Align frame advance and movies to full field boundaries

Source/Core/Core/Core.cpp

@@ -839,9 +839,12 @@ void Callback_VideoCopiedToXFB(bool video_update)
 {
   if (video_update)
     s_drawn_frame++;
+}
 
+// Called at field boundaries in `VideoInterface::Update()`
+void FrameUpdate()
+{
   Movie::FrameUpdate();
-
   if (s_frame_step)
   {
     s_frame_step = false;

Source/Core/Core/Core.h

@@ -26,6 +26,7 @@ bool GetIsThrottlerTempDisabled();
 void SetIsThrottlerTempDisabled(bool disable);
 
 void Callback_VideoCopiedToXFB(bool video_update);
+void FrameUpdate();
 
 enum class State
 {

Source/Core/Core/HW/VideoInterface.cpp

@@ -733,6 +733,12 @@ static void EndField()
 // Run when: When a frame is scanned (progressive/interlace)
 void Update(u64 ticks)
 {
+  // If this half-line is at a field boundary, potentially deal with frame-stepping
+  // and/or update movie state before dealing with anything else
+
+  if (s_half_line_count == 0 || s_half_line_count == GetHalfLinesPerEvenField())
+    Core::FrameUpdate();
+
   // If an SI poll is scheduled to happen on this half-line, do it!
 
   if (s_half_line_of_next_si_poll == s_half_line_count)