Download mp4 version of youtube video using javascript

copy dan paste code kat bawah nih kat address bar browser utk download high quality mp4 from youtube

javascript:if(document.location.href.match(/http:\/\/[a-zA-Z\.]*youtube\.com\/watch/)){document.location.href='http://www.youtube.com/get_video?fmt='+(isHDAvailable?'22':'18')+'&video_id='+swfArgs['video_id']+'&t='+swfArgs['t']}