Making Digital Cinema Tick
by Michael Karagosian
© 2001 MKPE Consulting All rights reserved worldwide
Published in the June 2001 issue of Digital Cinema Magazine
Digital cinema is clearly the future, but with only a little over 30 prototype installation sites worldwide the future doesn't seem to bein a very big hurry. While there are far more "electronic cinema" sites today, particularly in Europe, these tend to function as "community" theatres that exhibit non-Hollywood releases using video projectors, as opposed to the prototype digital cinema projection systems that are currently based on Texas Instruments' SXGA DLP Cinema technology.
Although TI has selected three licensees for their DLP Cinema technology (Christie, Barco, and Digital Projection, Inc.), most of the projectors in actual use are "prototype" units supplied directly by TI. These projectors have a native resolution of 1280 x 1024, and the "black chip" they employ is specified to have a contrast ratio greater than 1000:1. Neither TI nor its licensees will continue to monopolize this market, however. Other projection technologies are on the horizon, most notably JVC's D-ILA, which is finding favor with both Kodak and Sony for cinema-grade digital projection.
For storage and playback, the current 30-plus prototype sites use the QuVIS QuBit disk recorder as a server. Image data is stored at 10 bits component (Y/Cb/Cr) in 4:2:2 format. These units typically store two movies on their internal 100 GB of storage, thanks to QuVIS' built-in proprietary wavelet compression. Interfacing the QuBit box to the projector, however, hasn't been as simple. While the TI projectors have a SMPTE 292M HD serial interface, the QuBit unit employs a parallel SMPTE 274 HD interface. Thus, the little converter box that one sees when following the cable from QuBit to projector.
One of the criticisms of these current playback/projection systems is that the image data between server and projector is unprotected, or "in the clear." Later this year, an updated version of the QuBit is expected to employ a 292 serial interface modified with a proprietary link encryption. TI will employ the same link encryption on its boards, which will be used in production products by its licensees. While the link encryption will not be invincible, it is thought to be secure enough to deter pirating in the booth. Unfortunately, none of this prevents the more common movie theft that takes place using consumer-grade camcorders.
In its early days, the QuBit was a bottleneck for transferring movies. While it has an internal DVD-ROM drive for supporting data transfers, it typically takes from six to eight DVD discs per movie and on older units takes up to four hours to complete the transfer. Newer units can perform this task nearly at real time. The QuBit unit also has a 10b-T/100b-T Ethernet port for data transfers, but due to a limitation in hardware, the maximum data rate is below 10 Mbps (megabits per second). Using utility software supplied by QuVIS, movie transfers through the Ethernet port take longer than the movie time. QuVIS recently added Exabyte M2 tape-cartridge support, which can transfer an entire movie without reload in less than real time, taking much of the pain out of the process.
The Exabyte cartridge doesn't, however, work for everyone. The industry has shown great interest in transferring movies over land-based networks and over satellite. One year ago Qwest Communications and Cisco joined forces to stream the movie Titan A.E. from Burbank CA to Atlanta's Woodruff Arts Center. The transfer was accomplished with off-the-shelf equipment using the Cisco 7140 Virtual Private Network (complete with firewalls, security routers, and encryption). The movie file was uploaded from a QuVIS QuBit server prepared by VidFilm Services of Glendale CA, and downloaded to another QuBit in Atlanta using the QuVIS software utility and the unit's Ethernet port. Such multiple transfers of data can take over six hours.
More recently, in November, Boeing and Vyvx teamed up to "bounce" the movie Bounce over satellite from Topeka to New York. This transfer was a bit more complex in nature. Movie data stored on a QuVIS was sent over the satellite to a server residing in the New York's AMC Empire 25 Theatre. A satellite dish on top of the building was used to receive the signal. The satellite server acted as temporary storage for the movie data, which was then downloaded to the QuBit in a similar fashion to the Titan A.E. transfer.
Like TI, QuBit is not destined to keep its monopoly in digital cinema. Most of the 30-plus installations are managed by Technicolor Digital Cinema, which is a joint venture of Qualcomm and Technicolor (see "TK," page TK). Qualcomm has its own server and variable-block DCT (discrete cosine transform) compression method to employ, called ABSDCT. Other server technologies being readied include Grass Valley's Profile XP Media Platform, which can include the company's MPEG+ compression scheme, and Avica Technology's Filmstore, which is compression-scheme agnostic.
And what would great pictures be without audio? In current systems, the QuBit unit stores and reproduces eight channels of uncompressed 24-bit audio sampled at 48 kbit/sec. The QuBit provides four AES/EBU ports for transmitting the digital audio data. In newer installations, a Dolby CP650 processor has been employed with the optional AES/EBU input installed. For other models and brands of cinema audio processors, an outboard D/A converter must be used. It appears that the use of AES/EBU will be duplicated, if not improved upon, by the competing server companies. Qualcomm and Avica, for instance, will be offering up to 12 channels of uncompressed 24-bit audio in each of their systems. Avica alone is planning to provide analog audio outputs to complement their digital outputs.
Automation cues in current digital cinema installs are stored as events in the QuBit server. These time-stamped events are usually programmed at the theatre itself to accommodate the particular needs of the installation. The QuBit unit provides contact closure outputs, which can directly control automation points in the theatre, or more commonly can be used to trigger event sequences in the film-based automation system. Similar automation support will be provided by the competition. By preserving the existing automation system, the film-projection system that sits alongside the digital projector can be kept fully operational. This technique of using existing automation systems is expected to continue during the transition period, during which digital projection and film projection will live side-by-side.
One of the essential pieces yet to be employed and tested in the digital cinema environment is the conditional-access system. This system will handle the security aspects of the digital cinema system, providing the means by which facilities are authenticated to play the encrypted movie data. The QuBit unit provides password-protected encryption for its data, which prevents unauthorized data transfers. But the only digital cinema player to date that has announced a conditional access system worthy of full rollout is Qualcomm's. We may see the first of these systems installed later this year.
With increasing numbers of projector, server, distribution, and conditional access providers entering the arena, it's clear that the 30-plus digital cinemas currently in the world will increase in number as digital cinema evolves towards its rollout phase.