^.+(?|&)v=([a-zA-Z0-9]+).*$

hxxp://www.youtube.com/v/$1

hxxp://www.youtube.com/?watch="YoutubeID"

Youtube.com/v/youtubeID.

http://www.youtube.com/watch?v=67-YcLickUA

use strict;
use warnings;

my $string = 'http://www.youtube.com/watch?v=67-YcLickUA';

$string =~ s(.+watch?v=([0-9a-zA-Z-]+))(Youtube.com/v/$1);

print "$stringn";