PRACTICAL DIGITAL CINEMA DISTRIBUTION IN AN EVOLVING TECHNOLOGY ENVIRONMENT J. A. CLARK AND M. W. BRUNS ABSTRACT Introduction W H I T E P A P E R An effort is underway to enable digital cinema distribution with new products and new standards covering a wide range of technology. Exhibitors, studios, equipment manufacturers, and others involved in this effort require a universal, long-term digital cinema standard. Complicating the drive toward a single standard, however, are two issues: 1) not all players have the same priorities in specific technology areas, and 2) some technology areas are seeing rapid evolution. These issues make it difficult to pinpoint the exact specifications of a single, comprehensive standard. This paper shows how the digital cinema distribution chain is composed of mostly independent functional blocks, and how a modular approach may be used to achieve a broad set of standards with long-lasting relevance. An example is given of how operational equipment may be manufactured in compliance with modular standards while maintaining present and future costeffectiveness. The basic manner in which movies are distributed and displayed is experiencing the most significant change in its century-long history; film is being replaced by electronic (digital) images of equal or superior quality. This transition is now underway and capital equipment purchases will begin to support installations in many theaters in the United States and Europe in the coming year. The digital cinema revolution is not just a change in the technology of the medium. It is a completely new system that will add a variety of experiences for the viewing customer. It will change the way theaters do business, with the possibility of new revenue sources, new cost structures and new players. These new models obsolete the term film exhibition industry in favor of a more general term such as theatrical presentation industry. This paper reviews the drivers that have led to the deployment of digital cinema, from the perspectives of the different players in the industry. A standards basis for the technical components of digital cinema is key to a successful transition, but is difficult to obtain in view of the different priorities of the different players, and in the face of rapidly evolving technology. This paper suggests how to achieve a standard using a modular approach. As an example of a practical implementation using a modular standard approach, a digital cinema play-to-screen server is described based on a flexible, generic platform, upon which the functional blocks are implemented as interchangeable hardware and software modules. Multiple encryption and compression algorithms may be supported with relatively low cost for upgrade, or simultaneous use.
THE PRINCIPAL PLAYERS The Studios and Distributors Today, approximately $700 million is annually spent on movie distribution in the United States(1). Delivery of digital files in lieu of film prints promises media distribution cost reductions of up to 10 X(2). This is one driving force that will motivate the conversion of theaters to digital over time. For the creative directors, the motivation is to deliver to their audiences the same image quality that they see in their original answer print, with no degradation from playout to playout such as from dust and scratches accumulating on the release print. And since electronic projection does not have the mechanical limitations of a single screen format at one frame rate from a single media type, creative directors will have more artistic freedom. The image resolution for digital cinema is expected to advance along with display technology through a progression of standard sizes(2). Initial systems are playing now at 1.3 mega-pixels (MPixels) at 24 frames per second (fps)(3), which provides comparable quality to 35 mm film. In the next year, new systems will support over 2 MPixels at 24 fps(4). These formats are compatible with current interface standards for high-definition television production and distribution. There is motivation among content creators to move to even higher resolutions, up to 8 MPixels and higher frame rates than 24 fps, which will result in a sweeping overhaul of current practices and the production infrastructure upon which they are based. Future digital cinema releases will in all ways exceed the quality of present-day film, the first goal of the Motion Picture Association representing all major studios(5). The Exhibitors Digital cinema can help exhibitors reach broader audiences and compete more effectively for consumers disposable income because it makes possible the display of any image that can be supplied electronically. In addition to digitized film and digital renderings from movie studios, alternative sources including concerts, live events, recorded or live stage productions, and interstitials with national or local focus become available for theatrical quality display. These varied sources may be merged, edited and played out as data files. Further, management of these resources requires much less labor than today s film-based theater systems. Digital cinema also offers exhibitors increased operational efficiency. The electronic file media of digital cinema distribution allows a multiplex to instantaneously change its screen allocations and optimize revenue based on dynamic observation of attendance. Further cost savings can be realized from the reduction in labor required to set up a movie and interstitials at the theater since the assembly can be done in a simple graphical interface rather than by physically splicing film clips together. The capital cost of electronic projection systems, including projector and server equipment, is one impediment to digital implementation for exhibitors. Fortunately as this issue is probed, it is becoming more evident that exhibitors may expect some or all of the cost of conversion to be covered by distributors or others who also benefit from the digital distribution model. Equipment Manufacturers Manufacturers of digital cinema systems must balance development costs against a possible, undefined return on investment that is dependent on the success and swiftness of the transition. Standards-based designs will enable manufacturers to minimize these risks before they make significant investments. Standards help ensure that their designs will solve the customers needs, and help guarantee that the market for the product will be of sufficient size that they can absorb the development costs over reasonable time period. Electronic Content Delivery Providers The new digital source material will be delivered to theaters in a variety of ways. Initially, standard DVD-ROM or tape cartridge media will be carried by bonded couriers in the same manner as film reels are handled today, but with lower shipping costs. Broadcast by satellite may eventually become a dominant delivery method as distribution infrastructure details are fine-tuned. For smaller theaters and smaller population distributions, broadband wide area network (WAN) distribution will become viable. DSL modems, cable modems and telco T1 trunk connections all have sufficient bandwidth to deliver these data files to theaters. Conditional Access Providers With the emergence of digital presentations featuring releaseprint quality comes a daunting new challenge for movie distribution: security. Each digital data copy is a virtually perfect copy of the original, immune from degradation in the act of duplication. Since several hundred million dollars can be at stake with a movie release, new and highly-effective content protection measures must be incorporated; the media files must be encrypted using the best techniques available for commercial use with military-level sophistication and impenetrability. The encryption keys for the media file encryption algorithm are distributed using public key encryption in a conditional-access framework. This framework includes the aspects of rights management, authentication, and revocation embodied in film reel ownership. Conditional access providers may offer these services in the future.
End-to-End System Providers A number of companies have announced plans to integrate the content delivery, content protection, and equipment leasing and service functions under one end-to-end system. The acceptance of such a system will depend on a viable business model, and it depends on the existence of a digital cinema standard; having the choice between multiple, interoperable service providers in the digital cinema distribution chain is a core value among studios and exhibitors, who would be the customers of an end-to-end system. THE DIGITAL CINEMA STANDARD Functional Description MEDIA Digital Cinema DISTRIBUTION Distribution Master CONDITIONAL ACCESS SYSTEM Public Key Key File Store Media PLAY-TO-SCREEN SERVER Unpackage Media Files Decrypt Process Link Encrypt SECURE MODULE Encrypted Images AUDIO AMPLIFIER ELECTRONIC PROJECTOR Decrypt and Convert to Light Output SECURE MODULE Standards-Making Organizations INTERNET Remote Interface Control, Monitor, Audit Functions Several organizations are engaging in activities relating to operational standards for digital cinema distribution, including the SMPTE DC28 groups(6), the MPEG ad hoc group on Digital Cinema(7), and an Information Technology for European Advancement (ITEA) project(8). For some aspects the standards process may identify functional and physical interface standards that are applicable and are already in place. Standards such as SMPTE 292M for picture interface and SMPTE 360M for media file packaging, can form the backbone of systems that leverage existing operational equipment and can support digital cinema formats well into the future. Other aspects such as compression are in a much less established state due to the rapid evolution of algorithms and increases in the available computational power of silicon devices. It may not be practical to attempt a single comprehensive standard to serve the needs of all players over a long period of time. But a standard is needed because the capital cost of the server and projector will be high, and those players who pay will not be willing to invest in this conversion without some assurance that the equipment they install will be viable for many years. This points to the need for some element of flexibility as a key aspect in the standards and in system designs. Figure 1 - Digital cinema distribution chain, exhibitor side. Figure 1 shows an overview of the path a digital release follows from the distribution source to the screen. The digital release may be transported by one of a number of possible carriers including physical media such as DVD-ROM, satellite broadcast, or WAN. Real-time transmission of the media files is generally not required since it is the function of the play-toscreen server to capture and store the media locally and play it back in real time. The playback process includes a step to unpackage the digital release into playable media files containing images, audio, and other tracks of content. The purpose of the distribution package is to keep all the components of the presentation together in a generic format and to provide all the information needed to play the movie. To prevent theft in the digital distribution chain (transmission uses public carriers and material is stored in an insecure environment) media files must be protected using fail-safe encryption based on a standard algorithm. They are decrypted in the same secure module as the image decompression in the play-to-screen server. A second encryption of the uncompressed image stream is shown in Figure 1 to protect data on the link to the projector. This two-stage encryption strategy enables modular organization of the projection system and provides the benefit of interchangeable functional blocks as will be described in the next sections. The encryption key for the media file is provided via a separate low-speed path utilizing public key encryption according to a conditional access protocol between the distributor and the exhibitor. The local link encryption key management is kept local between the play-to-screen server and the projector.
A New Model for the Digital Cinema Standard The previous section described the digital cinema distribution chain in a dataflow model. It may also be represented as a set of functions as shown in Figure 2. This model suggests that an overall standard for digital cinema distribution may consist of a set of modular standards each describing some aspect of the distribution chain. Content Protection Protocol PROJECTION SYSTEM REQUIREMENTS Media File Packaging Transmission Medium (DVD-R, WAN, Satellite) Image Format Frame Rate Image Compression Algorithm Image Content Protection Format Content Protection Subtitles Figure 2 - Digital cinema standards. Each block represents a modular standard. Allowing flexibility in one standard has consequences on a limited number of other standards, as shown by the arrows. The consequential relationships between standards are shown as arrows. Note, for instance, the relationship of the projector s resolution capability to the performance requirements placed on the decompression algorithm. An increase in resolution in the projector head might be accompanied by a change in the decompression algorithm to support the higher resolution, whereas there is no consequence to the media file input or subtitle functional modules. There are relatively few consequential relationships between standards in Figure 2. This modularity can enable a methodology for developing standards for digital cinema as a sequence of steps: Step 1. Define the projection system requirements as a set of levels for present and future. For example, Level A = 2 Mpixels, Level B = 5 Mpixels Step 2. Define content protection protocols and media file packaging, but use generic references to the contents. Step 3. Define interfaces between functional blocks. Interchangeable standards may be defined for functions such as the projector interface, according to the levels of projection requirements. Step 4. Define interchangeable algorithms within functional blocks, such as for compression and media file encryption. In all steps, include by reference existing standards from the television, computer, and telecommunications industry where applicable. Only create new standards when none exists to satisfy the requirements. Avoid creating dependencies between standards where none needs to exist. For example, the subtitling function should be defined independently from the image compression algorithm. This approach opens the possibility for interchangeable standards in areas of rapid technology evolution or where different players have different priorities. There is the possibility for the digital cinema standard to flexibly address key functions with: multiple image formats to gain the benefit of advances in projection technology multiple encryption algorithms to improve security against increasingly aggressive attacks and to replace compromised encryption methods multiple compression algorithms to serve the needs of different content sources and to gain the benefit of advances in computational power. A modular approach extends the useful lifespan of the digital cinema standard and allows controlled growth in functionality while maintaining the usefulness of legacy capital equipment and content. Compression technology - example of need for modularity Compression technology is a component of the digital cinema distribution chain with a compelling reason for modularity; there are several algorithms proposed, and it is not yet possible to select one for a standard. The suitability and performance of a compression technology is gauged by many criteria: 1) image quality; 2) compression ratio; 3) license fee; 4) cost of silicon; 5) multiple interoperable sources; and 6) standards support. Image quality and compression ratio are the usual criteria for measuring performance, and are typically in opposition with each other. Much discussion is focused on achieving the best quality for a given compression ratio(9). A less obvious performance parameter is economic viability. If a compression technology is so complicated that the theater decoder becomes prohibitively expensive (e.g. half the cost of the electronic projector), then it is impractical. But with modern semiconductor technology, complexity does not necessarily relate directly to cost. A large volume market can support the huge development costs of a complex semiconductor IC. Economic viability of a compression algorithm suited to digital cinema may depend strongly on whether other markets, such as computers or consumer television can leverage the standard and share in its development costs. A standards based design helps to distribute the cost of developing technology for sophisticated functions such as image compression across a large single market or several smaller markets, and encourages interoperability between competing manufacturers. It also promotes crossover applications between related markets. In the case of digital cinema systems for theaters, some form of compatibility with widely implemented standards for high definition television allows the mainstream production of interstitials and alternative content targeted for playout in a theater.
An international standard also provides the basis for a licensing authority to administer license agreements between the owners of intellectual property and the users. Contributors of intellectual property are required to agree to license the technology on reasonable and non-discriminatory terms (10). Several compression algorithms have been proposed for digital cinema standards, all of which are represented to have sufficient compression ratio and picture quality for initial deployment. These include: 1) MPEG 2-based with constant quality; 2) Proprietary wavelet-based; and, 3) Proprietary DCT-based. The wavelet-based technologies have demonstrated excellent picture quality and compression ratio, especially in complex images that challenge other compression algorithms(11). Wavelet technology is also easily scalable from today s high definition picture formats to the highest resolutions being considered for digital cinema. But this technology is computationally very intense, and single-board implementations are just starting to become possible by advances in ASIC and FPGA technology. Wavelet technology also does not yet have a standards basis, so development of cost-effective solutions from multiple vendors is currently being debated. Motion JPEG-2000 is a similar wavelet-based compression algorithm that is currently in the Final Committee Draft stage of standardization(12). Its selectable parameters have not yet been adapted for digital cinema, nor has it been tested for cinema-level image quality. However, one might expect it to perform acceptably. There is currently no source for chip sets or IP cores featuring real-time compression and decompression based on this algorithm. A practical alternative is MPEG 2-based compression, which has the advantage of being able to leverage commodity integrated circuits developed under the MPEG-2 standard and can be adapted to use a constant quality bit-rate control method that supports digital cinema quality(13). This approach is not to be confused with HDTV image quality, which is constrained by terrestrial broadcast bandwidth limitations. A very important feature of MPEG-2-based compression is that theaters equipped with this technology can play back content created using high definition television production techniques, enabling a greater number of sources for alternative content and interstitials. Several proprietary DCT-based compression algorithms have also been proposed for digital cinema. These will gain relevance as they are incorporated into standards and are supported by silicon devices for realtime processing, with solutions from multiple manufacturers and a reasonable license fee structure. If the long term goals for image resolution are factored into requirements for a digital cinema compression standard today, then there is currently no single compression algorithm that meets all the criteria for suitability. A progression of compression algorithms can, however, meet all the criteria with initial deployments based on existing compression standards and future deployments based on new algorithms that are just beginning the standardization process. A digital cinema standard that recognizes the evolution of technology and incorporates a modular structure for multiple compression algorithms will help to guide the development of flexible projection systems that are not made obsolete by each change in algorithm. A Practical System for the rollout of Digital Cinema It is possible to manufacture practical operational equipment that can comply with a digital cinema standard that includes modular interchangeable functions. Figure 3 is an example of a modular play-to-screen server platform that supports interchangeable decoder modules, projector interface modules, and network interfaces, all functions that depend on modules of the digital cinema standard. The platform is based on two common, generic backplanes to interconnect the modules, both designed with sufficient bandwidth to support the highest data-rates and image resolutions envisioned for the useful lifespan of the server platform. One backplane is a high bandwidth global data bus to carry compressed, encrypted data between the network interface, the storage subsystem, and the decoder modules. Fibre Channel/IP 100 BaseT Ethernet DVD-R, Tape Network/ Removable Media Decrypt/ (MPEG+) Interface (2 MPixels) GPIO Disk Storage GPIO High Bandwidth System Bus Decrypt/ (Advanced) Decrypt/ (Advanced) Format Independent Video Router Interface (2 MPixels) Interface (5 MPixels) RS-422 Ethernet Control Output Figure 3 - Example of play-to-screen server with modular functional blocks.
The second backplane is a synchronous crosspoint switch fabric that routes uncompressed, encrypted pictures from any decoder module to any projector interface module. Neither backplane has any particular format or compression algorithm dependency, nor does it depend on any part of the digital cinema standard. The server platform is designed for the interchangeable modules to be logically and physically independent. There are multiple slots to allow multi-channel configurations. The architecture also allows decoder modules based on different compression algorithms, or projector interface modules based on different image resolutions, to function in the server simultaneously. Upgrades to support advances in technology may be accomplished by adding new printed circuit boards to unoccupied platform slots, without necessarily removing existing boards. With this kind of flexible design, the cost of the capital investment in the server platform is spread through generations of advances in compression and resolution. Current Product The following paragraphs describe the server s functional modules as implemented in the Profile XP Media Platform (14), which is based on the architecture shown in Figure 3. Input Module Media file ingest is supported by a SCSI interface to a removable media storage device such as DVD-ROM, or Ethernet/IP network interface. These interfaces leverage the physical layer and protocol standards established in the computer industry. Storage The encrypted digital media files are stored on a local RAID storage unit that serves all channels in the platform. RAID storage is designed to allow non-sequential access to the media files while providing the throughput capacity to support multiple simultaneous channels. DVD-ROM or large capacity tape cannot be used for this application because they lack the necessary throughput capability. these formats are not yet established, but they may be implemented as multiples of SMPTE 292M interfaces. If this is the case, the higher output data rates do not require changing the type of output module, but rather adding more of the same modules incrementally. Or, new interfaces such as high-end DVI may be developed to adapt to the existing platform architecture Decoder The decoder function includes decryption of the media file, decompression, and re-encryption for the local link to the projector. These functions need to be done on the same printed circuit board for reasons of data security. Media file decryption is based on a secret-key algorithm that handles the media file data rates and is closely linked to the decompression function. Re-encryption of the output image streams utilize an encryption algorithm that is optimized for speed to support the output data rate of greater than 1 Gb/s. Frequently changing encryption keys will make an exhaustive attack on this interface prohibitively expensive. The compression algorithm supported in the current implementation is MPEG+(13), which is based on the MPEG-2 standard and makes use commodity integrated circuits, but includes specific enhancements for cinema quality images: 1) a constant quality bit-rate control algorithm is used to ensure consistent image quality in every picture of the movie, and 2) an optional error diffusion step is included to give the effect a greater bit-depth and eliminate the possibility of banding artifacts. Obsolescence The modular architecture of the Profile XP Media Platform server system helps to prevent obsolescence. As today s servers are capable of providing more than 15 Mbytes per second per channel and can store several movies on one RAID unit, the bandwidth and capacity to handle larger frame sizes or frame rates is built in. Upgrading to new formats will be a matter of changing decoder board and projector interface. Today s server technology can provide cost-effective solutions that will support compression algorithm and image format changes required by the digital cinema market for years to come Interfaces The current uncompressed image stream interface to the projector is implemented for a 2 MPixel image resolution at 24 frames per second. This is based on the SMPTE 292M interface standard that is common with HDTV production. Its high bandwidth is sufficient to support both the current projector technology with resolution of 1.3 MPixels and nextgeneration projectors. Higher resolutions and higher frame rates are expected to become available within several years due to advancements in compression and projector technologies. interfaces for
Conclusion Standards for digital cinema are currently under development, and the supporting projector and compression technologies are in a state of rapid evolution. Yet even in this landscape of change it is already possible to offer the benefits of digital cinema in early deployment while managing the risks of obsolescence. This can be achieved by following a modular approach to the digital cinema standard and to the design of operational equipment. Initial installations which feature low-risk modular system architectures can build a digital distribution infrastructure that will support future improvements, help establish new business models, and even create consumer demand. A modular structure for the standard will help insure that implementations today will have a reasonable life span as capital equipment, without constraining the adoption of advanced implementations over the long haul. These advancements will provide image quality and flexibility that exceeds any film format today. Physical interface standards sufficient to support digital cinema are already available, but the image format, compression algorithms, encryption key management protocols and other aspects are still in a healthy state of flux. It is neither necessary nor wise to attempt to force a single comprehensive standard during the low-volume phase of early rollout. The infrastructure installed today must be able to readily accommodate multiple standards for key functions as they and the industry evolve. References 1 Motion Picture Association of America, 2001. MPAA 2000 US Economic Review, http://www.mpaa.org/useconomicreview/, Encino, California, pp. 10, 16-17. 2 von Sychowski, P., 2000. Electronic Cinema: the Big Screen Goes Digital, London: Screen Digest Limited, pp 24, 62. 3 DLP Cinema prototype is currently installed and showing movies daily in 30 theaters world-wide. Manufactured by Texas Instruments, Plano, Texas. 4 ILA and D-ILA projector technology by JVC Visual System Division, Carlsbad, California. 5 Motion Picture Association, August 31, 2000. Goals For Digital Cinema, http://www.mpaa.org/dcinema/, 2 p. 6 Rast, R. M., 2001. SMPTE Technology Committee on Digital Cinema -DC28: A Status Report, SMPTE Journal, Vol. 110, No. 2, February, 2001, pp. 78-84. 7 ISO/IEC JTC 1/SC 29/WG 11 N4066, Call for Proposals for digital cinema, Singapore, March 2001. 8 ITEA, 2001. Press Release: Consortium of European Companies Designs Complete Solution for Digital Cinema within Information Technology for European Advancement (ITEA) Project, http://www.itea-office.org/, Eindhoven, Netherlands, March 5, 2001. 9 See for example ISO/IEC JTC 1/SC 29/WG 11 N4067, Digital Cinema Evaluation Procedures, Singapore, March 2001. 10 The ISO/IEC statement on patent rights is included as an annex to reference (7). 11 Wavelet compression algorithm as implemented by QuVis, Inc., Topeka, Kansas. 12 ISO/IEC JTC 1/SC29/WG1 N1987, ISO/IEC 15444-3 (JPEG 2000, Part 3) Committee Draft, December, 2000. 13 Bruns, M. W. and Whittlesey, J. T., 2001. MPEG+ Compression of Moving Pictures for Digital Cinema Using the MPEG-2 Toolkit, SMPTE Journal, vol. 110, no. 6, June, 2001. 14 Profile XP Media Platform, Grass Valley Group, Nevada City, California. Grass Valley Group Headquarters P.O. Box 59900, M/S N4-2E Nevada City, CA 95959-7900 USA Profile Product Line P.O. Box 500, M/S 58-965 Beaverton, OR 97077 USA www.grassvalleygroup.com Copyright 2000 Grass Valley Group. All rights reserved. Printed in USA. Profile is a registered trademark of Grass Valley Group. All other tradenames are the service marks, trademarks or registered trademarks of their respective companies. Specifications subject to change without notice. 2AW-8109