1. Page 1
HD-DVD (AOD) Vs Blu-Ray (BD) - Page 1
There has been a lot of discussion lately regarding the two most prominent
recording formats being promoted for HDTV use. Looking back at the recent
past we could say that the same groups that had fought over DVD-Video formats
before it was finally standardized, are still fighting for two new formats.
On one side of the fence we have two Japanese giants of the consumer electronics
industry, NEC and Toshiba. They have jointly developed the "AOD" (Advanced
Optical Disc) format for HDTV recording applications. The main argument for
AOD is that it is play-compatible with DVD-Video, and so it is often called "HD-DVD" for
that reason. Sony and Philips along with Hitachi, Sharp and Samsung stand
on the other side. They are promoting the "BD" format, which is
better known as the "Blu-Ray Disc". Both formats initiate evolutionary
higher capacities than current DVD-Video.
Structurally, HD-DVD is identical to DVD-Video, employing two 0.60mm thick
discs that are bonded together to form the HD disc. It can store 15GB on
a single layer DVD. HD-DVD recordings can therefore be replicated on the
same equipment and manufacturing infrastructure used to replicate standard
DVD-Video recordings. As a result, this minimizes disc production costs.
BD Main Specifications
|
Read-only |
Rewritable |
Data capacity |
Single-layer 15GB/sideDual-layer 30GB/side |
Single-layer 20GB/sideDual-layer 40GB/side |
File format |
UDF |
User bit rate |
36Mbps |
Disc size |
120mm (diagonal), 1.2mm (thickness: 0.6mm x 2) |
Laser wavelength |
405nm |
Lens numerical aperture (NA) |
0.65 |
Track structure |
-- |
Land & groove |
Signal processing |
PRML |
Modulation |
2/3 conversion |
Toshiba and NEC insist that the provided 15GB of capacity is more than adequate
for HDTV software applications. The compression algorithms used in HD-DVD
are different from those currently in use, so there are claims that the 2/3
conversion could reduce picture quality. On the other hand, the format features
the same 0.6 numerical aperture for the object lens and disk structure as
the current DVD disk system. The companies stressed the importance of backward
compatibility. Taking advantage of this compatibility, NEC has developed
a HD DVD drive that employs a single optical head. The head has blue laser
and red laser diodes as light sources. However, the lasers share the same
object lens. Newly developed ICs handle the physical difference between DVD
and HD DVD.
NEC claims the single optical head structure enables production of smaller
and thinner HD DVDs at lower cost. Using the single head, NEC developed prototypes
of full-and half-height drives that achieved 15 Gbytes for a single-layer
ROM disk, 30 Gbytes for a double-layer ROM disk and 20 Gbytes for rewritable
disks.
2. Page 2
HD-DVD (AOD) Vs Blu-Ray (BD) - Page 1
Sony and Philips, along with Hitachi, LG, Matsushita, Pioneer Samsung Electronics,
Sharp and Thomson Multimedia are promoting the "BD" format, which
is better known as the "Blu-Ray Disc".
Blu-Ray main specifications
|
Read-only |
Data capacity |
23.3GB/25GB/27GB |
User bit rate |
36Mbps |
Disc diameter |
120mm |
Disc thickness |
1.2mm (optical transmittance protection layer: 0.1mm) |
Recording format |
Phase change recording |
Laser wavelength |
405nm (blue-violet laser) |
Lens numerical aperture (NA) |
0.85 |
Tracking format |
Groove recording |
Tracking pitch |
0.32um |
Addressing Method |
Groove recording |
Shortest pit length |
0.160/0.149/0.138um |
Recording phase density |
16.8/18.0/19.5Gbit/inch |
Video recording format |
MPEG2 video |
Audio recording format |
AC3, MPEG1, Layer2, etc. |
Cartridge dimension |
Approximately 129 x 131 x 7mm |
Video and audio multiplexing format |
MPEG2 transport stream |
Modulation |
1.7PP (Parity preserve/Prohibit RMTR) |
By adopting a 405nm blue-violet semiconductor laser, with a 0.85NA field lens
and a 0.1mm optical transmittance protection disc layer structure, it can record
up to 27GB video data on a single sided 12cm phase change disc. This means
that 2 hours of digital high definition video and more than 13 hours of standard
TV broadcasting (VHS/standard definition picture quality, 3.8Mbps) can be recorded
on a disc.
In addition, the Blu-Ray specification includes the usage of an optical disc
cartridge which protects the optical disc's recording and playback phase from
dust and fingerprints.
The basic disadvantage of the Blu-Ray format is that it requires a new manufacturing
infrastructure resulting in increased expense while implementation could prove
a long-term process. In addition, the Blu-ray Disk format lacks backward compatibility
with current DVDs.
Sony, a prime supporter of Blu-ray Disc, has already developed Professional
Disc. The format is available in two variants and is targeted at the specific
markets of high-definition broadcast quality video and data archiving and storage.
The BDZ-S77 is currently available in the Japanese market, but there are not
any plans for launching the recorder overseas. Several Japanese companies,
including Sony, Hitachi Maxell and TDK, already offer blank Blu-Ray disc media.
The recorders and media are expensive, but they are obviously first-generation
units whose prices will decline rapidly as market acceptance takes hold.
In contrast to the HD-DVD proposal, Blu-Ray rejects the use of a new video
compression format, sticking with existing audio/video codecs such as MPEG-2
and Dolby Digital that are specified by the U.S. digital HDTV system. Blu-Ray
media makes use of a completely new technology that requires no new advanced
compression algorithms, and is totally different from either DVD or HD-DVD
(AOD). It will therefore require new facilities for the manufacture of the
discs. Blu-Ray also makes use of a highly specialized high numerical aperture
(0.85) lens and what is called near-field recording technology, using a single
platter 1.1mm thick, with a special 0.1 focusing overlayer on the active side
of the disc. Both HD-DVD and Blu-Ray use 405nm blue-violet lasers for writing
and reading. All DVD-type products require 650nm red lasers and a conventional
focusing system, which are both much cheaper than the 405nm lasers and special
near-field high numerical aperture lens systems required for a Blu-Ray recorder
or player.
The DVD Forum appears to be considering several codecs as candidates for the
HD-DVD. These include H.264, the technical specification of which is scheduled
to be decided in March; MPEG-4 Advanced Simple Profile; MPEG-2 with a so-called "enhancement
layer;" and Microsoft Corp.'s Windows Media 9. All the codecs have reportedly
produced satisfactory high-definition quality pictures at the DVD Forum's technical
working group, packing 9 Gbytes of high-definition content onto a two-layer
DVD using a red laser, with encoding bit rates as low as 7 Mbits/second.
Some days ago, the rewritable HD-DVD (High Definition and High Density-DVD)
format was approved in the DVD Forum's general meeting, held in Tokyo. The
new format specifies a 12cm optical disc that can store up to 20Gb of data
on a single-sided disc. Toshiba and NEC have jointly developed the format,
while a read-only version of HD-DVD was approved late last year.
3. Page 3
HD-DVD (AOD) Vs Blu-Ray (BD) - Page 3
Although the DVD Forum seems to be currently backing HD-DVD, the format with
the largest number of backers is Blu-ray Disc, with 12 companies sitting in
on the format committee. Blu-Ray was initially targeted at recording of high-definition
video. However, the latest addition of Hewlett-Packard and Dell to the format
steering committee is expected to result in a widening of its target market
to include the computing space. Of course pricing makes such products unreachable
for the mid-user.
Plasmon has also launched its own format called UDO (Ultra Density Optical),
which is also targeted at the data archiving and storage market as a replacement
for MO (Magneto Optical) discs. UDO uses 405nm blue-violet laser and phase
change technology adapted from the Blu-Ray DVD-type products. UDO drives operate
with an 8KB sector size with direct overwrite capability.
Besides the “violet laser” solutions, the industry has also received
proposals based on red lasers. Warner Bros has proposed the HD DVD-9 compression
method, applied on regular red laser DVDs. This will allow for the format to
launch faster because current facilities can be used and the change in the
current way DVD players work are minimal. It supports development of backward
compatible players that can playback current and next generation DVD.
The weak part of the HD-DVD-9 format is that it can only store 4,7GB on a
single layer DVD. HD content has more than twice the resolution of normal
DVD and therefore also fills much more in raw data. However, it is questionable
whether the compression technology used will meet the increased requirements
for HDTV.
The Chinese answer for HDTV applications is called EVD (Enhanced Versatile
Disc). As with the case of HD-DVD-9, EVD is based on the current red-laser
technology. EVD uses a new, high-level compression system called VP6, developed
by New York-based On2 Technologies, to squeeze 120 minutes of HD movie footage
onto a single disc.
While all formats are physically incompatible, they all bring about a large
jump in data storage because of the same blue laser technology. On the other
hand, it ‘s very possible that there is going to be a major fight between
the two groups supporting the AOD and BD technologies. This cannot be avoided,
because the financial rewards that the winner will obtain will be immense.
Unfortunately, the end-user, as usual, will be the immediate loser, at least
for the first couple of years.