function youtube_parser(url){
        var regExp = /^.*((youtu.be\/)|(v\/)|(\/u\/\w\/)|(embed\/)|(watch\?))\??v?=?([^#\&\?]*).*/;
        var match = url.match(regExp);
        if (match&&match[7].length==11){
            return match[7];
        }else{
            alert("Url incorrecta");
        }
    }

    $('.url_video').html(function(){
        var video_id = youtube_parser(this);
        $('.img-video').append('<img src=http://i1.ytimg.com/vi/'+video_id+'/hqdefault.jpg width=595px>');

    });