HD ENG: Is it ready?

If you've noticed that the topic of HD ENG and local production has been popping up frequently in conversations around you, you're not alone. Interest
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If you've noticed that the topic of HD ENG and local production has been popping up frequently in conversations around you, you're not alone. Interest in HD at the local level has been increasing steadily since NAB2005. The factors that seem to be driving it include:

  • reasonably priced HD field cameras;
  • improved recording media with a range of new storage devices;
  • portable HD editing tools;
  • microwave ENG systems that support higher digital rates;
  • the increasing number of HDTV sets in homes; and
  • the need for ratings differentiators in highly competitive markets.

The actual implementation of HD for ENG has been slow up to now but should pick up this year as television networks and major groups begin standardization on equipment.

In the field

For example, in the USA, WRAL (Raleigh, North Carolina) began broadcasting news from an HD-equipped studio in 2000. Since then, the station has put more than two dozen DVCPRO HD camcorders in the field. And in November 2005, live HD ENG coverage expanded to include shots from the station's helicopter.

The station uses a handheld camera but plans to upgrade to a gyro-stabilized gimbal mount later this year. The HD-SDI from the camera drives a JVC HD encoder that feeds ASI to a Nucomm ChannelMaster COFDM ENG transmitter.

Cameras

Over the last few years, the price of HD field cameras has steadily dropped, and the flexibility has increased. Compatibility between cameras is another issue, however, as various manufacturers have adopted different recording formats. For the most part, all HD cameras provide an HD-SDI, component or composite output that can be connected to an HD encoder in an ENG or SNG vehicle.

Also, as camera manufacturers move toward tapeless recording, the storage media has taken on a life of its own. Many cameras are still available with tape transports, but the options now include hard drive, Flash RAM and laser discs. The connection between the camera and recording device may be USB 2.0, IEEE 1394 (also called i.LINK by Sony), 100BASE-T or Gigabit Ethernet. Each method has its own set of unique attributes.

Microwave systems

The current crop of digital ENG microwave systems includes a variety of interfaces that support 270Mb/s SDI in on-board encoders or ASI streams from external encoders. Until recently, the only way to support HD was via ASI from an external encoder running at rates up to 20Mb/s.

The data rate limitations have been imposed by the inherent capability of DVB-T COFDM, which tops out at just over 30Mb/s. In reality, COFDM must be operated in the more robust regions of the standard to survive in a hostile metro area environment, which drops the practical limit back down to the 20Mb/s area.

While it is possible to get good-quality HD in a 20Mb/s stream, most agree that rates of 30Mb/s to 50Mb/s are needed. To support these higher data rates, MRC and Nucomm have incorporated single-carrier modulation options in their ENG systems.

Nucomm chose the ATSC 8VSB technique and can vary the VSB rate. MRC uses a variable rate QAM modulator, similar to what has been used in classical digital radios for decades. Either way, the result is higher throughput from the field, but with a sacrifice in multipath resistance, making it applicable only when conditions are favorable.

Nucomm's view of a single carrier is that it is a temporary but necessary step until MPEG-4 develops to the point of becoming affordable. The company is betting that the superior processing power of MPEG-4 will drop the HD contribution rate down to the point that COFDM will be the only format needed.

MRC appears to be taking the approach that broadcasters will always want higher bit rates, even with improved encoding techniques. The new MRX4000 ENG decoder and demodulator includes DVB-T COFDM and single carrier QAM, as well as the capability of supporting high-speed video file transfers via IP using USB, IEEE 1394 or Ethernet protocols.

HD encoders

One of the more expensive items in an HD ENG system is the MPEG encoder; however, prices are dropping, and so are the barriers to entry.

The first DENG vans that hit the road in 1999 used expensive, rack-mounted MPEG-2 encoders to generate an ASI to be sent via COFDM microwave to the studio. Over time, MPEG-2 encoders have shrunk in size and cost to the point that most COFDM transmitters include the encoders as an integrated option.

As the early HD ENG systems get under way, the same scenario appears to be playing out with encoders. As proof of the size reduction, both Link Research and Global Microwave Systems introduced camera-mounted COFDM transmitters with built-in HD encoders at NAB2005. At NAB2006, Nucomm added an SD/HD model, and the companies all showed diversity receivers. Expect this generation of HD encoders to proliferate. But will they be needed?

With reference to Figure 1, video is captured by the HD ENG camera (shown on the left) and may be transmitted live through the microwave or recorded for later transmission. For live transmission, the HD-SDI is fed to an MPEG encoder in the ENG transmitter. A recorded scene can be downloaded to a laptop from the camera storage media via IEEE 1394, USB 2.0 or Ethernet, and a fully edited or cuts-only version can be sent via IP file transfer back to the studio. Transmission may be slower or faster than real-time transmission depending on the situation.

The paradigm shift that appears to be on the minds of many engineers and news producers is being able to connect the camera's integral encoder directly to the microwave for live shots. The data rate required depends on the camera encoding format, which ranges from 25Mb/s for HDV to 145Mb/s for Ikegami Editcam HD, with stops in-between for Sony XDCAM-HD, Panasonic DVCPRO HD and a host of SD formats. As the camera manufacturers turn to MPEG-4, these rates will drop also.

Strong evidence to support the camera-encoder trend can be seen in the products that Miranda and Computer Modules have introduced. These products provide a bridge between HDV with IEEE 1394 and ASI. Both products can take an HDV feed in IEEE 1394 protocol and produce an ASI output at a fraction of the cost of an HD encoder. If these prove to be successful, we should expect to see other versions or perhaps multiformat versions available soon.

Proceed with caution

There's no doubt that HD is working its way into news and that most of the hardware and software is ready to go. Still, it would be wise to look carefully at developing equipment trends and talk to someone who has been there before. Fortunately, the list is growing.

George Maier is the founder of Orion Broadcast Solutions, a broadcast consulting firm.