Comparison of high definition optical disc formats

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This article compares the technical specifications of HD DVD and Blu-ray Disc, two mutually incompatible, high definition optical disc formats that, beginning in 2006, attempted to improve upon and eventually replace the DVD standard. The two formats remained in a format war until February 19, 2008 when Toshiba, HD DVD's creator, announced plans to cease development, manufacturing and marketing of HD DVD players and recorders.^[1]

There are other high-definition optical disc formats including the multi-layered red-laser Versatile Multilayer Disc and a Chinese variant of HD DVD known as CH-DVD.

[edit] Technical details

^ a These maximum storage capacities apply to currently released media as of February 2008. The DVD Forum has approved a triple-layer version of HD DVD that would have a capacity of up to 51 GB, and Hitachi has proposed a modified Blu-Ray version that would support a capacity of up to 100 GB. However, neither has yet been mass-produced or released.
^ b All HD DVD players are required to decode the two primary channels (left and right) of any Dolby TrueHD track^[2][3]; however, every HD DVD player released thus far decodes 5.1 channels of TrueHD.
^ c On November 1, 2007 Secondary video and audio decoder became mandatory for new Blu-ray Disc players when the Bonus View requirement came into effect. However, players introduced to the market before this date can continue to be sold without Bonus View.
^ d There are some differences in the implementation of Dolby Digital Plus (DD+) on the two formats. On Blu-ray Disc, DD+ can only be used to extend a primary Dolby Digital (DD) 5.1 audiotrack. In this method 640 kbit/s is allocated to the primary DD 5.1 audiotrack (which is independently playable on players that do not support DD+), and up to 1 Mbit/s is allocated for the DD+ extension. The DD+ extension is used to replace the rear channels of the DD track with higher fidelity versions, along with adding additional channels for 6.1/7.1 audiotracks. On HD DVD, DD+ is used to encode all channels (up to 7.1), and no legacy DD track is required since all HD DVD players are required to decode DD+.
^ e On PAL DVDs, 24 frame per second content is stored as 50 interlaced frames per second and gets replayed 4% faster. This process can be reversed to retrieve the original 24 frame per second content. On NTSC DVDs, 24 frame per second content is stored as 60 interlaced frames per second using a process called 3:2 pulldown, which if done properly can also be reversed.
^ f As of April 2008, about 66.5% of Blu-ray discs are region-free and 33.5% use region codes.^[4]

[edit] Capacity/codecs

Blu-ray has a higher maximum disc capacity than HD DVD (50 GB vs. 30 GB for a single sided disc). In September 2007 the DVD Forum approved a preliminary specification for the triple-layer 51GB HD DVD (ROM only) disc though Toshiba never stated whether it was compatible with existing HD DVD players. In September 2006 TDK announced a prototype Blu-ray Disc with a capacity of 200GB^[5]. TDK was also the first to develop a Blu-Ray prototype with a capacity of 100GB in May 2005^[6]. In October 2007 Hitachi developed a Blu-Ray prototype with a capacity of 100GB. Hitachi has stated that current Blu-ray drives would only require a few firmware updates in order to play the disc^[7].

The first 50 GB dual-layer Blu-ray Disc release was the movie Click, which was released on October 10, 2006. As of April 2008, over 52% of Blu-ray movies are published on 50 GB dual layer discs with the remainder on 25 GB discs.^[8] 85% of HD DVD movies are published on 30 GB dual layer discs, with the remainder on 15 GB discs.^[9][10]

The choice of video compression technology (codec) complicates any comparison of the formats. Blu-ray Disc and HD DVD both support the same three video compression standards: MPEG-2, VC-1 and AVC, each of which exhibits different bitrate/noise-ratio curves, visual impairments/artifacts, and encoder maturity. Initial Blu-ray Disc titles often used MPEG-2 video, which requires the highest average bitrate and thus the most space, to match the picture quality of the other two video codecs. As of 2007, more and more titles have been authored with the newer compression standards: AVC and VC-1. HD DVD titles have used VC-1 and AVC almost exclusively since the format's introduction. Warner Bros., which used to release movies in both formats prior to June 1st, 2007, often uses the same encode (with VC-1 codec) for both Blu-ray Disc and HD DVD, with identical results. In contrast, Paramount, before they stopped releasing Blu-ray Discs, used different encodings for each format: VC-1 for HD DVD and either AVC or MPEG-2 for Blu-ray.

Whilst the two formats support similar audio codecs, their usage varies. Most titles released on the Blu-ray format include Dolby Digital tracks for each language in the region, a DTS-HD Master Audio track for all 20th Century Fox titles, Dolby TrueHD for current Sony Pictures titles and many also include a Linear PCM track for the primary language. On the other hand, most titles released on the HD DVD format include Dolby Digital Plus tracks for each language in the region, and some also include a Dolby TrueHD track for the primary language.

[edit] Interactivity

Both Blu-ray Disc and HD DVD have two main options for interactivity (on-screen menus, bonus features, etc.).

Blu-ray's basic mode is known as HDMV or BDMV ("High Definition Movie Mode" or "Blu-ray Disc Movie Mode"), whilst HD DVD's is known as "Standard Content". Both offer modest upgrades from standard DVD, such as the use of more buttons on-screen, a larger colour palette, and expanded programming environment. BDMV is more powerful than Standard Content, and has been used on many Blu-ray disc titles. Standard Content has been used less on HD DVDs^{[citation needed]}. HD DVD's Standard Content is a minor change from standard DVD's subpicture technology, while Blu-ray's BDMV is completely new. This makes transitioning from standard DVD to Standard Content HD DVD relatively simple^{[citation needed]} -- for example, Apple's DVD Studio Pro has supported authoring Standard Content since version 4.0.3.^{[citation needed]} For more advanced interactivity Blu-ray disc supports BD-J while HD DVD supports Advanced Content.

[edit] Disc construction

Blu-ray Discs contain their data relatively close to the surface (less than 0.1 mm) which combined with the smaller spot size presents a problem when the surface is scratched as data would be destroyed. To overcome this, TDK, Sony, and Panasonic each have developed a proprietary scratch resistant surface coating. TDK trademarked theirs as Durabis, which has withstood direct abrasion by steel wool and marring with markers in tests.^[11]

HD DVD uses traditional material and has the same scratch and surface characteristics of a regular DVD. The data is at the same depth (0.6 mm) as DVD as to minimize damage from scratching. As with DVD the construction of the HD DVD disc allows for a second side of either HD DVD or DVD.

A study performed by Home Media Magazine (August 5, 2007) concluded that HD DVD discs and Blu-ray discs are essentially equal in production cost. Quotes from several disc manufacturers for 25,000 units of HD DVDs and Blu-rays revealed a price differential of only 5-10 cents. (Lowest price: 90 cents versus 100 cents. Highest price: $1.45 versus $1.50.)^[12] Another study performed by Wesley Tech (February 9, 2007) arrived at a similar conclusion. Quotes for 10,000 discs show that a 15 gigabyte HD DVD costs $11,500 total, and 25 gigabyte Blu-ray or a 30 gigabyte HD DVD costs $13,000 total.^[13] For larger quantities of 100,000 units, the 30 gigabyte HD DVD was more expensive than the 25 gigabyte Blu-ray ($1.55 versus $1.49).^[14]

[edit] Hybrid discs

At the January 8, 2007 Consumer Electronics Show, Warner Bros. introduced a hybrid technology, Total HD, that would reportedly support both formats on a single disc.^[15]The new discs would overlay the Blu-ray and HD DVD layers, placing them respectively 0.1 mm and 0.5 mm beneath the surface. The Blu-ray top layer would act as a two-way mirror, reflecting just enough light for a Blu-ray reader to read and an HD DVD player to ignore. But the following September, Warner President Ron Sanders said that the technology was on hold due to Warner being the only one that would publish on it.^[16]

As of January 4, 2008, Warner Bros. announced that they will be supporting the Blu-Ray format exclusively after June 1, 2008. This news along with the end of the format war would indicate that the hybrid discs once announced by Warner Bros. will not be put into production.

[edit] Copy prevention

The primary means of copy prevention on both formats is the Advanced Access Content System (AACS). Use of AACS is optional for HD DVD, but mandatory for Blu-ray, which can add thousands of dollars to production costs.^[17] Other copy-prevention strategies include:

[edit] Region coding

Main article: Blu-ray Disc - Region codes

The Blu-ray specification and all currently available players support region coding. As of April 2008 about 66.5% of Blu-ray discs are region-free and 33.5% use region codes.^[18]

The HD DVD specification has no region coding, so an HD DVD disc from anywhere in the world will work in any player. The DVD Forum's steering committee has discussed a request from Disney to add it, but many of the 20 companies on the committee actively oppose it.^[19].

Many film titles that are exclusive to Blu-ray in the United States such as Sony's xXx, Fox's Fantastic Four: Rise of the Silver Surfer and Disney's The Prestige, are available on HD DVD in other countries due to different distribution agreements. Because of this, film titles that are exclusive to Blu-ray in the U.S. can be bought on HD DVDs by U.S. consumers purchasing them online from Europe or Asia. Since there is no region coding in HD DVDs, there are no restrictions playing these foreign-bought HD DVDs in an HD DVD player.^[20] Similarly, European customers can obtain HD DVD discs from American online retailers for titles that are Blu-ray exclusive or haven't yet been released in their own countries.

[edit] Retail price of consumer-writable discs

[edit] References

[edit] External links

Blu-ray Portal

• Blu-ray vs. HD DVD article by cdfreaks.com