency);
-	buffer_length = closest_power_of_2(latency * mix_rate / 1000);
-	buffer_length = godot_audio_create_processor(buffer_length, channel_count);
-	if (!buffer_length) {
-		return FAILED;
+	channel_count = godot_audio_init(mix_rate, latency, &_state_change_callback, &_latency_update_callback);
+	buffer_length = closest_power_of_2((latency * mix_rate / 1000));
+#ifndef NO_THREADS
+	node = memnew(WorkletNode);
+#else
+	node = memnew(ScriptProcessorNode);
+#endif
+	buffer_length = node->create(buffer_length, channel_count);
+	if (output_rb) {
+		memdelete_arr(output_rb);
 	}
-
-	if (!internal_buffer || (int)memarr_len(internal_buffer) != buffer_length * channel_count) {
-		if (internal_buffer)
-			memdelete_arr(internal_buffer);
-		internal_buffer = memnew_arr(float, buffer_length *channel_count);
+	output_rb = memnew_arr(float, buffer_length *channel_count);
+	if (!output_rb) {
+		return ERR_OUT_OF_MEMORY;
 	}
-
-	if (!internal_buffer) {
+	if (input_rb) {
+		memdelete_arr(input_rb);
+	}
+	input_rb = memnew_arr(float, buffer_length *channel_count);
+	if (!input_rb) {
 		return ERR_OUT_OF_MEMORY;
 	}
 	return OK;
 }
 
 void AudioDriverJavaScript::start() {
-#ifndef NO_THREADS
-	thread = Thread::create(_audio_thread_func, this);
-#endif
-	godot_audio_start(internal_buffer, &_audio_driver_process_start, &_audio_driver_process_end, &_audio_driver_process_capture);
+	if (node) {
+		node->start(output_rb, memarr_len(output_rb), input_rb, memarr_len(input_rb));
+	}
 }
 
 void AudioDriverJavaScript::resume() {
-	godot_audio_resume();
+	if (state == 0) { // 'suspended'
+		godot_audio_resume();
+	}
 }
 
 float AudioDriverJavaScript::get_latency() {
-	return godot_audio_get_latency();
+	return output_latency + (float(buffer_length) / mix_rate);
 }
 
 int AudioDriverJavaScript::get_mix_rate() const {
@@ -142,42 +158,128 @@ AudioDriver::SpeakerMode AudioDriverJavaScript::get_speaker_mode() const {
 }
 
 void AudioDriverJavaScript::lock() {
-#ifndef NO_THREADS
-	mutex.lock();
-#endif
+	if (node) {
+		node->unlock();
+	}
 }
 
 void AudioDriverJavaScript::unlock() {
-#ifndef NO_THREADS
-	mutex.unlock();
-#endif
+	if (node) {
+		node->unlock();
+	}
 }
 
 void AudioDriverJavaScript::finish() {
-#ifndef NO_THREADS
-	quit = true; // Ask thread to quit.
-	Thread::wait_to_finish(thread);
-	memdelete(thread);
-	thread = nullptr;
-#endif
-	if (internal_buffer) {
-		memdelete_arr(internal_buffer);
-		internal_buffer = nullptr;
+	if (node) {
+		node->finish();
+		memdelete(node);
+		node = nullptr;
+	}
+	if (output_rb) {
+		memdelete_arr(output_rb);
+		output_rb = nullptr;
+	}
+	if (input_rb) {
+		memdelete_arr(input_rb);
+		input_rb = nullptr;
 	}
 }
 
 Error AudioDriverJavaScript::capture_start() {
+	lock();
 	input_buffer_init(buffer_length);
+	unlock();
 	godot_audio_capture_start();
 	return OK;
 }
 
 Error AudioDriverJavaScript::capture_stop() {
 	godot_audio_capture_stop();
+	lock();
 	input_buffer.clear();
+	unlock();
 	return OK;
 }
 
 AudioDriverJavaScript::AudioDriverJavaScript() {
 	singleton = this;
 }
+
+#ifdef NO_THREADS
+/// ScriptProcessorNode implementation
+void AudioDriverJavaScript::ScriptProcessorNode::_process_callback() {
+	AudioDriverJavaScript::singleton->_audio_driver_capture();
+	AudioDriverJavaScript::singleton->_audio_driver_process();
+}
+
+int AudioDriverJavaScript::ScriptProcessorNode::create(int p_buffer_samples, int p_channels) {
+	return godot_audio_script_create(p_buffer_samples, p_channels);
+}
+
+void AudioDriverJavaScript::ScriptProcessorNode::start(float *p_out_buf, int p_out_buf_size, float *p_in_buf, int p_in_buf_size) {
+	godot_audio_script_start(p_in_buf, p_in_buf_size, p_out_buf, p_out_buf_size, &_process_callback);
+}
+#else
+/// AudioWorkletNode implementation
+void AudioDriverJavaScript::WorkletNode::_audio_thread_func(void *p_data) {
+	AudioDriverJavaScript::WorkletNode *obj = static_cast<AudioDriverJavaScript::WorkletNode *>(p_data);
+	AudioDriverJavaScript *driver = AudioDriverJavaScript::singleton;
+	const int out_samples = memarr_len(driver->output_rb);
+	const int in_samples = memarr_len(driver->input_rb);
+	int wpos = 0;
+	int to_write = out_samples;
+	int rpos = 0;
+	int to_read = 0;
+	int32_t step = 0;
+	while (!obj->quit) {
+		if (to_read) {
+			driver->lock();
+			driver->_audio_driver_capture(rpos, to_read);
+			godot_audio_worklet_state_add(obj->state, STATE_SAMPLES_IN, -to_read);
+			driver->unlock();
+			rpos += to_read;
+			if (rpos >= in_samples) {
+				rpos -= in_samples;
+			}
+		}
+		if (to_write) {
+			driver->lock();
+			driver->_audio_driver_process(wpos, to_write);
+			godot_audio_worklet_state_add(obj->state, STATE_SAMPLES_OUT, to_write);
+			driver->unlock();
+			wpos += to_write;
+			if (wpos >= out_samples) {
+				wpos -= out_samples;
+			}
+		}
+		step = godot_audio_worklet_state_wait(obj->state, STATE_PROCESS, step, 1);
+		to_write = out_samples - godot_audio_worklet_state_get(obj->state, STATE_SAMPLES_OUT);
+		to_read = godot_audio_worklet_state_get(obj->state, STATE_SAMPLES_IN);
+	}
+}
+
+int AudioDriverJavaScript::WorkletNode::create(int p_buffer_size, int p_channels) {
+	godot_audio_worklet_create(p_channels);
+	return p_buffer_size;
+}
+
+void AudioDriverJavaScript::WorkletNode::start(float *p_out_buf, int p_out_buf_size, float *p_in_buf, int p_in_buf_size) {
+	godot_audio_worklet_start(p_in_buf, p_in_buf_size, p_out_buf, p_out_buf_size, state);
+	thread = Thread::create(_audio_thread_func, this);
+}
+
+void AudioDriverJavaScript::WorkletNode::lock() {
+	mutex.lock();
+}
+
+void AudioDriverJavaScript::WorkletNode::unlock() {
+	mutex.unlock();
+}
+
+void AudioDriverJavaScript::WorkletNode::finish() {
+	quit = true; // Ask thread to quit.
+	Thread::wait_to_finish(thread);
+	memdelete(thread);
+	thread = nullptr;
+}
+#endif
diff --git a/platform/javascript/audio_driver_javascript.h b/platform/javascript/audio_driver_javascript.h
index 60ad6480c9..f112a1ede4 100644
--- a/platform/javascript/audio_driver_javascript.h
+++ b/platform/javascript/audio_driver_javascript.h
@@ -31,54 +31,96 @@
 #ifndef AUDIO_DRIVER_JAVASCRIPT_H
 #define AUDIO_DRIVER_JAVASCRIPT_H
 
-#include "servers/audio_server.h"
-
 #include "core/os/mutex.h"
 #include "core/os/thread.h"
+#include "servers/audio_server.h"
+
+#include "godot_audio.h"
 
 class AudioDriverJavaScript : public AudioDriver {
+public:
+	class AudioNode {
+	public:
+		virtual int create(int p_buffer_size, int p_output_channels) = 0;
+		virtual void start(float *p_out_buf, int p_out_buf_size, float *p_in_buf, int p_in_buf_size) = 0;
+		virtual void finish() {}
+		virtual void lock() {}
+		virtual void unlock() {}
+		virtual ~AudioNode() {}
+	};
+
+	class WorkletNode : public AudioNode {
+	private:
+		enum {
+			STATE_LOCK,
+			STATE_PROCESS,
+			STATE_SAMPLES_IN,
+			STATE_SAMPLES_OUT,
+			STATE_MAX,
+		};
+		Mutex mutex;
+		Thread *thread = nullptr;
+		bool quit = false;
+		int32_t state[STATE_MAX] = { 0 };
+
+		static void _audio_thread_func(void *p_data);
+
+	public:
+		int create(int p_buffer_size, int p_output_channels) override;
+		void start(float *p_out_buf, int p_out_buf_size, float *p_in_buf, int p_in_buf_size) override;
+		void finish() override;
+		void lock() override;
+		void unlock() override;
+	};
+
+	class ScriptProcessorNode : public AudioNode {
+	private:
+		static void _process_callback();
+
+	public:
+		int create(int p_buffer_samples, int p_channels) override;
+		void start(float *p_out_buf, int p_out_buf_size, float *p_in_buf, int p_in_buf_size) override;
+	};
+
 private:
-	float *internal_buffer = nullptr;
+	AudioNode *node = nullptr;
+
+	float *output_rb = nullptr;
+	float *input_rb = nullptr;
 
 	int buffer_length = 0;
 	int mix_rate = 0;
 	int channel_count = 0;
+	int state = 0;
+	float output_latency = 0.0;
 
-#ifndef NO_THREADS
-	Mutex mutex;
-	Thread *thread = nullptr;
-	bool quit = false;
-	bool needs_process = true;
+	static void _state_change_callback(int p_state);
+	static void _latency_update_callback(float p_latency);
 
-	static void _audio_thread_func(void *p_data);
-#endif
-	static void _audio_driver_process_start();
-	static void _audio_driver_process_end();
-	static void _audio_driver_process_capture(float p_sample);
-	void _audio_driver_process();
+protected:
+	void _audio_driver_process(int p_from = 0, int p_samples = 0);
+	void _audio_driver_capture(int p_from = 0, int p_samples = 0);
 
 public:
 	static bool is_available();
-	void process_capture(float sample);
 
 	static AudioDriverJavaScript *singleton;
 
-	const char *get_name() const override;
+	virtual const char *get_name() const;
 
-	Error init() override;
-	void start() override;
+	virtual Error init();
+	virtual void start();
 	void resume();
-	float get_latency() override;
-	int get_mix_rate() const override;
-	SpeakerMode get_speaker_mode() const override;
-	void lock() override;
-	void unlock() override;
-	void finish() override;
+	virtual float get_latency();
+	virtual int get_mix_rate() const;
+	virtual SpeakerMode get_speaker_mode() const;
+	virtual void lock();
+	virtual void unlock();
+	virtual void finish();
 
-	Error capture_start() override;
-	Error capture_stop() override;
+	virtual Error capture_start();
+	virtual Error capture_stop();
 
 	AudioDriverJavaScript();
 };
-
 #endif
diff --git a/platform/javascript/engine/utils.js b/platform/javascript/engine/utils.js
index 0c97b38199..10e3abe91e 100644
--- a/platform/javascript/engine/utils.js
+++ b/platform/javascript/engine/utils.js
@@ -4,6 +4,8 @@ var Utils = {
 		function rw(path) {
 			if (path.endsWith('.worker.js')) {
 				return execName + '.worker.js';
+			} else if (path.endsWith('.audio.worklet.js')) {
+				return execName + '.audio.worklet.js';
 			} else if (path.endsWith('.js')) {
 				return execName + '.js';
 			} else if (path.endsWith('.wasm')) {
diff --git a/platform/javascript/export/export.cpp b/platform/javascript/export/export.cpp
index a83ff44d20..d520931067 100644
--- a/platform/javascript/export/export.cpp
+++ b/platform/javascript/export/export.cpp
@@ -94,6 +94,9 @@ public:
 		} else if (req[1] == basereq + ".js") {
 			filepath += ".js";
 			ctype = "application/javascript";
+		} else if (req[1] == basereq + ".audio.worklet.js") {
+			filepath += ".audio.worklet.js";
+			ctype = "application/javascript";
 		} else if (req[1] == basereq + ".worker.js") {
 			filepath += ".worker.js";
 			ctype = "application/javascript";
@@ -440,6 +443,9 @@ Error EditorExportPlatformJavaScript::export_project(const Ref<EditorExportPrese
 		} else if (file == "godot.worker.js") {
 			file = p_path.get_file().get_basename() + ".worker.js";
 
+		} else if (file == "godot.audio.worklet.js") {
+			file = p_path.get_file().get_basename() + ".audio.worklet.js";
+
 		} else if (file == "godot.wasm") {
 			file = p_path.get_file().get_basename() + ".wasm";
 		}
@@ -566,6 +572,7 @@ Error EditorExportPlatformJavaScript::run(const Ref<EditorExportPreset> &p_prese
 		DirAccess::remove_file_or_error(basepath + ".html");
 		DirAccess::remove_file_or_error(basepath + ".js");
 		DirAccess::remove_file_or_error(basepath + ".worker.js");
+		DirAccess::remove_file_or_error(basepath + ".audio.worklet.js");
 		DirAccess::remove_file_or_error(basepath + ".pck");
 		DirAccess::remove_file_or_error(basepath + ".png");
 		DirAccess::remove_file_or_error(basepath + ".wasm");
diff --git a/platform/javascript/godot_audio.h b/platform/javascript/godot_audio.h
index 120fdbcc59..7ebda3ad39 100644
--- a/platform/javascript/godot_audio.h
+++ b/platform/javascript/godot_audio.h
@@ -38,18 +38,24 @@ extern "C" {
 #include "stddef.h"
 
 extern int godot_audio_is_available();
-
-extern int godot_audio_init(int p_mix_rate, int p_latency);
-extern int godot_audio_create_processor(int p_buffer_length, int p_channel_count);
-
-extern void godot_audio_start(float *r_buffer_ptr, void (*p_start)(), void (*p_end)(), void (*p_input)(float p_sample));
+extern int godot_audio_init(int p_mix_rate, int p_latency, void (*_state_cb)(int), void (*_latency_cb)(float));
 extern void godot_audio_resume();
 
-extern float godot_audio_get_latency();
-
 extern void godot_audio_capture_start();
 extern void godot_audio_capture_stop();
 
+// Worklet
+typedef int32_t GodotAudioState[4];
+extern void godot_audio_worklet_create(int p_channels);
+extern void godot_audio_worklet_start(float *p_in_buf, int p_in_size, float *p_out_buf, int p_out_size, GodotAudioState p_state);
+extern void godot_audio_worklet_state_add(GodotAudioState p_state, int p_idx, int p_value);
+extern int godot_audio_worklet_state_get(GodotAudioState p_state, int p_idx);
+extern int godot_audio_worklet_state_wait(int32_t *p_state, int p_idx, int32_t p_expected, int p_timeout);
+
+// Script
+extern int godot_audio_script_create(int p_buffer_size, int p_channels);
+extern void godot_audio_script_start(float *p_in_buf, int p_in_size, float *p_out_buf, int p_out_size, void (*p_cb)());
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/platform/javascript/native/audio.worklet.js b/platform/javascript/native/audio.worklet.js
new file mode 100644
index 0000000000..ad7957e45c
--- /dev/null
+++ b/platform/javascript/native/audio.worklet.js
@@ -0,0 +1,186 @@
+/*************************************************************************/
+/*  audio.worklet.js                                                     */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+class RingBuffer {
+
+	constructor(p_buffer, p_state) {
+		this.buffer = p_buffer;
+		this.avail = p_state;
+		this.rpos = 0;
+		this.wpos = 0;
+	}
+
+	data_left() {
+		return Atomics.load(this.avail, 0);
+	}
+
+	space_left() {
+		return this.buffer.length - this.data_left();
+	}
+
+	read(output) {
+		const size = this.buffer.length;
+		let from = 0
+		let to_write = output.length;
+		if (this.rpos + to_write > size) {
+			const high = size - this.rpos;
+			output.set(this.buffer.subarray(this.rpos, size));
+			from = high;
+			to_write -= high;
+			this.rpos = 0;
+		}
+		output.set(this.buffer.subarray(this.rpos, this.rpos + to_write), from);
+		this.rpos += to_write;
+		Atomics.add(this.avail, 0, -output.length);
+		Atomics.notify(this.avail, 0);
+	}
+
+	write(p_buffer) {
+		const to_write = p_buffer.length;
+		const mw = this.buffer.length - this.wpos;
+		if (mw >= to_write) {
+			this.buffer.set(p_buffer, this.wpos);
+		} else {
+			const high = p_buffer.subarray(0, to_write - mw);
+			const low = p_buffer.subarray(to_write - mw);
+			this.buffer.set(high, this.wpos);
+			this.buffer.set(low);
+		}
+		let diff = to_write;
+		if (this.wpos + diff >= this.buffer.length) {
+			diff -= this.buffer.length;
+		}
+		this.wpos += diff;
+		Atomics.add(this.avail, 0, to_write);
+		Atomics.notify(this.avail, 0);
+	}
+}
+
+class GodotProcessor extends AudioWorkletProcessor {
+	constructor() {
+		super();
+		this.running = true;
+		this.lock = null;
+		this.notifier = null;
+		this.output = null;
+		this.output_buffer = new Float32Array();
+		this.input = null;
+		this.input_buffer = new Float32Array();
+		this.port.onmessage = (event) => {
+			const cmd = event.data['cmd'];
+			const data = event.data['data'];
+			this.parse_message(cmd, data);
+		};
+	}
+
+	process_notify() {
+		Atomics.add(this.notifier, 0, 1);
+		Atomics.notify(this.notifier, 0);
+	}
+
+	parse_message(p_cmd, p_data) {
+		if (p_cmd == "start" && p_data) {
+			const state = p_data[0];
+			let idx = 0;
+			this.lock = state.subarray(idx, ++idx);
+			this.notifier = state.subarray(idx, ++idx);
+			const avail_in = state.subarray(idx, ++idx);
+			const avail_out = state.subarray(idx, ++idx);
+			this.input = new RingBuffer(p_data[1], avail_in);
+			this.output = new RingBuffer(p_data[2], avail_out);
+		} else if (p_cmd == "stop") {
+			this.runing = false;
+			this.output = null;
+			this.input = null;
+		}
+	}
+
+	array_has_data(arr) {
+		return arr.length && arr[0].length && arr[0][0].length;
+	}
+
+	process(inputs, outputs, parameters) {
+		if (!this.running) {
+			return false; // Stop processing.
+		}
+		if (this.output === null) {
+			return true; // Not ready yet, keep processing.
+		}
+		const process_input = this.array_has_data(inputs);
+		if (process_input) {
+			const input = inputs[0];
+			const chunk = input[0].length * input.length;
+			if (this.input_buffer.length != chunk) {
+				this.input_buffer = new Float32Array(chunk);
+			}
+			if (this.input.space_left() >= chunk) {
+				this.write_input(this.input_buffer, input);
+				this.input.write(this.input_buffer);
+			} else {
+				this.port.postMessage("Input buffer is full! Skipping input frame.");
+			}
+		}
+		const process_output = this.array_has_data(outputs);
+		if (process_output) {
+			const output = outputs[0];
+			const chunk = output[0].length * output.length;
+			if (this.output_buffer.length != chunk) {
+				this.output_buffer = new Float32Array(chunk)
+			}
+			if (this.output.data_left() >= chunk) {
+				this.output.read(this.output_buffer);
+				this.write_output(output, this.output_buffer);
+			} else {
+				this.port.postMessage("Output buffer has not enough frames! Skipping output frame.");
+			}
+		}
+		this.process_notify();
+		return true;
+	}
+
+	write_output(dest, source) {
+		const channels = dest.length;
+		for (let ch = 0; ch < channels; ch++) {
+			for (let sample = 0; sample < dest[ch].length; sample++) {
+				dest[ch][sample] = source[sample * channels + ch];
+			}
+		}
+	}
+
+	write_input(dest, source) {
+		const channels = source.length;
+		for (let ch = 0; ch < channels; ch++) {
+			for (let sample = 0; sample < source[ch].length; sample++) {
+				dest[sample * channels + ch] = source[ch][sample];
+			}
+		}
+	}
+}
+
+registerProcessor('godot-processor', GodotProcessor);
diff --git a/platform/javascript/native/library_godot_audio.js b/platform/javascript/native/library_godot_audio.js
index 1e6f787657..846359b8b2 100644
--- a/platform/javascript/native/library_godot_audio.js
+++ b/platform/javascript/native/library_godot_audio.js
@@ -27,89 +27,123 @@
 /* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
-var GodotAudio = {
+
+const GodotAudio = {
 
 	$GodotAudio__deps: ['$GodotOS'],
 	$GodotAudio: {
-
 		ctx: null,
 		input: null,
-		script: null,
-	},
+		driver: null,
+		interval: 0,
 
-	godot_audio_is_available__proxy: 'sync',
-	godot_audio_is_available: function () {
-		if (!(window.AudioContext || window.webkitAudioContext)) {
-			return 0;
-		}
-		return 1;
-	},
+		init: function(mix_rate, latency, onstatechange, onlatencyupdate) {
+			const ctx = new (window.AudioContext || window.webkitAudioContext)({
+				sampleRate: mix_rate,
+				// latencyHint: latency / 1000 // Do not specify, leave 'interactive' for good performance.
+			});
+			GodotAudio.ctx = ctx;
+			onstatechange(ctx.state); // Immeditately notify state.
+			ctx.onstatechange = function() {
+				let state = 0;
+				switch (ctx.state) {
+					case 'suspended':
+						state = 0;
+						break;
+					case 'running':
+						state = 1;
+						break;
+					case 'closed':
+						state = 2;
+						break;
+				}
+				onstatechange(state);
+			}
+			// Update computed latency
+			GodotAudio.interval = setInterval(function() {
+				let latency = 0;
+				if (ctx.baseLatency) {
+					latency += GodotAudio.ctx.baseLatency;
+				}
+				if (ctx.outputLatency) {
+					latency += GodotAudio.ctx.outputLatency;
+				}
+				onlatencyupdate(latency);
+			}, 1000);
+			GodotOS.atexit(GodotAudio.close_async);
+			return ctx.destination.channelCount;
+		},
 
-	godot_audio_init: function(mix_rate, latency) {
-		GodotAudio.ctx = new (window.AudioContext || window.webkitAudioContext)({
-			sampleRate: mix_rate,
-			// latencyHint: latency / 1000 // Do not specify, leave 'interactive' for good performance.
-		});
-		GodotOS.atexit(function(accept, reject) {
-			if (!GodotAudio.ctx) {
-				accept();
+		create_input: function(callback) {
+			if (GodotAudio.input) {
+				return; // Already started.
+			}
+			function gotMediaInput(stream) {
+				GodotAudio.input = GodotAudio.ctx.createMediaStreamSource(stream);
+				callback(GodotAudio.input)
+			}
+			if (navigator.mediaDevices.getUserMedia) {
+				navigator.mediaDevices.getUserMedia({
+					"audio": true
+				}).then(gotMediaInput, function(e) { out(e) });
+			} else {
+				if (!navigator.getUserMedia) {
+					navigator.getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
+				}
+				navigator.getUserMedia({
+					"audio": true
+				}, gotMediaInput, function(e) { out(e) });
+			}
+		},
+
+		close_async: function(resolve, reject) {
+			const ctx = GodotAudio.ctx;
+			GodotAudio.ctx = null;
+			// Audio was not initialized.
+			if (!ctx) {
+				resolve();
 				return;
 			}
-			if (GodotAudio.script) {
-				GodotAudio.script.disconnect();
-				GodotAudio.script.onaudioprocess = null;
-				GodotAudio.script = null;
+			// Remove latency callback
+			if (GodotAudio.interval) {
+				clearInterval(GodotAudio.interval);
+				GodotAudio.interval = 0;
 			}
+			// Disconnect input, if it was started.
 			if (GodotAudio.input) {
 				GodotAudio.input.disconnect();
 				GodotAudio.input = null;
 			}
-			GodotAudio.ctx.close().then(function() {
-				accept();
+			// Disconnect output
+			let closed = Promise.resolve();
+			if (GodotAudio.driver) {
+				closed = GodotAudio.driver.close();
+			}
+			closed.then(function() {
+				return ctx.close();
+			}).then(function() {
+				ctx.onstatechange = null;
+				resolve();
 			}).catch(function(e) {
-				accept();
+				ctx.onstatechange = null;
+				console.error("Error closing AudioContext", e);
+				resolve();
 			});
-			GodotAudio.ctx = null;
-		});
-		return GodotAudio.ctx.destination.channelCount;
+		},
 	},
 
-	godot_audio_create_processor: function(buffer_length, channel_count) {
-		GodotAudio.script = GodotAudio.ctx.createScriptProcessor(buffer_length, 2, channel_count);
-		GodotAudio.script.connect(GodotAudio.ctx.destination);
-		return GodotAudio.script.bufferSize;
+	godot_audio_is_available__proxy: 'sync',
+	godot_audio_is_available: function () {
+		if (!(window.AudioContext || window.webkitAudioContext)) {
+			return 0;
+		}
+		return 1;
 	},
 
-	godot_audio_start: function(buffer_ptr, p_process_start, p_process_end, p_process_capture) {
-		const audioDriverProcessStart = GodotOS.get_func(p_process_start);
-		const audioDriverProcessEnd = GodotOS.get_func(p_process_end);
-		const audioDriverProcessCapture = GodotOS.get_func(p_process_capture);
-		GodotAudio.script.onaudioprocess = function(audioProcessingEvent) {
-			audioDriverProcessStart();
-
-			var input = audioProcessingEvent.inputBuffer;
-			var output = audioProcessingEvent.outputBuffer;
-			var internalBuffer = HEAPF32.subarray(
-					buffer_ptr / HEAPF32.BYTES_PER_ELEMENT,
-					buffer_ptr / HEAPF32.BYTES_PER_ELEMENT + output.length * output.numberOfChannels);
-			for (var channel = 0; channel < output.numberOfChannels; channel++) {
-				var outputData = output.getChannelData(channel);
-				// Loop through samples.
-				for (var sample = 0; sample < outputData.length; sample++) {
-					outputData[sample] = internalBuffer[sample * output.numberOfChannels + channel];
-				}
-			}
-
-			if (GodotAudio.input) {
-				var inputDataL = input.getChannelData(0);
-				var inputDataR = input.getChannelData(1);
-				for (var i = 0; i < inputDataL.length; i++) {
-					audioDriverProcessCapture(inputDataL[i]);
-					audioDriverProcessCapture(inputDataR[i]);
-				}
-			}
-			audioDriverProcessEnd();
-		};
+	godot_audio_init: function(p_mix_rate, p_latency, p_state_change, p_latency_update) {
+		const statechange = GodotOS.get_func(p_state_change);
+		const latencyupdate = GodotOS.get_func(p_latency_update);
+		return GodotAudio.init(p_mix_rate, p_latency, statechange, latencyupdate);
 	},
 
 	godot_audio_resume: function() {
@@ -118,48 +152,21 @@ var GodotAudio = {
 		}
 	},
 
-	godot_audio_get_latency__proxy: 'sync',
-	godot_audio_get_latency: function() {
-		var latency = 0;
-		if (GodotAudio.ctx) {
-			if (GodotAudio.ctx.baseLatency) {
-				latency += GodotAudio.ctx.baseLatency;
-			}
-			if (GodotAudio.ctx.outputLatency) {
-				latency += GodotAudio.ctx.outputLatency;
-			}
-		}
-		return latency;
-	},
-
 	godot_audio_capture_start__proxy: 'sync',
 	godot_audio_capture_start: function() {
 		if (GodotAudio.input) {
 			return; // Already started.
 		}
-		function gotMediaInput(stream) {
-			GodotAudio.input = GodotAudio.ctx.createMediaStreamSource(stream);
-			GodotAudio.input.connect(GodotAudio.script);
-		}
-
-		function gotMediaInputError(e) {
-			out(e);
-		}
-
-		if (navigator.mediaDevices.getUserMedia) {
-			navigator.mediaDevices.getUserMedia({"audio": true}).then(gotMediaInput, gotMediaInputError);
-		} else {
-			if (!navigator.getUserMedia)
-				navigator.getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
-			navigator.getUserMedia({"audio": true}, gotMediaInput, gotMediaInputError);
-		}
+		GodotAudio.create_input(function(input) {
+			input.connect(GodotAudio.driver.get_node());
+		});
 	},
 
 	godot_audio_capture_stop__proxy: 'sync',
 	godot_audio_capture_stop: function() {
 		if (GodotAudio.input) {
 			const tracks = GodotAudio.input['mediaStream']['getTracks']();
-			for (var i = 0; i < tracks.length; i++) {
+			for (let i = 0; i < tracks.length; i++) {
 				tracks[i]['stop']();
 			}
 			GodotAudio.input.disconnect();
@@ -170,3 +177,165 @@ var GodotAudio = {
 
 autoAddDeps(GodotAudio, "$GodotAudio");
 mergeInto(LibraryManager.library, GodotAudio);
+
+/**
+ * The AudioWorklet API driver, used when threads are available.
+ */
+const GodotAudioWorklet = {
+
+	$GodotAudioWorklet__deps: ['$GodotAudio'],
+	$GodotAudioWorklet: {
+		promise: null,
+		worklet: null,
+
+		create: function(channels) {
+			const path = Module['locateFile']('godot.audio.worklet.js');
+			GodotAudioWorklet.promise = GodotAudio.ctx.audioWorklet.addModule(path).then(function() {
+				GodotAudioWorklet.worklet = new AudioWorkletNode(
+					GodotAudio.ctx,
+					'godot-processor',
+					{
+						'outputChannelCount': [channels]
+					}
+				);
+				return Promise.resolve();
+			});
+			GodotAudio.driver = GodotAudioWorklet;
+		},
+
+		start: function(in_buf, out_buf, state) {
+			GodotAudioWorklet.promise.then(function() {
+				const node = GodotAudioWorklet.worklet;
+				node.connect(GodotAudio.ctx.destination);
+				node.port.postMessage({
+					'cmd': 'start',
+					'data': [state, in_buf, out_buf],
+				});
+				node.port.onmessage = function(event) {
+					console.error(event.data);
+				};
+			});
+		},
+
+		get_node: function() {
+			return GodotAudioWorklet.worklet;
+		},
+
+		close: function() {
+			return new Promise(function(resolve, reject) {
+				GodotAudioWorklet.promise.then(function() {
+					GodotAudioWorklet.worklet.port.postMessage({
+						'cmd': 'stop',
+						'data': null,
+					});
+					GodotAudioWorklet.worklet.disconnect();
+					GodotAudioWorklet.worklet = null;
+					GodotAudioWorklet.promise = null;
+					resolve();
+				});
+			});
+		},
+	},
+
+	godot_audio_worklet_create: function(channels) {
+		GodotAudioWorklet.create(channels);
+	},
+
+	godot_audio_worklet_start: function(p_in_buf, p_in_size, p_out_buf, p_out_size, p_state) {
+		const out_buffer = GodotOS.heapSub(HEAPF32, p_out_buf, p_out_size);
+		const in_buffer = GodotOS.heapSub(HEAPF32, p_in_buf, p_in_size);
+		const state = GodotOS.heapSub(HEAP32, p_state, 4);
+		GodotAudioWorklet.start(in_buffer, out_buffer, state);
+	},
+
+	godot_audio_worklet_state_wait: function(p_state, p_idx, p_expected, p_timeout) {
+		Atomics.wait(HEAP32, (p_state >> 2) + p_idx, p_expected, p_timeout);
+		return Atomics.load(HEAP32, (p_state >> 2) + p_idx);
+	},
+
+	godot_audio_worklet_state_add: function(p_state, p_idx, p_value) {
+		return Atomics.add(HEAP32, (p_state >> 2) + p_idx, p_value);
+	},
+
+	godot_audio_worklet_state_get: function(p_state, p_idx) {
+		return Atomics.load(HEAP32, (p_state >> 2) + p_idx);
+	},
+};
+
+autoAddDeps(GodotAudioWorklet, "$GodotAudioWorklet");
+mergeInto(LibraryManager.library, GodotAudioWorklet);
+
+/*
+ * The deprecated ScriptProcessorNode API, used when threads are disabled.
+ */
+const GodotAudioScript = {
+
+	$GodotAudioScript__deps: ['$GodotAudio'],
+	$GodotAudioScript: {
+		script: null,
+
+		create: function(buffer_length, channel_count) {
+			GodotAudioScript.script = GodotAudio.ctx.createScriptProcessor(buffer_length, 2, channel_count);
+			GodotAudio.driver = GodotAudioScript;
+			return GodotAudioScript.script.bufferSize;
+		},
+
+		start: function(p_in_buf, p_in_size, p_out_buf, p_out_size, onprocess) {
+			GodotAudioScript.script.onaudioprocess = function(event) {
+				// Read input
+				const inb = GodotOS.heapSub(HEAPF32, p_in_buf, p_in_size);
+				const input = event.inputBuffer;
+				if (GodotAudio.input) {
+					const inlen = input.getChannelData(0).length;
+					for (let ch = 0; ch < 2; ch++) {
+						const data = input.getChannelData(ch);
+						for (let s = 0; s < inlen; s++) {
+							inb[s * 2 + ch] = data[s];
+						}
+					}
+				}
+
+				// Let Godot process the input/output.
+				onprocess();
+
+				// Write the output.
+				const outb = GodotOS.heapSub(HEAPF32, p_out_buf, p_out_size);
+				const output = event.outputBuffer;
+				const channels = output.numberOfChannels;
+				for (let ch = 0; ch < channels; ch++) {
+					const data = output.getChannelData(ch);
+					// Loop through samples and assign computed values.
+					for (let sample = 0; sample < data.length; sample++) {
+						data[sample] = outb[sample * channels + ch];
+					}
+				}
+			};
+			GodotAudioScript.script.connect(GodotAudio.ctx.destination);
+		},
+
+		get_node: function() {
+			return GodotAudioScript.script;
+		},
+
+		close: function() {
+			return new Promise(function(resolve, reject) {
+				GodotAudioScript.script.disconnect();
+				GodotAudioScript.script.onaudioprocess = null;
+				GodotAudioScript.script = null;
+				resolve();
+			});
+		},
+	},
+
+	godot_audio_script_create: function(buffer_length, channel_count) {
+		return GodotAudioScript.create(buffer_length, channel_count);
+	},
+
+	godot_audio_script_start: function(p_in_buf, p_in_size, p_out_buf, p_out_size, p_cb) {
+		const onprocess = GodotOS.get_func(p_cb);
+		GodotAudioScript.start(p_in_buf, p_in_size, p_out_buf, p_out_size, onprocess);
+	},
+};
+
+autoAddDeps(GodotAudioScript, "$GodotAudioScript");
+mergeInto(LibraryManager.library, GodotAudioScript);