8/7/2019 Lecture 14-Compression
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CS65 Computer Networks Department of EEE
S.Muralidharan 1
Before audio or video signals can be sent on the Internet, they
needBefore audio or video signals can be sent on the Internet, they
need
to be digitized. We discuss audio and video separately.to be
digitized. We discuss audio and video separately.
Digitizing Audio :Digitizing Audio :
Voice is sampled at 8000 samples per second with 8 bit per
sample. ThisVoice is sampled at 8000 samples per second with 8 bit
per sample. This
results in a digital signal of 64Kbps.results in a digital
signal of 64Kbps.
Music is sampled at 44,100 samples per second with 16 bits per
secondMusic is sampled at 44,100 samples per second with 16 bits
per secondresulting in a digital signal of 705.6Kbps for mono and
1.411Mbps forresulting in a digital signal of 705.6Kbps for mono
and 1.411Mbps for
stereo.stereo.
Digitizing Video :Digitizing Video :
A video consists of a sequence of frames. Each frame is divided
into smallA video consists of a sequence of frames. Each frame is
divided into small
grids, called picture elements or pixels. For black and white
TV, each 8grids, called picture elements or pixels. For black and
white TV, each 8--bitbit
pixel represents one of 256 different gray levels. For color TV,
each pixel ispixel represents one of 256 different gray levels. For
color TV, each pixel is
24 bits, with 8 bit for each primary color (red, green and
blue).24 bits, with 8 bit for each primary color (red, green and
blue).
To send audio or video over the Internet requires compression.
InTo send audio or video over the Internet requires compression.
In
this section, we discuss audio compression first and then
videothis section, we discuss audio compression first and then
video
compression.compression.
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