Images/iframes placeholder for better anchor menu

Hello! I have a problem with long landing pages ang anchor link menus. Also, problems seen in posts with table of content.
When loading page/post there are empty place and when we click at link the anchor mistakes. After scroll down to load all media, anchors works fine because all imeges/iframes at it’s places.

How about to do something like predefined transparent placeholders? The script looks at the page, searching media dimensions and creates placeholder for each object. Or something like this. It can be do when post/page publishing or editing.

Thanks!