DVD disk detection

Hello.
I'm working on a multimedia player based on PC.
It will be only an administrator for external aplications that will handle the 
diferent tasks.
I like that when you insert a media on the drive, press play, and it play
For that i have to identify what kind of media is inserted, i have no problem 
with cdroms (audio, vcd, data cds with divx) using ioctl calls, but i can't 
identify dvds
I'm using libdvdread for that, i thougt that if i try to open the dvd, and 
it's succeded, it's a dvd, if not, is a cdrom.
But it dosn't work.
this is the code (C++):

dvd_reader_t *dvd;
dvd=DVDOpen("dev/hdc");
if (&dvd!=0)
 {
    DVDClose(dvd);
    return 4; //type 4, dvd 
  }
else 
//is cdrom, cdrom code..

What i'm doing wrong?, anyone have other idea for doing this?
any help will be really appreciate.

Thanks
Paulo Richards