<s>
Video	O
is	O
an	O
electronic	O
medium	O
for	O
the	O
recording	O
,	O
copying	O
,	O
playback	O
,	O
broadcasting	B-Operating_System
,	O
and	O
display	O
of	O
moving	O
visual	O
media	O
.	O
</s>
<s>
Video	O
was	O
first	O
developed	O
for	O
mechanical	B-Architecture
television	I-Architecture
systems	O
,	O
which	O
were	O
quickly	O
replaced	O
by	O
cathode-ray	B-Device
tube	I-Device
(	O
CRT	B-Device
)	O
systems	O
which	O
,	O
in	O
turn	O
,	O
were	O
replaced	O
by	O
flat	B-General_Concept
panel	I-General_Concept
displays	I-General_Concept
of	O
several	O
types	O
.	O
</s>
<s>
Video	O
systems	O
vary	O
in	O
display	B-General_Concept
resolution	I-General_Concept
,	O
aspect	B-General_Concept
ratio	I-General_Concept
,	O
refresh	O
rate	O
,	O
color	O
capabilities	O
and	O
other	O
qualities	O
.	O
</s>
<s>
Analog	O
and	O
digital	O
variants	O
exist	O
and	O
can	O
be	O
carried	O
on	O
a	O
variety	O
of	O
media	O
,	O
including	O
radio	O
broadcast	B-Operating_System
,	O
magnetic	O
tape	O
,	O
optical	B-Device
discs	I-Device
,	O
computer	B-General_Concept
files	I-General_Concept
,	O
and	O
network	O
streaming	O
.	O
</s>
<s>
Video	O
technology	O
was	O
first	O
developed	O
for	O
mechanical	B-Architecture
television	I-Architecture
systems	O
,	O
which	O
were	O
quickly	O
replaced	O
by	O
cathode-ray	B-Device
tube	I-Device
(	O
CRT	B-Device
)	O
television	O
systems	O
,	O
but	O
several	O
new	O
technologies	O
for	O
video	O
display	B-Device
devices	I-Device
have	O
since	O
been	O
invented	O
.	O
</s>
<s>
Advances	O
in	O
computer	O
technology	O
allows	O
even	O
inexpensive	O
personal	B-Device
computers	I-Device
and	O
smartphones	B-Application
to	O
capture	O
,	O
store	O
,	O
edit	O
and	O
transmit	O
digital	O
video	O
,	O
further	O
reducing	O
the	O
cost	O
of	O
video	O
production	O
,	O
allowing	O
program-makers	O
and	O
broadcasters	O
to	O
move	O
to	O
tapeless	O
production	O
.	O
</s>
<s>
The	O
advent	O
of	O
digital	O
broadcasting	B-Operating_System
and	O
the	O
subsequent	O
digital	B-Application
television	I-Application
transition	O
is	O
in	O
the	O
process	O
of	O
relegating	O
analog	O
video	O
to	O
the	O
status	O
of	O
a	O
legacy	B-Device
technology	I-Device
in	O
most	O
parts	O
of	O
the	O
world	O
.	O
</s>
<s>
the	O
usage	O
of	O
digital	B-Device
cameras	I-Device
in	O
Hollywood	O
has	O
surpassed	O
use	O
of	O
film	O
cameras	O
.	O
</s>
<s>
Frame	O
rate	O
,	O
the	O
number	O
of	O
still	O
pictures	O
per	O
unit	O
of	O
time	O
of	O
video	O
,	O
ranges	O
from	O
six	O
or	O
eight	O
frames	O
per	O
second	O
(	O
frame/s	O
)	O
for	O
old	O
mechanical	B-Architecture
cameras	O
to	O
120	O
or	O
more	O
frames	O
per	O
second	O
for	O
new	O
professional	O
cameras	O
.	O
</s>
<s>
PAL	B-Language
standards	O
(	O
Europe	O
,	O
Asia	O
,	O
Australia	O
,	O
etc	O
.	O
)	O
</s>
<s>
Video	O
can	O
be	O
interlaced	O
or	O
progressive	B-Device
.	O
</s>
<s>
In	O
progressive	B-Device
scan	I-Device
systems	O
,	O
each	O
refresh	O
period	O
updates	O
all	O
scan	B-Algorithm
lines	I-Algorithm
in	O
each	O
frame	O
in	O
sequence	O
.	O
</s>
<s>
When	O
displaying	O
a	O
natively	O
progressive	B-Device
broadcast	B-Operating_System
or	O
recorded	O
signal	O
,	O
the	O
result	O
is	O
optimum	O
spatial	O
resolution	O
of	O
both	O
the	O
stationary	O
and	O
moving	O
parts	O
of	O
the	O
image	O
.	O
</s>
<s>
Interlacing	O
was	O
invented	O
as	O
a	O
way	O
to	O
reduce	O
flicker	O
in	O
early	O
mechanical	B-Architecture
and	O
CRT	B-Device
video	O
displays	O
without	O
increasing	O
the	O
number	O
of	O
complete	O
frames	O
per	O
second	O
.	O
</s>
<s>
Interlacing	O
retains	O
detail	O
while	O
requiring	O
lower	O
bandwidth	B-Algorithm
compared	O
to	O
progressive	B-Device
scanning	I-Device
.	O
</s>
<s>
In	O
interlaced	O
video	O
,	O
the	O
horizontal	O
scan	B-Algorithm
lines	I-Algorithm
of	O
each	O
complete	O
frame	O
are	O
treated	O
as	O
if	O
numbered	O
consecutively	O
,	O
and	O
captured	O
as	O
two	O
fields	O
:	O
an	O
odd	O
field	O
(	O
upper	O
field	O
)	O
consisting	O
of	O
the	O
odd-numbered	O
lines	O
and	O
an	O
even	O
field	O
(	O
lower	O
field	O
)	O
consisting	O
of	O
the	O
even-numbered	O
lines	O
.	O
</s>
<s>
Analog	O
display	B-Device
devices	I-Device
reproduce	O
each	O
frame	O
,	O
effectively	O
doubling	O
the	O
frame	O
rate	O
as	O
far	O
as	O
perceptible	O
overall	O
flicker	O
is	O
concerned	O
.	O
</s>
<s>
When	O
the	O
image	O
capture	O
device	O
acquires	O
the	O
fields	O
one	O
at	O
a	O
time	O
,	O
rather	O
than	O
dividing	O
up	O
a	O
complete	O
frame	O
after	O
it	O
is	O
captured	O
,	O
the	O
frame	O
rate	O
for	O
motion	O
is	O
effectively	O
doubled	O
as	O
well	O
,	O
resulting	O
in	O
smoother	O
,	O
more	O
lifelike	O
reproduction	O
of	O
rapidly	O
moving	O
parts	O
of	O
the	O
image	O
when	O
viewed	O
on	O
an	O
interlaced	O
CRT	B-Device
display	I-Device
.	O
</s>
<s>
NTSC	O
,	O
PAL	B-Language
and	O
SECAM	O
are	O
interlaced	O
formats	O
.	O
</s>
<s>
Abbreviated	O
video	B-General_Concept
resolution	I-General_Concept
specifications	O
often	O
include	O
an	O
i	O
to	O
indicate	O
interlacing	O
.	O
</s>
<s>
For	O
example	O
,	O
PAL	B-Language
video	B-Application
format	I-Application
is	O
often	O
described	O
as	O
576i50	O
,	O
where	O
576	O
indicates	O
the	O
total	O
number	O
of	O
horizontal	O
scan	B-Algorithm
lines	I-Algorithm
,	O
i	O
indicates	O
interlacing	O
,	O
and	O
50	O
indicates	O
50	O
fields	O
(	O
half-frames	O
)	O
per	O
second	O
.	O
</s>
<s>
When	O
displaying	O
a	O
natively	O
interlaced	O
signal	O
on	O
a	O
progressive	B-Device
scan	I-Device
device	O
,	O
overall	O
spatial	O
resolution	O
is	O
degraded	O
by	O
simple	O
line	O
doubling	O
—	O
artifacts	O
such	O
as	O
flickering	O
or	O
"	O
comb	O
"	O
effects	O
in	O
moving	O
parts	O
of	O
the	O
image	O
which	O
appear	O
unless	O
special	O
signal	O
processing	O
eliminates	O
them	O
.	O
</s>
<s>
A	O
procedure	O
known	O
as	O
deinterlacing	O
can	O
optimize	O
the	O
display	O
of	O
an	O
interlaced	O
video	B-Application
signal	I-Application
from	O
an	O
analog	O
,	O
DVD	O
or	O
satellite	O
source	O
on	O
a	O
progressive	B-Device
scan	I-Device
device	O
such	O
as	O
an	O
LCD	O
television	O
,	O
digital	B-Device
video	I-Device
projector	I-Device
or	O
plasma	O
panel	O
.	O
</s>
<s>
Deinterlacing	O
cannot	O
,	O
however	O
,	O
produce	O
video	B-Device
quality	I-Device
that	O
is	O
equivalent	O
to	O
true	O
progressive	B-Device
scan	I-Device
source	O
material	O
.	O
</s>
<s>
Aspect	B-General_Concept
ratio	I-General_Concept
describes	O
the	O
proportional	O
relationship	O
between	O
the	O
width	O
and	O
height	O
of	O
video	O
screens	O
and	O
video	O
picture	B-Algorithm
elements	I-Algorithm
.	O
</s>
<s>
All	O
popular	O
video	B-Application
formats	I-Application
are	O
rectangular	O
,	O
and	O
so	O
can	O
be	O
described	O
by	O
a	O
ratio	O
between	O
width	O
and	O
height	O
.	O
</s>
<s>
The	O
ratio	O
width	O
to	O
height	O
for	O
a	O
traditional	O
television	B-Device
screen	I-Device
is	O
4:3	O
,	O
or	O
about	O
1.33:1	O
.	O
</s>
<s>
High	O
definition	O
televisions	O
use	O
an	O
aspect	B-General_Concept
ratio	I-General_Concept
of	O
16:9	O
,	O
or	O
about	O
1.78:1	O
.	O
</s>
<s>
The	O
aspect	B-General_Concept
ratio	I-General_Concept
of	O
a	O
full	O
35mm	O
film	O
frame	O
with	O
soundtrack	O
(	O
also	O
known	O
as	O
the	O
Academy	O
ratio	O
)	O
is	O
1.375:1	O
.	O
</s>
<s>
Pixels	B-Algorithm
on	O
computer	O
monitors	O
are	O
usually	O
square	O
,	O
but	O
pixels	B-Algorithm
used	O
in	O
digital	O
video	O
often	O
have	O
non-square	O
aspect	O
ratios	O
,	O
such	O
as	O
those	O
used	O
in	O
the	O
PAL	B-Language
and	O
NTSC	O
variants	O
of	O
the	O
CCIR	O
601	O
digital	O
video	O
standard	O
,	O
and	O
the	O
corresponding	O
anamorphic	O
widescreen	O
formats	O
.	O
</s>
<s>
The	O
720	O
by	O
480	O
pixel	B-Algorithm
raster	O
uses	O
thin	O
pixels	B-Algorithm
on	O
a	O
4:3	O
aspect	B-General_Concept
ratio	I-General_Concept
display	O
and	O
fat	O
pixels	B-Algorithm
on	O
a	O
16:9	O
display	O
.	O
</s>
<s>
Vertical	O
video	O
ads	O
like	O
Snapchat	B-Application
’s	O
are	O
watched	O
in	O
their	O
entirety	O
nine	O
times	O
more	O
frequently	O
than	O
landscape	O
video	O
ads	O
.	O
</s>
<s>
There	O
are	O
several	O
such	O
representations	O
in	O
common	O
use	O
:	O
typically	O
YIQ	O
is	O
used	O
in	O
NTSC	O
television	O
,	O
YUV	O
is	O
used	O
in	O
PAL	B-Language
television	O
,	O
YDbDr	O
is	O
used	O
by	O
SECAM	O
television	O
and	O
YCbCr	O
is	O
used	O
for	O
digital	O
video	O
.	O
</s>
<s>
The	O
number	O
of	O
distinct	O
colors	O
a	O
pixel	B-Algorithm
can	O
represent	O
depends	O
on	O
color	O
depth	O
expressed	O
in	O
the	O
number	O
of	O
bits	O
per	O
pixel	B-Algorithm
.	O
</s>
<s>
Because	O
the	O
human	O
eye	O
is	O
less	O
sensitive	O
to	O
details	O
in	O
color	O
than	O
brightness	O
,	O
the	O
luminance	O
data	O
for	O
all	O
pixels	B-Algorithm
is	O
maintained	O
,	O
while	O
the	O
chrominance	O
data	O
is	O
averaged	O
for	O
a	O
number	O
of	O
pixels	B-Algorithm
in	O
a	O
block	O
and	O
that	O
same	O
value	O
is	O
used	O
for	O
all	O
of	O
them	O
.	O
</s>
<s>
For	O
example	O
,	O
this	O
results	O
in	O
a	O
50%	O
reduction	O
in	O
chrominance	O
data	O
using	O
2-pixel	O
blocks	O
(	O
4:2:2	O
)	O
or	O
75%	O
using	O
4-pixel	O
blocks	O
(	O
4:2:0	O
)	O
.	O
</s>
<s>
Video	B-Device
quality	I-Device
can	O
be	O
measured	O
with	O
formal	O
metrics	O
like	O
Peak	O
signal-to-noise	O
ratio	O
(	O
PSNR	O
)	O
or	O
through	O
subjective	B-Device
video	I-Device
quality	I-Device
assessment	O
using	O
expert	O
observation	O
.	O
</s>
<s>
Many	O
subjective	B-Device
video	I-Device
quality	I-Device
methods	O
are	O
described	O
in	O
the	O
ITU-T	O
recommendation	O
BT.500	O
.	O
</s>
<s>
Uncompressed	B-Device
video	I-Device
delivers	O
maximum	O
quality	O
,	O
but	O
at	O
a	O
very	O
high	O
data	O
rate	O
.	O
</s>
<s>
A	O
variety	O
of	O
methods	O
are	O
used	O
to	O
compress	O
video	O
streams	O
,	O
with	O
the	O
most	O
effective	O
ones	O
using	O
a	O
group	B-General_Concept
of	I-General_Concept
pictures	I-General_Concept
(	O
GOP	O
)	O
to	O
reduce	O
spatial	O
and	O
temporal	O
redundancy	B-General_Concept
.	O
</s>
<s>
Broadly	O
speaking	O
,	O
spatial	O
redundancy	B-General_Concept
is	O
reduced	O
by	O
registering	O
differences	O
between	O
parts	O
of	O
a	O
single	O
frame	O
;	O
this	O
task	O
is	O
known	O
as	O
intraframe	B-General_Concept
compression	O
and	O
is	O
closely	O
related	O
to	O
image	B-General_Concept
compression	I-General_Concept
.	O
</s>
<s>
Likewise	O
,	O
temporal	O
redundancy	B-General_Concept
can	O
be	O
reduced	O
by	O
registering	O
differences	O
between	O
frames	O
;	O
this	O
task	O
is	O
known	O
as	O
interframe	B-Algorithm
compression	O
,	O
including	O
motion	B-Algorithm
compensation	I-Algorithm
and	O
other	O
techniques	O
.	O
</s>
<s>
The	O
most	O
common	O
modern	O
compression	O
standards	O
are	O
MPEG-2	B-Algorithm
,	O
used	O
for	O
DVD	O
,	O
Blu-ray	O
and	O
satellite	O
television	O
,	O
and	O
MPEG-4	B-Algorithm
,	O
used	O
for	O
AVCHD	O
,	O
Mobile	O
phones	O
(	O
3GP	O
)	O
and	O
Internet	O
.	O
</s>
<s>
Stereoscopic	B-Algorithm
video	O
for	O
3d	B-Algorithm
film	I-Algorithm
and	O
other	O
applications	O
can	O
be	O
displayed	O
using	O
several	O
different	O
methods	O
:	O
</s>
<s>
Both	O
channels	O
may	O
be	O
viewed	O
simultaneously	O
by	O
using	O
light-polarizing	O
filters	O
90	O
degrees	O
off-axis	O
from	O
each	O
other	O
on	O
two	O
video	B-Device
projectors	I-Device
.	O
</s>
<s>
Anaglyph	B-Algorithm
3D	I-Algorithm
where	O
one	O
channel	O
is	O
overlaid	O
with	O
two	O
color-coded	O
layers	O
.	O
</s>
<s>
This	O
left	O
and	O
right	O
layer	O
technique	O
is	O
occasionally	O
used	O
for	O
network	O
broadcast	B-Operating_System
or	O
recent	O
anaglyph	O
releases	O
of	O
3D	B-Algorithm
movies	I-Algorithm
on	O
DVD	O
.	O
</s>
<s>
Simple	O
red/cyan	O
plastic	O
glasses	O
provide	O
the	O
means	O
to	O
view	O
the	O
images	O
discretely	O
to	O
form	O
a	O
stereoscopic	B-Algorithm
view	I-Algorithm
of	O
the	O
content	O
.	O
</s>
<s>
One	O
channel	O
with	O
alternating	O
left	O
and	O
right	O
frames	O
for	O
the	O
corresponding	O
eye	O
,	O
using	O
LCD	B-Algorithm
shutter	I-Algorithm
glasses	I-Algorithm
that	O
synchronize	O
to	O
the	O
video	O
to	O
alternately	O
block	O
the	O
image	O
to	O
each	O
eye	O
,	O
so	O
the	O
appropriate	O
eye	O
sees	O
the	O
correct	O
frame	O
.	O
</s>
<s>
This	O
method	O
is	O
most	O
common	O
in	O
computer	O
virtual	B-Application
reality	I-Application
applications	O
such	O
as	O
in	O
a	O
Cave	B-General_Concept
Automatic	I-General_Concept
Virtual	I-General_Concept
Environment	I-General_Concept
,	O
but	O
reduces	O
effective	O
video	O
framerate	O
by	O
a	O
factor	O
of	O
two	O
.	O
</s>
<s>
For	O
transmission	O
,	O
there	O
is	O
a	O
physical	O
connector	O
and	O
signal	O
protocol	O
(	O
see	O
List	B-Protocol
of	I-Protocol
video	I-Protocol
connectors	I-Protocol
)	O
.	O
</s>
<s>
A	O
given	O
physical	O
link	O
can	O
carry	O
certain	O
display	O
standards	O
that	O
specify	O
a	O
particular	O
refresh	O
rate	O
,	O
display	B-General_Concept
resolution	I-General_Concept
,	O
and	O
color	B-Algorithm
space	I-Algorithm
.	O
</s>
<s>
Many	O
analog	O
and	O
digital	O
recording	B-Device
formats	I-Device
are	O
in	O
use	O
,	O
and	O
digital	O
video	O
clips	O
can	O
also	O
be	O
stored	O
on	O
a	O
computer	B-Application
file	I-Application
system	I-Application
as	O
files	O
,	O
which	O
have	O
their	O
own	O
formats	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
physical	O
format	O
used	O
by	O
the	O
data	B-General_Concept
storage	I-General_Concept
device	I-General_Concept
or	O
transmission	O
medium	O
,	O
the	O
stream	O
of	O
ones	O
and	O
zeros	O
that	O
is	O
sent	O
must	O
be	O
in	O
a	O
particular	O
digital	O
video	B-Algorithm
coding	I-Algorithm
format	I-Algorithm
,	O
of	O
which	O
a	O
number	O
are	O
available	O
.	O
</s>
<s>
Analog	O
video	O
is	O
a	O
video	B-Application
signal	I-Application
represented	O
by	O
one	O
or	O
more	O
analog	O
signals	O
.	O
</s>
<s>
Analog	O
color	O
video	B-Application
signals	I-Application
include	O
luminance	O
,	O
brightness	O
(	O
Y	O
)	O
and	O
chrominance	O
(	O
C	O
)	O
.	O
</s>
<s>
When	O
combined	O
into	O
one	O
channel	O
,	O
as	O
is	O
the	O
case	O
,	O
among	O
others	O
with	O
NTSC	O
,	O
PAL	B-Language
and	O
SECAM	O
it	O
is	O
called	O
composite	O
video	O
.	O
</s>
<s>
Analog	O
video	O
may	O
be	O
carried	O
in	O
separate	O
channels	O
,	O
as	O
in	O
two	O
channel	O
S-Video	O
(	O
YC	O
)	O
and	O
multi-channel	O
component	O
video	B-Application
formats	I-Application
.	O
</s>
<s>
Digital	O
video	B-Application
signal	I-Application
formats	O
have	O
been	O
adopted	O
,	O
including	O
serial	B-Protocol
digital	I-Protocol
interface	I-Protocol
(	O
SDI	O
)	O
,	O
Digital	B-Protocol
Visual	I-Protocol
Interface	I-Protocol
(	O
DVI	B-Protocol
)	O
,	O
High-Definition	B-Protocol
Multimedia	I-Protocol
Interface	I-Protocol
(	O
HDMI	B-Protocol
)	O
and	O
DisplayPort	B-Protocol
Interface	O
.	O
</s>
<s>
Broadcast	B-Operating_System
or	O
studio	O
cameras	O
use	O
a	O
single	O
or	O
dual	O
coaxial	O
cable	O
system	O
using	O
serial	B-Protocol
digital	I-Protocol
interface	I-Protocol
(	O
SDI	O
)	O
.	O
</s>
<s>
See	O
List	B-Protocol
of	I-Protocol
video	I-Protocol
connectors	I-Protocol
for	O
information	O
about	O
physical	O
connectors	O
and	O
related	O
signal	O
standards	O
.	O
</s>
<s>
Digital	B-Application
television	I-Application
broadcasts	B-Operating_System
use	O
the	O
MPEG-2	B-Algorithm
and	O
other	O
video	B-Algorithm
coding	I-Algorithm
formats	I-Algorithm
and	O
include	O
:	O
</s>
<s>
Analog	O
television	O
broadcast	B-Operating_System
standards	O
include	O
:	O
</s>
<s>
An	O
analog	O
video	B-Application
format	I-Application
consists	O
of	O
more	O
information	O
than	O
the	O
visible	O
content	O
of	O
the	O
frame	O
.	O
</s>
<s>
Preceding	O
and	O
following	O
the	O
image	O
are	O
lines	O
and	O
pixels	B-Algorithm
containing	O
metadata	O
and	O
synchronization	O
information	O
.	O
</s>
<s>
Computer	O
display	O
standards	O
specify	O
a	O
combination	O
of	O
aspect	B-General_Concept
ratio	I-General_Concept
,	O
display	O
size	O
,	O
display	B-General_Concept
resolution	I-General_Concept
,	O
color	O
depth	O
,	O
and	O
refresh	O
rate	O
.	O
</s>
<s>
A	O
list	B-General_Concept
of	I-General_Concept
common	I-General_Concept
resolutions	I-General_Concept
is	O
available	O
.	O
</s>
<s>
Optical	O
storage	B-General_Concept
mediums	I-General_Concept
offered	O
an	O
alternative	O
,	O
especially	O
in	O
consumer	O
applications	O
,	O
to	O
bulky	O
tape	O
formats	O
.	O
</s>
<s>
A	O
video	O
codec	B-General_Concept
is	O
software	O
or	O
hardware	B-Architecture
that	O
compresses	B-General_Concept
and	O
decompresses	B-Device
digital	O
video	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
video	O
compression	O
,	O
codec	B-General_Concept
is	O
a	O
portmanteau	O
of	O
encoder	O
and	O
decoder	O
,	O
while	O
a	O
device	O
that	O
only	O
compresses	B-General_Concept
is	O
typically	O
called	O
an	O
encoder	O
,	O
and	O
one	O
that	O
only	O
decompresses	B-Device
is	O
a	O
decoder	O
.	O
</s>
<s>
The	O
compressed	B-General_Concept
data	I-General_Concept
format	O
usually	O
conforms	O
to	O
a	O
standard	O
video	B-Algorithm
coding	I-Algorithm
format	I-Algorithm
.	O
</s>
<s>
The	O
compression	O
is	O
typically	O
lossy	B-Algorithm
,	O
meaning	O
that	O
the	O
compressed	O
video	O
lacks	O
some	O
information	O
present	O
in	O
the	O
original	O
video	O
.	O
</s>
<s>
A	O
consequence	O
of	O
this	O
is	O
that	O
decompressed	O
video	O
has	O
lower	O
quality	O
than	O
the	O
original	O
,	O
uncompressed	B-Device
video	I-Device
because	O
there	O
is	O
insufficient	O
information	O
to	O
accurately	O
reconstruct	O
the	O
original	O
video	O
.	O
</s>
