According to this post, findnodes() uses the full XPath engine. Also, I noticed that the use of position selectors like range[1] isn't supported on twig_handlers or twig_roots.

#!/usr/bin/perl -l

use strict;
use warnings;
use XML::Twig::XPath;

$|=1;

my $file = '/root/Desktop/bitrate.xml';
my $twig =  XML::Twig::XPath->new( twig_roots => {
    "//range/rangeStartTime" => \&update });
$twig->parsefile($file);

sub update {
    my ($twig, $server) = @_;
    print $server->text;
}
[download]

<?xml version="1.0" encoding="UTF-8"?>
<bitrate name="1000">
  <track type="V">
    <range>
      <rangeStartTime>1261287</rangeStartTime>
      <rangeEndTime>1324271</rangeEndTime>
    </range>
    <range>
      <rangeStartTime>1324282</rangeStartTime>
      <rangeEndTime>0.000</rangeEndTime>
    </range>
  </track>
</bitrate>
[download]