You would anchor an video the same way you anchor an image. But the location will depend on the size of the text through which it is flowing. This will depend on the EPUB reader and the font size selected by the reader.
The only way to control it would be to put it on its own page, or starting at the start of a page. You would have to do this by making it into a chapter in a book, or preceding it by a paragaph style which you select to begin a page break. Or to edit the HTML and CSS.
What Steve said makes sense and I agree it would be best way of achieving this however
you can try using the "Article Panel" , you can create the article for different object on the page and sequence them as well.
When exporting the EPUB , select "layout based on the Article panel". , it may help but if doesn't then move to steve's idea.