1. Supplement, Chapters 6
MC Course, 2009

2. Chapter 6 H.264/MPEG4 Part 10 Macroblock syntax elements
Reference picture management
1/8 motion estimation
Motion vector prediction
Intra prediction
Deblocking filter
Transform and quantization
Direct and weighted predictions
Data partition
Raw byte sequence payload

3. H.264 Encoder/Decoder Forward path Reconstruction path 2018/11/23
unfiltered
unfiltered
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4. H.264 Profiles
FRExt
High profiles
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5. H.264 Slice Types
There is minimal inter-dependency between coded slices
which can help to limit the propagation of errors
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6. Slice Syntax
Skipped (not coded) MBs
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7. Macroblock Syntax Elements
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8. Reference Picture Management
Every reconstructed frame can be marked as
Unused for reference
Short term picture
Long term picture
None (directly output)
Adaptive memory control (Encoder  Decoder)
Managing the short and long term picture indexes.
Short term picture may be assigned a long term frame index
Short/long term picture may be marked as unused for reference
Instantaneous Decoder Refresh Picture (IDR)
An encoder sends an IDR to clear the reference picture buffer
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9. Reference Picture Management (P-slice)
Example: Current frame number=250
Number of reference frames=5
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10. Macroblock to slice group map types
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11. Slice Groups: dispersed 4 groups
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12. Slice Groups: Foreground and Background Map
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13. Slice Groups Box-out, Raster and Wipe
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14. Interpolation of Chroma: eight-sample
a = round ([(8-dx)(8-dy)A+dx(8-dy)B+(8-dx)dyC+dxdyD]/64)
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15. Motion Vector Prediction
leftmost
topmost
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16. Motion Vector Prediction (2)
For transmitted partitions excluding 16  8 and 8  16 partition sizes: MVp= median (MVA , MVB , MVC )
For upper 16  8 partitions: MVp = MVB
For lower 16  8 partitions: MVp = MVA
For left 8  16 partitions: MVp = MVA
For right 8  16 partitions: MVp = MVC
For skipped macroblocks:
MVp= (as if the block were encoded in 16  16 Inter mode)
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17. Intra Prediction Signaling intra prediction modes
The choice of intra prediction mode for each 44 block must be signaled to the decoder and this could potentially require a large number of bits.
However, intra modes for neighboring 44 blocks are often correlated.
Mode 1
Mode 1
Mode 1 probably
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18. Intra Prediction Signaling intra prediction modes
1:H 3
Signaling intra prediction modes
Calculate the “most probable” prediction mode of E in both the encoder and the decoder
Most probable mode
Minimum of the prediction modes of A and B
Flag: prev_intra4x4_pred_mode
1: Most probable mode = Prediction mode of E
If most probable mode  prediction mode of E
prev_intra4x4_pred_mode = 0
rem_intra4x4_pred_mode is used and sent to the decoder
only 3 bits are needed for 9 modes
Most probable mode
Prediction mode of E: 0, …, i-1, i, i+1, i+2, …, 8
rem_intra4x4_pred_mode: 0, …, i-1, -, i , i+1, …, 7
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19. Deblocking Filter Edge filtering order Boundary strength (bS)5 1 2 4 3 6 7 8 9 10 11 12
1616 luma
88 chroma
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20. Deblocking Filter Filter decision Filter implementation
(p2, p1, p0, q0, q1, q2) is filtered only if
bS > 0 and
|p0-q0| < , |p1-p0| <  , and |q1-q0| ≦ .
 and  depend on QPs of block p and q.
Filter implementation
bS  {1, 2, 3}
(p1, p0, q0, q1) → (p’0, q’0)
If |p2-p0|<, (p2, p1, p0, q0) → (p’1) (luma only)
If |q2-q0|<, (q2, q1, q0, p0) → (q’1) (luma only)
bS = 4
If luma block, |p2-p0|< , and |p0-q0|<round(/4)
(p2,p1,p0,q0,q1)→p’0, (p2,p1,p0,q0) →p’1, (p3,p2,p1,p0,q0) →p’2
otherwise (p1, p0, q1) → p’0
If luma block, |q2-q0|< , and |p0-q0|<round(/4)
(q2,q1,q0,p0,p1)→q’0, (q2,q1,q0,p0) →q’1, (q3,q2,q1,q0,p0) →q’2
otherwise (q1, q0, p1) → q’0
4-tap filter
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21. Digital Cosine Transform
Y = A X AT
X = AT Y A
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22. Digital Cosine Transform (2)
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23. Digital Cosine Transform (3)
scaling factor
core
To ensure orthogonal, b is modified
a = ½, b = , d = ½
(2nd, 4th rows of C, 2nd, 4th columns of CT)2, …
d = c/b  0.414
To simplify the implementation: d  0.5
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24. Transform and Quantization
4x4 residual transform and quantization
Quantization
Pre-scaling matrix
Transform
round( / Qstep)
Input matrix
(Implemented by right shift)
Integer arithmetic using +, - and SHIFT
16-bit arithmetic
MF / 2qbits
qbits=15+floor(QP/6)
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Table lookup

25. Transform and Quantization
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26. Transform and Quantization
4x4 rescaling (in inverse quantizer)
Table lookup 
Z × Qstep × × 64
2floor(QP/6)
The output doubles for every (QP/6)
Quantized value
scaling factor to avoid rounding errors
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27. Transform and Quantization
A complete process of Transform, quantization, rescaling, and inverse transform
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28. Direct Prediction Spatial direct mode Temporal direct mode 2018/11/23
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29. Weighted Prediction Three types ‘Explicit’ prediction
P slice with ‘explicit’ weighted prediction
B slice with ‘explicit’ weighted prediction
B slice with ‘implicit weighted prediction
‘Explicit’ prediction
The weighted factors are determined by the encoder.
‘Implicit’ prediction
The weighted factors are calculated based on the relative temporal positions of the reference pictures.
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30. Data Partitioned Slices
Different partitions can be placed in separate NAL unit.
Partition A
Slice header, macroblock header.
Partition B
Coded residual data for I and SI macroblocks.
Partition C
Coded residual data for inter coded macroblocks.
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31. Raw Byte Sequence Payload (RBSP)
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