I did the above changes and tried but no use.

Show the changed code :) your probably forgot to binmode ... you could simply use mirror( $url, $filename ) or get-flash-videos ...

Please see the modified code

use LWP;
use URI::Escape;
my $url;

foreach $_ (@ARGV) {
$_ =~ s[^.*[=/]?([\w\-]{11}).*][$1];

my $ua = LWP::UserAgent->new;
#$ua->proxy(['http', 'ftp'], 'http://192.16.3.254:8080/');

$c = uri_unescape($t = $ua->get("http://www.youtube.com/get_video_info
+?&video_id=$_&el=detailpage&ps=default&eurl=&gl=US&hl=en")->content);
$t =~ /&title=([^&]+)&/ ? $t = uri_unescape($1) : '';
$t =~ s[\+|/][ ]g ? $t = quotemeta $t : '';
$c =~ s/.*fmt_url_map=[\d\|]+([^,]+).*/$1/;

print $c."\n";

open(FILE, '>Test.mp4');
binmode (FILE);    

    my $resp = $ua->get( $c
                    ) or die;                

    if ( $resp->is_success) 
    {
        print FILE $resp->content;
        close(FILE);
    }
    else
    {
        print "Failed\n";
    }            
}
[download]

You're not fixing problems already identified in responses above, starting with the first, urging you to test your open (and, by implication, your close, too)...

open(FILE, '>Test.mp4');

which would be better written as

open(my $file, '>Test.mp4') or die "Can't open for writing, $FILE", $!;

and you just might find using strict and warnings helpful