Gray area during startup of video

In Google Chrome (newest version) it often happens (not always) that during refresh a gray block (or black depending on value of opacity) shows up a split second below the navbar until bottom, before the video starts running. This also happens on the joomlaplates demo site.
In Firefox the video always shows nicely.
The Edge browser does not show the video full width and also shows a video progress bar.
My Internet speed is 50MB.
Is there a solution for this the gray/black issue? Or is this perhaps the reason that you gave the Headerbar Overlay Background opacity a high value.

Hi there,
depends not on speed depends on the redering engine of the Browser.
But you can change the opacity of the background in theme settings