Ok, first off CSS (Cascading Style Sheets) is a method of specifying the desired layout for the content of a web page. The content itself should be in HTML or XHTML.

A video is definitely content and so needs to be specified in (x)html and so the <object /> tag is what needs to be used. CSS can be used to specify how you want that element to be displayed... eg you can specify its position, whether it should be inline or block etc but you can't use CSS to say what object should be embedded.