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Thread-Parallel MPEG-2, MPEG4 and H.264 Video Encoders for SoC Multi-Processor Architecture
Tom R. Jacobs, Vassilios A. Chouliars,
and David J. Mulvaney
IEEE Transactions on Consumer Electronics
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Outline
Introduction Background knowledge Main purpose
Previous work Methodology Experimental results Conclusions
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IntroductionBackground Knowledge (1/5)
A number of lossy video compression standards have been developed. MPEG-1, MPEG-2, MPEG4-PART2, H.264
In order to maintain image quality and reduce bit-rates
Additional computation and power consumption
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IntroductionBackground Knowledge (2/5)
Such processing-intense consumer application algorithms are generally implemented in System-On-Chip (SOC) devices.
Parallelism DLP Data-Level Parallelism TLP Thread-Level Parallelism
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IntroductionBackground Knowledge (3/5)
Data-Level Parallelism (DLP) Distributing the data across different parallel
processing nodes.Program:
…
if CPU="a" then
low_limit=1; upper_limit=5
else if CPU="b" then
low_limit=6; upper_limit=10
end if do i = low_limit , upper_limit
Task on d(i)
end do
...
end program
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IntroductionBackground Knowledge (4/5)
1 2 3 4 5 6 7 8 9 10
Data array D of size 10
Processing node
Processing node
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IntroductionBackground Knowledge (5/5)
Thread-Level Parallelism (TLP) TLP is the parallelism inherent in an
application that runs multiple threads at once.
Benefit- Distributing the workload of a single high-
performance processor among a number of slower and simpler processor cores.
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IntroductionMain Purpose (1/2)
Utilizing Thread-Level Parallel (TLP) techniques to improve the performance on video coding. Reduce DIC (Dynamic Instruction Count).
How to improve? Workload distribution among a number of
parallel-executing processors.
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IntroductionMain Purpose (2/2)
The results presented demonstrate that reductions in dynamic instruction count can be achieved.
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Previous Work
The majority of this research is focused on coarse-granularity TLP exploitation, with distribution the workload most commonly at GOP level.
GOP GOP GOP GOP GOP GOP
Multi-threading
Little inter-node communication
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Previous Work
In 1995, K. Shen, L. A. Rowe, and E.J. Delp implemented parallel MPEG-1 at GOP level.
In 1996, S. Bozoki, S. J. P. Westen, R. L. Lagendijk and J. Biemond performed a comparison between GOP and slice level on MPEG-1.
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Previous Work
In 1997, A. Bilas, J. Fritts and J. P. Singh evaluated the performance of MPEG-2 decoders using shared memory system.
Akramullah, Ahmad and Liou implemented a threaded MPEG-2 encoder at the MB level by using local memory.
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MethodologyOverview
The threaded MPEG-2 , MPEG-4 and H.264 implemented were compiled on multi-context instruction simulator (MT-ISS) based on SimpleScalar infrastructure.
The most important issue Data dependancies between processors. Avoid race hazards.
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MethodologyRace hazards
Integer i
Thread 1
0
Thread 2
1
i+1
01
12
i+1
2
Integer i
Thread 1 Thread 2
0
0 0
i+11 1
i+1
11 Race hazards
Expected condition
Error condition
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MethodologyThread-parallel MPEG-2 (1/5)
Test model 5 (TM5) of MPEG-2 encoder is used.
Computation analysis (QCIF) DIST1 52%~73% of total DIC for a search
window of 6 to 62 pels respectively. FullSearch 3.5%~23.2% of total DIC.
Can be improved by less complex algorithmic ME method. (such as 3-step, 4-step, diamond)
FDCT, and IDCT 2.1%~21% of total DIC.
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MethodologyThread-parallel MPEG-2 (2/5)
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MethodologyThread-parallel MPEG-2 (3/5)
Motion Estimation Kernel implementation can take advantage
of data parallel techniques. Store the information in mbinfo structure for
motion compensation. Maintain exclusivity of all variables during
the parallel sections.
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MethodologyThread-parallel MPEG-2 (4/5)
Forward transform FDCT first scans the MBs on a row-by-row
basis, process these MBs in a row individually.
Determine prediction error and applies the DCT to the block.
Thread-parallel transform function can be performed in block-level.
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MethodologyThread-parallel MPEG-2 (5/5)
Inverse transform IDCT scans the MBs first row-by-row and
then block-by-block. Due to the absence of data dependencies
between blocks Can executed as parallel.
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MethodologyThread-parallel MPEG-4 (1/8)
The implementation is based on XviD project with Advanced Simple Profile (ASP). Bidirectional frames Quarter-pel motion compensation Global motion compensation Trellis quantization Custom quantization matrices
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MethodologyThread-parallel MPEG-4 (2/8)
Computation analysis (QCIF)
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MethodologyThread-parallel MPEG-4 (3/8)
The nature of XivD encoder Intra-frame encoding Inter-frame encoding
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MethodologyThread-parallel MPEG-4 (4/8)
Intra-frame encoding FrameCodeI (row-by-row for each MBs) Parallelize the loop for encoding the MBs in a
row of the image. MB data structure pMB.
Shared memory array. The highest DIC metric in FrameCodeI is
MBTransQuantIntra.
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MethodologyThread-parallel MPEG-4 (5/8)
MBTransQuantIntra Forward transformation, quantization and
inverse transformation. Shared data structure pEnc
Includes a count of quantization values. Serial code section.
Transform specific MB pixel data into the frequency domain independently.
MBPrediction and MBCoding Responsible for VLC and write to bitstream.
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MethodologyThread-parallel MPEG-4 (6/8)
Inter-frame encoding FrameCodeP Part 1
Motion Estimation Part 2
Transformation Quantization
MC
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MethodologyThread-parallel MPEG-4 (7/8)
Motion Estimation Determine a MV for every MB and applies
certain criteria to indicate when Intra coding should be used.
Scanning in raster line order. Two kind of the process
Motion prediction from current frame. ME relative to reference frames.
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MethodologyThread-parallel MPEG-4 (8/8)
Motion Prediction Examining the MVs in neighbouring MBs and
determining an initial estimate for ME.
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Ideal pattern typical pattern TLP pattern
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MethodologyH.264 (1/6)
Using x264 for implementation. Frame slicing
Main problems of using MB-level Wide variation in processor workload. The modification of prediction algorithm is
needed.
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MethodologyH.264 (2/6)
Slice group in H.264 A group of MBs in a frame. Can be encoded or decoded separatedly
from the remainder of the frame. Not allowing motion prediction cross slice
boundaries. Drawback
The required bit-rate increase.
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MethodologyH.264 (3/6)
Comparison of different slice number
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MethodologyH.264 (4/6)
Comparison of different slice number
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MethodologyH.264 (5/6)
Different resolution with 4 slices
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MethodologyH.264 (6/6)
Computation analysis
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Experimental ResultsMPEG-2
SearchRange
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Experimental ResultsMPEG-4
QualitySetting
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Experimental ResultsH.264
QuantizationParameter
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Experimental ResultsComparative results
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Conclusions
The DIC metric of MPEG-2, MPEG-4, and H.264 can be greatly reduced by TLP.
For HD sequences, the improvement is around 84%, 92%, 96% respectively.
TLP has become more significant for each new generation of video encoders.
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