Yendif Player

The problem:
Assets from the Yendif Player plugin are blocked when the WP site URL uses HTTP and the request to the page is made using HTTPS.

The Cause:
WP core doesn't check the request scheme used by the browser and simply returns the value of get_option('siteurl') to be used as is by the WP_CONTENT_URL constant.

The Yendif Player plugin uses the WP constant WP_PLUGIN_URL to resolve it's assets URLs, however, the WP_PLUGIN_URL is based on the WP_CONTENT_URL, and when it hold the unsecure http:// scheme and the page request is secure using https://, the Yendif Player assets don't get loaded by browser security restrictions blocking the unsecured content.

The solution:
I would recommend removing the requested scheme from the WP_PLUGIN_URL so the assets are loaded based on the current request scheme.

define( 'YENDIF_PLAYER_PLUGIN_URL', str_replace(array('http:', 'https:', '', WP_PLUGIN_URL) . '/' . YENDIF_PLAYER_PLUGIN_NAME );

Then the plugin assets would be loaded from:
//domain.tld/wp-content/plugins/yendif-player/......

... and the browser will load the assets using the same scheme as the request.

Thanks for sharing the solution I'm very grateful to you