Short for
Moving Picture Experts Group,
and pronounced m-peg, is a working group of the
ISO. The term also refers to
the family of
digital video compression
standards and file formats developed by the group. MPEG generally produces
better-quality video than competing formats, such as
Video for Windows,
Indeo and
QuickTime. MPEG files previously on
PCs needed
hardware decoders
(codecs) for MPEG processing. Today, however, PCs can use
software-only
codecs including products from
RealNetworks, QuickTime or Windows Media Player.
MPEG algorithms compress data to form small bits that can be easily
transmitted and then decompressed. MPEG achieves its high compression rate by storing only the changes from one
frame to another, instead of each entire frame. The
video information is then
encoded using a technique called Discrete Cosine Transform
(DCT). MPEG uses a type of
lossy compression, since some data is
removed. But the diminishment of data is generally imperceptible to the human
eye.
The major MPEG standards include the following;
- MPEG-1: The most common implementations of the MPEG-1 standard
provide a video resolution of 352-by-240 at 30 frames per second (fps). This
produces video quality slightly below the quality of conventional VCR
videos.
- MPEG-2: Offers resolutions of 720x480 and 1280x720 at 60 fps,
with full CD-quality audio. This is sufficient for all the major TV
standards, including NTSC, and even HDTV. MPEG-2 is used by DVD-ROMs. MPEG-2
can compress a 2 hour video into a few gigabytes. While decompressing an
MPEG-2 data stream requires only modest computing power, encoding video in
MPEG-2 format requires significantly more processing power.
- MPEG-3: Was designed for HDTV but was abandoned in place of using
MPEG-2 for HDTV.
- MPEG-4: A graphics and video compression algorithm standard that
is based on MPEG-1 and MPEG-2 and Apple QuickTime technology. Wavelet-based
MPEG-4 files are smaller than JPEG or QuickTime files, so they are designed
to transmit video and images over a narrower bandwidth and can mix video
with text, graphics and 2-D and 3-D animation layers. MPEG-4 was
standardized in October 1998 in the ISO/IEC document 14496. See
MPEG-4.
- MPEG-7: Formally called the Multimedia Content Description
Interface, MPEG-7 provides a tool set for completely describing
multimedia content. MPEG-7 is designed to be generic and not targeted to a
specific application.
- MPEG-21: Includes a Rights Expression Language (REL)
and a Rights Data Dictionary. Unlike other MPEG standards that describe
compression coding methods, MPEG-21 describes a standard that defines the
description of content and also processes for accessing, searching, storing
and protecting the copyrights of content. See
MPEG-21.
