27-02-2013, 10:22 AM
Digital Theatre System
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INTRODUCTION
Digital Theatre System (Digital cinema, or d-cinema) is perhaps the most significant challenge to the cinema industry since the introduction of sound on film. As with any new technology, there are those who want to do it fast, and those who want to do it right. Both points of view are useful. This new technology will completely replace the conventional theatre system having projectors, film boxes, low quality picture, sound system. Let's not forget the lesson learned with the introduction of digital audio for film in the '90s. Cinema Digital Sound, a division of Optical Radiation Corporation, was the first to put digital audio on 35mm film. Very, very few remember CDS, who closed their doors long ago. Such are the rewards for being first.
1999 / 2000: MEETING THE CHALLENGE
Various forms of electronic cinema have been around for many years. Public demonstrations of modern day digital cinema, however, began in 1999 as an experimental effort privately funded by major motion picture studios. What better way to learn the many issues of a new technology than to jump in with both feet?
The block diagram below represents the typical trial digital exhibition system in the year 2000. Many of these systems are still in use today.
STEPS FORWARD
On July 17, 2001, a digital cinema milestone was crossed with the digital premiere of Jurasic Park III in Los Angeles. This particular presentation was compressed with a version of MPEG 2, as developed for digital cinema applications by Grass Valley Group. Called MPEG+, GVG's compression was based upon the MPEG 2 decompression standard, making this the first public digital cinema presentation to use an almost standard decompression scheme. Within weeks, a true MPEG 2 presentation was held in New York for Tim Burton's Planet of the Apes, this time using an Avica digital cinema server. Together, these presentations marked the beginning of a new phase for digital cinema by bringing new components to the scene.
INTRODUCING SECURITY
By early 2002, digital cinema installations were numbered in the 40's. They utilized several types of servers, including the QuBit, Avica, and EVS servers already mentioned, as well as the Technicolor Digital Cinema server designed by Qualcomm. These systems represented three different compression schemes, and four file formats.
On May 16th, 2002, another digital cinema milestone was crossed with the digital release of Star Wars: Episode II. Although they didn't financially contribute to the digital presentation of their movie, Lucasfilm heavily promoted that it should be seen as such, and the heyday increased the digital installation count to over 100. The movie was released in all four digital formats -- which proved to be a challenge all of its own.
PRESENTATION SYSTEM:
THE BROADCAST SERVER MODEL
There are two models for the secure storage and play out of digital cinema content: the Broadcast Server model, and the Data Server model. Within the realm of the Presentation System, there is no need find a winning model -- the market place is very efficient for determining winners and losers. (Which leads us back to the importance of interoperability as described.)The Broadcast Server model is based on broadcast-style servers, where image content leaves the server as a decompressed, real-time stream. The server must decrypt the content sent by the studio, decompress it, and stream it to the projector. Naturally, link encryption is needed to make the link between server and projector secure. Focusing on the image and audio paths, the block diagram below depicts the Broadcast Server model.
SECURITY
Security is perhaps both the most important and least understood aspect of digital cinema. Certainly, the encryption and decryption of content is not a major challenge. There is general agreement that movies will be symmetrically encrypted using a strong, public encryption algorithm such as AES (Advanced Encryption Standard) with very large keys. But there are as many ways of getting that symmetrical key securely to the theatre as there are security vendors. This is where things get difficult.
CONCLUSION
As you might expect, there's more to the digital cinema story than we have covered here. Digital cinema is not television -- it is much more complex, flexible, and quality-oriented. While not always visible to the public, there are a lot of people working to move this technology forward. In time, you'll be able to enjoy the fruits of their labor!