-By Peter Wilson, HDDC Ltd.

The digital-cinema networks in the U.S. and Europe are now becoming well-established, though far from complete. While the specifications and requirements for file-based storage and forward digital-cinema delivery are extensively specified and are well on the way to being fully standardized by the SMPTE and ISO, the situation for live delivery is quite unclear. There are now many events being relayed to the existing digital-cinema locations, but the method and approach tend to be quite variable and case-by-case.

A new factor is the surprising speed at which 3D content is growing, first with feature movies and now by satellite with live 3D production techniques being rapidly developed. Avatar was the catalyst for drastically increasing the conversion to digital.

There is now an urgent need to specify the required methods to successfully broadcast live events to the rapidly increasing installed base of digital cinemas.

Although there are now emerging expert networks, there are still many inconsistencies with sound processing and subtitles, for instance.

In addition to live events, there are many other possibilities which may include the connection of rights-paid DVDs, gaming machines, commercials and signage.

The first examples of alternative content delivery are live events such as opera and sports.

Broadcasters when producing and transmitting live TV to the home consider the whole process as a system and they plan and execute every step, from the capture at the outside broadcast truck through to the aerial. In digital cinema, this level of system planning is in its infancy. The result of this is problems which crop up unexpectedly, like subtitle failure in some cinemas but not others and disappointing sound quality.

Mismatches in signal levels or interconnection incompatibilities are often caused by poor system design. In the new digital world, this often means no picture or sound at all.

There is a large choice of communications satellites across the world. These tend to have footprints chosen according to a combination of commercial or political reasons. It may also be necessary to use more than one to achieve the area of service required. These satellites may have differing operational frequency bands and differing power outputs, necessitating a selection of dish sizes for reliable operation. Although it may be possible to hop across the Atlantic direct to the cinema, it might be better to intercept the signals and convert them to local standards before retransmitting them to the venues.

Though the program distributor will contract with the teleport operators to deliver the signal, it is important that there is a minimum level of cooperation to ensure that the right dish sizes will be fitted and pointed in the right direction.

Planning applications will also need to be made for the larger dish sizes which may be necessary for some satellites in some locations.
In Europe and many other parts of the world, the satellite data delivery format follows a set of standards invented by the European Digital Video Broadcast Group.

The original standard was DVB-S, but now DVB-S2 is coming on-stream and receiving equipment is coming on the market. DVB-S2 offers a higher data rate capability in the satellite channel than was available before.

DVB-S is used with MPEG2 compression and DVB-S2 is specified to work with either MPEG2 or MPEG4 (H264/AVC). Most of the live cinema delivery uses the older MPEG2 system of compression, which is more readily available and better understood but less efficient.

Digital-cinema delivery uses JPEG2000 for compression of the picture. JPEG2000 has only a moderate compression factor, so it is not appropriate for live transmission of content to the movie theatre. Compression factor means compression efficiency, and the Hollywood studios chose several encoding parameters more appropriate to JPEG2000 than to the more normal MPEG standards.

MPEG2 is commonly used for standard-definition services around the world and HDTV in the USA. With the advent of HDTV in Europe, most services will move to MPEG4 (H264/AVC), though some care is needed when choosing the parameters.

So an ideal receiver/decoder would have the possibility of receiving and decoding the chosen compression format with the chosen modulation standard. Many cinemas use very low-cost consumer set-top boxes as the satellite receivers, which can lead to compatibility problems. The more integrated operators use professional receivers with the added benefit that they can deliver the main cinema content and be monitored and controlled from a NOC (Network Operations Centre). The audio system will most likely be stereo or Dolby AC3.

The cinema sound system is used in a very different way from the TV in the home, so special provisions need to be made to create a cinema mix. This may require that the OB truck or separate audio production truck can simulate the cinema X curve in its monitoring system. The audio from the decoder will need to be injected into the cinema sound system.

Interconnections are vitally important for both picture and sound, so the correct connectors are important. Professional integrated receiver decoders have professional connectors, whereas consumer set-top boxes do not. Many of the consumer set-top boxes are not built to the correct specifications, so audio and picture sync commonly drifts over time. The temporary cure for this is to switch channels when the box will reset to the correct audio-to-picture sync.

Digital-cinema projectors have two different interfaces. One interface is a pair of HDSDI BNC connectors which can be encrypted with local link encryption for connection with the server/media block. On Texas Instruments-based projectors when using the internal scaler, this limits the frame rate to 48 fps. The second interface is a DVI connector; this interface supports up to 60 fps, but any scaling has to happen in an external processor.
The external processor also has to de-interlace any interlace inputs, as most digital-cinema projectors are progressive scan only.

Ideally, any alternative sound and picture equipment should be remote-controlled by the main digital-cinema control system so the user-control interfaces are minimized and the necessary interlocks can be achieved.

There is now a lot of interest in live sporting events and live concerts being shot and produced in stereoscopic 3D. Live events need to generate left and right streams which need to be transmitted in perfect synchronism and the auditorium will need to be equipped with one of the proprietary 3D display systems with active or passive glasses.

Early live delivery of 3D stereoscopic events can be fraught with problems when mixing consumer and professional systems, and the simpler consumer transmission systems like frame-compatible side-by-side result in rather poor pictures on a big screen. Diligent research is a must to achieve the best presentation.

Peter Wilson is the principal at High Definition and Digital Cinema Ltd. and chairman of the technical support group at the European Digital Cinema Forum. He will moderate a seminar on distribution of alternative content on June 21 at Cinema Expo International in Amsterdam.