HDTV

Added by Howard Gilbert, last edited by Howard Gilbert on Feb 17, 2009  (view change)

Computers, Video Files, and HDTV

Today, every TV station broadcasts two signals on two different channels. One signal is the traditional analog TV signal that has been used for the last 65 years. The other is a new digital signal in which the TV program is encoded as a stream of numbers (essentially computer data). Between Feb. 17 and June 12 2009 broadcasters will stop transmitting the old over-the-air analog signal. Only signals from rabbit ears or rooftop antennas will change. Cable companies will convert the new digital signal to an old analog signal and continue to broadcast all the local TV channels to old TV sets. All your DVD players, satellite receivers, cable set top boxes, and other devices you connect to your TV will continue to generate analog signals.

If you have an old TV set and receive programming using rabbit ears or a rooftop antenna, then you can go to the "dtv.gov" Web site for information on the change and how to get government coupons that discount the purchase of a box to convert standard definition digital TV broadcast signals to a traditional analog signal your old set can use. However, if you are currently getting poor reception from distant TV stations, then you may need to upgrade your rooftop antenna in order to receive any signal. In digital TV, the picture is either perfect or else you get nothing at all, and the converter box can't fix that.

Analog TV was standardized in a period where vacuum tube amplifiers and frequency filters were about the only technology available. It represents a black and white picture as a radio wave that varies the intensity of a light source drawing the picture in lines across the screen. A smaller color signal was added later (in the 1950s). The entire system today is designed to guarantee that anyone still watching a 1955 vacuum tube color TV will be able to watch Letterman on Channel 2. To maintain compatibility with obsolete technology, we have missed the opportunity to get better pictures and more channels. Finally the government gained the political will to move on to something better.

Everyone with a DVD player has been watching digital TV for years. Digital TV is simply a stream of computer data that happens to encode a TV picture and one or more sound tracks. Cable and Satellite TV systems have used digital transmission for years to carry the most programming in limited bandwidth. However, until recently "digital TV" was something done by an external box connect to your TV set. Now it can be done by the TV set itself.

For as little as $30 (sometimes $15 on sale) you can buy a small USB stick that receives a digital TV signal from antenna or cable and generates a stream of data to your computer. Bundled software can tune the various network TV stations and can record the program on computer disk or display it on your screen. For a little more you can purchase a device with a more sensitive tuner that can receive weaker signals.

It used to be that more expensive TVs used higher quality components and could receive a better picture. Better quality tape recording devices could record a sharper playback, but the copy was never as good as the original. Those were the analog days. The data from the TV networks is a string of numbers. You either receive them or you don't. If you receive them and write them to a computer disk, then you have made an exact copy of the network transmission. Pass them on later to a TV and you get a picture identical to the original network broadcast.

Digital TV is either perfect or else it doesn't work at all. If you are far away from a TV station and get a bad picture now, you will probably get no picture at all after the cutover. No converter box will solve this problem. If you cannot subscribe to cable, you need a satellite dish. A better antenna on a higher pole and a slightly higher quality receiver may be enough to bring in the station, but areas of marginal reception are the real problem with the digital TV cutover.

While today we may use this technology only to broadcast what seems like 90 repeat episodes of Law and Order every day, there are other possibilities. The TV cable has 130 channels each transmitting 40 million bits per second. That is a total of 500 megabytes of data transmitted constantly into every home. The entire Encyclopedia Britannica could be transmitted in less than a second (although since a single device only receives one channel at a time it would take a minute to receive it all on just one of the 130 TV channels). One has to assume that there is some data more valuable to broadcast than reruns of Family Feud. The network and technology are in place. We just have to decide to use it for something better.

Consumers may confront Digital TV as a purely consumer product. They will buy TV sets, Blu-Ray players, and Tivo boxes. This does not require an understanding of technology, but knowing something may make them more confident about the purchase. Others may want to connect their computers to the TV signal, either as part of the home entertainment system or to play around with the technology. They need to know more about how this all works.

Resolution

Since the 1940's, analog TV in the US has been transmitted as 240 lines that refresh the screen 60 times a second (because the alternating current the electric company delivers to your house switches 60 times a second). These numbers reflect a trick used to get a better picture on old fashioned picture tube TVs. Although there were only 240 lines on the screen, the network recorded 480 lines and transmitted alternating groups of all the even and then all the odd numbered lines ("interlace"). Your eye and brain are not good at separating things that are only 1/60th of a second apart, so you saw a picture that reflected at least some of the detail of all 480 lines.

Today everyone who might read this article on the internet has a Plasma or LCD digital TV set. It has far more than 240 lines, so even when receiving an old interlaced analog signal it restores the original 480 lines of "Standard Definition" (SD) programming. The original analog signal had no specific number of dots per line, so with modern technology we choose a number of horizontal dots that, when combined with a height of 480 lines) produces an image about the same shape as a TV set. That number is around 720 dots per line. In technical jargon, the Plain Old Standard Definition TV picture we have been watching for sixty years is called 480i (480 lines interlaced).

High Definition (HD) programming has two formats: 720p (720 lines of 1280 dots per line) and 1080i (1080 lines of 1920 dots per line, but transmitted interlaced as pairs of 540 lines). The existence of any interlaced HD standard is today a technological oddity. You can only really interlace on an old picture tube TV set. When the first HD programming was broadcast back around 2001, there were a few HD picture tube TVs. Today all HD TVs are LCD or plasma screens that cannot interlace. They have to take the alternating sets of even and odd numbered lines and reassemble them back to the 480 lines of SD programming or the 1080 lines of HD programming.

If you have a set with 720 lines, then it can display a broadcast that has 1080 lines by using a computer chip to calculate a reduced resolution. Similarly, a set with 1080 lines can expand the 720p signal brodcast by some networks so that it fills the entire screen. If you go to Best Buy, you will find less expensive Plasma and LCD TV sets with 1280x720 resolution, and more expensive sets with 1920x1080 resolution.

Streams of Packets

On a movie film, the image was represented as a stream of still pictures shown 24 per second. An audio track was recorded along the side of the film. In digital TV the picture is encoded as numbers representing compressed data. A complete still image may appear only once every 3 seconds, while the rest of the data represents pixel changes for each 1/30th of a second. The sound cannot be embedded along with this complex picture stream, so it is included as a separate data stream. That allows multiple languages or a director's commentary to appear as alternate sound tracks.

So the "stream of numbers" has to be organized into meaningful units. When transmitted (as on a network) they are called "packets", but when recorded (as on a disk) they are called "records". Each unit has some error checking to make sure the data has been read correctly.

Broadcast over the air TV and Cable TV transmit data in "Transport Stream" format as 188 byte packets. DVD, Blu-Ray, and most software to record on computer disk uses the "Program Stream" format of 2048 byte records. However you organize it, the stream of video data (in MPEG 2, H.264, or VC1 format) is stored in a sequence of packets with one ID number, while each audio stream is stored in separate sequences of packets with other ID numbers.

In broadcast over-the-air or Cable, more than one program can be transmitted in the same 20 or 40 megabit TV channel. TV stations broadcast one HD picture, one SD picture, and maybe some other content. Cable transmits two HD pictures or up to 10 SD programs on what used to be one analog channel.

Connections

Ten years ago there were a few High Definition picture tube TV sets, so "digital TV" did not necessarily mean "digital monitor". The flat panel screens came later, and standards for computers and monitors are still changing. Therefore, between your set top box, Tivo, computer, and TV there can be a wide range of connections.

RF - The cable that comes in through the wall, whether from a rooftop antenna or cable system, is the RF signal (Radio Frequency). It is also an "RG6" cable with a screw on "F" type connector (if you want to impress your friends with your Geek factor). Twenty five years ago, TV sets didn't have any other inputs, so the cable TV box would connect to the VCR  and the VCR would connect to the TV with additional short RF cables. Today TV sets come with dozens of connection options. The original RF signal from the antenna or cable system carries the original digital data, so you split that cable signal and connect it separately to the set top box, Tivo, and all your Digital TV computer adapters, but you do not want to use RF to connect two boxes to each other because the other options provide a better picture.

Analog - Analog connectors between two boxes carry a single TV program. There are four types of analog cables listed by improving picture quality:

  • Composite carries an entire SD TV program on one RCA connector.
  • SVideo (Y/C) carries an SD TV program on two pairs of wires, one for the Black and White ("Y") signal and a combined color ("C") signal.
  • VGA (RGB) is a 1987 computer monitor standard that is still in wide use. It has three rows of 15 pins in a D-shaped shell. The pins carry signals for red, green, and blue colors. VGA is a computer, not a TV standard, but most TVs today have a VGA input.
  • Component (Y Pr Pb) cables can be SD or HD. They carry the Black and White signal ("Y") on a green RCA connector,  and two separate color signals on red and blue RCA connectors.

Digital - Digital is better. Since digital is a stream of numbers transmitted without error, different types of digital cable carry the same quality of signal and differ in the size and type of connector. All cables can handle 1080p, the highest TV resolution.

  • DVI is an older mostly computer standard. There is standard DVI, and then a dual link DVI (twice the pins, twice the wires in the cable) that is only needed to drive one of those Dell or Apple 30 inch computer monitors with 8 million dots on the screen.
  • HDMI is a newer mostly TV standard. It has a smaller connector, but is otherwise the same as standard (single link) DVI. You can buy a cable that is DVI on one end and HDMI on the other to convert between the two.
  • DisplayPort is a new standard with a cable the size of HDMI but the bandwidth of dual link DVI. It will be the wave of the future, but in the future. Today you can only find two or three devices in the world that support DisplayPort.

Digital connections transmit data exactly, so the movie companies became scared that someone would use them to make exact copies of movies. So licensed Blu-Ray movie players will only transmit data on one of these three digital connections if it is scrambled by the HDCP encryption technology. The Sony PS3 is a Blu-Ray player, so it requires HDCP before it will talk to a monitor over an HDMI cable.

OTA (over the air), cable company, phone company

Digital TV is broadcast over the same frequencies as traditional TV, and it can be picked up with the same Radio Shack rooftop antenna or rabbit ears. The frequency that for decades we have associated with one analog TV "channel" can now carry a stream of 20 million bits or a little more than 2 megabytes per second. Most of it will be used to broadcast one High Definition and one old standard definition TV program. The rest could be used to broadcast more programming, or it could be used to send a stock ticker tape, traffic report, text news stories, even software updates. TV stations negotiated with the FCC so that they could put any kind of data they wanted onto the unused packets. In the US, the standard for turning data into a broadcast over the air signal is called "8VSB". Europe uses another standard.

A cable TV system is immune to interference. It transmits digital data without the error correction and redundancy, so it can get twice as much data or 40 megabits per second on each of its 135 TV channels. This allows cable to carry two HD programs on the same channel frequency, or up to 10 standard definition programs on a digital channel. Comcast recently demonstrated a system where it used 4 TV channels in combination to create an Internet data feed of 160 megabits per second. In Cable, the standard for getting twice as much data onto a TV channel is called "QAM".

Verizon has a system called FiOS where they run a fiber optic cable to each house. This provides nearly unlimited bandwidth for TV and internet.

AT&T has an alternate system called U-Verse that is a little cheaper. They run fiber to a big box in your neighborhood, but then they run traditional copper wire pairs from the box to your house. On those copper wires they run a heavy duty version of DSL with 20 megabits per second (30 or 40 in some test systems). This 20 megabit connection then carries internet traffic, TV, and other content to your house.

Cable TV could transmit 135 channels of 40 megabits per second simultaneously to every room of every house. Everyone in the neighborhood gets the same signal. If you hook up a cable modem to get your internet traffic, then the modem sees all the traffic to all the computers in the neighborhood and filters out just the part addressed to you.

U-Verse has only one 20-40 megabit connection, but it is private between your house and the neighborhood concentrator. It can carry a certain amount of internet traffic, and one or two highly compressed TV programs. Your set top box tells the neighborhood box what channels you want to see. The box gets all the channels over its fiber connection, but it only forwards to your house the one or two programs you indicate an interest in.

Why Digital?

The first analog recording device was the Edison phonograph. Sound waves in the air vibrate a needle that makes an impression in a wax cylinder. Later the cylinder can be used to vibrate another needle that in turn vibrates a horn that recreates the original sound. Then Bell learned how to replace the wax cylinder with an electric wire to create the telephone. Others replaced the wire with radio waves to produce broadcast audio. Finally, Philo Farnsworth in 1927 used radio to modulate a rapidly moving beam of electrons striking a cathode ray tube to produce the first TV.

Each time an analog signal is received, recorded, and retransmitted, the process is imperfect and adds some noise or distortion. In the 1950's long distance phone system, a voice call became harder to understand as the signal was amplified again and again as it travelled from coast to coast or under the sea. A copy of a video or audio tape is not as good as the original.

Analog information can be digitized. To digitize sound, replace the Edison recording needle with a sensor. Let it vibrate as before, but instead of using it to create waves in a surface, have a computer record the position of the sensor as a sequence of numbers. Write these numbers anywhere a computer can store data. Later on, you can use the sequence of numbers to drive the position of a rod that drives the cones in a speaker system. With video, use a digital camera system to record numbers that represent the color of every dot in the picture.

The problem is that the numbers in the digital data take up a lot more room on any recording medium. A magnetic tape can be used to record sound or data. If you digitize the sound, the data takes up a lot more tape than you would have used to store an analog tape recording of the same sound.  Two things fix this problem. Modern computer technology allows this data to be compressed. When the phone company began to digitize voice telephone calls, they needed 64,000 bits per second to transmit the data. Cell phones compress voice down to less than 10% of that original size. Technology also allows an awful lot of digital data to be transmitted over the same physical connection that used to carry old analog data. The two copper wires that carry one plain old telephone call can also (even at the same time) transmit 20 to 40 million bits per second of data. Fiber optic cable bumps that into the tens of billions of bits per second.

Unlike analog systems, digital data can be received and retransmitted precisely. There is no loss of data, and no errors are introduced. A digital phone call around the world sounds the same as a phone call across the street. If you record the data from a digital TV broadcast onto a computer disk, you make an exact copy. You can view the program the next day or next week, and the picture quality will be identical to what you would have seen viewing the broadcast live.

Why the PC?

Because it's data. You can certainly buy consumer electronic devices with remote controls that don't look like a PC, but ultimately every device that processes digital TV signals is some kind of computer. You can buy a TV, a DVR, a Blu-Ray player, a DVD recorder. They are all computers. If you already have a computer, then for $22 you might buy the KWorld 340U USB tuner dongle and you get the data there too. Then you can record it to disk, display it on the screen, or burn it to a DVD.

You can buy a Blu-Ray reader for a PC for about $180. It comes with a copy of PowerDVD that plays the Blu-Ray formatted disks. However, PowerDVD and other licensed Blu-Ray software is contractually obligated to refuse to display a movie on a monitor connected to a PC over a DVI cable. You either have to switch back to the old analog VGA cable, or else find a monitor with a new HDMI connector with HDCP encryption. Of course, you could reconnect your existing monitor using the VGA cable (all monitors with DVI also typically have the old VGA video connector) but now there is a different problem. The logic that uses a modern video adapter to do all the work of decompressing video for the screen only works on a digital DVI or HDMI connection. Hook up a VGA, and now all the work has to be done on the CPU, and that is enough work to keep a 2.5 GHz Dual Core CPU 100% busy throughout the movie.

Normally I would not suggest anything that appears to be improper, but at this point it is easy to find yourself screwed by hardware problems and software that has intentionally created problems. Rather than buying a new monitor, at this point you might Google for AnyDVD HD from slysoft.com. This program disables the encryption on most Blu-Ray disks, allowing you to play the disks on your existing DVI monitor.

The remaining problem is to choose hardware to pick up the broadcast or cable TV programs, record them, and then display them later on. These options will be discussed below.

Different Types of "Digital TV"?

Generically, Digital TV is any system that transmits the TV picture as a series of numbers. There is a common set of core technologies, but they can be deployed in several different packages. You should not confused completely different system simply because both use the words "digital" and "TV" at the same time.

  • A "digital versatile disk" (DVD) is an updated version of the CD. The CD holds 700 megabytes of data. A manufactured DVD can hold up to 9000 megabytes of data to hold a movie in MPEG 2 format, plus several sound tracks and extras. A DVD movie is "Standard Definition" which means that it is designed for traditional TV sets. When displayed on a new HD TV, the DVD displays 480 lines of 720 dots per line.
  • Digital OTA (over the air) Broadcast TV transmits data at 20 Million bits per second on the same frequencies previously used for analog transmission. It uses a signal called "8VSB" to carry the data on top of a standard TV channel. You pick this up with the same Radio Shack rooftop antenna (or rabbit ears) that you used for old broadcast TV. This single 20 Mb/s stream of data is organized into 188 byte packets each identified by a number called its PID. Packets with the same PID number form a stream of video or audio for a single TV program. You could squeeze four to six standard definition TV programs in this amount of bandwidth, but networks now transmit one HD program and a second SD copy of the same program for display on older TV sets (although the two programs can share the same audio stream).
  • "Digital cable" transmits a stream of 40 million bits per second over each of the available channels from the 135 frequencies previously used for analog TV.  They get twice as much data into a TV channel as broadcast TV because there is no interference in a cable system, so they can use a more efficient technique called "QAM" to hold the signal rather than the "8VSB" that broadcasters have to use. The raw 40 Mb/s data stream can then be used to deliver two 15 Mb/s MPEG 2 broadcast HD channels or up to 10 standard definition 4 Mb/s MPEG 2 channels. 
    • Digital Cable Box: For over a decade, cable TV systems have offered a service they call "digital cable" that allows dozens of premium movie channels, plus pay per view, plus sports packages, to be received by a digital cable set top box. This stuff is all "encrypted" content, which means that it can only be received by the either the old cable box or by new devices with a slot to plug in a "CableCard" rented from the cable company. The cable company likes "digital" because each old TV channel can carry up to 10 pay per view or premium channels bringing extra revenue.
    • "Clear QAM": Your local broadcast TV station transmits a digital signal. The cable companies receive this signal from an antenna, then retransmit each 188 byte packet (maybe with a different PID number) as unencrypted data on the cable system. When the local TV stations stop broadcasting analog signals, most cable companies will also convert this digital signal to analog and broadcast it to old TV sets on the same channels that now carry the analog SD signal to old "cable ready" analog TV sets. This means that Comcast in New Haven transmits three different formats of Despirate Housewives each Sunday night. There is an analog signal on channel 7, an HD digital signal, and an SD digital signal. These last two unecrypted digital signals can be received by new "digital cable ready" TV sets (or devices that connect to your computer). The buzzword is "Clear QAM". QAM is the digital modulation technique used by cable companies, and the "clear" part means that the signal is not encypted because it is ordinary broadcast network content. You may not appreciate this, but the cable companies also transmit unencrypted versions of shopping channels like QVC and HSN, and public service channels like CSPAN.
  • Satellite TV systems (DirectTV) transmit a digital signal in a format very similar to that of digital cable, but it is all encrypted. Therefore, you need a separate satellite receiver device for every TV set or computer adapter card.
  • Blu-Ray is a new version of the DVD/CD media. Blu-Ray holds 25 Gigabytes of data per layer, so a two layer movie disk can be 50 Gigabytes instead of the 8 Gigabytes on a two layer DVD.

The Source

If you start with Over The Air broadcast to an antenna, then for the next few months there will still be some analog broadcast. After Feb. 2009, there will only be a digital signal. If you have old analog equipment, you can use the government coupon to buy an external box that will convert the SD digital broadcast signal into an old style analog TV signal. Computers can receive the digital signal directly using adapters that start at $15.

If you start with cable TV, then even after Feb 2009 you will still get analog signals on the radio frequencies associated with channels from 2 to sixty-something. Higher channels carry digital QAM traffic, but most of it is encrypted and requires a subscription. The local network broadcast programs, however, are unencrypted and can be picked up by devices that support "clear QAM". The subscription stuff requires a set top box (which will convert the encrypted digital data to various box-to-box analog (composite, SVideo, component, VGA) and digital (DVI, HDMI) cables. There are two devices, the Tivo HD and the Dell Digital TV Tuner, that can receive and record encrypted cable TV programs directly using something called a CableCard that you can rent from your cable company. The Dell tuner only works with Windows Media Center.

Currently US satellite TV is all based on vendor specific conventions. The only way to receive the signal is with a proprietary box.

Receiver

Old TV sets receive only analog signals. After June, they will only be able to receive the 60 or so analog channels transmitted on your cable system, or the output from existing external devices (DVD players, Tivo or other DVRs, VHS, cable boxes, or converter boxes you buy with government coupons). This is not a good time to be considering a new pure analog receiver.

New TV sets can receive digital over the air broadcast from a rooftop antenna, and if they have Clear QAM capability they can also receive broadcast network programming directly from the cable (without an external cable box). Devices are available to receive the same signals and pass it on to your PC as computer data.

During the transition, some computer devices were "hybrid" They could receive one analog and one digital program at the same time. While there will still be useful analog signal on cable systems for the next few years, you have to decide if analog (and that means Standard Definition) is worth spending money on today.

Other devices do not tune a TV program at all. They record a program from one of the analog output cables (composite or SVideo for SD programming) from the cable TV set top box. One device, the Hauppague HD PVR, can record HD output from the component analog cables from your cable TV HD set top box or your HD satellite receiver.

Analog Connector Details

Everything in a computer is based on separate values for Red, Green, and Blue (RGB). The adapter maintains a separate byte of data for each color, the adapter then generates a separate voltage level for each color one one of the pairs of pins on the plug that connects the computer to the monitor. Inside the display adapter, and for that matter inside the TV set itself, three electrodes generate a flow of electrons for each of the three colors.

So it may be surprising that TV sets operate on an entirely different system. If TV started out as a color picture, then it probably would work the same as computers. However, the first TV sets produced a black-and-white image. Black-and-white TV was available for more than a decade before color signals were added to existing TV channels. Unfortunately, the black-and-white part already took up most of the channel, so the color was squeezed into a smaller part of the spectrum.

The black-and-white part of the signal is called luminance and is represented in the standard by the letter "Y". This signal is not equal parts of red, green, and blue. The human eye sees the three colors differently, and the black-and-white signal has been weighted to reflect what looks best to the eye.

In high school geometry everyone learns that conventional "Cartesian" coordinates (x, y, z) can be translated to "Polar" coordinates. In 3D, the Polar coordinates are represented by the vector length (magnitude or absolute value) and two angles from the origin direction. In the same way, any combination of red, green, and blue can be represented by the black-and-white "Y" signal (like magnitude or absolute value) and two other values that represent color differences (like angles) from a pure black and white origin.

There are three colors. In the TV system, there is one Y value and two chrominance values. You can translate from either system to the other. In the modern world of computers, we add and subtract numbers to do the translation. However, the old TV systems did not have computer chips. The Y value and the two chrominance values were analog waves picked up through the antenna and amplified through the vacuum tubes. Two waves can be "added" together by combining them directly. One can be subtracted from the other by flipping its value (positive to negative) and then combining it with the other wave. The three waves can be combined together through various filters, and the output fed to the red, green, and blue electrodes in the back of the TV tube.

TV Component (Y Pr Pb)

A High Definition cable TV set top box, Blu-Ray player, or even most DVD players these days provide a Component video connection. This supports three RCA jacks that are typically colored red, green, and blue but have entirely different signals. The green jack is the black and white intensity signal labeled "Y". The other two cables are labeled Pb and Pr and they carry color information. So Component connectors are often labelled "Y Pr Pb".

With three separate wires to carry the three separate signals, the receiver does not have to apply any filter to split a signal. There is, therefore, no currently important limit on the frequency of the signal or the resolution of the screen. Component cables can be used for anything from Enhanced Definition up to High Definition TV.

Computer VGA

In 1987 IBM introduced the "VGA" adapter for its new line of computers. The VGA has three sets of pins that generate a Red, Green, and Blue analog signal. The first VGA monitors had a resolution of 640x480, but the connector itself has survived up to today's high resolution monitors. Since it has been around for twenty years, computer users probably have a stack of these things in a closet. The difference between the VGA and Component analog connectors is that Component has a black and while signal, then two color signals that can be combined with the black and white to generate Red, Green, and Blue values. VGA just generates the Red, Green, and Blue directly. Most flat screen displays have a VGA connector, but few consumer TV devices support this connection.

Good: S-Video (1 round jack, two pair of wires)

[Standard Definition only] Almost all DVDs, SVHS tape devices, and moderately priced conventional TV sets have an S-Video connector. This is also called a Y/C connector because it has two pair of wires. One carries the Y black-and-white signal. The other carries the two color signals combined together using standard wave multiplexing technology.

Because the two color components have been combined, they have to be separated by a filter on the receiver. This is fairly simple to do on the plain old standard resolution TV. As the resolution increases, the frequency of the signal increases. The conventional technology for filtering the C signal into two elements does not work correctly at higher frequencies. That is why the three component connectors are required for HDTV.

OK: Composite (1 yellow jack)

[Standard Definition only] The oldest and most widely supported standard combines all three video signals as a compound wave form in a single "composite" signal. Typically this is represented as a single yellow RCA jack, typically combined with the red and white stereo audio jacks. If you go to Radio Shack or Circuit City, one of these three-connector audio/video cables is typically called a "dubbing cable". You get a few of them with every VCR, DVD player, or computer sound card. Since the device wears out or becomes obsolete long before the cable develops a problem, you probably have a drawer full of dubbing cables at home.

Radio Frequency Connector

RG6 Cable with an F-connector

If you have an antenna on the roof or you get cable service, the signal enters the house as as a standard TV cable (RG6). At the end of the cable the installer will have stripped off the plastic cover and attached a screw cap around the core wire. This is called an "F connector".

There is absolutely nothing wrong with the original cable that brings in the original signal. It will have around 135 cable TV channels or all the broadcast signals your antenna can pick up. However, the worst way to connect two devices inside your system to each other is to use a short version of this TV cable. While a set top box can send the TV program out on Channel 3 or 4, it can only do this by combining the three orginal signals as in a composite cable, and then transmit that signal over the radio frequency assigned to the channel. This adds errors, and then the device that receives it has to tune the frequency and separate out the three components.

Monster Rip Off

The biggest opportunity for a rip off is the high cost premium cables. Over the one meter connection between the TV and an external tuner box, there is little measurable difference between the cables that came free with the box and some monster $60 cables sold separately. Use standard cables initially and upgrade to something better only if there is a problem. When it doubt, see if you can borrow some premium cables from some friend who already got suckered into buying them. Do a "blind" test where someone switches the cables and someone else judges the picture without knowing which type of cable is currently being used.

Digital Cables

Internally, the computer generates three numbers for the colors of each dot on the screen. Internally the flat panel monitor or TV has to generate three numbers for each dot on the screen. Now you can use one of the analog cables (the component Y Pb Pr cables or the 15 pin VGA cable) to convert each number into an amount of voltage difference sent over the cable in a short time window that corresponds to each dot. Or you can use a digital cable to simply send the numbers as a stream of data just like the USB, firewire, Ethernet, or other computer cables.

Digital cables produce a sharper picture because the numbers can be transmitted precisely. An analog connection is less sharp because some information is lost converting the numbers to analog voltage and then converting them back to numbers.

DVI

There are different versions of DVI connectors for digital only (DVI-D) and digital+analog (DVI-I). Nobody uses DVI-A because if you wanted an analog connector, you would use the VGA instead.

The analog pins are on the left in these diagrams, the four pins above and below the horizontal connector. The digital signals can be single or dual link. Single link is adequate for any reasonably priced display, but if you buy one of those 30 inch super high resolution monitors, then you need an adapter card that supports dual link connectors and a dual link cable.

Most video adapter cards have one DVI-I single link connector and one VGA analog connector, though a few have two DVI-I connectors. Such cards may come with a DVI-I to VGA adapter plug, that takes the analog pins (shown in the bottom DVI-A diagram) and turns them into the familiar 15 pin D-shaped VGA connector. At power up, the card tests the digital and analog lines and uses whichever one is connected to something.

HDMI

HDMI is a smaller plug that supports only digital data. You can convert the digital part of DVI into an HDMI plug and visa versa, but HDMI cannot be adapted to analog. HDMI also contains wires for digital audio.

DVI is a computer standard, although some TV sets and cable TV set top boxes have a DVI plug. HDMI is a TV and consumer electronics standard, although some PC video cards support it.

HDMI is typically associated with HDCP, a standard for encrypting the data that is transferred between the device and the flat screen display. Movie studios were afraid that their high definition video data would be captured and recorded. Given that Blu-Ray encryption has been cracked, this is a lot of trouble for no good purpose at all.

DisplayPort

The next video connector standard will be DisplayPort. It can support a higher resolution in a 3 foot cable, or it can support the current 1080p highest resolution TV standard in a a longer 15 foot cable. The first DisplayPort adapter cards have been announced, but this is not a connection mechanism that will be of much practical use until 2009.

Computer File Formats

A computer file that contains a TV program has to have both audio and video data. There are different compression formats available for video and audio data.

MPEG 2 was a good standard. It had basically one format for the file, and one way to compress both the video and audio data. MPEG 2 files can be in Program Stream or Transport Stream format. Generally, data that is recorded onto a computer hard disk or that comes from a DVD is in Program Stream format with 2048 byte records. It has an extension of ".mpg" on disk and ".vob" on the DVD. Data transmitted in over the air broadcast or over cable TV systems tends to be in Transport Stream format, in 188 byte packets. It has an extension of ".ts" or ".tp". Utilities can convert between Program and Transport stream formats.

Microsoft has its own version of a simple MPEG 4 class video file format for its Windows Media Player program. Video compressed by the Microsoft packages has a WMV extension.

The problem with all other standards is that they separate the video compression and audio compression into two different decisions. As a result, there isn't a completely standard format.

CODEC

Software that encodes and COmpresses and DECompresses a multimedia file format is called a CODEC.

Windows has a convention where a CODEC registers itself with the system and can then be used by any media player that needs to decode a file in that format. Windows comes with some CODECs supplied by Microsoft, but there are many other standard and non-standard CODECs available for other file formats.

Divx is the name of a company that specializes in versions of the simple MPEG 4 standard. You can download their software from the company web site.

Several groups accumulate packages of the most popular CODECs and distribute 32 and 64 bit versions of them for Windows XP and Vista. You might look at www.free-codecs.com.

However, a CODEC at best decodes a video stream or audio stream. It doesn't specify a file format. Microsoft has a generic format called AVI for files containing video and audio data encoded by arbitrary CODECS. Every other vendor has their own file format and extension.

Storage

A writable DVD costs around $.20 and holds 4.7 gigabytes of storage. That is way more than an hour of standard definition TV. However, HD TV requires 4 to 7 gigabytes per hour even after you remove all the commercials (the actual file size depends on the format the network uses for HD). You can fit some shows on a DVD, and split others across two DVDs.

You should also consider the cost of disk. A 750 gigabyte hard disk costs $120. That means that one gigabyte of hard disk costs about the same as 4.7 gigabytes of DVDR. DVD is still cheaper for long term storage of things you really want to keep. For storage of something you just want to see more than once, but not keep for years, a few large disks are much simpler.

Packet Format

No matter which type of modulation is used, the output of the tuner is a stream of bits that form a sequence of 188 byte packets. If the tuner is connected to an antenna, the stream is 20 million bits per second, while the clear QAM of a cable TV system yields 40 million bits per second.

Each packet as a Packet ID or PID value. When you tune to a new stream of bits on a new radio frequency, you first have to wait for a packet with a PID of 0.

The PID 0 packet contains a definition of the logical TV program streams contained on that physical channel. A broadcast over the air TV station typically transmits one HD program stream and one standard definition stream for old TV sets. On a cable channel, there can be up to 10 different standard definition streams.

Each logical TV program has its own control PID. If you select one and then wait for the next packet with that PID number, it will contain information about the PID of the video component of that program and the PIDs of each audio component (because TV shows can be broadcast with both English and Spanish audio tracks).

In addition to this minimal control information, there are other optional control packets that identify a logical channel number and sometimes the call letters of the station. Cable TV also transmits information about the program including its title and some episode information. However, the availability and use of this data is not assured.

So if you want to view or record a particular TV program, you tune to the physical channel frequency, wait for the PID 0 packet, select a program stream, wait for its first control packet, and then start to process all the packets that contain the desired video and audio PID numbers  (typically ignoring everything else).

Computer TV Adapters

You may want to look at Newegg or at a specialty source like PC Alchemy.

It is getting rather late to buy an analog-only PC TV card, although cable systems will still carry analog programs for the useful life of the device. Remember, analog data has to be sampled and digitzed, then compressed to a rational file size. The $40 analog adapters rely on your PC CPU to do the compression, and that can put a strain on the system. Serious users pay a little more to get an adapter with hardware compression of the TV program to MPEG 2 or 4 in the device itself. Then the CPU is free to do other work.

Adapters can plug into the PCI or PCI-e slots, or with hardware compression they can be attached to the computer over a USB port.

Adapters can handle one or two programs, and some will handle one analog and one digital program.

Digital TV adapters should have Clear QAM capability if you are ever going to subscribe to cable.

Other than that, all adapters are pretty much the same. This article will now consider devices of special technical merit.

The Hauppauge HD DVR 1212

Every analog adapter card can process SD signals from a composite or SVideo cable. This allows you to record premium programs off the cable or satellite TV set top box.

High Definition analog signals operate at a higher speed that cannot be supported by composite or SVideo. They require the three connector Component cables (Y Pr Pb with the green, red, and blue RCA connectors). The HD signal is four times as fast as SD. Big deal. We have had TV adapters for SD analog for over 10 years now, and clearly the chips have gotten a lot more than 4 times faster. However, until now there has not been a device to record HD analog signals off the Component cable.

Finally Hauppauge announced the HD PVR (model 1212). You plug the Component cables from your HD Cable TV set top box or HD Satellite receiver into the HD PVR. It digitizes the HD signal and compresses it internally using a chip that does H.264 AVC (the most modern, best video compression standard). The bad news is that this box costs $250. For a little bit more than that, you could buy an HD Tivo unit and just be an ordinary user of consumer electronics, or you could invest in one of the Dell systems that has the industry's only CableCard capable digital TV tuner that can receive the encrypted raw data off the cable TV system.

Of course, other solutions have Digital Rights Managment encryption, so the file that you record can only be used on the one system. The programs recorded on the Hauppauge can be stored on disk, written to DVD, or transmitted through the network to one of your other computers.

The signal you record with the HD PVR started out as MPEG 2 data transmitted on encrypted QAM over the cable (or satellite) system. It was decrypted, decompressed, and then converted from a digital number to an analog voltage level inside the Set Top Box. Now the HD DVR samples the voltage levels on the three component cables and generates a number that is close but maybe not exactly the same as the original.  Then the chip in the HD DVR compresses this sampled data using Advanced MPEG 4 instead of the original MPEG 2. Some loss of picture quality occurred throughout this process. The file you get will not be as good as the Blu-Ray commercial disk that comes out with the same show. However, the HD picture will be better than any SD picture you might have recorded.

If you keep the recording below the size of a single or dual layer DVD, the Hauppauge HD PVR comes with software that will write the recorded file to the DVD in a format where it can be played on any Blu-Ray player. This is a regular DVD+/-R disk, not one of the super expensive Blu-Ray writable disks. However, Blu-Ray players will also play DVDs, and this particular DVD will be written with the same file structure as a Blu-Ray disk, only smaller with less capacity.

HDHomeRun

The most interesting digital-only device is from a small company called Silicondust Engineering. They build a box called HDHomeRun that receives the digital TV signal and transmits it to your computer over your home Ethernet network. All the other TV tuners are devices that connect to the PC through USB or by being plugged into the PCI bus. Since they are real devices, they need real device drivers. However, writing a device driver is a complex programming task and the company doesn't always have great programmers.

The HDHomeRun box internally has the tuner devices and an embedded operating system. It handles all the hardware level programming inside its own box. Then it transmits the HD TV data as ordinary Internet traffic.

Your computer receives data from the HDHomeRun just as it would read any other data from the Internet. Hundreds of programs on your computer read data though the internet. This is very simple coding that almost any programmer can do. As a test, the author spent a few minutes and wrote a 20 line program from scratch that received the TV program from the HDHomeRun and recorded it as file on disk. When something is that simple, it is much, much easier to get it right, and the vendor is much quicker to adapt it to new situations.

The HDHomeRun drivers support a nifty remapping file. In the file, you can configure the over the air broadcast channel and program ID that you would use to receive a network program with an antenna, and then you configure the frequency and program id that the data actually has on the cable system. Software tells the driver to tune to what it thinks is an antenna broadcast station, but the driver remaps the request and sends the actual cable TV information to the box. This way, all the software packages support the box.

Software - Media Center, Beyond TV, or Sage

Each adapter card comes with some sort of recording/viewing application. Third party programs (or Windows Media Center) will optimize your TV recording across all your adapter cards using a common internal program guide.

If you only have network broadcast service and if the networks only show each program in one timeslot, then "scheduling" consists of counting up the number of devices you have to record programs and determining if there are any time slots where there are more shows to record than devices to record them on. If there are, then the shows have to be prioritized so the system can decide to ignore your least favorite show.

However, today there is SD and HD programming on analog, clear QAM, and encrypted (requires the Set Top Box) cable. Different devices can be set to to receive each type of programming. The same program is available on analog and digital, HD and SD.

"Priority" can now mean different things. In a single conflicted timeslot it determines which program will not be recorded. Otherwise, it can select which programs are recorded in HD and which slip to less desirable SD. Finally, when some cable programs are shown in multiple time slots, it might indicate which is recorded first in prime time and which is recorded at 3:00 AM.

Windows Media Center is built into some premium editions of Vista. If you have it you may want to try it out. There are two commercial products that you can add on to XP or Vista and may be more attractive than spending money to upgrade Vista.

BeyondTV is sold by Snapstream Media. You install the main program on the computer that is connected to the TV adapter hardware, and then you can install the less expensive BeyondTV Link program on other computers to that server machine through your home network. Check the list of supported adapters to make sure your hardware is supported. BTV pops up a window (or full screen) application that looks list the menus and lists you see on your TV set when you use the remote control to navigate through the various Comcast or DirectTV windows. This is often called the "ten foot interface" because it is designed to be used on a TV screen from across the room using only a remote control. However, it also lauches a Web Service on port 8129 that you can browse to from the same computer or from another computer on the network. The Web pages show a lot more information with long lists of programs and more complicated configuration options.

SageTV is the competition. Sage believes strongly in the "ten foot" interface with big letters and not a lot of words or choices on the screen. Without a browser interface, Sage allows you to drill down with your remote control (or simulated remote control) to nested levels of screens that contain almost all the options you can imagine.

Consider setting up you channel lineup. Of course, you can simply take all the channels that the cable company delivers, but in the long run it will save you some time if you disable display of the shopping networks and all the foreign language programming you don't understand. BTV displays web pages with 130 channels per page, and you can disable a channel by clicking a check box. Sage displays channels 5 at a time and you toggle whether the channel is displayed by clicking on it. BTV certainly makes it easier to manage a large number of channels, but it introduces the concept of an abstract "lineup" that is separate from any particular recording device. When you have more than one device that shares the same lineup, this abstraction saves you time. Otherwise, it is one more quirk to learn and the Sage practice of assigning a custom lineup to each device seems simpler to learn (even if it is a bit tedious to set up).

It is not possible to provide a comprehensive review of both programs. A few obvious points:

  Beyond TV Sage TV
OS .NET, so Windows only Java, so runs on Windows, Mac, Linux
UI Remote Control "across the room" menus for simple things, Web pages for complex tasks or more detailed reports. Remote Control "across the room" style menus for everything, so this one type of configuration can become quite complex and has lots of options.
Hardware support Supports all types of devices, and has some more detailed options through the Web page interface Supports all types of devices, and tends to be weeks ahead of BeyondTV in supporting the latest device.
Complexity Every program has a piriority position, so the program you like most tends to be scheduled to record first. Every device has a priority, so the device you prefer tends to be scheduled to be used first. Shows can have a preferred channel. You influence and control everything, but the bad news is that the BTV people don't explicitly tell how the choices you make are used. You can figure it out by changing the priority of shows in the same timeslot and then checking to see how things have changed. You choose a bunch of shows. You define some devices. Internally it knows what devices are HD or SD. It knows what shows are HD or SD. Since Sage doesn't let you give priorities to shows, devices or shows, it is free to "do the right thing" almost all the time without bothering you with the details. If it doesn't make the right choice, you have to override by manually scheduling shows yourself.
Service Runs in the trey of a logged in Windows user Runs as a service. Records when nobody is logged in
Look Ahead Web page lists next two weeks of recordings in calendar format. Does not disclose what devices (HD or SD) will be used to record a show, but you can get this from a third party tool called BTV Negotiator. Knows the TV schedules for the next  two weeks, but only formally schedules recording for the next three days. After three days, it will not tell you when episodes of recurring series will be recorded. For the three fully scheduled days, it optionally tells which device will be used to record each show.
STB control Knows the commands of lots of cable and satellite boxes. Select yours from the list. No list, but uses ability of IR controller to receive as well as send. Point your STB remote control at the device and press each number key. Learns each signal so it can control the STB itself.

Both programs have a free trial period, but you need enough equipment to test complex scenarios and make the best choice.

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