Optimizing Baseline Profile in H.264/AVC Video Coding by
Parallel Programming and Fast Intra and Inter Predictions
BY
VINOOTHNA GAJULA
ID 1000803103
MS Electrical Engineer
Under the Guidance of
Dr. K. R. RAO
Objective

1.
2.
3.
In this project, the computational complexity and encoding
time of baseline profile of H.264 are reduced by :
Using parallel programming [1] , [7].
Then using fast adaptive termination (FAT) algorithm in
intra prediction [2],[8]
Finally by FAT inter prediction mode decision and motion
estimation [3],[9],[20].
Introduction
H.264 also known as MPEG Part10/ AVC (MPEG-4’s
Advanced Video Coding) was jointly published in 2003
by
international standards bodies International
Telecommunication Union (ITU-T) and International
Organization for Standardization / International Electrotechnical Commission (ISO / IEC) called as Joint Video
Team (JVT) [4].
It has many advantages over previous coding standards
MPEG-2 and MPEG-4, like significant rate distortion
efficiency achieving higher bit rate reduction, error
resilience and is most network friendly compared to other
standards [4],[5].

Profiles in H.264
Fig.1: Various profiles of H.264 [5]
Encoder-Decoder of H.264
Fig. 2 H.264 encoder block diagram [6]
Fig. 3 H.264 decoder block diagram [6]
Prediction modes
INTRA PREDICTION MODES:
Table 1: Various intra prediction block sizes and properties[4]
INTER PREDICTION MODES:
The macroblocks(MB) are split into four types [4] as shown:
a. One 16x16 MB partition.
b. Two 8x16 MB partitions.
c. Two 16x8 MB partitions.
d. Four 8x8 partitions and
e. Combination of any of b, c and d.
Optimization of baseline profile:
H.264 provides the best compression but is
computationally much more complex than any of the
previous standards and also time consuming for real
time applications. So as to make H.264 adaptable for
practical application the encoding time is to be
reduced. In this project this is achieved by applying
the following methods simultaneously.
1. Parallel programming in baseline[7]
2. Fast algorithm for intra mode Selection[8]
3. Fast algorithm for inter mode Selection [9]

The joint model (JM 18.0) implementation of the H.264
encoder is used in this project. [10]
1. Parallel programming in baseline[7]




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Step 1. Partition the total number of frames to encode into 2
equal sets.
Ex. If the total number of frames to encode is 30, then set1
contains frame numbers from 1 to 15 and set 2 contains
frame numbers from 16 to 30.
Step 2. Perform intra coding parallelly on initial two frames in
both partitions
Ex. frame 1 and frame 16 together. Frame 1 can be used as a
reference frame for frame 2 and frame 16 can be used as a
reference frame for frame 17 and so on.
Step 3. Perform inter coding on frame 2 and frame 17 by
incorporating changes in the encoding algorithm. Repeat for
frame 3 and frame 18 and so on till all the frames are
encoded.
Fig.4: Parallel processing of frames to
reduce encoding time[7]
FRAME 1
FRAME 2
FRAME 3
FRAME 15
INTRA
INTER
INTER
INTER
PARALLEL
ENCODING
PARALLEL
ENCODING
PARALLEL
ENCODING
PARALLEL
ENCODING
INTRA
INTER
INTER
INTER
FRAME 16
FRAME 17
FRAME 18
FRAME 30
Rate Distortion optimization [6][8][9]

Once the prediction is obtained and residual is calculated and the best mode among these
modes is chosen based on the least residual, the H.264/AVC encoder performs the ratedistortion optimization (RDO) technique for each macro block to obtain.

Set macro block parameters : QP (quantization parameter) and Lagrangian multiplier λ

Calculate : λMODE = 0.85⋅2(QP-12)/3 ………………………………..(1)

Then calculate cost, which determines the best mode


Cost = D + λ MODE. R,………………………………………(2)
D – Distortion
R - Bit rate with given QP

Considering the RDO procedure for intra mode selection in H.264/AVC, the number of mode
combinations in one macro block is

N8x (16xN4 + N16)=8x(16+16)=592

N8 – number of modes of an 8x8 chroma block

N4 – number of modes of an 4x4 luma block

N16 – number of modes of an 16x16 luma block

The H.264/AVC encoder carries out 592 RDO calculations to choose the best matching MB .
As a result, the complexity of the encoder increases extremely.
Fast algorithm for intra mode selection[8]

Proposed intra mode selection algorithm for a 4x4 luma
block [2][8]:
Fig5: Pixel indices and modes of adjacent blocks used in the proposed intra mode selection algorithm. (a) indices
used in (3) to (10) for a 4x4 luma block, (b) modes of upper and left blocks for additional candidate modes. [8]
Step 1 - For a 4x4 luma block, obtain average(avg) and sum of
difference(S). [8]
 Step 2a - If S is larger than a threshold, T1(set to 32), carry out RDO
procedure for at most 4 candidate modes: two modes with minimum
and second minimum difference(diff), and at most two modes from
adjacent blocks. [8]
 Step 2b - If S is smaller than a threshold, T1, carry out RDO procedure
for at most 4 candidate modes: one mode with minimum Diff, at most
two modes from adjacent blocks, and DC mode. [8]

Proposed intra mode selection algorithm for a
16x16 luma block [2] [8]:
Step 1 - Examine sizes of adjacent blocks: if both blocks (upper block and
left block) are 16x16, go to Step 2, otherwise go to Step 4. [8]
 Step 2 - Examine modes of adjacent blocks: if both modes are same, go to
Step 3, otherwise select the best mode for a 16x16 luma block, which
results in the minimum SATD (sum of absolute transformed differences)
between two adjacent modes of modeA and modeB. [8]
 Step 3 - If both adjacent modes are DC mode, go to Step 4, and otherwise
select the best mode for a 16x16 luma block, which results in the
minimum SATD between the adjacent mode and DC mode. [8]
 Step 4 - Let ΔV be a vertical difference between upper boundary pixels of
the current block and boundary pixels of the upper block, and ΔH be a
horizontal difference between left boundary pixels of the current block
and boundary pixels of the left block as follows. [8]






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ΔV = Σ |u(i)-q(i)| for i =0 to 15.
ΔH = Σ |l(i)-r(i)| for i =0 to 15.
where u(i) -> upper block boundary pixels
q(i) -> upper boundary pixels of current block
l(i) -> boundary pixels of the left block
r(i) -> left boundary pixels of the current block
Obtain candidate modes by using two difference values, ΔV and ΔH: if |ΔV −
ΔH | is smaller than 2xT2, candidate modes are DC mode and plane mode; if
(ΔV − ΔH) is larger than threshold,T2 (set to 8), candidate modes are DC
mode and horizontal mode; if (ΔV − ΔH) is smaller than − T2, candidate
modes are DC and vertical mode, where T2 is a positive value. The
threshold T2 is set equal to 32.
Finally, select the best mode between each candidate mode by choosing the
mode with minimum SATD(sum of absolute transformed differences).
Fig. 6: Calculation for ΔV and ΔH i n 16x16 luma block. [2] [8]
3. Fast algorithm for inter mode
selection [9]

3. Fast algorithm for inter mode selection [9], [20]:

FAT for mode decision exploits statistical similarity between current
macro block and predicted macro block. Predicted mode is obtained from
the spatial and temporal macro blocks.

For accuracy, the rate distortion cost is checked against adaptive Threshold I
and adaptive Threshold II

Adaptive Threshold I: RD thres = RD pred x (1-8xβ)

Adaptive Threshold II: RD thres = RD pred x (1+10xβ)

Such that

Where, β is the modulator, N is the rows of the image and M is number of
columns of N X M MB. If the predicted mode is less than P 8 x 8, it is
checked if the current macro block is homogeneous or not. Further
partitioning is done into 8x4, 4x8 and 4x4 blocks, if the current macro
block is not homogenous.
………. (4)
FAT inter prediction algorithm [9]
Fig 7: Flow chart for inter prediction [9],[20]
CONCLUSION
As proposed by implementing parallel programming in
baseline profile along with FAT algorithm in intra and
inter prediction modes on numerous test sequences,
and by obtaining various quality measurements like
PSNR and SSIM , the optimized baseline profile will be
obtained.
The performance of the optimized H.264 baseline profile is
compared with the H.264 baseline profile using the quality
measurements, and thus the faster computation speed,
video quality and bit rates can be calculated based on
various test sequences.

REFERENCES:

[1]
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
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
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
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
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
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