Enhance frame pacing logic for HDR renderers

app/streaming/video/ffmpeg-renderers/d3d11va.cpp

@@ -581,8 +581,8 @@ void D3D11VARenderer::renderFrame(AVFrame* frame)
     }
     else {
         // Otherwise, we'll submit as fast as possible and DWM will discard excess
-        // frames for us. If frame pacing is also enabled, our Vsync source will keep
-        // us in sync with VBlank.
+        // frames for us. If frame pacing is also enabled or we're in full-screen,
+        // our Vsync source will keep us in sync with VBlank.
         flags = 0;
     }
 
@@ -993,8 +993,19 @@ bool D3D11VARenderer::checkDecoderSupport(IDXGIAdapter* adapter)
 
 int D3D11VARenderer::getRendererAttributes()
 {
+    int attributes = 0;
+
     // This renderer supports HDR
-    return RENDERER_ATTRIBUTE_HDR_SUPPORT;
+    attributes |= RENDERER_ATTRIBUTE_HDR_SUPPORT;
+
+    // This renderer requires frame pacing to synchronize with VBlank when we're
+    // in full-screen. In windowed mode, we will render as fast we can and DWM
+    // will grab whatever is latest at the time unless the user opts for pacing.
+    if (SDL_GetWindowFlags(m_DecoderParams.window) & SDL_WINDOW_FULLSCREEN) {
+        attributes |= RENDERER_ATTRIBUTE_FORCE_PACING;
+    }
+
+    return attributes;
 }
 
 bool D3D11VARenderer::needsTestFrame()

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

@@ -443,6 +443,9 @@ int DrmRenderer::getRendererAttributes()
     // This renderer supports HDR
     attributes |= RENDERER_ATTRIBUTE_HDR_SUPPORT;
 
+    // This renderer does not buffer any frames in the graphics pipeline
+    attributes |= RENDERER_ATTRIBUTE_NO_BUFFERING;
+
     return attributes;
 }
 

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

@@ -208,6 +208,7 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
 {
     m_MaxVideoFps = maxVideoFps;
     m_DisplayFps = StreamUtils::getDisplayRefreshRate(window);
+    m_RendererAttributes = m_VsyncRenderer->getRendererAttributes();
 
     if (enablePacing) {
         SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
@@ -225,6 +226,8 @@ bool Pacer::initialize(SDL_Window* window, int maxVideoFps, bool enablePacing)
         // immediately like they used to.
     #endif
 
+        SDL_assert(m_VsyncSource != nullptr || !(m_RendererAttributes & RENDERER_ATTRIBUTE_FORCE_PACING));
+
         if (m_VsyncSource != nullptr && !m_VsyncSource->initialize(window, m_DisplayFps)) {
             return false;
         }
@@ -259,22 +262,31 @@ void Pacer::renderFrame(AVFrame* frame)
     // Drop frames if we have too many queued up for a while
     m_FrameQueueLock.lock();
 
-    int frameDropTarget = 0;
-    for (int queueHistoryEntry : m_RenderQueueHistory) {
-        if (queueHistoryEntry == 0) {
-            // Be lenient as long as the queue length
-            // resolves before the end of frame history
-            frameDropTarget = 2;
-            break;
+    int frameDropTarget;
+
+    if (m_RendererAttributes & RENDERER_ATTRIBUTE_NO_BUFFERING) {
+        // Renderers that don't buffer any frames but don't support waitToRender() need us to buffer
+        // an extra frame to ensure they don't starve while waiting to present.
+        frameDropTarget = 1;
+    }
+    else {
+        frameDropTarget = 0;
+        for (int queueHistoryEntry : m_RenderQueueHistory) {
+            if (queueHistoryEntry == 0) {
+                // Be lenient as long as the queue length
+                // resolves before the end of frame history
+                frameDropTarget = 2;
+                break;
+            }
         }
-    }
 
-    // Keep a rolling 500 ms window of render queue history
-    if (m_RenderQueueHistory.count() == m_MaxVideoFps / 2) {
-        m_RenderQueueHistory.dequeue();
-    }
+        // Keep a rolling 500 ms window of render queue history
+        if (m_RenderQueueHistory.count() == m_MaxVideoFps / 2) {
+            m_RenderQueueHistory.dequeue();
+        }
 
-    m_RenderQueueHistory.enqueue(m_RenderQueue.count());
+        m_RenderQueueHistory.enqueue(m_RenderQueue.count());
+    }
 
     // Catch up if we're several frames ahead
     while (m_RenderQueue.count() > frameDropTarget) {

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

@@ -52,4 +52,5 @@ private:
     int m_MaxVideoFps;
     int m_DisplayFps;
     PVIDEO_STATS m_VideoStats;
+    int m_RendererAttributes;
 };

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

@@ -110,7 +110,8 @@ private:
 #define RENDERER_ATTRIBUTE_FULLSCREEN_ONLY 0x01
 #define RENDERER_ATTRIBUTE_1080P_MAX 0x02
 #define RENDERER_ATTRIBUTE_HDR_SUPPORT 0x04
-#define RENDERER_ATTRIBUTE_SELF_PACING 0x08
+#define RENDERER_ATTRIBUTE_NO_BUFFERING 0x08
+#define RENDERER_ATTRIBUTE_FORCE_PACING 0x10
 
 class IFFmpegRenderer : public Overlay::IOverlayRenderer {
 public:

app/streaming/video/ffmpeg.cpp

@@ -290,7 +290,8 @@ bool FFmpegVideoDecoder::completeInitialization(const AVCodec* decoder, PDECODER
     // Don't bother initializing Pacer if we're not actually going to render
     if (!testFrame) {
         m_Pacer = new Pacer(m_FrontendRenderer, &m_ActiveWndVideoStats);
-        if (!m_Pacer->initialize(params->window, params->frameRate, params->enableFramePacing)) {
+        if (!m_Pacer->initialize(params->window, params->frameRate,
+                                 params->enableFramePacing || (params->enableVsync && (m_FrontendRenderer->getRendererAttributes() & RENDERER_ATTRIBUTE_FORCE_PACING)))) {
             return false;
         }
     }