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An Efficient Mode Decision Algorithm for H.264/AVC Encoding Optimization

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... element of is multiplied by the element in the same position in matrix ... overhead of calculation (10) (13) ... Based Prediction. We define two thresholds ... – PowerPoint PPT presentation

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Title: An Efficient Mode Decision Algorithm for H.264/AVC Encoding Optimization

1
An Efficient Mode Decision Algorithm for
H.264/AVC Encoding Optimization
• IEEE TRANSACTION ON MULTIMEDIA
• Hanli Wang, Student Member, IEEE,
• Sam Kwong, Senior Member, IEEE, and Chi-Wah Kok,
Senior Member, IEEE

2
Outline
• Introduction
• Proposed Early Termination of Motion Estimation
and Mode Decision
• Proposed Algorithm for H.264 Mode Decision
• Experimental Results
• Conclusion

3
Introduction
• The computational complexity in H.264 is
increased due to mode decision where variable
block size ME is employed
• In this paper, we propose a more efficient and
robust algorithm than Variable Block size Best
Motion Detection (VBBMD) to early terminate ME
and mode decision.
• L.Yang, K. Yu, J. Li, and S. Li, An effective
variable block-size early termination algorithm
for H.264 video coding, IEEE Trans. Circuits
Syst. Video Technol., vol 15, no. 6, pp. 784-788,
Jun. 2005.

4
Proposed Early Termination of Motion Estimation
and Mode Decision
• In video coding, its common that all DCT
coefficients in a block are quantized to zeros.
• ME can be early terminated if an all-zero block
is detected.

5
Proposed Early Termination of Motion Estimation
and Mode Decision
• 4x4 DCT
• C(n) , for n0, C(n)1, otherwise
• denotes to round x to the nearest integer
• Quantization
• f is

6
A. Sufficient Condition to Detect All-Zero Blocks
• From(2), the sufficient condition for
to be quantized to zero is
• From(1)
• indicates each element of is multiplied by
the element in the same position in matrix

7
A. Sufficient Condition to Detect All-Zero Blocks
• The case of uv1 is firstly analyzed.
• A 4x4 block is divided into four regions ,
• The sum of absolute difference , for each
region
• The sum of absolute difference SAD for a 4x4 block

8
A. Sufficient Condition to Detect All-Zero Blocks
• Considering (4)-(7)
• Form(3)(4), the sufficient condition to detect
zero quantized DCT coefficient at (u,v) is
. Thus

9
A. Sufficient Condition to Detect All-Zero Blocks
• According to the three categories in Table I,
three threshold are derived as
• If , then all the DCT
coefficients in the ith category will be
quantized to zeros.
• The sufficient condition to detect all-zero block

10
A. Sufficient Condition to Detect All-Zero Blocks
• False rejection rate (FRR)
• The smaller FRR is, the more efficiency all-zero
DCT blocks can be detected.
• False acceptance rate (FAR)
• The smaller FAR is, the less the video quality
• 10 Y.H. Moon, G. Y. Kim, and J. H. Kim, An
improved early detection algorithm for all-zero
blocks in H.264 video coding, IEEE Trans.
Circuits Syst. Video Technol., vol. 15, no. 8,
pp. 1053-1057, Aug. 2005.

11
B. Early Termination of Motion Estimation and
Mode Decision
• Early Motion Estimation Termination
• We can early terminate ME if all the 4x4 blocks
within current block are determined as all-zero
blocks under the condition(13).
• In the assumption on spatial-temporal
vector
• Early Mode Decision Termination
• If EMET is true for all the partitioned blocks in
a MB, we can consider this MB is an all-zero MB
and skip checking the other modes.
• gtwe can early stop checking EMET if one of
the 4x4 blocks does not satisfy the condition in
(13).

12
Proposed Algorithm for H.264 Mode Decision
• We have executed a number of experiments and
observed that
• 1. SKIP and 16x16 have a large proportion in MB
partitions.
• 2. 8x8 occupies a large proportion in sub-MB
partitions.
• 3. INTRA4 and INTRA16 have a very small
proportion in inter coding.
• M16 the best mode of SKIP and 16x16
• RD cost of M16
• RD cost of 8x8

13
A. Temporal-Spatial Checking
• M(n,x,y) a MB which is in the nth frame with
top left pixel in (x,y)
• The temporal set is defined as
• The spatial set is defined as
• If( nonboundary MBs in and were encoded
as SKIP or 16x16)
• gt skip 8x4, 4x8, 4x4, INTRA4 and INTRA16
• If( )
• gt skip 16x8 and 8x16
operations

14
B. Thresholds Based Prediction
• We define two thresholds and
• If( )
• gt skip 8x4, 4x8, 4x4, INTRA4, and INTRA16
• If( )
• gt skip 16x8 and 8x16
• From our exhaustive experiments, we found good
results can be achieved when and are
set to 50 and 200 respectively.

15
C. Monotonic Error Surface Based Prediction
• RD cost of 4x4
• If( )
• gt skip 16x8 and 8x16
• If( )
• gt only check 16x8 and 8x16 and skip all the
other unchecked modes

16
D. Overall Algorithm
Set all modes active. Select M16 and record C16
16x8 inactive
TSC
Record C4 and EMDT C4
True
false
false
True
True
false
EMDT 16x8
Set 8x4,4x8,4x4,I4, and I16 to inactive
Done
True
True
EMDT C16
C16gtC8 and C8gtC4
false
Done
Done
8x16 inactive
False, record C8
True
True
false
True
false
C8-C16gtTh16
EMDT C8
C16ltC8 and C8ltC4
false
Done
EMDT 8x16
True
false
True
false
True
false
Done
C16-C8gtTh8
false
Set 8x4,4x8,I4, and I16 to inactive
TSC and C16ltC8
True
Done
8x4 inactive
Set 16x8 and 8x16 to inactive
True
Set 16x8 and 8x16 to inactive
false
True
false
17
D. Overall Algorithm
false
True
EMDT 8x4
True
Done
false
4x8 inactive
True
false
EMDT 4x8
True
Done
false
Check I4 and I16 if they are active. Select the
best mode
18
Experimental Results
• H.264 reference software JM9.5
• ME with ¼ pixel resolution
• Number of reference frames 1
• Motion search range 16
• Without B-frames
• The period of I-frames 10
• Five values 24, 28, 32, 36, and 40

19
Experimental Results
20
Experimental Results
21
Experimental Results
• With B-frames
• The period of I-frames 4
• GOP structure is IBBP
• The other encoding parameters are the same.

22
Experimental Results
23
Experimental Results
24
Conclusion
• A theoretical analysis is carried out to study
the sufficient condition to detect all-zero
blocks in H.264.
• The proposed algorithm also introduces TSC, TBP,
and MESBP methods to further skip examining
redundant modes.
• In the future, we will consider other fast mode
decision techniques such as 3,4,7 to
further optimize the proposed algorithm.