<s>
Quarter-pixel	B-Algorithm
motion	I-Algorithm
(	O
also	O
known	O
as	O
Q-pel	O
motion	O
or	O
Qpel	B-Algorithm
motion	O
)	O
refers	O
to	O
using	O
a	O
quarter	O
of	O
the	O
distance	O
between	O
pixels	B-Algorithm
(	O
or	O
luma	O
sample	O
positions	O
)	O
as	O
the	O
motion	O
vector	O
precision	O
for	O
motion	O
estimation	O
and	O
motion	B-Algorithm
compensation	I-Algorithm
in	O
video	O
compression	O
schemes	O
.	O
</s>
<s>
It	O
is	O
used	O
in	O
many	O
modern	O
video	O
coding	O
formats	O
such	O
as	O
MPEG-4	B-Application
ASP	I-Application
,	O
H.264/AVC	B-Application
,	O
and	O
HEVC	B-Algorithm
.	O
</s>
<s>
Video	O
encoding	O
software	O
products	O
such	O
as	O
Xvid	B-Algorithm
,	O
3ivx	B-Algorithm
,	O
and	O
DivX	O
Pro	O
Codec	O
,	O
which	O
are	O
based	O
upon	O
the	O
MPEG-4	B-Algorithm
specification	O
,	O
use	O
motion	O
estimation	O
algorithms	O
to	O
significantly	O
improve	O
video	O
compression	O
.	O
</s>
<s>
The	O
default	O
level	O
of	O
resolution	O
for	O
motion	O
estimation	O
for	O
most	O
MPEG-4	B-Application
ASP	I-Application
implementations	O
is	O
half	O
a	O
pixel	B-Algorithm
,	O
although	O
quarter	O
pixel	B-Algorithm
is	O
specified	O
under	O
the	O
standard	O
.	O
</s>
<s>
H.264	B-Application
decoders	O
always	O
support	O
quarter-pixel	B-Algorithm
motion	I-Algorithm
.	O
</s>
<s>
Quarter-pixel	O
resolution	O
can	O
improve	O
the	O
quality	O
of	O
the	O
video	O
prediction	O
signal	O
as	O
compared	O
to	O
half-pixel	O
resolution	O
,	O
although	O
the	O
improvement	O
may	O
not	O
always	O
be	O
enough	O
to	O
offset	O
the	O
increased	O
bit	O
cost	O
of	O
the	O
quarter-pixel-precision	O
motion	O
vector	O
;	O
additional	O
techniques	O
such	O
as	O
rate-distortion	B-General_Concept
optimization	I-General_Concept
,	O
which	O
takes	O
both	O
quality	O
and	O
bit	O
cost	O
into	O
account	O
,	O
are	O
used	O
to	O
significantly	O
improve	O
the	O
effectiveness	O
of	O
quarter-pel	O
motion	O
estimation	O
.	O
</s>
<s>
Quarter-pixel	B-Algorithm
motion	I-Algorithm
compensation	O
,	O
much	O
like	O
half-pixel	O
,	O
is	O
achieved	O
through	O
interpolation	B-Algorithm
.	O
</s>
<s>
VC-1	B-Operating_System
uses	O
bicubic	B-Algorithm
interpolation	I-Algorithm
.	O
</s>
<s>
H.264/AVC	B-Application
uses	O
a	O
6-tap	O
filter	O
for	O
half-pixel	O
interpolation	B-Algorithm
and	O
then	O
simple	O
linear	O
interpolation	B-Algorithm
to	O
achieve	O
quarter-pixel	O
precision	O
from	O
the	O
half-pixel	O
data	O
.	O
</s>
<s>
HEVC	B-Algorithm
uses	O
separable	O
7-tap	O
or	O
8-tap	O
filtering	O
.	O
</s>
<s>
Videos	O
encoded	O
with	O
quarter-pixel	O
precision	O
motion	O
vectors	O
require	O
up	O
to	O
twice	O
as	O
much	O
processing	O
power	O
to	O
encode	O
,	O
and	O
30-60	O
%	O
more	O
processing	O
power	O
to	O
decode	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
to	O
enable	O
wider	O
hardware	O
compatibility	O
,	O
Qpel	B-Algorithm
is	O
disabled	O
in	O
the	O
default	O
DivX	O
encoding	O
profiles	O
.	O
</s>
<s>
However	O
,	O
with	O
newer	O
stand-alone	O
players	O
supporting	O
more	O
complex	O
formats	O
such	O
as	O
VC-1	B-Operating_System
and	O
H.264	B-Application
,	O
Qpel	B-Algorithm
support	O
in	O
MPEG-4	B-Application
ASP	I-Application
has	O
become	O
more	O
common	O
.	O
</s>
