Multicasting

What is multicasting?

When not transmitting in HDTV, broadcasters will be able to transmit four or more channels of standard definition television (SDTV) programming simultaneously. This is called multicasting. 

Although SDTV will not match HDTV in quality, it will offer a higher quality picture than with traditional analog TV.

The option to multicast was made possible by digital technology to allow each digital broadcast station to split its bit stream into 2, 3, 4 or more individual channels of programming and/or data services. For example, on channel 55, you could watch 55.1, 55.2, 55.3 or 55.4, or if the station were  broadcasting in HDTV, you could watch a single High-Definition program.

Multicasting opens up an entirely new world of possibilities.

Like Enhanced TV, multicasting opens up an entirely new world of possibilities, allowing TV broadcasters to provide very targeted ("niched") services to kids, for distance-learning, for arts programs and other worthwhile television - depending on the needs of the local community and a Member Station's own resources.

Multicasting also permits "time-shifting" of the same programming, either by providing blocks of shows repeated on the same multicast channel or on a station's other multicast channels during different day-parts, to allow students and other viewers to watch at times most convenient to them.

FAQ - DTV

What is digital television?

Digital TV is turbo-charged television, yielding clearer pictures, better sound, more network channels, and more viewing excitement than traditional analog television. Digital TV offers a picture free of "ghosts," "snow" or interference. The crisper, sharper image is due to the increased number of pixels the digital signal puts on the screen - the higher the number, the sharper the picture - and High-definition Television (HDTV) has the highest resolution available. Furthermore, Digital TV provides 5.1 channels of Dolby Digital CD-quality surround sound, adding to the ultimate home theater experience. Digital TV also enables broadcasters to multicast, delivering up to three or more simultaneous programs in a Standard-Definition (SDTV) format.

What is HDTV?

DTV or high definition television is an entirely new system that will ultimately replace today's existing analog “NTSC” television system. The term “HDTV” refers to a television system that can transmit, receive and display high-quality digital images. The image on the best HDTV set has five times more detail than analog televisions. HDTV has higher resolution meaning sharper, clearer pictures. Many HDTV programs also contain six-channel (5.1) Dolby Digital surround sound to provide an immersive audio experience to complement the improved picture quality on HDTV.

Why is Digital TV better than "regular" analog TV?

DTV brings viewers five times the picture resolution and clarity of analog TV, making viewers feel like they are right in the middle of the action on their screens. Digital TV uses binary code, the same system of ones and zeroes that run on computers and digitally recorded compact discs. Switching TV broadcasts to digital is like switching from cassette tape to Compact Disc or from a VHS tape to a DVD - the pictures are clearer and sound is improved, giving viewers the opportunity to experience their favorite programs on a whole new level. What's more, with a 16:9 aspect ratio compared to today's 4:3 aspect ratio of analog television, Digital TV lets viewers see much wider images.

Will consumers have to pay to receive Digital TV broadcasts?

No. Unlike digital cable where consumers pay monthly fees for services, Digital TV provides high quality programming and more content via free over-the-air broadcasts.

What about my existing analog TV?

Until the total conversion to Digital TV is made, broadcasters will generally simulcast the same programs on two different channels - one in a digital format and one in analog. Viewers with analog sets will be able to convert a digital signal to an analog signal by hooking up a digital tuner decoder box to their sets; however, they will not be able to experience the crystal clear pictures and sound quality that a DTV set provides, nor will they experience the advantages of datacasting or interactive television.

What are the different signals that viewers will see on a Digital TV?

Digital TV gives broadcasters the flexibility to bring viewers programming on different types of digital signals - ranging from high definition to standard definition. Digital TV signals have better resolution than analog TV, which has been in use for more than 50 years. High-definition digital broadcasting is much clearer and sharper than digital cable. With Digital TV, broadcasters can send various signals to consumers, including:

• High-Definition Television (HDTV) - An HDTV signal allows a broadcaster to transmit a wide screen picture with many times more detail than is contained in current analog TV pictures. HDTV brings viewers programming so crisp and so clear, it produces an image as sharp as reality. In addition, HDTV offers unsurpassed audio quality.
• Standard-Definition Television (SDTV) - A SDTV signal is another type of signal that viewers experience through DTV. While a SDTV signal also has higher-quality video and audio than an analog signal, SDTV is particularly remarkable because it can bring viewers multiple channels of free over-the-air programming from the same station. In effect, one digital television signal has the ability to carry either a program broadcast in HDTV, and in some cases one additional standard definition signal, or several programs broadcast simultaneously in standard definition television on different channels.

What should consumers look for when shopping for a new TV set today?

•  An integrated Digital TV set -- This option allows viewers to receive analog and digital signals. An integrated set can project high-definition (HD), enhanced-definition (ED) or standard-definition (SD) signals. An HDTV set has the highest resolution available and provides the ultimate home theater experience. An integrated Digital TV set provides consumers the most convenient, hassle-free way to experience Digital TV.

•  A Digital TV monitor and a separate digital tuner decoder box. This option allows consumers to upgrade to Digital TV when ready. If consumers choose to purchase only a Digital TV monitor, they will get a wide-screen format and improved picture. In order to receive an over-the-air signal with a Digital TV monitor, consumers must purchase a set-top decoder box. These boxes may be used with HD, ED or SD monitors.

•  An analog set. If consumers buy an analog set today, they will not receive any of the benefits of Digital TV, including the clearest pictures and sound ever available. Because an analog set does not have a digital tuner, consumers will have to purchase a digital tuner decoder box to watch Digital TV.

What is aspect ratio?

Aspect ratio refers to the relationship between the width and height of the screen. Most analog sets have an aspect ratio of 4:3, or 4 units wide by 3 units high. High definition television sets come in a widescreen display, which is 16:9, or 16 units wide by 9 units high.

What is datacasting?

Because DTV is digital, curriculum materials, full interview transcripts, children's games and still photographs can be delivered to your television while you are watching a program. DTV's broader bandwidth channel provides a digital pipeline into the home with a transmission rate many times that of a PC modem.

What is multicasting?

When not transmitting in HDTV, broadcasters will be able to transmit four or more channels of standard definition television (SDTV) programming simultaneously. This is called multicasting. Although SDTV will not match HDTV in quality, it will offer a higher quality picture that we have today.

Are the new DTV sets readily available?

Digital TV sets are available at both retail stores nationwide as well as online. Like CD players, computers and personal digital assistants, the prices for Digital TV sets continue to drop as the technology becomes more prominent. In fact, prices for Digital TV sets have decreased by 50 percent over the last two years and are available in stores today starting at under $2,000.

Equally important, sales of DTV monitors and sets (monitors with integrated tuners) are rising each month. According to the Consumers Electronics Association, manufacturer-to-retailer sales figures of DTV monitors and sets in October 2001 showed a 113 percent increase over October of the previous year. October 2001 alone saw 187,464 Digital TV sets and monitors shipped from manufacturers to retailers. As of the end of October, 1,050,460 Digital TV units had been sold in 2001. CEA projects that 2.1 million Digital TV products will be sold in 2002, 5.4 million in 2004, 8 million in 2005 and 10.5 million in 2006.

Do I need to convert to digital right away?

The Digital TV transition is happening now. 1,060 local stations in over 202 markets are broadcasting a digital signal, ensuring that 99 percent of U.S. TV households are in a market with a digital signal. The government has loaned each broadcaster an additional TV channel to permit the transition to the new system. Throughout the transition, the government will review penetration of new Digital TV receiver sales every two years. This will ensure that the penetration of Digital TV is progressing as anticipated, so that the total conversion to digital will be a smooth one.

If I have digital cable, do I have digital television and if I buy a Digital TV, will it work with digital cable?

Digital cable is not the same as digital television. In fact, most cable companies do not yet carry broadcasters' digital signals. Digital cable refers only to how signals are transferred across cable. Moreover, because there are not yet universal interoperability standards, a digital set that is plugged into a digital cable set-top box will only receive an analog signal, withholding all the advantages of digital television from a consumer. While inter-industry cooperation is yielding some progress on these issues, digital cable does not yet deliver digital signals into digital television sets. However, it is expected that this will change for the better very soon and cable companies will indeed deliver DTV signals. Check with your local cable provider to see if digital signals are available in your area.

A
Analog TV
Analog technology has been in use for the past 50 years to transmit conventional TV signals to consumers. "Standard" television broadcasts in analog TV. Analog signals vary continuously, creating fluctuations in color and brightness.

Aspect Ratio
A numerical expression of the relationship of width to height of a TV screen. 4:3: This numerical sequence refers to the aspect ratio of the National Television Systems Committee (NTSC) TV screen, with "4" unit width corresponding to "3" unit height, proportionally, regardless of the actual size of the screen. 16:9: This numerical sequence refers to the aspect ratio of wide screen DTV formats for all HDTV and some SDTV (Standard Definition) video. A "16" unit width corresponds to "9" unit height proportionally, regardless of the actual size of the screen. The widescreen 16:9 numerical sequence provides a viewing experience very similar to that of 35 mm movies.

ATSC: An acronym for advanced television systems committee, and the name of the DTV system used by broadcasters in the U.S.

B
Barn Doors
A term used in television production to describe the effect that occurs when a 4:3 image is viewed on a 16:9 screen. When this happens, viewers see black bars on the sides of the screen or "barn doors."

C
Codec
This term is short for "Coder-decoder." A codec is a device that converts analog video and audio signals into a digital format for transmission. It also converts received digital signals back into an analog format.

Compression
Compression refers to the reduction of the size of digital data files by removing redundant and/or non-critical information ("data" being the elements of video, audio and other "information"). Digital TV in the U.S. would not be possible without compression.

Computer Input
Some HDTV sets have an input like SVGA or VGA that allows the TV sets to be connected to computers.

D
Datacasting
Also known as "enhanced TV." Datacasting is the act of providing enhanced options offered with some digital programming to provide additional program material or non-program related resources. This allows viewers the ability to download data (video, audio, text, graphics, maps, services, etc.) to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

Decoder
See "codec." A device or program that translates encoded data into its original format (i.e., it decodes the data.)

Digital Cable
A service provided by many cable providers, digital cable offers viewers more channels. Contrary to many consumers' beliefs, digital cable is not the same as High-Definition Television or digital television; rather digital cable simply offers cable subscribers the options of paying for more services.

Digital Monitor
DTV monitors are televisions that can display a digital signal but lack an integrated tuner (unlike an integrated digital set), and thus cannot receive a digital broadcast signal without an additional set-top box.

Digital Television (DTV)
Digital TV is the umbrella term encompassing High-definition Television and several other applications, including Standard Definition Televison, datacasting, multicasting and interactivity.

Digital Tuner
A digital tuner serves as the decoder required to receive and display digital broadcasts. It can be included inside TV sets or via a set-top box.

Down Converting
Process by which a high-definition signal is converted to a standard definition picture.

E
Enhanced TV
Also known as "datacasting." This term is used for certain digital on-air programming that includes additional resources downloaded to viewers. Some forms of enhanced TV allow live interaction; other forms are not visible on-screen until later recalled by viewers. Producers add these options to some digital programming to enhance program material -- allowing viewers the ability to download related program resources to specially equipped computers, cache boxes, set-top boxes, or DTV receivers.

EDTV
This acronym stands for "Enhanced Definition Television." It refers to a complete products/system with at least a digital receiver display scanning format, and Dolby Surround Sound audio output capabilities.

H
HDTV: "High-definition Television."
This is the most superior video picture available in Digital TV. In the U.S., the 1080i and 720p formats in a 16:9 aspect ratio are the two acceptable HDTV formats. HDTV is a component of DTV.

Interactive Television
This is when TV programming features interactive content and enhancements, blending traditional TV viewing with the interactivity of a personal computer.

L
Letterbox
Letterbox refers to the image of a wide-screen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. It is used to maintain the original aspect ratio of the original source (usually a theatrical motion picture of 16:9 aspect ratio or wider).

M
Multicasting
The option to multicast was made possible by digital technology to allow each digital broadcast station to split its bit stream into 2, 3, 4 or more individual channels of programming and/or data services. (For example, on channel 7, you could watch 7-1, 7-2, 7-3 or 7-4.)

N
NTSC
NTSC is the acronym that stands for National Television Systems Committee"and the name of the current analog transmission standard used in the U.S., which the committee created in 1953.

P
Pixel
Pixel is actually two words jammed together ( ¾ picture and element). A pixel is a tiny sample of video information, the "little squares" that make up an overall picture.

Pixels Per Inch
Pixels per inch (PPI) is a measure of the sharpness (that is, the density of illuminated points) on a television display screen.

R
Resolution
The level of resolution directly affects picture quality. The higher the resolution, the more picture detail there is. Many things affect picture quality, including number of bits, pixel count, format, receiver quality, cameras, lenses and lighting used for live or taped programming. Resolution is measured by the number of pixels displayed. One of the high-definition picture formats is composed of 1080 active lines, and each line is composed of 1920 active pixels. Therefore, each frame has over 2 million (1080x1920=2,073,600) color pixels creating the image. By way of contrast, today's typical analog television is roughly equivalent to 480 active lines, with each line holding about 440 pixels. So, each frame has a little over 200,000 color pixels in use creating the image.

S
Sampling
This is the digital process by which analog information is measured, often millions of times per second, in order to convert analog to digital.

Standard Definition TV Format (SDTV)
There are two main digital formats - HDTV and SDTV. SDTV typically does produce better quality images than that of traditional analog TV and pictures somewhat akin to digital cable. However, its images are not nearly as sharp as the images from the ultimate form of digital television ¾ High-definition TV (HDTV).

Set-top Converter Box
This unit sits on top of the viewer's analog TV, receives the Digital TV signal, converts it to an analog signal, and then sends that signal on to the analog TV.

SVGA
This acronym is short for the "Super Video Graphics Array" display mode. SVGA resolution is 800 x 600 pixels.

T
Terrestrial Broadcasting
This is a broadcast signal transmitted "over-the-air" to an antenna.

U
Upconverting
Process by which a standard definition picture is changed to a simulated high-definition picture.

V
VGA
This acronym is short for the "Video Graphics Array" display mode. VGA resolution is 640 x 480 pixels.

W
Wide screen
A term given to picture displays with a wider aspect ratio than NTSC 4:3. Digital HDTV or SDTV is referred to as "16:9 wide screen." Most motion pictures also have a 16:9 wide screen aspect ratio. Most Digital TVs have a screen that is wider than it is tall (if a Digital TV screen is nine inches high, it's 16 inches wide.) When watching a show recorded in the wide screen format on a Digital TV, viewers see more of the movie, while when viewing wide screen format on an analog TV, cropped edges are evident.