Preserve fractional frame budget when downsampling cameras

tools/chatgui/src/call_video_cadence.h

@@ -1,20 +1,21 @@
 #pragma once
 #include <cstdint>
 
-// Бюджет 30 fps с запасом четверти кадра на дрожание PTS, без накопления после паузы.
+// Бюджет 30 fps с запасом одного кадра; интервал >=25мс запрещает burst после паузы.
 class CallVideoCadence {
-    int64_t lastPts = -1, credit = 1250000;
+    int64_t lastPts = -1, lastAccepted = -1, credit = 1250000;
 public:
     bool accept(int64_t pts) {
         if (lastPts >= 0) {
             if (pts <= lastPts) return false;
             const int64_t elapsed = pts - lastPts;
-            credit = elapsed >= 41667 ? 1250000 : credit + elapsed * 30;
+            credit = elapsed >= 66667 ? 2000000 : credit + elapsed * 30;
-            if (credit > 1250000) credit = 1250000;
+            if (credit > 2000000) credit = 2000000;
         }
         lastPts = pts;
-        if (credit < 1000000) return false;
+        if (credit < 1000000 || (lastAccepted >= 0 && pts - lastAccepted < 25000)) return false;
         credit -= 1000000;
+        lastAccepted = pts;
         return true;
     }
 };