<s>
The	O
X	B-Protocol
video	I-Protocol
extension	I-Protocol
,	O
often	O
abbreviated	O
as	O
XVideo	B-Protocol
or	O
Xv	O
,	O
is	O
a	O
video	O
output	O
mechanism	O
for	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
Without	O
XVideo	B-Protocol
,	O
X	B-Operating_System
would	O
have	O
to	O
do	O
this	O
scaling	O
on	O
the	O
main	O
CPU	B-General_Concept
.	O
</s>
<s>
Similarly	O
,	O
the	O
X	B-Protocol
video	I-Protocol
extension	I-Protocol
can	O
have	O
the	O
video	O
controller	O
perform	O
color	B-Algorithm
space	I-Algorithm
conversions	I-Algorithm
,	O
and	O
change	O
the	O
contrast	O
,	O
brightness	O
,	O
and	O
hue	O
of	O
a	O
displayed	O
video	O
stream	O
.	O
</s>
<s>
The	O
device	B-Application
driver	I-Application
software	O
for	O
the	O
video	O
controller	O
and	O
the	O
X	B-Operating_System
display	O
server	O
program	O
have	O
to	O
implement	O
the	O
XVideo	B-Protocol
interface	O
.	O
</s>
<s>
Most	O
modern	O
video	O
controllers	O
provide	O
the	O
functions	O
required	O
for	O
XVideo	B-Protocol
;	O
this	O
feature	O
is	O
known	O
as	O
hardware	O
scaling	O
and	O
YUV	O
acceleration	O
or	O
sometimes	O
as	O
2D	O
hardware	O
acceleration	O
.	O
</s>
<s>
The	O
XFree86	B-Device
X	B-Operating_System
display	O
server	O
has	O
implemented	O
XVideo	B-Protocol
since	O
version	O
4.0.2	O
.	O
</s>
<s>
To	O
check	O
whether	O
a	O
given	O
X	B-Operating_System
display	O
server	O
supports	O
XVideo	B-Protocol
,	O
one	O
can	O
use	O
the	O
utility	O
xdpyinfo	O
.	O
</s>
<s>
To	O
check	O
whether	O
the	O
video	O
controller	O
provides	O
the	O
required	O
functions	O
and	O
whether	O
the	O
X	B-Operating_System
device	B-Application
driver	I-Application
implements	O
XVideo	B-Protocol
for	O
any	O
of	O
them	O
,	O
one	O
can	O
use	O
the	O
xvinfo	O
program	O
.	O
</s>
<s>
Video	O
playback	O
programs	O
that	O
run	O
under	O
the	O
X	B-Operating_System
Window	I-Operating_System
system	I-Operating_System
,	O
such	O
as	O
MPlayer	B-Application
,	O
MythTV	B-Application
or	O
xine	B-Application
,	O
typically	O
have	O
an	O
option	O
to	O
enable	O
XVideo	B-Protocol
output	O
.	O
</s>
<s>
It	O
is	O
very	O
advisable	O
to	O
switch	O
on	O
this	O
option	O
if	O
the	O
system	O
GPU	B-Architecture
video-hardware	O
and	O
device	B-Application
drivers	I-Application
supports	O
XVideo	B-Protocol
and	O
more	O
modern	O
rendering	O
systems	O
such	O
as	O
OpenGL	O
and	O
VDPAU	O
are	O
unavailable	O
–	O
the	O
speedup	O
is	O
very	O
noticeable	O
even	O
on	O
a	O
fast	O
CPU	B-General_Concept
.	O
</s>
<s>
Under	O
X	B-Operating_System
,	O
how	O
video	O
is	O
finally	O
drawn	O
depends	O
largely	O
on	O
the	O
X	B-Application
window	I-Application
manager	I-Application
in	O
use	O
.	O
</s>
<s>
With	O
properly	O
installed	O
drivers	O
,	O
and	O
GPU	B-Architecture
hardware	O
such	O
as	O
supported	O
Intel	O
,	O
ATI	O
,	O
and	O
nVidia	O
chip	O
sets	O
,	O
some	O
window	B-Application
managers	I-Application
,	O
called	O
compositing	B-Operating_System
window	I-Operating_System
managers	I-Operating_System
,	O
allow	O
windows	O
to	O
be	O
separately	O
processed	O
and	O
then	O
rendered	O
(	O
or	O
composited	O
)	O
.	O
</s>
<s>
XVideo	B-Protocol
can	O
also	O
be	O
used	O
to	O
accelerate	O
video	O
playback	O
during	O
the	O
drawing	O
of	O
windows	O
using	O
an	O
OpenGL	O
Framebuffer	B-Library
Object	I-Library
or	O
pbuffer	B-Library
.	O
</s>
<s>
Metacity	B-Language
,	O
an	O
X	B-Application
window	I-Application
manager	I-Application
uses	O
compositing	O
in	O
this	O
way	O
.	O
</s>
<s>
Other	O
compositing	B-Operating_System
window	I-Operating_System
managers	I-Operating_System
such	O
as	O
Compiz	B-Language
also	O
use	O
compositing	O
.	O
</s>
<s>
However	O
,	O
on	O
a	O
system	O
with	O
limited	O
OpenGL	O
acceleration	O
function	O
,	O
specifically	O
the	O
lack	O
of	O
an	O
OpenGL	O
Framebuffer	B-Library
Object	I-Library
or	O
pbuffer	B-Library
,	O
the	O
use	O
of	O
an	O
OpenGL	O
environment	O
like	O
Xgl	B-Application
makes	O
xv	O
hardware	O
accelerations	O
impossible	O
.	O
</s>
<s>
In	O
the	O
event	O
that	O
the	O
window	B-Application
manager	I-Application
does	O
n't	O
directly	O
support	O
compositing	O
,	O
it	O
is	O
more	O
difficult	O
to	O
isolate	O
where	O
the	O
video	O
stream	O
should	O
be	O
rendered	O
,	O
because	O
by	O
the	O
time	O
it	O
can	O
be	O
accelerated	O
the	O
output	O
has	O
already	O
been	O
turned	O
into	O
a	O
single	O
image	O
.	O
</s>
<s>
The	O
only	O
way	O
to	O
do	O
this	O
is	O
usually	O
to	O
employ	O
a	O
post	O
processed	O
hardware	B-Architecture
overlay	I-Architecture
,	O
using	O
chroma	O
keying	O
.	O
</s>
<s>
This	O
same	O
process	O
was	O
also	O
the	O
only	O
available	O
option	O
to	O
render	O
hardware	O
accelerated	O
video	O
under	O
Microsoft	B-Application
Windows	I-Application
XP	I-Application
and	O
earlier	O
,	O
since	O
its	O
window	B-Application
management	I-Application
features	O
were	O
so	O
deeply	O
embedded	O
into	O
the	O
operating	O
system	O
that	O
accelerating	O
them	O
would	O
have	O
been	O
impossible	O
.	O
</s>
<s>
If	O
the	O
window	B-Application
manager	I-Application
does	O
n't	O
support	O
compositing	O
,	O
post	O
processed	O
hardware	B-Architecture
overlays	I-Architecture
using	O
chroma	O
keying	O
as	O
described	O
in	O
the	O
previous	O
paragraph	O
can	O
make	O
it	O
impossible	O
to	O
produce	O
a	O
proper	O
screenshots	B-Application
of	O
Xvideo	B-Protocol
applications	O
.	O
</s>
