Hello,
I’ve made a patch to make QGC use hardware decoding on Windows. This patch has fixed all of the latency and video grey screen glitches in the few cases we have tested so far. In order to merge this patch into stable, we need more testing and feedback. Information about the patch is here.
There is a windows installer for the test build here.
If you are having issues with the video performance in QGC 4.0 on Windows, please try the test build, and report your feedback. (A good thing to report beside the video performance is the CPU/GPU usage from task manager in the stable 4.0 version vs this test version).