Explanation of common compression standards in the DVR field
MPEG
Stands for the Moving Picture Experts Group MPEG is an ISO/IEC working group,
established in 1988 to develop standards for digital audio and video formats.
There are five MPEG standards being used or in development. Each compression
standard was designed with a specific application and bit rate in mind, although
MPEG compression scales well with increased bit rates. They include:
MPEG-1
Designed for up to 1.5 Mbit/sec, this is the standard for the compression of
moving pictures and audio. This was based on CD-ROM video applications, and
is a popular standard for video on the Internet, transmitted as .mpg files.
In addition, level 3 of MPEG-1 is the most popular standard for digital compression
of audio--known as MP3. MPEG-1 is the standard of compression for VideoCD,
the most popular video distribution format throughout much of Asia.
MPEG-2
Designed for between 1.5 and 15 Mbit/sec, this is the standard on which Digital
Television set top boxes and DVD compression is based. It is based on MPEG-1,
but designed for the compression and transmission of digital broadcast television.
The most significant enhancement from MPEG-1 is its ability to efficiently
compress interlaced video. MPEG-2 scales well to HDTV resolution and bit rates,
obviating the need for an MPEG-3.
MPEG-4
This is the standard for multimedia and Web compression. MPEG-4 is based on
object-based compression, similar in nature to the Virtual Reality Modeling
Language. Individual objects within a scene are tracked separately and compressed
together to create an MPEG4 file. This results in very efficient compression
that is very scalable; from low bit rates to very high. It also allows developers
to control objects independently in a scene, and therefore introduce interactivity.
MPEG-7
This standard, currently under development, is also called the Multimedia Content
Description Interface. When released, the group hopes the standard will provide
a framework for multimedia content that will include information on content
manipulation, filtering and personalization, as well as the integrity and security
of the content. Contrary to the previous MPEG standards, which described actual
content, MPEG-7 will represent information about the content.
MPEG-21
Work on this standard, also called the Multimedia Framework, has just begun.
MPEG-21 will attempt to describe the elements needed to build an infrastructure
for the delivery and consumption of multimedia content, and how they will relate
to each other.
JPEG
This stands for Joint Photographic Experts Group. It is also an ISO/IEC working
group, but works to build standards for continuous tone image coding. JPEG
is a compression technique used for full-color or gray-scale images, by exploiting
the fact that the human eye will not notice small color changes.
JPEG 2000
An initiative that will provide an image coding system using compression techniques
based on the use of wavelet technology.
DV
A high-resolution digital video format used with video cameras and camcorders.
The standard uses DCT to compress the pixel data and is a form of compression.
The resulting video stream is transferred from the recording device via FireWire
(IEEE 1394), a high-speed serial bus capable of transferring data up to 50
MB/sec.
H.261
An ITU standard designed for two-way communication over ISDN lines (video conferencing)
and supports data rates which are multiples of 64Kbit/s. The algorithm is based
on DCT and can be implemented in hardware or software and uses intraframe and
interframe compression. H.261 supports CIF and QCIF resolutions.
H.263
This is based on H.261 with enhancements that improve video quality over modems.
It supports CIF, QCIF, SQCIF, 4CIF and 16CIF resolutions.
H.264
This is also known as MPEG-4 AVC (Advanced Video Coding). It
is a video compression standard that offers significantly greater compression
than its predecessors. The standard offers up to twice the compression of the
current MPEG-4 ASP (Advanced Simple Profile), in addition to improvements in
perceptual quality. The H.264 standard can provide DVD-quality video at less
than 1 Mbps, and is optimal for full-motion video over wireless, satellite,
and ADSL Internet connections.
DivX
DivX is a software application that uses the MPEG-4 standard to compress digital
video, so it can be downloaded over a DSL/cable modem connection in a relatively
short time with no reduced visual quality. The latest version of the codec,
DivX 4.0, is being developed jointly by DivX Networks and the open source community.
DivX works on Windows 98, ME, 2000, CE, Mac and Linux.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Video codec".
