Respect GPU pipeline capacity before submitting a new camera frame

tools/chatgui/src/call_video_engine.cpp

@@ -282,7 +282,7 @@ void CallVideoEngine::transmit() {
                 call_video_port_applied(m->id, format.generation, request, 0);
         }
 #ifdef HAVE_STREAM_CAPTURE
-        bool submit = state.can_encode && pts > lastPts;
+        bool submit = state.can_encode && pts > lastPts && encoder.pendingFrames() < 8;
         if (submit && (image.isNull() || nowUs() - pts > CallCameraMaxFrameAgeUs)) {
             DEBUG_WARN(DEBUG_CATEGORY_CALL, "video TX skips old capture age_us=%lld", (long long)(nowUs() - pts));
             lastPts = pts; ++expired; continue;