From c88651939a37e875bc9362161570b3aaae96ef5a Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Sun, 23 Jun 2019 13:14:55 -0700
Subject: [PATCH] Re-add latency bounding on the SDL audio renderer

---
 app/streaming/audio/renderers/sdl.h      |  2 ++
 app/streaming/audio/renderers/sdlaud.cpp | 20 ++++++++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/app/streaming/audio/renderers/sdl.h b/app/streaming/audio/renderers/sdl.h
index 53716fa7..63410a06 100644
--- a/app/streaming/audio/renderers/sdl.h
+++ b/app/streaming/audio/renderers/sdl.h
@@ -21,4 +21,6 @@ public:
 private:
     SDL_AudioDeviceID m_AudioDevice;
     void* m_AudioBuffer;
+    int m_FrameDurationMs;
+    int m_FrameSize;
 };
diff --git a/app/streaming/audio/renderers/sdlaud.cpp b/app/streaming/audio/renderers/sdlaud.cpp
index 84d3e096..aa43dd2a 100644
--- a/app/streaming/audio/renderers/sdlaud.cpp
+++ b/app/streaming/audio/renderers/sdlaud.cpp
@@ -33,6 +33,9 @@ bool SdlAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION*
     // Specifying non-Po2 seems to work for our supported platforms.
     want.samples = opusConfig->samplesPerFrame;
 
+    m_FrameSize = opusConfig->samplesPerFrame * sizeof(short) * opusConfig->channelCount;
+    m_FrameDurationMs = opusConfig->samplesPerFrame / 48;
+
     m_AudioDevice = SDL_OpenAudioDevice(NULL, 0, &want, &have, 0);
     if (m_AudioDevice == 0) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
@@ -41,7 +44,7 @@ bool SdlAudioRenderer::prepareForPlayback(const OPUS_MULTISTREAM_CONFIGURATION*
         return false;
     }
 
-    m_AudioBuffer = malloc(opusConfig->samplesPerFrame * sizeof(short) * opusConfig->channelCount);
+    m_AudioBuffer = malloc(m_FrameSize);
     if (m_AudioBuffer == nullptr) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                      "Failed to allocate audio buffer");
@@ -92,6 +95,18 @@ bool SdlAudioRenderer::submitAudio(int bytesWritten)
         return true;
     }
 
+    // Don't queue if there's already more than 30 ms of audio data waiting
+    // in Moonlight's audio queue.
+    if (LiGetPendingAudioFrames() * m_FrameDurationMs > 30) {
+        return true;
+    }
+
+    // Provide backpressure on the queue to ensure too many frames don't build up
+    // in SDL's audio queue.
+    while (SDL_GetQueuedAudioSize(m_AudioDevice) / m_FrameSize > 10) {
+        SDL_Delay(1);
+    }
+
     if (SDL_QueueAudio(m_AudioDevice, m_AudioBuffer, bytesWritten) < 0) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                      "Failed to queue audio sample: %s",
@@ -103,5 +118,6 @@ bool SdlAudioRenderer::submitAudio(int bytesWritten)
 
 int SdlAudioRenderer::getCapabilities()
 {
-    return CAPABILITY_DIRECT_SUBMIT;
+    // Direct submit can't be used because we use LiGetPendingAudioFrames()
+    return 0;
 }