From 8551c187775fdca9e27dc46aac4e671085fafc44 Mon Sep 17 00:00:00 2001
From: OpenSauce04 <opensauce04@gmail.com>
Date: Thu, 16 May 2024 15:53:13 +0100
Subject: [PATCH] Improve playback consistency for realtime audio during
 inconsistent framerates

Implements and uses `GetStableFrameTimeScale` instead of `GetLastFrameTimeScale` for realtime audio playback
---
 src/audio_core/hle/hle.cpp |  2 +-
 src/core/core.cpp          |  4 ++--
 src/core/core.h            |  2 +-
 src/core/perf_stats.cpp    | 11 +++++++++++
 src/core/perf_stats.h      |  6 ++++++
 5 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/audio_core/hle/hle.cpp b/src/audio_core/hle/hle.cpp
index a5e2cf63a..3687f9647 100644
--- a/src/audio_core/hle/hle.cpp
+++ b/src/audio_core/hle/hle.cpp
@@ -419,7 +419,7 @@ void DspHle::Impl::AudioTickCallback(s64 cycles_late) {
     // Reschedule recurrent event
     const double time_scale =
         Settings::values.enable_realtime_audio
-            ? std::clamp(Core::System::GetInstance().GetLastFrameTimeScale(), 1.0, 3.0)
+            ? std::clamp(Core::System::GetInstance().GetStableFrameTimeScale(), 1.0, 3.0)
             : 1.0;
     s64 adjusted_ticks = static_cast<s64>(audio_frame_ticks / time_scale - cycles_late);
     core_timing.ScheduleEvent(adjusted_ticks, tick_event);
diff --git a/src/core/core.cpp b/src/core/core.cpp
index 3a3f2f551..7f0d6c4d1 100644
--- a/src/core/core.cpp
+++ b/src/core/core.cpp
@@ -392,8 +392,8 @@ PerfStats::Results System::GetLastPerfStats() {
     return perf_stats ? perf_stats->GetLastStats() : PerfStats::Results{};
 }
 
-double System::GetLastFrameTimeScale() {
-    return perf_stats->GetLastFrameTimeScale();
+double System::GetStableFrameTimeScale() {
+    return perf_stats->GetStableFrameTimeScale();
 }
 
 void System::Reschedule() {
diff --git a/src/core/core.h b/src/core/core.h
index 7b2f00784..a5587edf3 100644
--- a/src/core/core.h
+++ b/src/core/core.h
@@ -193,7 +193,7 @@ public:
 
     [[nodiscard]] PerfStats::Results GetLastPerfStats();
 
-    double GetLastFrameTimeScale();
+    double GetStableFrameTimeScale();
 
     /**
      * Gets a reference to the emulated CPU.
diff --git a/src/core/perf_stats.cpp b/src/core/perf_stats.cpp
index c05cf80e5..9f694f75f 100644
--- a/src/core/perf_stats.cpp
+++ b/src/core/perf_stats.cpp
@@ -129,6 +129,17 @@ double PerfStats::GetLastFrameTimeScale() const {
     return duration_cast<DoubleSecs>(previous_frame_length).count() / FRAME_LENGTH;
 }
 
+double PerfStats::GetStableFrameTimeScale() const {
+    std::scoped_lock lock{object_mutex};
+
+    constexpr double FRAME_LENGTH_MILLIS = (1.0 / SCREEN_REFRESH_RATE) * 1000;
+    const short num_frames = std::min(50ul, current_index + 1);
+    const double sum = std::accumulate(perf_history.begin() + current_index - num_frames,
+                                       perf_history.begin() + current_index, 0.0);
+    const double stable_frame_length = sum / num_frames;
+    return stable_frame_length / FRAME_LENGTH_MILLIS;
+}
+
 void FrameLimiter::WaitOnce() {
     if (frame_advancing_enabled) {
         // Frame advancing is enabled: wait on event instead of doing framelimiting
diff --git a/src/core/perf_stats.h b/src/core/perf_stats.h
index 5cd69afb2..a6ecc7004 100644
--- a/src/core/perf_stats.h
+++ b/src/core/perf_stats.h
@@ -82,6 +82,12 @@ public:
      */
     double GetLastFrameTimeScale() const;
 
+    /**
+     * Has the same functionality as GetLastFrameTimeScale, but uses the mean frame time over the
+     * last 50 frames rather than only the frame time of the previous frame.
+     */
+    double GetStableFrameTimeScale() const;
+
     void AddArticBaseTraffic(u32 bytes) {
         artic_transmitted += bytes;
     }