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 be 5/05/2009 10:58 PM Eastern

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

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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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.

Interfacing and Switching

Now comes the fun part–getting those HD images up on the screen. You'll need some sort of media player or converter box to take apart your transport stream and separate it into video, audio, and control packets. Once you get past the modulation system (VSB, OFDM, QPSK, QAM) or transport protocol (TCP/IP or whatever proprietary system is in use), it all comes out the same way.

Crestron Digitalmedia Switcher

Crestron Digitalmedia Switcher

Even though you've had plenty of experience dealing with analog video and computer display connections, you'll want to move to digital–and stay there–going forward. That's because the new crop of flat-panel monitors and TVs and front projection systems are moving towards digital interfaces exclusively and phasing out analog interfaces.

There are a few reasons for this change. One is the addition of copy protection layers to digital interfaces used on consumer HDTVs, specifically through High Definition Multimedia Interface (HDMI) connectors. HDMI, which evolved from the older Digital Video Interface (DVI) standard, can carry video and audio, as well as control data, as fast as 10.7 Gbps (DVI is limited to display data only).

One thing that digital video interfaces bring to the mix is the ability to communicate with the video signal source and automatically setup the optimum display resolution and image timing parameters. This is done with Electronic Display Interface Data, a "handshake" between display and media player or computer. (In the language of HDMI, those are known as the sink and source, respectively.)

While HDMI wasn't really intended for the professional marketplace, it is now appearing on numerous LCD and plasma monitors and projectors. That can cause big problems for switching and distributing the signals, as the EDID connection typically works only with a direct connection from source to sink.

As a result, a new crop of EDID-friendly switchers and distribution amplifiers are now coming to market–and you'd better figure on using them to avoid problems with image dropout and lost connections. These interfaces can store EDID info from many displays and reflect it back to a source (or sources) to prevent them from shutting down or, in the case of computers, going into sleep mode.

EDID-friendly interfaces can also poll multiple displays that are being fed and determine the highest common display resolution that all can use, even as one or more display are powered down or "hot switched" out of the loop. Note that this "smart" EDID emulation and configuration ability applies to both HDMI and DVI signal connections.

How you choose to make your DVI and HDMI connections is up to you; conventional cables, ultra-long cables with repeaters, conversions to optical fiber, and even conversions to Cat-5 cables are all being used successfully. Just remember that digital data is agnostic about how it moves around–it only cares that it has enough bandwidth to get there.

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.

The Display

Sony Bravia 1080p LCD

Sony Bravia 1080p LCD

Last but not least, it's time to view those HD images that have been encoded, compressed, captured to a hard drive, streamed over a fast network, and converted to a digital display format, with or without embedded audio.

Did we mention earlier that all HD video is in the 16:9 widescreen aspect ratio? That's not to say you wouldn't have high-resolution computer video in the mix, which can use almost any aspect ratio, although much of that is now moving to widescreen formats as well (1280x800, 1366x758, and 1920x1200 being three examples).

Because your system may support multiple formats of SD and HD signals, it would be a smart idea to try and standardize all incoming video and PC signals to the native resolution of your displays. That means format up and down conversion for anything other than native display rates, plus aspect ratio re-sizing to ensure you don't wind up with "fat people" on the screen (4:3 standard definition video expanded with a linear stretch) or "stick figures" (16:9 video compressed to fit a 4:3 ratio that winds up on a 16:9 or 16:10 display anyway).

Image processing can also include the addition of side bars for 4:3 upconverted content (pillarboxed). There's still a lot of it out there and it's likely to wind up in your new system. You may find that ads created in 16:9 appear letterboxed because they were downconverted to 4:3 beforehand, creating a "window box" effect. Digital image zooming can fix that.

The use of image upscaling, for example, is something the hospitality industry really needs help to get a handle on. How many times have you checked into a hotel to see a brand-new LCD or plasma HDTV in your room, only to discover it showing stretched analog Composite video? That's just inexcusable these days.

As for your working resolution, pick something that gives you adequate HD resolution subject to the bandwidth limits of your system. You may find after you do the math that supporting 1920x1080 playback is too much to ask from your distribution network, but that 1280x720 will do fine and possibly even lower the average statistical bit rate.

You could even whip up your own HD resolution, as long as you are 100 percent certain the displays you've chosen are compatible with that resolution and the digital signal format you've selected. Many LCD and plasma HDTVs sold for hospitality and digital signage functions only accept 720p and 1080i video (sometimes 1080p) through HDMI or DVI connections, but will not recognize relatively common widescreen PC formats like 1280x768 or 1366x768–even if that's the native resolution of their pixel matrix. Oops!

A Different Ball Game

Streamzhd Encoding Server

Streamzhd Encoding Server

As you can see, building an infrastructure for HD content storage, playback, and distribution is a very different animal than analog signal distribution.

The challenge? You'll need a lot of bandwidth to do it and faster devices to capture, play back, and transport HD content. Fortunately, there are lots of clever solutions and products being offered to build HD infrastructures without breaking the bank, from media servers to portable storage and smart digital audio and display interfaces.

And the upside? Cabling requirements are a lot simpler: You can combine video, audio, and control signals in the data stream through any distribution system–coax, Cat-5, fiber optics, even wireless.

And all of that intelligence built into servers, switchers, distribution amplifiers, and displays gets you closer to a true "plug-and-play" installation. Maybe even one that will forever rid us of those stretched-out people dancing across hotel flat-screens.

Contributing editor Pete Putman is InfoComm's 2008 Educator of the Year.

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