在H.264之前的标准中，比如H.263，其比特流中的数据是按照一个宏块接一个宏块的方式排列的，一旦发生丢包，很多相邻宏块信息都会丢失，很难进行错误隐藏处理。在H.264中加入了一项新特性：把宏块在比特流中的数据按照一定的映射规则进行排列，而不一定按照原本的光栅扫描顺序排列，这种方称为灵活的宏块重拍FMO(Flexible Macroblock Ordering)。
FMO是基于组的方式将宏块集合起来，把一帧内的宏块划分到不同的条带组（slice group）。当然在最后也需要对条带组按光栅扫描顺序划分条带（slice）。在h.264中，当slice group被设为大于1时才使用FMO。在代码端看来，FMO时，主要是对映射表（数组）的设置，如下第一个表：
对一帧进行FMO：
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
得到slice group有三个：
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 |
然后再对每个slice group按照光栅扫描顺序进行排序，分割出slice，下面为分割slice group 0（假设slice长度为16）
slice 1 in slice group 0:
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
slice 2 in slice group 0:
| 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
FMO在h.264中有7种（FMO0 ~ FMO6）
FMO0
FMO0，交织映射。交织映射是指不同的slice group交替出现。
如下设置了slice group 0 = 10，slice group 1 = 15，slice group 2 = 18
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
JM code如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
/*!
************************************************************************
* \brief
* Generate interleaved slice group map type MapUnit map (type 0)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType0MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned iGroup, j;
unsigned i = 0;
do
{
for
( iGroup = 0;
(iGroup <= pps->num_slice_groups_minus1) && (i < PicSizeInMapUnits);
i += pps->run_length_minus1[iGroup++] + 1)
{
for
( j = 0; j <= pps->run_length_minus1[ iGroup ] && i + j < PicSizeInMapUnits; j++ )
MapUnitToSliceGroupMap[i+j] = iGroup;
}
}
while
( i < PicSizeInMapUnits );
}
|
FMO1
FMO1，分散映射。每个宏块相邻的宏块都不在同一组。x方向上的宏块按照slice group序号递增分配，y方向第一个宏块按照0，slice group numbers/2交替分配。
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
| 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 |
| 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 | 2 | 0 | 1 |
JM code 如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
|
/*!
************************************************************************
* \brief
* Generate dispersed slice group map type MapUnit map (type 1)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType1MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned i;
for
( i = 0; i < PicSizeInMapUnits; i++ )
{
MapUnitToSliceGroupMap[i] = ((i%img->PicWidthInMbs)+(((i/img->PicWidthInMbs)*(pps->num_slice_groups_minus1+1))/2))
%(pps->num_slice_groups_minus1+1);
}
}
|
FMO2
FMO2，前后景映射。以整个帧作为背景，该模式可以通过（左上角坐标，右下角坐标）的方式指定前景，每个前景都为一个slice group，最先指定的前景可以覆盖后来指定的前景。
假设有
slice group 0（3,4）（8,8）
slice group 1（1,2）（6,6）
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| 2 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 |
| 2 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 2 | 2 | 2 |
| 2 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 |
| 2 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 |
| 2 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 |
| 2 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 |
| 2 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 |
JM code如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
|
/*!
************************************************************************
* \brief
* Generate foreground with left-over slice group map type MapUnit map (type 2)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType2MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
int
iGroup;
unsigned i, x, y;
unsigned yTopLeft, xTopLeft, yBottomRight, xBottomRight;
for
( i = 0; i < PicSizeInMapUnits; i++ )
MapUnitToSliceGroupMap[ i ] = pps->num_slice_groups_minus1;
for
( iGroup = pps->num_slice_groups_minus1 - 1 ; iGroup >= 0; iGroup-- )
{
yTopLeft = pps->top_left[ iGroup ] / img->PicWidthInMbs;
xTopLeft = pps->top_left[ iGroup ] % img->PicWidthInMbs;
yBottomRight = pps->bottom_right[ iGroup ] / img->PicWidthInMbs;
xBottomRight = pps->bottom_right[ iGroup ] % img->PicWidthInMbs;
for
( y = yTopLeft; y <= yBottomRight; y++ )
for
( x = xTopLeft; x <= xBottomRight; x++ )
MapUnitToSliceGroupMap[ y * img->PicWidthInMbs + x ] = iGroup;
}
}
|
FMO3
FMO3，环形扫描映射。在JM中，环形扫描映射把一帧分为两个slice group，一个是以一帧为背景，另一个是以环作为的前景（其实环可以扩展到更多的group）。环的起点是帧的中心位置，通过指定环的运动方向（顺时针或逆时针）以及环的长度即可得到前景。
以下为顺时针，环长度为32
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 20 | 21 | 22 | 23 | 24 | 25 | 1 | 1 |
| 1 | 1 | 1 | 19 | 6 | 7 | 8 | 9 | 26 | 1 | 1 |
| 1 | 1 | 1 | 18 | 5 | 0 | 1 | 10 | 27 | 1 | 1 |
| 1 | 1 | 1 | 17 | 4 | 3 | 2 | 11 | 28 | 1 | 1 |
| 1 | 1 | 1 | 16 | 15 | 14 | 13 | 12 | 29 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 31 | 30 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
JM code 如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
|
/*!
************************************************************************
* \brief
* Generate box-out slice group map type MapUnit map (type 3)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType3MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned i, k;
int
leftBound, topBound, rightBound, bottomBound;
int
x, y, xDir, yDir;
int
mapUnitVacant;
unsigned mapUnitsInSliceGroup0 = min((pps->slice_group_change_rate_minus1 + 1) * img->slice_group_change_cycle, PicSizeInMapUnits);
for
( i = 0; i < PicSizeInMapUnits; i++ )
MapUnitToSliceGroupMap[ i ] = 2;
x = ( img->PicWidthInMbs - pps->slice_group_change_direction_flag ) / 2;
y = ( img->PicHeightInMapUnits - pps->slice_group_change_direction_flag ) / 2;
leftBound = x;
topBound = y;
rightBound = x;
bottomBound = y;
xDir = pps->slice_group_change_direction_flag - 1;
yDir = pps->slice_group_change_direction_flag;
for
( k = 0; k < PicSizeInMapUnits; k += mapUnitVacant )
{
mapUnitVacant = ( MapUnitToSliceGroupMap[ y * img->PicWidthInMbs + x ] == 2 );
if
( mapUnitVacant )
MapUnitToSliceGroupMap[ y * img->PicWidthInMbs + x ] = ( k >= mapUnitsInSliceGroup0 );
if
( xDir == -1 && x == leftBound )
{
leftBound = max( leftBound - 1, 0 );
x = leftBound;
xDir = 0;
yDir = 2 * pps->slice_group_change_direction_flag - 1;
}
else
if
( xDir == 1 && x == rightBound )
{
rightBound = min( rightBound + 1, (
int
)img->PicWidthInMbs - 1 );
x = rightBound;
xDir = 0;
yDir = 1 - 2 * pps->slice_group_change_direction_flag;
}
else
if
( yDir == -1 && y == topBound )
{
topBound = max( topBound - 1, 0 );
y = topBound;
xDir = 1 - 2 * pps->slice_group_change_direction_flag;
yDir = 0;
}
else
if
( yDir == 1 && y == bottomBound )
{
bottomBound = min( bottomBound + 1, (
int
)img->PicHeightInMapUnits - 1 );
y = bottomBound;
xDir = 2 * pps->slice_group_change_direction_flag - 1;
yDir = 0;
}
else
{
x = x + xDir;
y = y + yDir;
}
}
}
|
FMO4
FMO4，光栅扫描映射。该模式只支持两个slice group，按照光栅扫描顺序来分组，方向有正向与反向之分。
如下为反向FMO4(始于右下角):
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
JM code 如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
|
/*!
************************************************************************
* \brief
* Generate raster scan slice group map type MapUnit map (type 4)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType4MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned mapUnitsInSliceGroup0 = min((pps->slice_group_change_rate_minus1 + 1) * img->slice_group_change_cycle, PicSizeInMapUnits);
unsigned sizeOfUpperLeftGroup = pps->slice_group_change_direction_flag ? ( PicSizeInMapUnits - mapUnitsInSliceGroup0 ) : mapUnitsInSliceGroup0;
unsigned i;
for
( i = 0; i < PicSizeInMapUnits; i++ )
if
( i < sizeOfUpperLeftGroup )
MapUnitToSliceGroupMap[ i ] = pps->slice_group_change_direction_flag;
else
MapUnitToSliceGroupMap[ i ] = 1 - pps->slice_group_change_direction_flag;
}
|
FMO5
FMO5，擦式扫描映射。仅支持两个slice group，扫描方式为纵向，也有正反两个方向
如下为正向FMO5（始于左上角）：
| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
JM code 如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
/*!
************************************************************************
* \brief
* Generate wipe slice group map type MapUnit map (type 5)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType5MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned mapUnitsInSliceGroup0 = min((pps->slice_group_change_rate_minus1 + 1) * img->slice_group_change_cycle, PicSizeInMapUnits);
unsigned sizeOfUpperLeftGroup = pps->slice_group_change_direction_flag ? ( PicSizeInMapUnits - mapUnitsInSliceGroup0 ) : mapUnitsInSliceGroup0;
unsigned i,j, k = 0;
for
( j = 0; j < img->PicWidthInMbs; j++ )
for
( i = 0; i < img->PicHeightInMapUnits; i++ )
if
( k++ < sizeOfUpperLeftGroup )
MapUnitToSliceGroupMap[ i * img->PicWidthInMbs + j ] = 1 - pps->slice_group_change_direction_flag;
else
MapUnitToSliceGroupMap[ i * img->PicWidthInMbs + j ] = pps->slice_group_change_direction_flag;
}
|
FMO6
FMO6，显示控制映射。可以在配置文件中自由地指定每个宏块所属的slice group。
| 0 | 1 | 0 | 2 | 1 | 1 | 0 | 2 | 1 | 1 | 1 |
| 1 | 2 | 0 | 0 | 0 | 1 | 0 | 2 | 0 | 1 | 0 |
| 3 | 5 | 4 | 1 | 0 | 0 | 3 | 5 | 4 | 0 | 1 |
| 0 | 0 | 5 | 5 | 3 | 1 | 0 | 2 | 5 | 0 | 1 |
| 4 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 4 | 4 | 2 |
| 0 | 2 | 2 | 3 | 2 | 3 | 2 | 1 | 5 | 2 | 3 |
| 0 | 1 | 2 | 0 | 1 | 1 | 2 | 0 | 5 | 5 | 5 |
| 3 | 2 | 1 | 4 | 1 | 4 | 4 | 0 | 3 | 3 | 2 |
| 4 | 2 | 3 | 5 | 0 | 0 | 1 | 4 | 1 | 2 | 3 |
顺带一提JM支持一帧中最多为8个slice group
JM code 如下：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
|
/*!
************************************************************************
* \brief
* Generate explicit slice group map type MapUnit map (type 6)
*
* \param img
* Image Parameter to be used for map generation
* \param pps
* Picture Parameter set to be used for map generation
************************************************************************
*/
static
void
FmoGenerateType6MapUnitMap (ImageParameters * img, pic_parameter_set_rbsp_t * pps )
{
unsigned i;
for
(i=0; i<PicSizeInMapUnits; i++)
{
MapUnitToSliceGroupMap[i] = pps->slice_group_id[i];
}
}
|
