Something like this...

if( $string =~ m/MTV\s*=\s*(0x[a-f0-9]+)/i ) {
    print $1, "\n";
}
[download]

It's just a matter of anchoring to something predictable, and capturing the right pattern. ;)

Update: By the way, [a-f0-9] could also be represented by [[:xdigit:]] The POSIX character class for a hexidecimal digit. In that case, the RE would look like this:

if( $string =~ m/MTV\s*=\s*(0x[[:xdigit:]]+)/ ) {
    print $1, "\n";
}
[download]

It's not really gaining anything to spell it that way, but perhaps could be seen as a little clearer reading.