Youtube BBCode v1 - IF

var pt=document.getElementsByClassName('postcolor'),rx=/\[youtube=(small|large|medium)\]([a-z0-9]+)\[\/youtube\]/gim;
for(i=0;i<pt.length;i++){if(rx.test(pt[i].innerHTML)){pt[i].innerHTML=pt[i].innerHTML.replace(rx,'<iframe class="yt-$1" src="http://www.youtube.com/embed/$2"></iframe>');}}