you could hack a forced https return in the functions.php file to search for iframes that have a src starting with https://www.youtu or https://youtu and replace with https://www.yout and https://yout respectively. [I left off the ‘be’ of these urls since some of the share urls are youtu.be and youtube.com]
//Embed Video Fix
function add_secure_video_options($html) {
if (strpos($html, "<iframe" ) !== false) {
$search = array('src="https://www.youtu','src="https://youtu');
$replace = array('src="https://www.youtu','src="https://youtu');
$html = str_replace($search, $replace, $html);
return $html;
} else {
return $html;
}
}
add_filter('the_content', 'add_secure_video_options', 10);