Hi, here the images. It seems that the Toolset Bootstrap theme does not define the content_width of the theme > see http://www.wpbeginner.com/wp-themes/how-to-set-oembed-max-width-in-wordpress-3-5-with-content_width/.
Anyways, if I have a page without sidebar this page also has a other content width then a page with sidebar, so even adding that code of the previous article to my own functions.php does not give me a solution for this. I now use this plugin: https://wordpress.org/plugins/advanced-responsive-video-embedder/. They add some CSS and Javascript so that the video's are fluid and always are 100% width.
But maybe still a good idea to do something with the content_width anyways, don't know if it's also important for other things (like galleries or so…). But for me this specific problem is now solved because of the plugin.
Kind regards,
Willem