As each video element wrapped in `.ossnembed<guid>` class so you mean use below example to change CSS for videos.

~~~
<?php
function my_component_init(){
ossn_add_hook('embed', 'video:css', 'my_component_hook');
}
function my_component_hook($hook, $type, $videcss = "", $params){
//$params['guid'] post guid, width , height.
error_log(print_r($params, true));
$videocss = "<style>.ossnembed{$params['guid']}{some text here}</style>";
return $videocss;
}
ossn_register_callback('ossn', 'init', 'my_component_init');
~~~