If you enter individual videos, as ShortCodes or links, and find that small thumbnails do not flow across the page as expected, even though there is sufficient space, this is due to WP’s auto-formatting of post text at display time whereupon extra <p> tags are added where line breaks occur.
You will not see these extra tags in your WP editor but they can be seen if you look at the page source text in your browser.
The simplest way around this is to place the ShortCodes or links all on one line.
People familiar with writing HTML often disable WP’s autoformatting. One way is to add :
remove_filter (‘the_content’, ‘wpautop’);
to your theme’s functions.php file, just before the last ?>
There are various plugins available too, such as PS Disable AutoFormatting; though we have not tested it.