You can use a ternary to push onto either the complete URL array or the filename array. To save space I have simplified the URLs and pattern but the principle would still hold for your data. Things would get more complicated if your URLs broke across lines.

$ perl -Mstrict -Mwarnings -MData::Dumper -e '
open my $xmlFH, q{<}, \ <<EOF or die $!;
blarg http://a.b.co.uk/path/to/file.mp3 bloop http://x.y.com/stuff.mp3
blooble http://some.firm.com/downloads/glooble.mp3 sploffle
EOF

my $rx = qr{(?x) ( http:// .*? ( [^/]+ \.mp3 ) ) };
my( @comp, @fn );

my $xmlText = do {
   local $/;
   <$xmlFH>;
   };

push @{ $_ =~ m{^http://} ? \ @comp : \ @fn }, $_ for
   $xmlText =~ m{$rx}g;

print Data::Dumper->Dumpxs( [ \ @comp, \ @fn ], [ qw{ *comp *fn } ] );
+'
@comp = (
          'http://a.b.co.uk/path/to/file.mp3',
          'http://x.y.com/stuff.mp3',
          'http://some.firm.com/downloads/glooble.mp3'
        );
@fn = (
        'file.mp3',
        'stuff.mp3',
        'glooble.mp3'
      );
$
[download]

I hope this is helpful.

Update: Corrected unescaped dot in regex and added (?x) extended syntax to space things out for readability.