From 4af1d096deebdebbca6d19456b19eb00ae42c01a Mon Sep 17 00:00:00 2001
From: Flyinghead <raphael.jean@gmail.com>
Date: Fri, 13 Dec 2024 15:58:32 +0100
Subject: [PATCH] audio: reset buffer on loadstate/term. Fix null audio driver
 on windows

Eliminate audio clicks when loading a state or starting the next game.
Fix overflow in null audio driver on windows. Detect fast forward and
reset time counter.
---
 core/audio/audiobackend_null.cpp | 19 +++++++++++--------
 core/audio/audiostream.cpp       | 20 ++++++++++++++++++++
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/core/audio/audiobackend_null.cpp b/core/audio/audiobackend_null.cpp
index 67c935a7b..95a6b5647 100644
--- a/core/audio/audiobackend_null.cpp
+++ b/core/audio/audiobackend_null.cpp
@@ -19,17 +19,20 @@ public:
 
 	u32 push(const void* frame, u32 samples, bool wait) override
 	{
-		if (wait)
+		if (wait && last_time.time_since_epoch() != the_clock::duration::zero())
 		{
-			if (last_time.time_since_epoch() != the_clock::duration::zero())
-			{
-				auto fduration = std::chrono::nanoseconds(1000000000L * samples / 44100);
-				auto duration = fduration - (the_clock::now() - last_time);
+			auto fduration = std::chrono::nanoseconds(1'000'000'000LL * samples / 44100);
+			auto duration = fduration - (the_clock::now() - last_time);
+			if (duration > std::chrono::nanoseconds::zero())
 				std::this_thread::sleep_for(duration);
-				last_time += fduration;
-			}
-			else
+			if (duration < -std::chrono::milliseconds(67))
+				// if ~4 frames ahead, reset time (fast forward detection)
 				last_time = the_clock::now();
+			else
+				last_time += fduration;
+		}
+		else {
+			last_time = the_clock::now();
 		}
 		return 1;
 	}
diff --git a/core/audio/audiostream.cpp b/core/audio/audiostream.cpp
index 4a6694edf..15f9a3965 100644
--- a/core/audio/audiostream.cpp
+++ b/core/audio/audiostream.cpp
@@ -1,5 +1,8 @@
 #include "audiostream.h"
 #include "cfg/option.h"
+#include "emulator.h"
+
+static void registerForEvents();
 
 struct SoundFrame { s16 l; s16 r; };
 
@@ -60,6 +63,7 @@ void WriteSample(s16 r, s16 l)
 
 void InitAudio()
 {
+	registerForEvents();
 	TermAudio();
 
 	std::string slug = config::AudioBackend;
@@ -138,3 +142,19 @@ void StopAudioRecording()
 		currentBackend->termRecord();
 	audio_recording_started = false;
 }
+
+static void registerForEvents()
+{
+	static bool done;
+	if (done)
+		return;
+	done = true;
+	// Empty the audio buffer when loading a state or terminating the game
+	const auto& callback = [](Event, void *) {
+		writePtr = 0;
+	};
+	EventManager::listen(Event::Terminate, callback);
+	EventManager::listen(Event::LoadState, callback);
+}
+
+