Merge pull request #517 from cscd98/audio-fix

Update libretro.h, fix audio stutter on mode 1/2

Source/Core/AudioCommon/SoundStream.h

@@ -25,5 +25,7 @@ public:
 #ifdef __LIBRETRO__
   virtual void Update(unsigned int num_samples) {}
   virtual void ProcessCallBack() {}
+  // On the CPU thread at each emulated field boundary
+  virtual void NewField() {}
 #endif
 };

Source/Core/Core/Core.cpp

@@ -1004,6 +1004,10 @@ void Callback_NewField(Core::System& system)
 #ifdef __LIBRETRO__
   if (system.IsDualCoreMode())
     system.GetFifo().StopGpuLoop();
+  // frontend waiting on audio here holds the thread while
+  // the frame is presented.
+  if (SoundStream* sound_stream = system.GetSoundStream())
+    sound_stream->NewField();
 #endif
 }
 

Source/Core/DolphinLibretro/Audio.cpp

@@ -24,7 +24,8 @@ enum CallBackMode
 {
   // Dolphin will Push samples into the soundstream
   PUSH_SAMPLES = 0,
-  // Samples are pushed per frame in retro_run, but use frame time callback to set pace
+  // One emulated frame's samples are pushed in each retro_run, so the frontend's audio sync and
+  // rate control pace the core
   SYNC_PER_FRAME = 1,
   // RetroArch requests audio samples based on its callbacks (target refresh rate/buffer status)
   ASYNC_CALLBACK = 2,
@@ -77,7 +78,7 @@ unsigned int GetActiveSampleRate()
 void Reset()
 {
   g_use_call_back_audio = Libretro::Options::GetCached<int>(Libretro::Options::audio::CALL_BACK_AUDIO,
-    CallBackMode::PUSH_SAMPLES);
+    CallBackMode::SYNC_PER_FRAME);
   g_audio_state_cb = false;
 }
 
@@ -89,6 +90,11 @@ void Init()
   if (g_use_call_back_audio == CallBackMode::PUSH_SAMPLES)
     return;
 
+  // a frontend audio callback would make the frontend treat the core's
+  // audio as callback driven, outside its audio sync and rate control
+  if (g_use_call_back_audio == CallBackMode::SYNC_PER_FRAME)
+    return;
+
   retro_audio_callback racb = {};
   racb.callback = &retroarch_audio_cb;
   racb.set_state = &retroarch_audio_state_cb;
@@ -217,34 +223,29 @@ void Stream::MixAndPush(unsigned int num_samples)
   }
 }
 
+// Per frame sync: each field's samples go to the frontend from the CPU thread as the field ends,
+void Stream::NewField()
+{
+  PushAudioForFrame();
+}
+
 void Stream::PushAudioForFrame()
 {
   if (g_use_call_back_audio != CallBackMode::SYNC_PER_FRAME || !m_mixer || !batch_cb)
     return;
 
-  // Calculate samples needed for this frame at output rate
-  unsigned samples_for_frame;
-  
-  if (FrameTiming::IsEnabled())
-  {
-    samples_for_frame = GetSamplesForFrame(m_sample_rate);
-  }
-  else
-  {
-    if (Libretro::g_core_refresh_rate <= 0.0)
-    {
-      if (retro_get_region() == RETRO_REGION_NTSC)
-        samples_for_frame = m_sample_rate / 60;
-      else
-        samples_for_frame = m_sample_rate / 50;
-    }
-    else
-    {
-      samples_for_frame =
-        static_cast<unsigned>(std::lround(m_sample_rate / Libretro::g_core_refresh_rate));
-    }
-  }
-  
+  // The DSP fills the mixer at the game's refresh rate, not the
+  // display's, so that rate is used and the fraction carried over: the mixer then neither fills up
+  // nor runs dry, and the frontend's rate control covers the display's difference.
+  double frame_rate = Libretro::g_core_refresh_rate;
+  if (frame_rate <= 0.0)
+    frame_rate = (retro_get_region() == RETRO_REGION_NTSC) ? 60.0 / 1.001 : 50.0;
+
+  static double carry = 0.0;
+  const double exact = m_sample_rate / frame_rate + carry;
+  unsigned samples_for_frame = static_cast<unsigned>(exact);
+  carry = exact - samples_for_frame;
+
   samples_for_frame = std::clamp(samples_for_frame, MIN_SAMPLES, MAX_SAMPLES);
 
   MixAndPush(samples_for_frame);
@@ -276,9 +277,10 @@ void Stream::ProcessCallBack()
 
   if (Libretro::Audio::g_buf_support.load(std::memory_order_relaxed))
   {
+    constexpr unsigned FULL_PERCENT = 75;
     unsigned occ = Libretro::Audio::g_buf_occupancy.load(std::memory_order_relaxed);
 
-    if (occ >= MAX_SAMPLES)
+    if (occ >= FULL_PERCENT)
       return;
 
     // Use frame time to decide how much to push

Source/Core/DolphinLibretro/Audio.h

@@ -39,6 +39,7 @@ public:
   void Update(unsigned int num_samples) override;
 
   void ProcessCallBack() override;
+  void NewField() override;
 
 private:
   s16 m_buffer[MAX_SAMPLES * 2];

Source/Core/DolphinLibretro/Common/Options.cpp

@@ -603,7 +603,7 @@ static struct retro_core_option_v2_definition option_defs[] = {
       { "2",  "Async - driven by callbacks using refresh rate and audio buffer status" },
       { nullptr, nullptr }
     },
-    "0"
+    "1"
   },
 
   // ========== SYSCONF (GC) ==========

Source/Core/DolphinLibretro/Main.cpp

@@ -500,15 +500,6 @@ void retro_run(void)
 
   RETRO_PERFORMANCE_STOP(dolphin_main_func);
 
-  if (auto* sound_stream = system.GetSoundStream())
-  {
-    auto* libretro_stream = static_cast<Libretro::Audio::Stream*>(sound_stream);
-    if (libretro_stream)
-    {
-      libretro_stream->PushAudioForFrame();
-    }
-  }
-
   if (Libretro::Input::g_has_microphone_support)
     poll_microphone();
 }