Trace desktop stream stalls across playback and preview UI

tools/chatgui/src/stream_publish_engine.cpp

@@ -146,6 +146,8 @@ struct StreamPublishEngine::Impl {
     QVideoFrame previewFrame;
     QVideoFrame presentedPreview;
     int64_t lastImageCaptureAt = 0;
+    int64_t previewTickAt = 0, previewReportAt = 0, previewGapMax = 0, previewDispatchMax = 0;
+    unsigned previewUpdates = 0; // Диагностика GUI-предпросмотра; только GUI-поток.
 #endif
 };
 
@@ -164,12 +166,29 @@ StreamPublishEngine::StreamPublishEngine(QObject* parent) : QObject(parent), m(s
     connect(qGuiApp, &QGuiApplication::screenRemoved, this, &StreamPublishEngine::sourcesChanged);
     m_previewTimer.setTimerType(Qt::PreciseTimer); m_previewTimer.setInterval(33);
     connect(&m_previewTimer, &QTimer::timeout, this, [this] {
-        if (!m->running) return;
+        if (!m->running) {
+            m->previewTickAt = m->previewReportAt = m->previewGapMax = m->previewDispatchMax = 0;
+            m->previewUpdates = 0; return;
+        }
+        int64_t tickAt = monotonicUs();
+        if (m->previewTickAt) m->previewGapMax = std::max(m->previewGapMax, tickAt - m->previewTickAt);
+        m->previewTickAt = tickAt;
+        if (!m->previewReportAt) m->previewReportAt = tickAt;
         QVideoFrame frame;
         { std::lock_guard<std::mutex> guard(m->lock);
-          if (m->previewFrame == m->presentedPreview) return;
-          frame = m->presentedPreview = m->previewFrame; }
-        if (frame.isValid()) emit previewVideoChanged(QVariant::fromValue(frame));
+          if (m->previewFrame != m->presentedPreview) frame = m->presentedPreview = m->previewFrame; }
+        if (frame.isValid()) {
+            int64_t dispatchAt = monotonicUs();
+            emit previewVideoChanged(QVariant::fromValue(frame));
+            m->previewDispatchMax = std::max(m->previewDispatchMax, monotonicUs() - dispatchAt); m->previewUpdates++;
+        }
+        if (tickAt - m->previewReportAt >= 1000000) {
+            DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG,
+                "desktop preview GUI id=%llu source_generation=%llu interval_us=%lld updates=%u tick_gap_max_us=%lld dispatch_max_us=%lld",
+                (unsigned long long)m->id, (unsigned long long)m->sourceGeneration, (long long)(tickAt - m->previewReportAt),
+                m->previewUpdates, (long long)m->previewGapMax, (long long)m->previewDispatchMax);
+            m->previewReportAt = tickAt; m->previewUpdates = 0; m->previewGapMax = m->previewDispatchMax = 0;
+        }
     });
     m_previewTimer.start();
 #endif