From 80a40ac5f9601d3bd613635ab0e0e1d245bbf165 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <aicommander@gmail.com>
Date: Fri, 15 Feb 2019 23:51:20 -0800
Subject: [PATCH] Increase frame drop threshold

---
 .../video/ffmpeg-renderers/pacer/pacer.cpp    | 40 ++++++++++++++-----
 .../video/ffmpeg-renderers/pacer/pacer.h      |  1 +
 2 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp b/app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp
index 653ad28c..27d80633 100644
--- a/app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp
+++ b/app/streaming/video/ffmpeg-renderers/pacer/pacer.cpp
@@ -14,8 +14,6 @@
 #include "dxvsyncsource.h"
 #endif
 
-#define PACING_HISTORY_ENTRIES 8
-
 // We may be woken up slightly late so don't go all the way
 // up to the next V-sync since we may accidentally step into
 // the next V-sync period. It also takes some amount of time
@@ -135,7 +133,8 @@ void Pacer::vsyncCallback(int timeUntilNextVsyncMillis)
             }
         }
 
-        if (m_PacingQueueHistory.count() == PACING_HISTORY_ENTRIES) {
+        // Keep a rolling 500 ms window of pacing queue history
+        if (m_PacingQueueHistory.count() == m_DisplayFps / 2) {
             m_PacingQueueHistory.dequeue();
         }
 
@@ -220,19 +219,38 @@ void Pacer::renderFrame(AVFrame* frame)
     m_VideoStats->renderedFrames++;
     av_frame_free(&frame);
 
-    // If a frame has arrived while rendering, our renderer probably
-    // was blocked waiting on V-Sync. Drop a frame to allow the
-    // queued frame to drain.
+    // Drop frames if we have too many queued up for a while
     m_FrameQueueLock.lock();
-    if (!m_RenderQueue.isEmpty()) {
-        frame = m_RenderQueue.dequeue();
+
+    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;
+        }
+    }
+
+    // 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());
+
+    // Catch up if we're several frames ahead
+    while (m_RenderQueue.count() > frameDropTarget) {
+        AVFrame* frame = m_RenderQueue.dequeue();
+
+        // Drop the lock while we call av_frame_free()
         m_FrameQueueLock.unlock();
         m_VideoStats->pacerDroppedFrames++;
         av_frame_free(&frame);
+        m_FrameQueueLock.lock();
     }
-    else {
-        m_FrameQueueLock.unlock();
-    }
+
+    m_FrameQueueLock.unlock();
 }
 
 void Pacer::submitFrame(AVFrame* frame)
diff --git a/app/streaming/video/ffmpeg-renderers/pacer/pacer.h b/app/streaming/video/ffmpeg-renderers/pacer/pacer.h
index 4a7a7203..20bab6f9 100644
--- a/app/streaming/video/ffmpeg-renderers/pacer/pacer.h
+++ b/app/streaming/video/ffmpeg-renderers/pacer/pacer.h
@@ -34,6 +34,7 @@ private:
     QQueue<AVFrame*> m_RenderQueue;
     QQueue<AVFrame*> m_PacingQueue;
     QQueue<int> m_PacingQueueHistory;
+    QQueue<int> m_RenderQueueHistory;
     QMutex m_FrameQueueLock;
     QWaitCondition m_RenderQueueNotEmpty;
     QWaitCondition m_PacingQueueNotEmpty;