no prob if u want u can try

Here are a valid YouTube link, but your regex detects an error

http://www.youtube.com/watch?gl=FR&hl=fr&v=BZmE3fUKU5U

your regex can be check all that valide links?? no!!

but look Here are 3 invalid YouTube links but your regex does not detect any error

1- http://www.youtube.com/watch?v=RFMT_IzT4&feature=rec-HM-fresh+div

RFMT_IzT4 <==== 9 characters not 11 !!!

2- http://ww.youtube.com/watch?v=Pc3yFlYlhCQ&feature=fvw

ww. <====== not www. !!

3- http://wwwxyoutubexcom/watch?v=Pc3yFlYlhCQ&feature=fvw

no dots!!!

so finally, my own opinion is

$regex($1,http:\/\/www\.youtube\..+\/watch\?(gl=..&..=..&v|v)=[^&]{11})

this regex will check if the link is

http://www.youtube.<something(.com .fr) mabe>/watch?= over 11 characters not include "&"

u can try that regex with all that links and that checking better