$(document).ready(function() {
    $("iframe").each(function(){
        var ifr_source = $(this).attr('src');
        var wmode = "wmode=transparent";
        if(ifr_source.indexOf('?') != -1) {
            var getQString = ifr_source.split('?');
            var oldString = getQString[1];
            var newString = getQString[0];
            $(this).attr('src',newString+'?'+wmode+'&'+oldString);
        }
        else $(this).attr('src',ifr_source+'?'+wmode);
    });
});