embed youtube not working

I have a problem to embedding youtube in my wordpress pages/posts, simply when I but youtube link directly in visual tap of my pages/posts (https://www.youtube.com/watch?v=YDGnMK8_4pU) it doesn’t work, when I put the embed code (<object width="560" height="315"><param name="movie" value="//www.youtube.com/v/EeIJiGQVcVc?hl=en_US&version=3&rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="//www.youtube.com/v/EeIJiGQVcVc?hl=en_US&version=3&rel=0" type="application/x-shockwave-flash" width="560" height="315" allowscriptaccess="always" allowfullscreen="true"></embed></object>) it works.
I tried the direct link on my localhost wordpress (https://www.youtube.com/watch?v=YDGnMK8_4pU) and it works.
so I tried to deactivate all plugins put no result.
I tried to add the following code to functions.php:

add_action( 'init', 'ag_add_oembed_handlers' );
function ag_add_oembed_handlers() {
	wp_oembed_add_provider( '#https://(www\.)?youtube\.com/watch.*#i', 'https://www.youtube.com/oembed', true );
}

but also not working.
I discovered this problem when I tried to use Youtube Channel Gallery plugin, so this plugin not working because of this problem.

any help please