1. HEVC CABAC A PROJECT UNDER THE GUIDANCE OF DR. K. R. RAO
COURSE: EE MULTIMEDIA
PROCESSING, SPRING 2016
SUBMITTED BY: Satya Avasarala ( )
Mohammed Mahmood Quraishi( )
Sai Kumar Pola( ) ID

2. LIST OF ACRONYMS: AVC : Advance Video Coding
BD-BR: Bjontegaard Delta Bit rate.
CTU : Coding Tree Unit
CU : Coding Unit
CABAC: Context Adaptive Binary Arithmetic Coding.
DBF: De-blocking Filter
PU : Prediction Unit
MPEG : Moving Picture Experts Group
HDTV : High Definition Television
PSNR : Peak Signal To Noise Ratio
ISO: International Organization for Standardization
HEVC: High Efficiency Video Coding.
HM: HEVC Test Model.
DCT: Discrete Cosine Transform
MPEG: Moving Picture Experts Group.
JCT: Joint Collaborative Team.
JCT-VC: Joint Collaborative Team on Video Coding

3. Introduction : H.264
H.264 also known as Advanced Video Coding (MPEG-4 AVC)[2] is a video coding format is developed by ITU-T [4], Video Coding Experts Group (VCEG) together with the ISO/IEC JTC1[2] Moving Picture Experts Group (MPEG).[1]
It has been said that 80% of the internet videos use this compression standard .
It has 50% more video coding efficiency than MPEG 2.
The Applications Of H.264 were :
1) HDTV broadcast satellite.
2) Real-time video chat and Video Conferencing
3) Internet and mobile videos and many more.
Advantages Over Previous Standards(MPEG 2)
1) Prediction- Intra prediction using neighboring sample.
2) Transform – It implemented 4x4/8x8 integer transforms and 2x2/4x secondary Hadamard.[6]
3) Entropy Coding- Context Adaptive Variable Length Coding(CAVLC) and CABAC.[8]

4. It uses huge bandwidth approximately 40-45% over HEVC [5]
DISADVANTAGES OF H.264
It uses huge bandwidth approximately 40-45% over HEVC [5]
At the same bit rate HEVC performs far more better video quality compared to H.264
Failure to support UHD,2K and 4K standard.
 H.264 encoding and decoding is more computationally complex than some other codecs such as MPEG-4 [9] Part 2 (DivX, XviD).
Figure 1: Comparison of various codecs [1]

5. REDUNDANCY & IT’S TYPES [11]:
SPATIAL REDUNDANCY – FRAME TO FRAME
STATISTICAL REDUNDANCY- FROM THE STATISTICS OF AN IMAGE
TEMPORAL REDUNDANCY-FROM ONE TIME TO ANOTHER
PERCEPTUAL REDUNDANCY- FROM ONE FRAME TO ANOTHER IN TERMS OF PERCEPTION.

6. HEVC:
HEVC was developed by the JCT-VC organization, a collaboration between
the ISO/IEC MPEG and ITU-T VCEG. [2]
It is an extension of the concepts in H.264/MPEG-4 AVC. [11]
It offers about double the data compression ratio at the same level of video
quality, or substantially improved video quality at the same bit rate.[6]
A parallel pipeline approach is most promising and gives highest throughput.
It incorporates the extension of the correlation and contrast coding areas
from 16×16 pixel to sizes up to 64×64 [14], enhanced variable-square size division,
enhanced "intra" expectation inside of the same picture, enhanced
movement vector forecast and enhanced movement pay sifting.

7. FLEXIBLE CODING BLOCK STRUCTURES: Each frame is divide into blocks
Key Features Of HEVC:
FLEXIBLE CODING BLOCK STRUCTURES:
Each frame is divide into blocks
In HEVC CTU can have up-to 64x64 pixels which may be a combination of inter and intra coded blocks [6]
Figure 2:Block partitioning [3]

8. Different Prediction Units For Intra-Coded and Inter-Coded CU
In the intra-coded CU we can only divide into square partition units like 4 PU or a single PU [8]
Inter Coded Cu Can be divided into non Square and Square PU’S [9]

9. EXTENSIVE TRANSFORMS
HEVC supports wide range of integer transform like 4x4, 8x8,16x16 and 32x32 [6]
Two Types of 4x4 transforms IDST-intra and IDCT-inter
Due to this there has been an increased computational complexity like:
- 8x more computations per coefficient. [12]
- 16x larger transpose memory.
There has be an increase of 5-10% in coding efficiency. [13]

10. HEVC CABAC
HEVC uses CABAC as it’s entropy coding engine which does lossless coding of syntax elements.
Thereby, achieves 10-15% coding efficiency when compared to CAVLC used by AVC/H.264. [19]
Figure 3 : HEVC CABAC block diagram [11]

11. HEVC CABAC & its main steps
Binarization : Maps the syntax elements to binary symbols (bins). [12]
2) Context Modelling : Estimates the probability of the bins.
3) Arithmetic Coding : Compresses the bins to bits based on the estimated probability [18]
Figure 4 :Basic encoding process [12]

12. Key steps in CABAC 1.Binarization:
It involves mapping the syntax elements to the binary symbols.
Combinations of Binarizations can be used in HEVC and AVC. [12]
Example: Fixed length, Exp-Golomb, truncated unary, etc..,
Different types of prefix and suffix can be used.
Truncated unary can be used as prefix and Fixed length as suffix. [10]

13. 2. Arithmetic Coding
In this, bins(binary symbols) are mapped to bits. [16]
In here, there is a recursive sub-interval process which is based on probability of symbol being compressed. [15]
The encoded bits represent an offset value which when converted to a fraction selects one of the two intervals indicated as a decoded bin

14. 3. Context Selection
The context modelling and selection is used to accurately model the probability of each bin. [13]
Probability of each bin depends on syntax element and bin index.
There are several hundred context models in AVC and CABAC. [1]
The context and probability of next bin is determined by previous bin.
But these operations should be traded off in term of Power and Area.

15. ENCODER IMPLEMENTATION STANDARDS:
Throughput: Achieve target pixel-rate and bit-rate for real time applications. Reduce latency of bits to pixels and pixels to bits for interactive applications.
Energy and Power Consumption:Minimize energy consumption to extend battery life for portable devices. Minimize power consumption to reduce heat dissipation.
Platform Cost : Reduce amount of data to be stored in memory and amount of logic. Reduce bandwidth requirements such as reads/writes from memory to reduce demands on off-chip components.

16. Throughput improvements in HEVC 1. Reduce total number of bins
The binarization of coefficient levels was modified to reduce the total number of bins as a constitute up to 15-25% of total number of bins. [12]
HEVC and AVC have same number of bins but upon coefficient values above 12, the binarization used in HEVC has fewer bins when compared to AVC bins. [3]
In a worst case scenario for a given 16*16 block of pixels the total number of bins were reduced by 1.5 times when compared to AVC/H.264. [6]

17. 2. Reducing number of context coded bins
The number of context coded bins was reduced considerably when compared to AVC by 8 times.
Table 1 &2 : Various context coded bins [12] [11]

18. 3.Grouping of bypass bins
By grouping of bypass bins, we can improve the coding efficiency.
This can be done by setting up run length of bin streams from different syntax elements. [3]
Formula for PSNR [7]
Figure 5 :Rate distortion curve [8]

19. Flowchart For HEVC Encoding:
Figure 6 :HEVC Encoding flow chart [11]

20. HEVC Decoding:
Figure 7 :HEVC decoding flow chart [11]

21. Entropy Coding In HEVC-CABAC Algorithm
The HEVC video compression technology uses Context based Adaptive Binary Arithmetic Coding(CABAC) entropy
which is a modified version of CABAC encoder that is used in MPEG-4 AVC/H.26 video compression standard [9]
Figure 8 :General Block Diagram of CABAC Encoder [12]

22. Entropy Coding In HEVC-CABAC Algorithm Continued…
The distinctive feature of CABAC algorithm is application the binary arithmetic codec core that is able to encode
binary symbols.
225 models are defined in CABAC with HEVC. [4]
CABAC introduces two essential simplifications in order to speed up computations:
-Probabilities of symbols are calculated in a simplified way using pre-defined Finite State Machine(FSM) with 64
states.
-Some symbol are encoded in the so-called bypass coding made with no data statistics modelling stage.
Simplifications made in CABAC [2] context modeler block significantly reduces accuracy of symbol probabilities which
negatively affects compression performance. [5]

23. Improved Version Of CABAC Algorithm in HEVC
Main idea of improved CABAC uses more accurate mechanism of data statistics estimation relative to original algorithm.
In the improved CABAC, the CTW method is used by every statistical model to calculate conditional probability of symbols
more accurately. [8]
Figure 9: Improved version of CABAC [8]

24. Efficiency Of Improved HEVC- Consequences
Application of the improved CABAC within HEVC increases compression performance of video encoder.
As seen in the table below an average of 2.6% bitrate reduction was obtained for used video sequences
Table 3: Performance comparison of both version of HEVC [16]
Compression performance of forthcoming HEVC technology can be further increased when using improved entropy
encoder [15]
Better data statistics estimation in CABAC leads to 1.6% - 4.5% reduction of HEVC bit-stream.

25. HM CODE: (Source – HM software Lib)
Void TEncBinCABAC::start() { m_uiLow = 0; m_uiRange = 510; m_bitsLeft = 23; m_numBufferedBytes = 0; m_bufferedByte = 0xff; #if FAST_BIT_EST m_fracBits = 0; #endif }

26. Void TEncBinCABAC::finish() { if ( m_uiLow >> ( 32 - m_bitsLeft ) ) //assert( m_numBufferedBytes > 0 ); //assert( m_bufferedByte != 0xff ); m_pcTComBitIf->write( m_bufferedByte + 1, 8 ); while ( m_numBufferedBytes > 1 ) m_pcTComBitIf->write( 0x00, 8 ); m_numBufferedBytes--; } m_uiLow -= 1 << ( 32 - m_bitsLeft );

27. else { if ( m_numBufferedBytes > 0 ) m_pcTComBitIf->write( m_bufferedByte, 8 ); } while ( m_numBufferedBytes > 1 ) m_pcTComBitIf->write( 0xff, 8 ); m_numBufferedBytes--; m_pcTComBitIf->write( m_uiLow >> 8, 24 - m_bitsLeft );

28. Void TEncBinCABAC::flush() { encodeBinTrm(1); finish(); m_pcTComBitIf->write(1, 1); m_pcTComBitIf->writeAlignZero(); start(); }

29. FUTURE WORK:
Requirement for backing differing customers with fluctuating capabilities.
H.264/AVC does not support combined scalable and multi-view coding. [22]
HEVC allows for combined scalable and multi-view coding.
Scalable video coding: As there is need for more compression efficiency & huge requirement for mixed format content so we need to go for Scalable video coding. It regulates the encoding of an amazing video bit stream that likewise contains one or more subset bit streams.
Lastest advancements include the HEVC screen content coding which started in 2014 April. [29]

30. FUTURE WORK: contd
Figure 10 : Scalable extension of HEVC [9]

31. REFERENCES
[1] J. Ohm, et al“ Comparison of the Coding Efficiency of Video Coding Standards – Including High Efficiency Video Coding (HEVC),” IEEE Trans. on CSVT, vol.22, no. 12, pp. 1669–1684, 2012.
[2] G. Sullivan, et al, “The H.264/AVC Advanced Video Coding Standard: Overview and Introduction to the Fidelity Range Extensions,” SPIE Conference on Applications of Digital Image Processing XXVII, vol. 5558, pp , Aug
[3]M. Goldman, "High-Efficiency Video Coding (HEVC): The Next-Generation Compression Technology", SMPTE Mot. Imag. J, vol. 121, no. 5, pp , 2012.
[4] D. Marpe, et al, “Context-based adaptive binary arithmetic coding in the H.264/AVC video compression standard,” IEEE Trans. on CSVT, vol. 13, no. 7, pp. 620– 636, July 2003.

32. [5] M. Zhou, et al "Parallel tools in HEVC for high-throughput processing", Applications of Digital Image Processing XXXV, [6]T. Wiegand, et al" Overview of the H.264/AVC video coding standard", IEEE Trans. Circuits Syst. Video Technol., vol. 13, no. 7, pp , [7]S. Kim, et al, "Efficient entropy coding scheme for H.264/AVC lossless video coding", Signal Processing: Image Communication, vol. 25, no. 9, pp , [8] V.Sze & M.Budagavi, M. 2012, "High Throughput CABAC Entropy Coding in HEVC", IEEE Transactions on Circuits and Systems for Video Technology, vol. 22, no. 12, pp

33. [9] Dajiang Zhou, et al, "Ultra-High-Throughput VLSI Architecture of H
[9] Dajiang Zhou, et al, "Ultra-High-Throughput VLSI Architecture of H.265/HEVC CABAC Encoder for UHDTV Applications", IEEE Trans. Circuits Syst. Video Technol., vol. 25, no. 3, pp , [10] V.Sze et al. (2014). High efficiency video coding (HEVC): Algorithms and architectures. New York;Cham;: Springer. [11]S. Choi and S. Chae, "Comparison of CABAC rate estimation models for HEVC rate distortion optimization", Electronics Letters, vol. 50, no. 6, pp , [12]J. Choi and Y. Ho, "Efficient residual data coding in CABAC for HEVC lossless video compression", Signal, Image and Video Processing, vol. 9, no. 5, pp , 2013.

34. [13] HM C++ Code: https://hevc.hhi.fraunhofer.de/svn/svn_HEVCSoftware/
[14] HM software manual:
.hhi.fraunhofer.de/svn/svn_HEVCSoftware/trunk/doc/software-manual.pdf.
[15] HEVC tutorial by I.E.G. Richardson:
[16] G. J. Sullivan, et al, “Standardized Extensions of High Efficiency Video Coding (HEVC)”,
IEEE Journal of selected topics in Signal Processing, Vol. 7, No. 6, pp , Dec

35. [17] Test sequences: https://media.xiph.org/video/derf/
[18] C. Fogg, “Suggested figures for the HEVC specification”, ITU-T / ISO-IEC Document: JCTVC J0292r1, July 2012.
[19] M. Wien, "High Efficiency Video Coding : Coding Tools and Specification" , Springer , 2014.
[20] G. Correa et al , " Fast HEVC Encoding Decisions Using Data Mining " , IEEE Transactions on Circuits and Systems for Video Technology , Vol . 25 , No. 4 , pp , Apr

36. [21] N. Ling, “High efficiency video coding and its 3D extension: A research perspective,” Keynote Speech, ICIEA, pp , Singapore, July 2012.
[22] Video Sequences: html
[23] ITU-T website:
[24] T.Nguyen et al,"Transform Coding Techniques in HEVC", IEEE Journal of Selected Topics in Signal Processing, vol.7, pp.978–989, Dec

37. [25] X. Wang et al,“Paralleling Variable Block Size Motion Estimation of HEVC on Multicore CPU plus GPU platform”, IEEE International Conference on Image Processing (ICIP),vol.22, pp , Sep.2013.
[26] Y.L. Lee et al, "Improved lossless intra coding for H.264/MPEG-4 AVC", IEEE Trans on Image Process, vol.15, no.9, pp , Sep.2006.
[27] M. Jakubowski and G. Pastuszak, “Block-based motion estimation algorithms- a survey”, Journal of Opto-Electronics Review, vol. 21, pp , Mar.2013.
[28] Tortoise SVN:
[29] Website on PSNR:
[30] White paper on PSNR-NI: