DVD at 10 - a primer

The 12-cm optical disc has been with us for 25 years and looks set to continue as a means to distribute music and movies in a digital format. But with each new generation, the technical challenges increase and format wars seem to dominate, at least in the early years. GRAHAM SHARPLESS, a technology consultant, tells the story so far.

format war between Blu-ray and HD DVD ended in early 2008, two years after both were launched on the US market in the spring of 2006 and nearly one year after the launch in Europe. There were also two competing formats for DVD, but this war was not fought in the market place.

In 1994 the Hollywood studios were looking for an optical disc format that would store 90 minutes of high quality video and surround sound audio. Video CD did not offer either the playing time or the quality and so a new higher capacity disc was needed.

Meanwhile two groups of mainly consumer electronic companies were developing new disc formats to meet these requirements.

The MultiMedia CD (MMCD), developed by Philips and Sony, was based on the CD but used a red laser and smaller pits for a capacity of 3.7 GB on a single layer.

The Super Density disc (SD) from Toshiba and Warner also used a red laser and smaller pits, but each disc comprised two thinner substrates bonded together and offering a capacity of 5 GB on one layer. Toshiba adopted this approach not specifically to allow double sided or dual layer discs, but to make the discs easier to manufacture.

In April 1995, the two competing groups held seminars in San Francisco and invited CD replicators to attend. Warner gave presentations extolling the virtues of the SD format. On the following day, at a hotel across the road, Philips and Sony did the same for MMCD.

The reaction from the industry was that there should be a single format. But it was the computer industry which succeeded in persuading the two groups to agree on one format. In September that year a single DVD format was agreed in principle and the first draft specification was completed in December 1995. The new format was a combination of SD’s two substrates plus MMCD’s EFM+ modulation, giving a capacity of 4.7 GB per layer. The first DVD players and discs were launched in Japan in November 1996, in the US in March 1997 and in Europe in 1998.

Manufacturing discs

DVD replication requires two moulding machines, with new moulds, and a new process to bond the two substrates together. It was discovered that bonding of the two substrates needed to be carried out either immediately after moulding and metallising or after a period of about 24 hours; otherwise the resulting discs could suffer from excessive tilt (warping).

The Japanese adopted the latter approach and developed systems which included a separate ‘offline’ bonder, which meant storing the substrates for the necessary 24 hours in a dust-free atmosphere. Most DVDs were replicated in this way in the early years.

In Europe, the preference was to bond the substrates immediately after moulding and metallising. This required one piece of equipment plus two integrated moulding machines.

Having overcome the problems of replicating single layer discs, the next step was dual layer, which presented a number of challenges including the semi-reflective and bonding layers. Gold was used initially for the semi-reflective layer but it was expensive. Another option was silicon but was found to be too brittle. Finally a silver alloy offered an affordable solution without any significant problem.

For the next generation formats, HD DVD discs are similar to DVDs, but, for best results, new machines are needed, but which were also capable of replicating DVDs. Blu-ray discs each include a ‘cover layer’ of only 0.1 mm, compared with 0.6 mm for DVD and 1.2 mm for CD. This proved difficult to manufacture to the tight tolerances in thickness and optical properties that were needed. A plastic film bonded to the substrate was used initially, but spin coating techniques have been developed that meet the tolerances and were less costly to implement. In addition to these difficulties, the very thin cover layer made it necessary to protect the surface of discs from finger prints and scratches that could make discs unplayable.

formats and applications

The term DVD originally meant ‘Digital Video Disc’, then ‘Digital Versatile Disc’ but now has no meaning except a disc with a substantially higher capacity than the CD that can carry high quality movies, surround sound audio, computer software or a combination of these. New versions of the DVD were developed after the original DVD-Video and DVD-ROM were launched:

DVD-Audio was intended to provide the highest quality audio in up to five-channel surround sound. But it has never proved popular, probably because the discs require special DVD-Audio players and expensive audio equipment for best results.

SACD was developed by Sony and Philips and competed with DVD-Audio. Most SACD discs included a CD layer to play on CD players. The multi-channel content on SACD discs could not be played on DVD players. Most SACD discs have been bought as CDs by people who do not own SACD players.

DVD-Plus was an attempt to combine DVD and CD data on the same disc, but discs were thicker than normal (1.5 mm instead of 1.2 mm) and did not become as successful as expected by the developers.

The DVD-ROM format is used for games, but it took several years for the games developers to move from CD-ROM because the penetration of PCs with DVD drives was not high enough. However, Sony’s PS2 made use of DVD-ROM discs from its launch and the newer PS3 was designed to play Blu-ray discs.

licensing

Licensing a technology is a way for developers to be compensated for the investment in research and development, but it also helps prevent non-standard products from entering the market place and to control piracy.

All replicators, plus equipment and player manufacturers, need to be licensed to use the DVD technology and the associated logos. For the CD formats, Philips handles all licensing but for DVD, there are several licensing organisations involved.

In late 1997 the 10-member DVD Consortium that had developed the DVD specifications was renamed the DVD Forum which invited the industry to become members. The DVD Forum decided to set up a separate organisation for licensing the formats and logos. The DVD Format & Logo Licensing Corp established the first five-year DVD licensing period starting in January 2000. Replicators were obliged to pay $10,000 per five-year period for each DVD format replicated. The fee, which could amount to $30,000 for all read-only formats, was independent of the number of discs produced and was the same for large and small replicators.

But the licensing burden did not end there. Patent royalties have to be paid to two bodies (known as 6C and 3C) and at least one individual company. The patents were reviewed for essentiality by an independent patent lawyer. But since the start of patent licensing in 2000, there have been a number of challenges to their validity.

IODRA, the trade association for replicators, mounted a challenge via the European Union and other groups of replicators have also tried to challenge the validity of the patents. Licensing fees have been reduced over the years, but still represent a substantial proportion of the overall cost of a DVD disc.

Replicators are also faced with yet more licensing. MPEG LA was set up to license the MPEG-2 video contained on every DVD-Video disc. The fee per disc depends on the number of movies and their length, but has been simplified so that there is a single fee payable for most discs.

There is also content protection licensing. CSS has no fee per disc, but replicators are charged a flat fee per year, plus very substantial penalties if keys fall into the wrong hands. Other content protection, if used, requires a fee to be paid to the technology supplier for each disc.

Licensing fees are currently 4 US cents for 6C, 5 US cents for 3C (but compliant replicators pay only 3.75 cents) and 3 cents for most discs containing MPEG-2 files. Fees for content protection, apart from CSS, depend on the technology but are usually at least 5 US cents per disc.

Blu-ray licensing includes payments for an Information Agreement as well as a Format and Logo Licensing Agreement. MPEG LA, which also licenses other video coding formats, was asked to carry out patent licensing on behalf of Blu-ray patent holders, but this is still in development while Blu-ray patents from many companies are reviewed.
Content protection for Blu-ray comprises AACS (Advanced Access Content System) plus SPDC (Self Protecting Digital Content) developed by Cryptography Research Inc. This combination offers advanced encryption with the ability to renew the protection for future discs after any hacking of the content protection.

lessons for the future

DVD has been a significant challenge for replicators, hardware manufacturers and equipment suppliers. DVD-Video has proved to be extremely successful and has eclipsed other DVD formats and applications. But the format is not perfect and did not, for example, take full account of the growth of the internet. DVD-Video has suffered from its poor content protection system, CSS, which was hacked at an early stage. Ideally a content protection system should be renewable and include a practical method for revoking players that have been compromised. What the developers of DVD did get right is to agree on a single format, long before any public launch.

Blu-ray and HD DVD were launched on an unsuspecting market with the same purpose in mind. While DVD had offered improved quality compared with broadcast TV, the launch of HDTV has made DVD look poor in comparison. Like DVD the new generation formats are primarily for movies, but the formats do support audio and video games. Titles and players will also support internet connectivity and local storage. In addition AACS and SPDC provide a big improvement in content protection.

It would seem that the two formats have learnt some of the lessons from DVD. But attempts to agree on a single format before the launch were ill-fated. Both formats met the Hollywood requirements; Blu-ray offered the most capacity, but presented a bigger challenge for replicators. HD DVD discs can be replicated on lines that will also replicate DVDs, but Blu-ray lines cannot be used for DVD. With the certainty that two formats could not exist side-by-side for very long, any company investing in Blu-ray risked losing its investment should HD DVD have prevailed. But with Blu-ray the winner of the format war, replicators can concentrate on manufacturing this format and using existing HD DVD lines for DVD.

Price wars

The replication industry is extremely competitive, with some replicators finding it difficult to compete effectively. Legitimate methods for reducing costs include maximising yield, utilising capacity and negotiating lower prices with suppliers. But some replicators have resorted to non-payment of royalties, but have not always been chased by the licensors. Most replicators want to work on a level playing field, but this is not always possible.

When DVD was launched it became a premium product and replicators were able to be profitable again. Prices in the first year or so were close to US $2 for single layer and up to US $3 for dual layer discs. But over the years prices have tumbled dramatically, although costs have also come down to less than 50 US cents per disc, including patent royalties but not including packaging and paper parts. However costs are now rising due to increased cost of raw materials such as polycarbonate.

Large scale manufacturing at high yields with maximum capacity utilisation allowed the major DVD replicators to survive. Smaller replicators can survive by servicing niche markets where price is not as important. Ten years ago only larger replicators could consider investing in DVD. Now equipment is less expensive and more reliable, but, as a few replicators who entered the market at a late stage have found, DVD replication still requires skilled people to make good discs at high yield.

Blu-ray requires even more skill but should offer replicators a new opportunity to produce a product at a premium price. But the expectations of Hollywood even before the format was launched were that disc prices would be similar to DVD. During the format war the Blu-ray group encouraged this view to show that discs would be affordable.

the future of optical discs

When CD was launched in Europe in 1983, it was the only new music format and the first to use digital technology for consumers. When DVD was launched in Europe in 1998, the internet was growing, illegal music downloading was beginning to grow, internet connectivity was via dial-up but CD copying was beginning to be a problem. When Blu-ray and HD DVD launched in early 2007, internet downloading of music and video was already established and broadband penetration was high in the UK.

So how long will optical discs continue, faced with the threat from the internet? The lesson from the music industry is that many consumers want their content in a convenient form, which often means downloading it from the internet. Low price and instant access seem to be more important than high quality.

With fast broadband speeds it is possible to stream video via the internet and the use of the more advanced video codecs such as H.264 allows high definition video to be streamed at lower bit rates than when using MPEG-2. Ironically these new codecs can allow an HD movie to be stored on a DVD-9 disc, but without any extra content. Although existing DVD players would not be able to play the video, PCs with suitable software and Blu-ray players should be capable.

A fourth generation optical disc format for consumers is unlikely. Blu-ray’s 0.1 mm cover layer and blue-violet laser diode represent the maximum capacity per layer using conventional technology. The use of multiple layers can increase capacity further but is likely to be used for archiving and computer backup on recordable discs. Holographic discs are expensive and unwieldy and unlikely to be used for consumer purposes, at least in the short term.

Higher definition video is unlikely in the foreseeable future, as HD video already requires large screen sizes or short viewing distances. There may be other applications in the future needing more storage capacity, but at the same time internet download speeds will increase making it difficult for optical discs, even with higher capacities, to compete, except for archival purposes that need physical media.

CD, DVD and Blu-ray will not disappear soon, but the market for optical discs will continue to be eroded by internet distribution of content. But in nine years time it is not clear whether we will be celebrating 10 years of Blu-ray in Europe or we will have abandoned optical discs as the main distribution medium for audio and video content....

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