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Life in An HD World

High-definition video. Those words represent a dream come true for everyone from video engineers and camera manufacturers to retailers and consumers. The idea of higher-resolution video images has been discussed, researched, debated, and tested since the 1930s, and finally came to fruition as part of a process that started 40 years ago in Japan.

High-definition video. Those words represent a dream come true for everyone from video engineers and camera manufacturers to retailers and consumers. The idea of higher-resolution video images has been discussed, researched, debated, and tested since the 1930s, and finally came to fruition as part of a process that started 40 years ago in Japan.

Today, HD is seemingly ubiquitous. LCD and plasma HD displays are widely available at affordable prices. HD programming, once derided by certain networks as a boondoggle, is now a vital part of broadcast, cable, and satellite TV networks' marketing campaigns. We have a new HD optical disc format (Blu-ray) to replace red-laser DVDs. HD camcorders can be had for a few hundred dollars, and the HD idea has even spread into digital radio (which actually isn't HD).

Digital Projection WUXGA Projector

Digital Projection WUXGA Projector

In short, if your video isn't HD, then you're hopelessly stuck in the 20th century (at least, it seems that way). And we all know that, in the new world order, what drives the consumer marketplace winds up driving much of the professional AV channel–just look at all the new HD flat-panel TVs that started out in Best Buy and were later adapted by their manufacturers as monitor and TV products for systems integration.

You probably have customers who are requesting HD in their next installation, whether it be plasma and LCD monitors for a hotel chain, point of purchase digital signage in retail stores, or videoconferencing and distance-learning facilities in corporate and educational campuses. Hey, no problem. "Going HD" is just an exercise in plug-and-play, right?

Well, not exactly. The infrastructure requirements for recording, playing back, storing, distributing, and showing HD video are quite a bit more advanced than those for analog Composite, Component, and PC video sources. The good news is, the pipelines are much simpler to deal with. The bad news, they're very different than what you've been used to working with in the past.

The Basics

High-definition video is itself a subset of digital video. And to work with digital video, you need to focus more on bit rates and system bandwidth, and less on the actual image resolution. That's because digital video is almost always compressed for distribution in one format or another. The compression/decompression (codec) used may vary, as may the distribution method (coax, Cat-5, wireless, optical). But the only efficient way to move HD video images (plus audio) from point A to point B is to pack it up using lossless compression, and then unpack it at the other end for playback and display.

One thing that's been greatly simplified from the older analog video world is the number of video signal formats. Digital video is almost always formatted into a component structure, with a luma channel plus two color difference channels for conventional video, and discrete red, green, and blue channels plus Composite or Component sync for computer display signals.

Here's another change from analog video: Sync pulses are now replaced with sync "bits," or flags that signal the end of one frame and the start of the next frame. More often than not, all of this picture information travels in a serial data format. One popular implementation is the Serial Digital Video (SDI) format, used extensively by the broadcast and film production industries.

Typical bit rates for SDI video (standard definition) are about 270 Mbps of data. There's also a high-definition version, HD SDI, with nominal bit rates of 1.2 Gbps. Not surprisingly, fiber-optic connections are frequently used to move HD SDI video from one place to another, although coaxial cable is the most common interconnect. Cat-5 cable has even been used to do the trick.

We mentioned codecs before. The most common codec for digital video is the Motion Picture Experts Group codec, better known as MPEG. There are many levels and forms of MPEG compression, but the most common would be MPEG-2 (used for broadcasting, cable, satellite, and DVD video), and MPEG-4 (Blu-ray, Apple TV, AT&T U-Verse, FiOS, and now becoming the preferred codec for DirecTV and Dish Network).

The big difference between MPEG-4 and MPEG-2 is that the former can perform sub-pixel encoding, which should lower the bit rate for the same number of pixels of picture information. And indeed, the European Broadcasting Union recently demonstrated that MPEG-4 encoding of 1920x1080 HD content could indeed be done at half the bit rate of MPEG-2 with equivalent picture quality at the receiving end.

And this is where the importance of bit rates and bandwidth versus pixels of resolution comes into play. The fact is, you can choose to transport a high-quality 1280x720p HD signal at 15 Mbps, or a not-so-nice 1920x1080i HD signal at the same bit rate.

Both signals will arrive where they're supposed to arrive, but the higher resolution image will suffer from more compression artifacts. Yes, they're called "lossless" codecs, but there's always some deterioration in the signal. So when you plan out the "last mile" of your HD distribution infrastructure (i.e., transmission to the display), you'll need to think bit rates and bandwidth to get the picture your client wants.

Storage and Playback

Magenta HD-One Transmitter/Receiver

Magenta HD-One Transmitter/Receiver

OK, you're undaunted so far. If you intend to record, store, or playback HD content through your new system, you'll need sufficient storage space to hold everything. Just how much storage should you plan for? Use a few rules of thumb to get you into the ballpark.

Figure on 3 GB of storage space per hour of MPEG-2 standard definition video. (A standard DVD has 4.7 GB of space, but uses variable bit-rate MPEG-2 encoding to pack 6 hours down to under 4 GB.) HD video encoded in the MPEG-2 format will require about three times that amount of space, or 9 GB per hour of programming.

Note that variable bit-rate encoding is not used with HD video to the extent it is with SD video for mass distribution. But it does get packed down. Uncompressed 1920x1080 interlaced HD video, encoded as MPEG-2 4:2:0 (four samples of luma for every two samples of both color difference channels) has an uncompressed rate of 995 Mbps.

By the time it arrives at the antenna, through a cable TV connection or from a direct broadcast satellite, it's been packed down by as much as a 60:1 ratio. A 1280x720 progressive-scan video, encoded in the same space, has an uncompressed bit rate of 885 Mbps and is packed down by nearly 50:1 before it reaches the intended viewer.

It would not be at all unusual to start with a capacity of 500 GB for an HD media server. That's good for over 55 hours of content, and as we all know, hard drives are cheap and getting cheaper and larger by the day. Even 1 terabyte (TB) hard drives are now available for reasonable prices.

For removable storage, you might as well skip conventional DVD-R/+R/RW drives and install Blu-ray recordable (BD-R) drives, which are also widely available at reasonable prices, starting at around $300. Recordable media (BD-R discs) with 25 GB capacity can be found for under $20 each, and a quick check on the Internet shows some retailers selling them for under $10.

Note that, at present, it's not possible to find combination Blu-ray video recorder/players in the United States, although they're quite common in Japan.

Copy protection issues are to blame, and apparently those aren't a big deal across the Pacific. On a recent trip to Osaka, I saw numerous models of combination BD media hubs with a BD-R drive, Ethernet connection, RF tuner, and internal hard drives ranging in size from 250 GB to 1 TB. (All yours, starting at $800 and climbing as high as $2,200!)

A more practical solution would be a dedicated HD DVR with similar disc capacity. Copy protection issues aside, you can put together a media center PC/server with considerable record/playback capabilities for less than $2,000.

Transport Issues

Now we need to return to bit rates. You've got to move your content around at a sufficiently high bit rate to all clients without bogging down your streaming bit rates. Using shared-bandwidth network (SBN) protocols like 100BaseT Ethernet isn't going to do the trick–Gigabit Ethernet is the minimum you'll need for an SBN, as multiple HD video clients will dramatically slow down the network to a trickle in no time at all.

This is a problem that plagues cable system operators, and one that realistically only fiber optics can solve. (Either that, or use a low bit rate for streaming and localized storage for later playback.) You could also consider a proprietary network structure with higher sustained bit rates, such as Asynchronous Transfer Mode (ATM) or a more costly dedicated connection such as Optical Carrier (OC) or T3 lines.

Serial digital video can move across the same network, or through dedicated coaxial connections. But those are only good for one program at a time. Multiple program streams will almost certainly force a move to optical fiber, or to dedicated, single-purpose Cat-5 backbones.

The good thing about digital signals is that they don't care how they move from one place to another. All that matters is enough forward error correction (FEC) to ensure dropped bits are replaced before the program is viewed. The less reliable the connection, the more FEC you'll need, which of course introduces a time delay, or latency.

Latency is our ace in the hole for recovering lost data of any kind. With TCP/IP protocol, packets can be sent, re-sent, and received out of order, but still be reconstituted into a usable photo, e-mail, video file, or spreadsheet. In fact, transmitting HD video via Internet Protocol is the next big thing for digital video distribution.

Just remember that bandwidth is usually fixed, so bit rates (and picture quality) are often compromised to handle multiple programs from a service provider. Take a look at the differences in picture quality of the same 1080i HD sports program direct from a terrestrial broadcaster, over an HD cable channel, or from a direct broadcast satellite network, and you can tell who's trying to conserve bandwidth the most (usually, the satellite service).



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