my $ifilename = 'file.in';
my $ofilename = $ifilename . '.bin';

open my $ifile, '<', $ifilename or die "could not open input file $!";
open my $ofile, '>', $ofilename or die "could not open output file $!";

binmode $ifile;
binmode $ofile;

my $n = eof($ifile) ? "" : getc($ifile);
while ((my $c = $n) ne "") {
        $n = eof($ifile) ? "" : getc($ifile);
        print $ofile "$c$n" eq "\x4F\xFF" .. 1 ? $c : "\x0";
}

close $ifile;
close $ofile;