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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Figure 1: MPEG-1 encoding process.One disadvantage of the MPEG format is that it can-
not easily be edited because video cannot be entered at
any point. And the quality of the resulting video is im-
pacted by the amount of motion in the video. The more
motion in the video, the greater the probability that the
quality will be reduced. The MPEG encoding and de-
coding process can require a large amount of computa-
tional resources, which requires the use of specialized
computer hardware or a computer with a powerful proce-
ssor.
MPEG-2 was released in 1994 and was designed to be
compatible with MPEG-1. It is used primarily for deliv-
ering digital cable and satellite video to homes. It is the
basis of DVD and HDTV. MPEG-2 utilizes the same com-
pression techniques as MPEG-1. However, it has been en-
hanced so that it has better compression efficiency than
MPEG-1. MPEG-2 supports two encoding schemes de-
pending on the application. The first scheme has a vari-
able bit rate, which keeps the quality constant. The sec-
ond scheme involves varying the quality to keep the bit
rate constant. MPEG-2 is not considered an ideal format
for streaming over the Internet because it works best at
transmission rates higher than most networks can handle
(Cunningham & Francis, 2001).
MPEG-4 is one of the most recent video formats and is
geared toward Internet and mobile applications includ-
ing video conferencing, video terminals, Internet video
phones, wireless mobile video, and interactive home shop-
ping. It was originally designed to support data rates less
than 64 Kbps but has been enhanced to handle data rates
ranging from 8 Kbps to 35 Mbps. MPEG-4 is different
from MPEG-1 and -2 in that it has been enhanced to han-
dle the transmission of objects described by shape, tex-
ture, and motion, versus just the transmission of rectan-
gular frames of pixels. In fact, it is very similar to H.263,
which is the video conferencing standard (Compaq, 1998).
This feature makes MPEG-4 well suited to handle multi-
media objects, which are used in interactive DVD, inter-
active Web pages, and animations.
MPEG-7 is the newest standard. It is designed for mul-
timedia data and can be used independent of the other
MPEG standards. Work is being done on an extension of
the MPEG-7 standard, called MPEG-21.
The H.261 and H.263 standards are designed for video
conferences and video phone applications that are trans-
mitted over an ISDN network. H.261 has the ability to
adapt the image quality to the bandwidth of the trans-
mission line. The transmission rate for H.261 is usually
around 64 Kbps (Fischer & Schroeder, 1996). H.263 was
developed as an enhancement to H.261 and was designed
to support lower bit rates than H.261. It has a higher pre-
cision for motion compensation than H.261. H.263 is very
similar to the MPEG standards, particularly MPEG-4, anduses the same compression techniques (Vantum Corpora-
tion, 2001).
MJPEG stands for Motion JPEG, and JPEG stands for
Joint Photographic Experts Group. JPEG is an interna-
tional standard for compressing still frames. MJPEG is a
sequence of JPEG compressed still images that represent
a moving picture. Thus, MJPEG is a compression method
that is applied to each frame without respect to the pre-
ceding or following image (Vantum Corporation, 2001).
MJPEG can be edited easily but it is not able to handle
audio.AUDIO COMPRESSION ALGORITHMS
Each of the three major streaming technologies has its
preferred algorithms for compressing audio. In addition,
the MPEG group has defined an audio standard called
MPEG-1 for audio. As discussed previously, audio com-
pression is different than video, although it uses similar
techniques. The MPEG audio compression uses psychoa-
coustic principles, which deal with the way the human
brain perceives sound (Filippini, 1997).
The first principle utilized in the MPEG audio compres-
sion is the masking effect. This means that weak sounds
are not heard, or they are masked, when they are near a
strong sound. For example, when audio is digitized, some
compression occurs because data are removed and noise
is added to the audio. This noise can be heard during silent
moments, or between words or sentences. However, this
noise is not heard during talking or when music is playing.
This is because the noise is a weaker sound and is masked
by the louder talking or music. MPEG uses this masking
effect to raise the noise floor around a strong sound be-
cause the noise will be masked anyway. And, by raising the
noise floor, fewer data bits are used, and the signal (or file)
is compressed. MPEG uses an algorithm to divide up the
sound spectrum into subbands. It then calculates the op-
timum masking threshold for each band (Filippini, 1997).
The second psychoacoustic principle is that the human
ear is less sensitive to high and low frequencies, versus
middle frequencies. In essence, MPEG employs a filtering
technique along with the masking effect to remove data
from the high and low frequencies where the changes will
not be noticed. It maintains the data in the middle fre-
quencies to keep the audio quality as high as possible.DELIVERING THE VIDEO
Once the video has been compressed and encoded for
streaming, the next step is to serve the video to the users
on the Internet. As discussed earlier in this chapter, deliv-
ering video over the Internet is usually accomplished with
a streaming server, instead of a Web server. A streaming