The way WordPress handles Youtube embeds is awesome - just copy-and-paste the link into the editor.  

Unfortunately, when echoing custom fields in a theme, it isn't that easy.  

Thanks to Convoy for this fix:


_e( wp_oembed_get( get_field( 'youtube_link' ) ) ); 

NOTE: My example, uses Advanced Custom Fields' "get_field" function. You could replace get_field( 'youtube_link' ) with get_post_meta().