Works fine for me:

#! perl
use strict;
use warnings;
use File::Basename;

my $item = 'L:\My-Folder.mkv';
my($filename, $dirs, $suffix) = fileparse($item, qr/\.[mM][kK][vV]/);

print "filename:    $filename\n";
print "directories: $dirs\n";
print "suffix:      $suffix\n";
[download]

Output:

16:23 >perl 1018_SoPW.pl
filename:    My-Folder
directories: L:\
suffix:      .mkv

16:23 >
[download]

I think you’ll need to provide a minimal but complete, working script together with your test data and the output you are seeing.

From the backslash in the path I assume you’re on Windows?

Hope that helps,