Allow a renderer to opt-out of the render thread and use that for SDL on OGL

app/streaming/video/ffmpeg-renderers/pacer/pacer.h

@@ -26,9 +26,15 @@ public:
 
     void vsyncCallback(int timeUntilNextVsyncMillis);
 
+    void renderOnMainThread();
+
 private:
     static int renderThread(void* context);
 
+    void enqueueFrameForRenderingAndUnlock(AVFrame* frame);
+
+    void renderLastFrameAndUnlock();
+
     void renderFrame(AVFrame* frame);
 
     void dropFrameForEnqueue(QQueue<AVFrame*>& queue);