With my PLEXTOR DVDR PX-712A every DVD video-disc is always recognized as
'volume_empty_dvd_rom' which e.g. prevents playback with totem or xine when the
device is mounted by gnome-volume-manager. The output of hal-device for the
mentioned DVD-type and player is as follows:

0: udi = '/org/freedesktop/Hal/devices/volume_empty_dvd_rom'
  org.freedesktop.Hal.Device.Volume.method_execpaths = {
'hal-system-storage-eject' } (string list)
  org.freedesktop.Hal.Device.Volume.method_signatures = { 'as' } (string list)
  org.freedesktop.Hal.Device.Volume.method_names = { 'Eject' } (string list)
  info.interfaces = { 'org.freedesktop.Hal.Device.Volume' } (string list)
  info.udi = '/org/freedesktop/Hal/devices/volume_empty_dvd_rom'  (string)
  volume.disc.capacity = 8170489856  (0x1e6ffc800)  (uint64)
  volume.disc.is_rewritable = false  (bool)
  volume.disc.is_appendable = false  (bool)
  volume.disc.is_blank = true  (bool)
  volume.disc.has_data = false  (bool)
  volume.disc.has_audio = false  (bool)
  volume.disc.type = 'dvd_rom'  (string)
  volume.size = 8170489856  (0x1e6ffc800)  (uint64)
  volume.num_blocks = 15957988  (0xf37fe4)  (int)
  volume.block_size = 2048  (0x800)  (int)
  info.capabilities = { 'volume', 'block' } (string list)
  info.category = 'volume'  (string)
  volume.is_partition = true  (bool)
  volume.is_disc = true  (bool)
  volume.is_mounted = false  (bool)
  volume.mount_point = ''  (string)
  volume.label = ''  (string)
  volume.uuid = ''  (string)
  volume.fsversion = ''  (string)
  volume.fsusage = ''  (string)
  volume.fstype = ''  (string)
  storage.model = ''  (string)
  block.storage_device = '/org/freedesktop/Hal/devices/storage_serial_179131' 
(string)
  block.is_volume = true  (bool)
  block.minor = 64  (0x40)  (int)
  block.major = 3  (0x3)  (int)
  block.device = '/dev/hdb'  (string)
  linux.hotplug_type = 3  (0x3)  (int)
  info.parent = '/org/freedesktop/Hal/devices/storage_serial_179131'  (string)
  linux.sysfs_path_device = '/sys/block/hdb/fakevolume'  (string)
  linux.sysfs_path = '/sys/block/hdb/fakevolume'  (string)

 [..]

11: udi = '/org/freedesktop/Hal/devices/storage_serial_179131'
  info.addons = { 'hald-addon-storage' } (string list)
  block.storage_device = '/org/freedesktop/Hal/devices/storage_serial_179131' 
(string)
  info.udi = '/org/freedesktop/Hal/devices/storage_serial_179131'  (string)
  storage.cdrom.write_speeds = { '16620', '11080', '8310', '5540', '3324' }
(string list)
  storage.cdrom.write_speed = 16620  (0x40ec)  (int)
  storage.cdrom.read_speed = 11080  (0x2b48)  (int)
  storage.cdrom.support_media_changed = true  (bool)
  storage.cdrom.hddvdrw = false  (bool)
  storage.cdrom.hddvdr = false  (bool)
  storage.cdrom.hddvd = false  (bool)
  storage.cdrom.bdre = false  (bool)
  storage.cdrom.bdr = false  (bool)
  storage.cdrom.bd = false  (bool)
  storage.cdrom.dvdplusrdl = false  (bool)
  storage.cdrom.dvdplusrw = true  (bool)
  storage.cdrom.dvdplusr = true  (bool)
  storage.cdrom.dvdram = false  (bool)
  storage.cdrom.dvdrw = false  (bool)
  storage.cdrom.dvdr = true  (bool)
  storage.cdrom.dvd = true  (bool)
  storage.cdrom.cdrw = true  (bool)
  storage.cdrom.cdr = true  (bool)
  storage.requires_eject = true  (bool)
  storage.hotpluggable = false  (bool)
  info.capabilities = { 'storage', 'block', 'storage.cdrom' } (string list)
  info.category = 'storage'  (string)
  info.product = 'PLEXTOR DVDR PX-712A'  (string)
  storage.removable = true  (bool)
  storage.physical_device = '/org/freedesktop/Hal/devices/pci_10de_36e_ide_0_1'
 (string)
  storage.firmware_version = '1.05'  (string)
  storage.serial = '179131'  (string)
  storage.vendor = ''  (string)
  storage.model = 'PLEXTOR DVDR PX-712A'  (string)
  storage.drive_type = 'cdrom'  (string)
  storage.automount_enabled_hint = true  (bool)
  storage.media_check_enabled = true  (bool)
  storage.no_partitions_hint = true  (bool)
  storage.bus = 'ide'  (string)
  block.is_volume = false  (bool)
  block.minor = 64  (0x40)  (int)
  block.major = 3  (0x3)  (int)
  block.device = '/dev/hdb'  (string)
  linux.hotplug_type = 3  (0x3)  (int)
  info.parent = '/org/freedesktop/Hal/devices/pci_10de_36e_ide_0_1'  (string)
  linux.sysfs_path_device = '/sys/block/hdb'  (string)
  linux.sysfs_path = '/sys/block/hdb'  (string)