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HOME                                  REVIEWS                                CONTACT                             ABOUT                         April 9, 2009

 

      

HDTV Compressed Digital Video (CDV) For Non-Geeks

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Technology

Bandwidth Requirement

Standard Definition (SDTV)

3 Gb/Hour

1280 X 720 (HDTV)

150 Gb/Hour

1920 X 1080 (HDTV)

350 Gb/Hour

MPEG-2 (CDV) HDTV

9 Gb/Hour

MPEG-4 (CDV) HDTV

5 Gb/Hour

 

 
 

 

Compressed Digital Video (CDV) is comparable to using MP3 files

 for music.  It makes the file smaller without significantly damaging

it (at least we hope so), so that it takes less time to download

(less bandwidth), and more songs can be stored on your player.

 

Similarly, CDV reduces the signal bandwidth requirements of

a TV signal to enable its transmission via the Internet, DVD,

cable, or satellite.  This is necessary because an uncompressed

video signal is very large.  High definition (HDTV) files are

much larger than standard definition files. 

 

 

 

 

 

 

The early use of CDV (for standard definition programming) was pioneered by the satellite TV companies, DirecTV and the Dish Network.

 

Signal compression is the process of discarding data for that information that would be invisible to the viewer. However, too much compression will significantly distort the output. The higher the level of CDV, the more data that must be discarded.  Discard too much, and the distortion is very noticeable.

 

CDV is a tradeoff between file size and video quality. CDV operates on pixel neighborhoods, called a macroblock. The compression algorithm records only the changes within those blocks. This works well if the video is primarily static images like text.

 

In a basketball game, when Kobe takes it to the basket, more pixels change from one frame to the next. When this happens, the video compression algorithm must work harder.  The picture quality after compression depends on the complexity and predictability of the image.

 

The most common CDV standards are authored by the Moving Picture Experts Group (MPEG). Applying CDV to video is an intensive computer operation, but uncompressing (undoing the CDV) MPEG data to video is much less difficult.   A C-Cube real-time MPEG-1 video encoder using 8 custom-designed video processor chips sells for $120,000.

 

MPEG standards are not owned by anyone. Various companies and researchers have MPEG patents, but one does not have to pay a license fee to use MPEG technology. 

 

DVD and Blu-ray discs have CDV used during the mastering process (Blu-ray has enough disc capacity that the CDV is not aggressive, thus does not add significant distortion).  High bitrate video algorithms with little CDV exist for video post-production work, but these still create an enormous file, and for this reason are seldom used for the distribution of video.

 

There are several MPEG standards being used but only three are in general use for commercial video distribution:

 

MPEG-1

 

MPEG-1 was the first widely used video (and audio) CDV standard. MP3 is an abbreviation of "MPEG-1 audio layer 3".  MPEG-1  supports a video resolution of 352 x 240 at 30 FPS (frames per second).  It is the standard for the CDV of moving pictures (and audio). This standard has roots in CD-ROM video applications, and is a popular for video found on the Internet (.mpg files).

 

MPEG-2

 

MPEG-2 can support video resolutions of 720 x 480 and 1280 x 720, at 60 FPS. MPEG-2 is capable for both standard definition TV and HDTV.  The MPEG-2 standard is also used to store data on a DVD.  This is the algorithm used by DirecTV and the Dish Network.

 

MPEG-2 is the standard on which Digital Television set top boxes and DVD CDV is based. It is based on MPEG-1, but modified for use by digital broadcast television. Different algorithms have been developed and have been integrated into the standard. MPEG-2 is well suited to HDTV resolution and bit rates.  With this technique, CDV can compress video data by 15 to 25 times while still producing a picture quality that is generally considered high quality. 

 

MPEG-4

 

This standard is the future CDV standard that will almost certainly be used by most services delivering HDTV.  This includes AT&T, DirecTV, and the Dish Network.  A number of cable operators have also started MPEG-4 trials. This standard was originally designed for the Internet. Individual objects within a scene are tracked separately.  This is very efficient.  

 

The move to MPEG-4 by the satellite companies is not designed to improve picture quality, but because this algorithm is much more efficient. An MPEG-2 HDTV channel utilizes the bandwidth of six standard definition TV channels; An MPEG-4 HDTV channel would only consume the bandwidth of three standard definition TV channels.  MPEG-4 uses half the bandwidth of MPEG-2, and so your service provider will be able to offer twice the number of channels.

 

OpenCable Application Platform (OCAP)

 

Consumers are now able to purchase their own cable box/DVR combos from electronics retailers. OCAP is a way for cable operators and other service providers to deploy interactive services like a PC.  This will enable your American Idol voter to cast their vote with the remote control for their TV. 

 

Consumers want their HDTV, and service providers who can supply the programming will thrive. MPEG-4 is the best and most cost-efficient option for cable operators and other service providers.

 

 

 

 

 

 

 

 

 

 About the Author:

 

Brian Bradshaw is an InfoComm Certified Technical Specialist (CTS), Microsoft Certified Technology Specialist (MCTS), and CompTIA A+ Computer Technologist.  Areas of expertise include Video, HDTV, Audio, Computation, SATCOM Systems, and Communications.


Web site: http://bradshaw-vacuum-technology.com/