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Ed's AV Handbook
Batting Practice for the AV Professional
and primer for the novice

Chapter 4  Page 3

Video Reproduction
Digital Television


Off-air, Cable, Satellite, Internet

Digital TV decodes five voltages from digitally encoded component video* to create a television picture.     
*refer to previous page

1. Red    2. Green    3. Blue   
4. Horizontal Sync   5. Vertical Sync      

(Horizontal and vertical sync are the start and finish points of each video frame.)

A digital TV decoder processor converts component video to red, green, blue sub-pixels while progressively building each picture frame line by line.  OLED, IOLED, Micro LED, LCD, and plasma processors hold the progressive-lines of data until they have a complete frame.  They then flash the entire video frame to the television screen.  DLP projectors build each frame progressively line by line on the screen. 

Digital TV Broadcast / Cable

Digital broadcasted - local off-air & satellite - component video does not fit within allocated data bandwidth and storage as is.  Broadcasters reduce the data with MPEG video compression.  Off-air ATSC TV also employs ATSC 8VSB codec, and cable TV providers use QAM codec to accommodate MPEG audio and video compression.

Handbook Notes: codec is an acronym for compress/decompress.

MPEG Video Compression


MPEG video compression is a cycle of incomplete video frames inserted between complete uncompressed frames.  MPEG compression eliminates redundant video data.  It is somewhat similar to animation.  Unchanging elements of moving scenes, such as the static background of a blue sky, are held and repeated frame after frame.  Changing data of motion passes without interruption.

The data reduction, plus the number of incomplete frames placed between complete frames, is determined by the version of MPEG employed: MPEG-2, MPEG-4 AVC H.264, MPEG HEVC H.265, MPEG VCC H.266.  Each succeeding version increases the amount of data reduction.

- MPEG2 supports ATSC HDTV off-air broadcast.
- MPEG4 supports satellite broadcast.
- MPEG HEVC H.265 (High Efficiency Video Coding) supports ATSC 3.0 Next GenTV, UltraHDTV.
- MPEG VCC H.266 (Versatile Video Coding) supports ATSC 3.0 NextGenTV, UltraHDTV, UHD-8K TV, & UHD-16K TV. 

The final stage of an off-air digital ATSC broadcast also employs ATSC 8VSB RF modulation.  8VSB divides MPEG video and audio into interleaving packets of data called PIDS.  It is a continuing cycle of a video PID followed by an audio PID.  An ATSC 8VSB television tuner decoder restores order.

The digital cable TV provider's final stage utilizes QAM modulation.  QAM is similar to 8VSB interweaving of the video and audio data.  As an 8VSB, a QAM cable television tuner decodes and restores order.

Satellite TV Distribution

An umbrella of communication satellites distributes TV programming to local broadcasters, cable companies, and 'small dish' satellite providers.  Several dozen communication satellites hover in geosynchronous orbit more than 22,000 miles above the equator of the earth.  They receive and redirect programming to your TV provider's 'tree farm' of large dish satellite antennas.

Sat TV Dist

- Local broadcasters re-transmit programming via a broadcast tower to indoor and rooftop antennas. 
- Cable TV providers redistribute programming via cable wired directly to residences. 
- Small dish satellite providers up-link their programming to proprietary satellites that bounce the programming back to small rooftop dish antennas.

Dish antenna, why?
A local TV broadcaster may engage thousands of watts of broadcast power.  As a result, the local TV receiving antenna can be as little as a "rabbit ear" antenna sitting on the TV.  In contrast, satellites are limited to only five to fifteen watts of down-link broadcast power.  Also, they broadcast at radio frequencies that are impractical for a satellite receiving tuner to manage.  Consequently, the satellite receiving system needs a major-assist.

Assistance comes in the form of a satellite dish with a low-noise-block-feed-horn (LNBF) mounted in front of the satellite dish.  The satellite dish magnifies incoming signal hundreds of fold by reflecting and focusing the energy at a mounting arm that holds the antenna element located in the LNBF.  The LNBF amplifies the signal still further and shifts the incoming-signal from the 12GHz region to the more manageable neighborhood of 950 MHz to 1450 MHz.  Small dish operators also employ MPPEG4 digital compression to squeeze hundreds of channels within their bandwidth.  The combination of the dish antenna, the LNBF, and MPEG4 produces a signal that a satellite receiver can handle and display on a TV.

Internet Streaming / IPTV

Online Streaming

Expanding Internet bandwidth has allowed Internet protocol television (IPTV) to become the leading means of TV program distribution via Internet service providers (ISP) -- local cable TV, telephone DSL, cellular phone, satellite, and NextGenTV terrestrial broadcast.
H.264 AVC (Advanced Video Compression) compression supports most Internet video streaming.

Internet service providers deliver programming via a managed or unmanaged network.  An un-managed network is a single programming website such as Netflix, Amazon, Hulu.  A managed multichannel-video-program-distributor (MVPD), such as YouTubeTV, offers a package of un-managed sites.
Both are known as OTT (over the top) programming.

Digital TV Result

Red, Green, Blue, horizontal sync, and vertical sync data, derived from television camera CCD sensors, are converted to component video. A digital TV provider compresses the component video within allocated data storage.  The digital TV restores the component video data to RGBHV to recreate the original sequence of pixel framed images on the TV screen

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Ed's AV Handbook   
Copyright 2007 Txu1-598-288 Revised 2024

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