Add PoC VsyncSource for Windows using DwmFlush(). Soon to be replaced with D3DKMTWaitForVerticalBlankEvent().

app/app.pro

@@ -34,7 +34,7 @@ win32 {
         LIBS += -L$$PWD/../libs/windows/lib/x64
     }
 
-    LIBS += ws2_32.lib winmm.lib dxva2.lib ole32.lib
+    LIBS += ws2_32.lib winmm.lib dxva2.lib ole32.lib dwmapi.lib
 }
 macx {
     INCLUDEPATH += $$PWD/../libs/mac/include $$PWD/../libs/mac/Frameworks/SDL2.framework/Versions/A/Headers
@@ -159,8 +159,13 @@ config_SLVideo {
 win32 {
     message(DXVA2 renderer selected)
 
-    SOURCES += streaming/video/ffmpeg-renderers/dxva2.cpp
-    HEADERS += streaming/video/ffmpeg-renderers/dxva2.h
+    SOURCES += \
+        streaming/video/ffmpeg-renderers/dxva2.cpp \
+        streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.cpp
+
+    HEADERS += \
+        streaming/video/ffmpeg-renderers/dxva2.h \
+        streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.h
 }
 macx {
     message(VideoToolbox renderer selected)

app/streaming/session.cpp

@@ -821,7 +821,7 @@ void Session::exec()
             // Destroy the old decoder
             delete m_VideoDecoder;
 
-            // Chose a new decoder (hopefully the same one, but possibly
+            // Choose a new decoder (hopefully the same one, but possibly
             // not if a GPU was removed or something).
             if (!chooseDecoder(m_Preferences.videoDecoderSelection,
                                m_Window, m_ActiveVideoFormat, m_ActiveVideoWidth,

app/streaming/video/ffmpeg-renderers/dxva2.cpp

@@ -11,6 +11,7 @@ DEFINE_GUID(DXVADDI_Intel_ModeH264_E, 0x604F8E68,0x4951,0x4C54,0x88,0xFE,0xAB,0x
 
 DXVA2Renderer::DXVA2Renderer() :
     m_SdlRenderer(nullptr),
+    m_Pacer(this),
     m_DecService(nullptr),
     m_Decoder(nullptr),
     m_SurfacesUsed(0),
@@ -27,6 +28,8 @@ DXVA2Renderer::DXVA2Renderer() :
 
 DXVA2Renderer::~DXVA2Renderer()
 {
+    m_Pacer.drain();
+
     SAFE_COM_RELEASE(m_DecService);
     SAFE_COM_RELEASE(m_Decoder);
     SAFE_COM_RELEASE(m_Device);
@@ -430,12 +433,16 @@ bool DXVA2Renderer::isDecoderBlacklisted()
     return result;
 }
 
-bool DXVA2Renderer::initialize(SDL_Window* window, int videoFormat, int width, int height, int)
+bool DXVA2Renderer::initialize(SDL_Window* window, int videoFormat, int width, int height, int maxFps)
 {
     m_VideoFormat = videoFormat;
     m_VideoWidth = width;
     m_VideoHeight = height;
 
+    if (!m_Pacer.initialize(window, maxFps)) {
+        return false;
+    }
+
     // FFmpeg will be decoding on different threads than the main thread that we're
     // currently running on right now. We must set this hint so SDL will pass
     // D3DCREATE_MULTITHREADED to IDirect3D9::CreateDevice().
@@ -493,6 +500,11 @@ bool DXVA2Renderer::initialize(SDL_Window* window, int videoFormat, int width, i
 }
 
 void DXVA2Renderer::renderFrame(AVFrame* frame)
+{
+    m_Pacer.submitFrame(frame);
+}
+
+void DXVA2Renderer::renderFrameAtVsync(AVFrame *frame)
 {
     IDirect3DSurface9* surface = reinterpret_cast<IDirect3DSurface9*>(frame->data[3]);
     HRESULT hr;
@@ -632,7 +644,6 @@ void DXVA2Renderer::renderFrame(AVFrame* frame)
         SDL_LogWarn(SDL_LOG_CATEGORY_APPLICATION,
                     "SDL_RenderClear() failed: %s",
                     SDL_GetError());
-        av_frame_free(&frame);
 
         // We're going to cheat a little bit here. It seems SDL's
         // renderer may flake out in scenarios like moving the window
@@ -646,8 +657,6 @@ void DXVA2Renderer::renderFrame(AVFrame* frame)
     }
 
     hr = m_Processor->VideoProcessBlt(m_RenderTarget, &bltParams, &sample, 1, nullptr);
-    av_frame_free(&frame);
-
     if (FAILED(hr)) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
                      "VideoProcessBlt() failed: %x",

app/streaming/video/ffmpeg-renderers/dxva2.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "renderer.h"
+#include "pacer/pacer.h"
 
 #include <d3d9.h>
 #include <dxva2api.h>
@@ -9,7 +10,7 @@ extern "C" {
 #include <libavcodec/dxva2.h>
 }
 
-class DXVA2Renderer : public IFFmpegRenderer
+class DXVA2Renderer : public IFFmpegRenderer, public IVsyncRenderer
 {
 public:
     DXVA2Renderer();
@@ -21,6 +22,7 @@ public:
                             int maxFps);
     virtual bool prepareDecoderContext(AVCodecContext* context);
     virtual void renderFrame(AVFrame* frame);
+    virtual void renderFrameAtVsync(AVFrame* frame);
 
 private:
     bool initializeDecoder();
@@ -44,6 +46,7 @@ private:
     int m_DisplayHeight;
 
     SDL_Renderer* m_SdlRenderer;
+    Pacer m_Pacer;
 
     struct dxva_context m_DXVAContext;
     IDirect3DSurface9* m_DecSurfaces[19];

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.cpp

@@ -0,0 +1,49 @@
+#include "dxvsyncsource.h"
+
+#include <dwmapi.h>
+
+DxVsyncSource::DxVsyncSource(Pacer* pacer) :
+    m_Pacer(pacer),
+    m_Thread(nullptr)
+{
+    SDL_AtomicSet(&m_Stopping, 0);
+}
+
+DxVsyncSource::~DxVsyncSource()
+{
+    if (m_Thread != nullptr) {
+        SDL_AtomicSet(&m_Stopping, 1);
+        SDL_WaitThread(m_Thread, nullptr);
+    }
+}
+
+bool DxVsyncSource::initialize(SDL_Window* window)
+{
+    m_Thread = SDL_CreateThread(vsyncThread, "DX Vsync Thread", this);
+    if (m_Thread == nullptr) {
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                     "Unable to create DX V-sync thread: %s",
+                     SDL_GetError());
+        return false;
+    }
+
+    return true;
+}
+
+int DxVsyncSource::vsyncThread(void* context)
+{
+    DxVsyncSource* me = reinterpret_cast<DxVsyncSource*>(context);
+
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
+
+    while (SDL_AtomicGet(&me->m_Stopping) == 0) {
+        // FIXME: We should really use D3DKMTWaitForVerticalBlankEvent() instead!
+        // https://bugs.chromium.org/p/chromium/issues/detail?id=467617
+        // https://chromium.googlesource.com/chromium/src.git/+/c564f2fe339b2b2abb0c8773c90c83215670ea71/gpu/ipc/service/gpu_vsync_provider_win.cc
+        DwmFlush();
+
+        me->m_Pacer->vsyncCallback();
+    }
+
+    return 0;
+}

app/streaming/video/ffmpeg-renderers/pacer/dxvsyncsource.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "pacer.h"
+
+class DxVsyncSource : public IVsyncSource
+{
+public:
+    DxVsyncSource(Pacer* pacer);
+
+    virtual ~DxVsyncSource();
+
+    virtual bool initialize(SDL_Window* window);
+
+private:
+    static int vsyncThread(void* context);
+
+    Pacer* m_Pacer;
+    SDL_Thread* m_Thread;
+    SDL_atomic_t m_Stopping;
+};

app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp

@@ -4,6 +4,10 @@
 #include "displaylinkvsyncsource.h"
 #endif
 
+#ifdef Q_OS_WIN32
+#include "dxvsyncsource.h"
+#endif
+
 #define FRAME_HISTORY_ENTRIES 8
 
 Pacer::Pacer(IVsyncRenderer* renderer) :
@@ -18,9 +22,6 @@ Pacer::Pacer(IVsyncRenderer* renderer) :
 
 Pacer::~Pacer()
 {
-    // Stop V-sync callbacks
-    delete m_VsyncSource;
-
     drain();
 }
 
@@ -105,8 +106,10 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps)
                 "Frame pacing: target %d Hz with %d FPS stream",
                 m_DisplayFps, m_MaxVideoFps);
 
-#ifdef Q_OS_DARWIN
+#if defined(Q_OS_DARWIN)
     m_VsyncSource = new DisplayLinkVsyncSource(this);
+#elif defined(Q_OS_WIN32)
+    m_VsyncSource = new DxVsyncSource(this);
 #else
     SDL_assert(false);
 #endif
@@ -126,6 +129,10 @@ void Pacer::submitFrame(AVFrame* frame)
 
 void Pacer::drain()
 {
+    // Stop V-sync callbacks
+    delete m_VsyncSource;
+    m_VsyncSource = nullptr;
+
     while (!m_FrameQueue.isEmpty()) {
         AVFrame* frame = m_FrameQueue.dequeue();
         av_frame_free(&frame);

app/streaming/video/ffmpeg.cpp

@@ -96,10 +96,10 @@ void FFmpegVideoDecoder::reset()
         }
     }
 
-    avcodec_free_context(&m_VideoDecoderCtx);
-
     delete m_Renderer;
     m_Renderer = nullptr;
+
+    avcodec_free_context(&m_VideoDecoderCtx);
 }
 
 bool FFmpegVideoDecoder::completeInitialization(AVCodec* decoder, int videoFormat, int width, int height, bool testOnly)