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  foreach (1 .. $dvd->titles_count) {
    print "$_ : ";
    print $dvd->title_chapters_count($_);
    print " chapters\n";
    my $title = $dvd->get_title($_);
    # ...
  }

=head1 DESCRIPTION

This module provide way to query video DVD using libdvdread.

=head2 Dvd Structure

  Dvd (device, directory, iso file...)
  |
  \_ VMG (VIDEO_VTS.IFO)
     ` title_one => title1 (chapters map)
     ` title_two => title2 (chapters map)
     ` ...
  |
  \_ VTS title1 (VIDEO_1_VTS.IFO)
     ` audio track 1
     ` audio track 2
     ` audio track ...
     ` subtitle track 1
     ` subtitle track 2
     ` subtitle track ...
     ` chapters location in VOB
  |
  \_ VTS title2 (VIDEO_2_VTS.IFO)
  \_ VTS title...

=head2 This Module

=over 4

=item The DVD and VGM information are provide by DVD::Read module.

=item The VTS (per title) are provide by L<DVD::Read::Title> module.

=back

=head2 Technical Notes

=head3 Video Sector

The 'first_sector' and 'last_sector' from module can disagree with
'tcprobe' (from transcode) results.

After wasting some times to look the code, it seems 'tcprobe' code wrong.

In a nutshell, Title is made of chapter, chapter point to first cells,
each cells have a first and last sector. But a chapter can have severals
cells. This is what is used by lsdvd to count cells.

'tcprobe' assume each chapter have only one cells, then fetch cells[chapter]
to get sectors number. Which is wrong, according 'lsdvd' code.

Notice both VGM and VTS are often need to get title information.
This module will transparently fetch information need to retrieve
information you want.

=head2 PERFORMANCE NOTICE

You have two way to fetch title object:

    my $dvd = DVD::Read->new('/dev/crom');
    my $title = $dvd->get_title(1);
    # or in another way
    my $title = DVD::Read::Title->new($dvd, 1);

or by calling directly the DVD::Read::Title module
with a location:

    my $title = DVD::Read::Title->new('/dev/cdrom', 1);

Notice in the second case, calling another title will force to
read again the main information table (if need) because the
DVD::Read object will not be transmitted, so another will be created.

This can be important when using real DVD reader device since waking
up it can take time.

=head1 FUNCTIONS

=cut

=head2 new($device)

Return a new DVD::Read object for $device. $device can either
a real device, an iso image file, a directory, or anything supported
by libdvdread:

 * If the path given is a directory, then the files in that directory may be
 * in any one of these formats:
 *
 *   path/VIDEO_TS/VTS_01_1.VOB
 *   path/video_ts/vts_01_1.vob
 *   path/VTS_01_1.VOB
 *   path/vts_01_1.vob

=cut

sub new {
    my ($class, $device) = @_;

    my $dvd = DVD::Read::Dvd->new($device) or return;

    bless({
        device => $device,
        dvd => $dvd,
        vmg => undef,
        vts => [],
    }, $class);
}

sub _vmg {
    my ($self) = @_;
    return $self->{vmg} ||= DVD::Read::Dvd::Ifo::Vmg->new($self->{dvd});
}