<s>
Flexible	B-General_Concept
Macroblock	I-General_Concept
Ordering	I-General_Concept
or	O
FMO	O
is	O
one	O
of	O
several	O
error	O
resilience	O
tools	O
defined	O
in	O
the	O
Baseline	O
profile	O
of	O
the	O
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
video	O
compression	O
standard	O
.	O
</s>
<s>
One	O
of	O
the	O
characteristics	O
of	O
the	O
H.264/AVC	B-Application
standard	O
is	O
the	O
possibility	O
of	O
dividing	O
an	O
image	O
into	O
regions	O
called	O
slices	O
,	O
each	O
of	O
which	O
contains	O
a	O
sequence	O
of	O
macroblocks	B-General_Concept
and	O
can	O
be	O
decoded	O
independently	O
of	O
other	O
slices	O
.	O
</s>
<s>
These	O
macroblocks	B-General_Concept
are	O
processed	O
in	O
a	O
scan	O
order	O
,	O
normally	O
left	O
to	O
right	O
,	O
beginning	O
at	O
the	O
top	O
.	O
</s>
<s>
Flexible	B-General_Concept
Macroblock	I-General_Concept
Ordering	I-General_Concept
enhances	O
this	O
by	O
allowing	O
macroblocks	B-General_Concept
to	O
be	O
grouped	O
and	O
sent	O
in	O
any	O
direction	O
and	O
order	O
,	O
and	O
can	O
be	O
used	O
to	O
create	O
shaped	O
and	O
non-contiguous	O
slice	O
groups	O
.	O
</s>
<s>
This	O
way	O
,	O
FMO	O
allows	O
more	O
flexibly	O
deciding	O
what	O
slice	O
macroblocks	B-General_Concept
belong	O
to	O
,	O
in	O
order	O
to	O
spread	O
out	O
errors	O
and	O
keep	O
errors	O
in	O
one	O
part	O
of	O
the	O
frame	O
from	O
compromising	O
another	O
part	O
of	O
the	O
frame	O
.	O
</s>
<s>
FMO	O
builds	O
on	O
top	O
of	O
another	O
error-resilience	O
tool	O
,	O
Arbitrary	B-General_Concept
slice	I-General_Concept
ordering	I-General_Concept
,	O
because	O
each	O
slice	O
group	O
can	O
be	O
sent	O
in	O
any	O
order	O
and	O
can	O
optionally	O
be	O
decoded	O
in	O
order	O
of	O
receipt	O
,	O
instead	O
of	O
in	O
the	O
usual	O
scan	O
order	O
.	O
</s>
<s>
Individual	O
slices	O
still	O
have	O
to	O
be	O
continuous	O
horizontal	O
regions	O
of	O
macroblocks	B-General_Concept
,	O
but	O
with	O
FMO	O
's	O
slice	O
groups	O
,	O
motion	O
compensation	O
can	O
take	O
place	O
within	O
any	O
contiguous	O
macroblocks	B-General_Concept
through	O
the	O
entire	O
group	O
;	O
effectively	O
,	O
each	O
slice	O
group	O
is	O
treated	O
as	O
one	O
or	O
more	O
contiguous	O
shaped	O
slices	O
for	O
the	O
purposes	O
of	O
motion	O
compensation	O
.	O
</s>
<s>
Nearly	O
all	O
video	O
codecs	O
allow	O
Region	O
of	O
Interest	O
coding	O
,	O
in	O
which	O
specific	O
macroblocks	B-General_Concept
are	O
targeted	O
to	O
receive	O
more	O
or	O
less	O
quality	O
,	O
the	O
canonical	O
example	O
being	O
a	O
newscaster	O
's	O
head	O
being	O
given	O
a	O
higher	O
ratio	O
of	O
bits	O
than	O
the	O
background	O
.	O
</s>
<s>
A	O
structure	O
called	O
the	O
MBAmap	O
maps	O
each	O
macroblock	B-General_Concept
to	O
a	O
slice	O
group	O
,	O
and	O
can	O
be	O
updated	O
at	O
any	O
time	O
,	O
with	O
a	O
few	O
default	O
patterns	O
defined	O
,	O
such	O
as	O
Slice	O
Interleaving	O
(	O
groups	O
alternate	O
every	O
scanline	O
)	O
or	O
Scattered	O
Slices	O
(	O
groups	O
alternate	O
every	O
block	O
)	O
.	O
</s>
<s>
In	O
H.264/AVC	B-Application
,	O
P	O
(	O
predicted	O
)	O
and	O
B	O
(	O
bipredicted	O
)	O
frames	O
may	O
contain	O
I	O
(	O
intra	O
)	O
blocks	O
,	O
which	O
store	O
independent	O
picture	O
.	O
</s>
<s>
When	O
using	O
FMO	O
,	O
the	O
image	O
can	O
be	O
divided	O
in	O
different	O
scan	O
patterns	O
of	O
the	O
macroblocks	B-General_Concept
,	O
with	O
several	O
built-in	O
patterns	O
defined	O
in	O
the	O
spec	O
,	O
signaled	O
as	O
0-5	O
in	O
the	O
unit	O
slice_group_map_type	O
,	O
and	O
one	O
option	O
to	O
include	O
an	O
entire	O
explicitly	O
assigned	O
MBAmap	O
,	O
signaled	O
as	O
6	O
.	O
</s>
<s>
Scattered	O
or	O
dispersed	O
slice	O
groups	O
,	O
type	O
1	O
:	O
Every	O
macroblock	B-General_Concept
is	O
a	O
different	O
slice	O
.	O
</s>
<s>
With	O
two	O
slice	O
groups	O
,	O
it	O
creates	O
a	O
checkerboard	O
pattern	O
;	O
four	O
or	O
more	O
groups	O
also	O
interleave	O
rows	O
,	O
and	O
with	O
six	O
slice	O
groups	O
,	O
no	O
macroblock	B-General_Concept
will	O
ever	O
touch	O
another	O
from	O
the	O
same	O
slice	O
group	O
in	O
any	O
direction	O
,	O
maximizing	O
error	O
concealment	O
opportunities	O
.	O
</s>
<s>
(	O
In	O
the	O
above	O
image	O
,	O
"	O
Type	O
0	O
"	O
shows	O
standard	O
H.264	B-Application
slices	O
,	O
not	O
interleaved	O
slice	O
groups	O
.	O
)	O
</s>
