$(document).ready(function(){
    // I added the video size here in case you wanted to modify it more easily
    var vidWidth = 480;
    var vidHeight = 290;

    var obj = '<iframe width="480" height="290" src="http://www.youtube.com/embed/[vid]?autoplay=0&autohide=1" frameborder="0" allowfullscreen></iframe>';

    $('p:contains("youtube.com/watch")').each(function(){
        var that = $(this);
        var vid = that.html().match(/(?:v=)([\w\-]+)/g); // end up with v=oHg5SJYRHA0
        var fullMovieUrl = "http://www.youtube.com/watch?" + vid;
        //alert(fullMovieUrl);
        $("*").each(function () { 
            if ($(this).children().length == 0) { 
                $(this).text($(this).text().replace(fullMovieUrl,'')); 
            } 
        });

        if (vid.length) {
            $.each(vid, function(){
                that.append(obj.replace(/\[vid\]/g, this.replace('v=','')) );
            });
        }
    });
});