From 38d4e356811a59efef6139f9bbdb3f8ca316eeea Mon Sep 17 00:00:00 2001
From: squidbus <175574877+squidbus@users.noreply.github.com>
Date: Mon, 30 Dec 2024 04:00:06 -0800
Subject: [PATCH] sdl_audio: Set sample frames hint and use smarter wait loop.

---
 src/core/libraries/audio/cubeb_audio.cpp |  2 +-
 src/core/libraries/audio/sdl_audio.cpp   | 26 ++++++++++++++++++------
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/src/core/libraries/audio/cubeb_audio.cpp b/src/core/libraries/audio/cubeb_audio.cpp
index 4127931b7..fa4a06e7e 100644
--- a/src/core/libraries/audio/cubeb_audio.cpp
+++ b/src/core/libraries/audio/cubeb_audio.cpp
@@ -42,7 +42,7 @@ public:
             .layout = get_channel_layout(),
             .prefs = CUBEB_STREAM_PREF_NONE,
         };
-        u32 latency_frames = 512;
+        u32 latency_frames = port.samples_num;
         if (const auto ret = cubeb_get_min_latency(ctx, &stream_params, &latency_frames);
             ret != CUBEB_OK) {
             LOG_WARNING(Lib_AudioOut,
diff --git a/src/core/libraries/audio/sdl_audio.cpp b/src/core/libraries/audio/sdl_audio.cpp
index 598941ba7..86144c923 100644
--- a/src/core/libraries/audio/sdl_audio.cpp
+++ b/src/core/libraries/audio/sdl_audio.cpp
@@ -3,6 +3,7 @@
 
 #include <thread>
 #include <SDL3/SDL_audio.h>
+#include <SDL3/SDL_hints.h>
 
 #include "common/logging/log.h"
 #include "core/libraries/audio/audioout.h"
@@ -10,13 +11,20 @@
 
 namespace Libraries::AudioOut {
 
-constexpr int AUDIO_STREAM_BUFFER_THRESHOLD = 65536; // Define constant for buffer threshold
-
 class SDLPortBackend : public PortBackend {
 public:
-    explicit SDLPortBackend(const PortOut& port) {
+    explicit SDLPortBackend(const PortOut& port) : buffer_size(port.buffer_size) {
+        // We want the wait time for delivering frames out to be as small as possible,
+        // so set the sample frames hint to the number of samples per buffer.
+        // Note that this will only apply when the device is first opened, but it still
+        // helps to get a sample of what the game expects from at least one port.
+        const auto samples_num_str = std::to_string(port.samples_num);
+        if (!SDL_SetHint(SDL_HINT_AUDIO_DEVICE_SAMPLE_FRAMES, samples_num_str.c_str())) {
+            LOG_WARNING(Lib_AudioOut, "Failed to set SDL audio sample frames hint to {}: {}",
+                        samples_num_str, SDL_GetError());
+        }
         const SDL_AudioSpec fmt = {
-            .format = port.is_float ? SDL_AUDIO_F32 : SDL_AUDIO_S16,
+            .format = port.is_float ? SDL_AUDIO_F32LE : SDL_AUDIO_S16LE,
             .channels = port.channels_num,
             .freq = static_cast<int>(port.freq),
         };
@@ -46,11 +54,16 @@ public:
         if (!stream) {
             return;
         }
-        SDL_PutAudioStreamData(stream, ptr, static_cast<int>(size));
-        while (SDL_GetAudioStreamAvailable(stream) > AUDIO_STREAM_BUFFER_THRESHOLD) {
+        // Game expects audio output to wait. To prevent choppy audio, we wait when
+        // there are two or more of the guest buffer size already queued.
+        while (SDL_GetAudioStreamQueued(stream) >= buffer_size * 4) {
+            SDL_FlushAudioStream(stream);
             // Yield to allow the stream to drain.
             std::this_thread::yield();
         }
+        if (!SDL_PutAudioStreamData(stream, ptr, static_cast<int>(size))) {
+            LOG_ERROR(Lib_AudioOut, "Failed to output to SDL audio stream: {}", SDL_GetError());
+        }
     }
 
     void SetVolume(const std::array<int, 8>& ch_volumes) override {
@@ -66,6 +79,7 @@ public:
     }
 
 private:
+    u32 buffer_size;
     SDL_AudioStream* stream;
 };