As an alternative to expect, here is a basic setup for IPC::Open3. You should be able to get the error thrown by cdrecord when you run this. Just put the reads in a while(1) loop, and check for your percentage done.

#!/usr/bin/perl
use warnings;
use strict;
use IPC::Open3;

my $pid = open3(\*WRITE, \*READ,0,"/usr/bin/cdrecord -v -dummy -eject 
+/mnt/my.iso");
            #if \*ERROR is false, STDERR is sent to STDOUT  

#while(1){ 

#select(undef,undef,undef,.01); 

chomp(my $output = <READ>);
print "$output\n";

#do some split and test to extract percentage 

#} 

waitpid($pid, 1);
# It is important to waitpid on your child process,   
# otherwise zombies could be created.
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