Low Complexity H.265/HEVC Coding Unit Size Decision for a Videoconferencing System

Transcription

1 BULGARIAN ACADEMY OF SCIENCES CYBERNETICS AND INFORMATION TECHNOLOGIES Volume 15, No 6 Special Issue o Logistics, Iformatics ad Service Sciece Sofia 2015 Prit ISSN: ; Olie ISSN: DOI: /cait Low Complexity H.265/HEVC Codig Uit Size Decisio for a Videocoferecig System Zhaoqig Pa 1,2,3, Limig Che 1,2, Wejie Ya 3 1 School of Computer ad Software, Najig Uiversity of Iformatio Sciece ad Techology, Najig , Jiagsu, Chia 2 Jiagsu Egieerig Cetre of Network Moitorig, Najig Uiversity of Iformatio Sciece ad Techology, Najig , Jiagsu, Chia 3 School of Computer Sciece ad Egieerig, Hebei Uiversity of Techology, Tiaji , Tiaji, Chia s: zhaoqigpa@uist.edu.c leeged_che@outlook.com wejieya@scse.hebut.edu.c Abstract: With the developmet of Iteret ad video capture techiques, videocoferecig becomes still more popular. However, with the icreased size of the video resolutio, the volume of the raw videocoferecig video data icreases dramatically. The H.265/HEVC video compressio stadard ca efficietly compresses the videocoferecig video, while the high compressio rate is at the cost of heavy ecodig complexity. Hece, reducig the complexity is vital to be used for the H.265/HEVC ecoder i videocoferecig systems. I this paper we proposed a low complexity H.265/HEVC codig uit size decisio algorithm for a videocoferecig system, by cosiderig the codig cotet property of the codig uit, i which the codig uit size decisio process is termiated if the predictio residuals of the codig uit are all trasformed ad quatized to zeroes. The experimetal results show that the proposed algorithm achieves 62.79% o average i ecodig time savig, while the rate distortio degradatio is acceptable. Keywords: Videocoferecig system, H.265/HEVC, Codig uit, quadtree, low complexity. 1. Itroductio VideoCoferecig (VC) is the coduct of a videocoferece by a group of telecommuicatio techiques which allows more tha oe locatios to commuicate by simultaeous two-way video ad audio trasmissios. With the icreased size of the video resolutio, the amout of raw video data eeds to be 159

2 compressed ad trasmitted. However, the curret computig ad trasmissio capabilities are still limited. As a result, the high compressio rate ad low complexity are the key requiremets for high defiitio videos to be widely used i VC. The H.265/HEVC (High Efficiecy Video Codig) stadard [1-3] ca efficietly address the compressio rate problem. However, the achieved compressio rate is at the cost of high computatioal complexity of a group of advaced codig tools used i the H.265/HEVC, such as the quadtree structure based Codig Tree Uit (CTU). Therefore, reducig the computatioal complexity is essetial for the H.265/HEVC ecoder to be applied i the VC system. To compress the videocoferecig video, the video is separated ito a umber of frames, ad the frames are sequetially ecoded. Furthermore, the frame is partitioed ito slices, the slices are split ito a group of CTUs, which are the basic compressio uit of the H.265/HEVC ecoder. Accordig to the quadtree structure, the CTUs are further partitioed ito Codig Uits (CUs), ad the HEVC supports flexible CU sizes from the size of to the size of 8 8, which are correspodig to the CU quadtree depth of 0 up to depth 3. I CU ecodig process, the HEVC ecoder checks 4 i, i [0, 1, 2, 3], CU partitios for each quadtree depth level, there are totally 85 CU partitios. Fig. 1 gives a example of the H.265/HEVC quadtree based CU partitio process. At last, the best CU quadtree * depth level d is determied accordig to the rate distortio cost fuctio [4, 5], as show: * d = arg mi Jd, (1) d D Jd = Dd ( ) + λ Rd ( ), where D is the cadidate CU quadtree depth level, D(d) is the distortio betwee the origial CU ad its recostructed CU which is obtaied by ecodig the origial CU with a quadtree depth level d; is the Lagragia multiplier; R(d) represets the umber of total bits for ecodig the CU with depth d. This try all ad select the best CU quadtree depth decisio method cosumes high computatio, which could limit the H.265/HEVC ecoder to be used i real time VC systems. To reduce the computatioal complexity, may researchers have devoted their efforts to reducig the computatioal complexity of H.265/HEVC CU size decisio process. C h o i, P a r k ad J a g [6] proposed a codig tree pruig based CU early termiatio method for a low complexity H.265/HEVC ecoder, i which the CU size decisio process is termiated, if the curret CU selects the Skip mode as its best predictio mode. By usig the spatial ad temporal CU depth selectio correlatio, P a et al. [7] have proposed a fast CU size decisio method for H.265/HEVC ecoder. Based o the texture complexity, H o u et al. [8] proposed a fast CU size decisio algorithm for H.265/HEVC itra codig. A h, L e e ad K i m [9] proposed a fast CU ecodig method by usig spatiotemporal ecodig parameters for H.265/HEVC iter codig. Based o statistical aalysis, L e e et al. [10] proposed a fast CU size decisio algorithm by cosiderig the Skip mode decisio, CU skip estimatio ad early CU termiatio. Based o the depth iformatio correlatio betwee the spatial-temporal adjacet codig tree uits ad the curret codig tree uit, Z h a g, W a g ad L i [11] proposed a fast codig 160

3 uit depth decisio algorithm for iterframe codig i H.265.HEVC. M u et al. [12] proposed a fast CU depth decisio method by exploitig the relatioship betwee the rate distortio cost ad CU depth. H u a g et al. [13] proposed a adaptive depth search rage for HEVC codig uit size selectio accordig to the coded block flag ad the iformatio of the quatizatio parameter. However, these methods caot efficietly remove the complexity of H.265/HEVC ecoder of a videocoferecig system due to the fact that video cotet properties are ot cosidered by these methods (Fig. 1). Fig. 1. A example of the H.265/HEVC quadtree based CU partitio process I this paper we propose a fast CU size decisio method for the low complexity H.265/HEVC ecoder of a videocoferecig system by cosiderig the video cotet property. The rest of this paper is orgaized as follows. The motivatios ad statistical aalyses are preseted i Sectio 2. The the details of the proposed fast CU size decisio algorithm are give i Sectio 3. Experimetal results are give i Sectio 4. Fially, Sectio 5 cocludes the paper. 2. Motivatios ad statistical aalyses To aalyze the ecodig complexity of the best CU quadtree depth level decisio process, three differet HD video sequeces with a resolutio , icludig FourPeople, Johy, ad Vidyo1 are tested; detailed iformatio of these three sequece is give i Table 1. The HEVC referece software HM12.0 is used as a software platform. The test coditios are listed as follows: the maximum CU size is 64 64, ad the maximum CU quadtree depth is 4; the fast motio estimatio method is TZSearch; four Quatizatio Parameters (QPs) are adopted. The statistical results are give i Table 2, where the CU ecodig complexity, C complexity is computed by (2) Ccomplexity = Tc / Te, where T c represets the total ecodig time of the CU size decisio process, T e idicates the total ecodig time of the H.265/HEVC ecoder. 161

4 Table 1. Test sequeces Sequece FourPeople Johy Vidyo1 Size Frame rate, Codig Frames fps structure ecoded Low-Delay- Mai 65 Table 2. Statistical results of CU ecodig complexity Sequece QP=22 QP=27 QP=32 QP=37 FourPeople Johy Vidyo From Table 1 it ca be see that the ecodig complexity of the CU size decisio process is rather large, the value of C complexity is from up to From these values, we ca draw a coclusio that the try all ad select the best CU size decisio process cosumes most of the total ecodig time. Thus, if the CU size decisio process could be optimized, much more ecodig time could be saved. 3. The proposed fast CU size decisio algorithm for a low complexity H.265/HEVC ecoder 3.1. The proposed all-zero block based fast CU size decisio algorithm The videocoferecig video has may homogeous regios, such as the backgroud, sice a big size CU could ecode the predictio residual i a few umber of symbols tha possible uder the coditio of may small size CUs; the homogeous regios are rather suitable for ecodig i a big size CU partitio. I additio, the iterpredictio residuals of these homogeous regios are easy trasformed ad quatized ito zeroes. Hece, desigig a early termiatio for the CU size decisio process based o the quatizatio coefficiets is practicable. I video codig, the All-Zero Block (AZB) meas that the predictio residuals of this block are all trasformed ad quatized ito zeroes. To fid the correlatio betwee the AZB ad the optimal CU quadtree depth, the evet M idicates after ecodig the CUs of depth level i with the merge ad iter 2N 2N PU mode, they are all AZBs. The evet N represets that the CU quadtree depth i is selected as the optimal CU quadtree depth level, the coditioal probabilities of P(N M) are tested. The statistical results are show i Table 3. Table 3. The coditioal probabilities of P(N M) Sequece QP=22 QP=27 QP=32 QP=37 Average FourPeople 80.10% 86.97% 89.79% 91.82% 87.17% Johy 80.56% 86.01% 89.20% 91.69% 86.87% Vidyo % 85.70% 88.66% 90.70% 85.85% Average 79.67% 86.23% 89.22% 91.40% 86.63% 162

5 From Table 3 it ca be observed that the CU has a quite large probability to choose the quadtree depth level i as its best CU quadtree depth level, whe the CUs with depth i are all AZBs. The coditioal probability of P(N M) holds a average of 86.63%, ad is from 78.34% up to 91.82%. It ca also be see that the coditioal probability of P(N M) icreases as the QP value gets bigger, this is because more iter predictio redials are trasformed ad quatized to zeroes due to the fact that the codig cotet becomes simple as the QP icreases. Therefore, accordig to the above aalyses, the best CU quadtree depth level selectio process is completed if (3) QM + QI = 0, i where idicates the umber of total CU partitios, i [ ] = 4, 0,1, 2, 3, i is the CU quadtree depth level. After ecodig the CU with the merge mode, if its predictio residuals are trasformed ad quatized ito zeroes, the the value of QM is equal to 0, otherwise, the value of QM is bigger tha 0; after ecodig the CU with the iter 2N 2N mode, if its predictio residuals are trasformed ad quatized ito zeroes, the the value of QI is equal to 0; otherwise, the value of QI is bigger tha The overall algorithm Accordig to the above aalysis, the low complexity H.265/HEVC CU size decisio algorithm for videocoferecig video codig is summarized i Algorithm Experimetal results I order to evaluate the efficiecy of the low complexity CU size decisio algorithm, the HEVC referece software HM12.0 is used as a software platform. The hardware platform is Itel Xeo CPU E GHz ad 3.50 GHz, 4.00 GB RAM with Microsoft Widows 7 64-bit operatig system. The test coditios are idicated i Table 4. Six videocoferecig video sequeces, icludig FourPeople, Johy, KristeAdSara, Vidyo1, Vidyo3, Vidyo4 are adopted. These six video sequeces are show i Fig. 2. The iformatio of these six sequeces is that the resolutio is , the frame rate is 60 fps, ad the umber of ecoded frames is 97. Algorithm 1. The low complexity H.265/HEVC CU size decisio algorithm Step 1. Iput: The maximum CU size: 64 64, the maximum quadtree depth: 4 Step 2. for Quadtree depth level=0 to 3 do Step 3. Ecode the curret CU with the Merge mode Step 4. Ecode the curret CU with the Iter 2N 2N mode Step 5. if QM + QI = 0 The 163

6 Step 6. The CU size decisio process is termiated Step 7. else Step 8. Ecode the curret CTU with the ext quadtree depth level Step 9. ed if Step 10. Output: The best CU quadtree depth level Step 11. ed for Step 12. Process the ext codig tree uit Table 4. Test coditios The maximum CU size The maximum quadtree depth 4 Motio estimatio method TZSearch Motio estimatio search rage ±64 Quatizatio parameters 22, 27, 32, 37 We compared the ecodig performace of the proposed algorithm with C h o i, P a r k ad J a g [6] i terms of the Peak Sigal to Noise Ratio (PSNR), Bit Rate (BR) ad total ecodig time savig. The experimetal results are summarized i Table 5. I the table PSNR, BR ad T deote the PSNR decrease, BR icrease ad the total ecodig CPU time savig [14, 15], ad they are computed as give below: Δ PSNR = PSNRφ PSNR HM, (4) where PSNR, BR, T φ φ φ BR Δ = Tφ T Δ T = T φ HM BR, BR HM HM BR HM, preset the PSNR, BR ad total ecodig time of the algorithm, {Choi [6], Proposed}; HM HM HM PSNR, BR, T deote the PSNR, BR ad total ecodig time of the origial HM12.0, respectively. From Table 5 we ca see that Choi s method reduces the total ecodig time from up to 70.17%, 55.47% o average. Meawhile, the PSNR decreases from up to db, db o average; ad the BR decreases from 0.38 up to 1.99%, 1.04% o average. The proposed method saves the total ecodig time up to 76.36%, 62.79% o average. At the same time, the PSNR degrades from up to db, db o average, ad the BR decreases from 0.30 up to 2.12%, 1.07% o average. From these values we ca see that the proposed method achieves a quite similar rate distortio performace with Choi s method, while it obtais more ecodig time savig tha Choi s method. Thus, we ca coclude that the proposed method efficietly removes the ecodig complexity of the H.265/HEVC ecoder, meawhile maitaiig a comparable rate distortio performace. 164

7 Table 5. Summary of the ecodig results Choi [6] Proposed Sequece QP PSNR, BR, T, PSNR, BR, T, db % % db % % FourPeople Average Johy Average KristeAdSara Average Vidyo Average Vidyo Average Vidyo Average Average

8 Fig. 2 shows the test sequeces. (d) (e) (f) Fig. 2. Test sequeces: FourPeople (a); Johy (b); KristeAdSara (c); Vidyo1 (d); Vidyo3 (e); Vidyo4 (f) 5. Coclusio The CU size decisio process cosumes the greatest proportio of the total ecodig time of H.265/HEVC ecoder, so i order to make the H.265/HEVC ecoder meet the complexity requiremets of a videocoferecig system we proposed a low complexity 265/HEVC CU size decisio algorithm. The experimetal results show that the proposed algorithm ca efficietly reduce the computatioal complexity of the H.265/HEVC ecoder, while the rate distortio performace degradatio is acceptable. Ackowledgemets: This work was supported i part by the Natioal Natural Sciece Foudatio of Chia uder Grat , i part by the Natioal Natural Sciece Foudatio of Jiagsu Provice of Chia uder Grat BK , i part by the Natural Sciece Foudatio of the Jiagsu Higher Educatio Istitutios of Chia uder Grat 15KJB510019, i part by the Project through the Priority Academic Program Developmet of Jiagsu Higher Educatio Istitutios, i part by the Startup Foudatio for Itroducig Talet of NUIST uder Grat , i part by the Natural Sciece Foudatio of Hebei Provice of Chia uder Grat F ad Grat F R e f e r e c e s 1. Sulliva, G. J., J.-R. Ohm, W.-J. Ha, T. Wiegad. Overview of the High Efficiecy Video Codig (HEVC) Stadard. IEEE Tras. Circuits Syst. Video Techol., Vol. 12, 2012, No 12, pp Iformatio Techology-High Efficiecy Codig ad Media Delivery i Heterogeeous Eviromets-Part 2: High Efficiecy Video Codig. ISO/IEC :2013 ITU-T Rec. H.265,

9 3. P a, Z., S. K w o g, M.-T. S u, J. L e i. Early MERGE Mode Decisio Based o Motio Estimatio ad Hierarchical Depth Correlatio for HEVC. IEEE Trasactios o Broadcastig, Vol. 60, 2014, No 2, pp Ohm, J.-R., G. J. Sulliva, H. Schwarz, T. K. Ta, T. Wiegad. Compariso of the Codig Efficiecy of Video Codig Stadards-Icludig High Efficiecy Video Codig (HEVC). IEEE Tras. Circuits Syst. Video Techol., Vol. 22, 2012, No 12, pp P a, Z., Y. Z h a g, S. K w o g. Efficiet Motio ad Disparity Estimatio Optimizatio for Low Complexity Multiview Video Codig. IEEE Trasactios o Broadcastig, Vol. 61, 2015, No 2, pp C h o i, K., S.-H. P a r k, E. S. J a g. Codig Tree Pruig Based CU Early Termiatio. ITU-T/ISO/IEC Joit Collaborative Team o Video Codig (JCT-VC) Documet JCTVC- F092, July P a, Z., S. K w o g, Y. Z h a g, J. L e i, H. Y u a. Fast Codig Tree Uit Depth Decisio for High Efficiecy Video Codig. I Proc. of 2014 IEEE Iteratioal Coferece o Image Processig (ICIP), Paris, Frace, May 2014, pp H o u, J., D. L i, Z. L i, X. J i a g. Fast CU Size Decisio Based o Texture Complexity for HEVC Itra Codig. I Proc. of 2013 Iteratioal Coferece o Mechatroic Scieces, Electric Egieerig ad Computer (MEC), Sheyag, Chia, December 2013, pp A h, S., B. L e e, M. K i m. A Novel Fast CU Ecodig Scheme Based o Spatiotemporal Ecodig Parameters for HEVC Iter Codig. IEEE Trasactios o Circuits ad Systems for Video Techology, Vol. 25, 2015, No 3, pp Lee, J., S. Kim, K. Lim, S. Lee. A Fast CU Size Decisio Algorithm for HEVC. IEEE Trasactios o Circuits ad Systems for Video Techology, Vol. 25, 2015, No 3, pp Z h a g, Y., H. W a g, Z. L i. Fast Codig Uit Depth Decisio Algorithm for Iterframe Codig i HEVC. I Proc. Data Compressio Coferece (DCC), Sowbird, UT, Mar., pp M u, F., L. S o g, X. Y a g, Z. L u o. Fast Codig Uit Depth Decisio for HEVC. I Proc. of 2014 IEEE Iteratioal Coferece o Multimedia ad Expo Workshops (ICMEW), Chegdu, Chia, July 2014, pp H u a g, X., C. K u o, C. M a o, Y. C i o u. Adaptive Depth Search Rage for HEVC Codig Uit Size Selectio. I Proc. of 2014 Aual Summit ad Coferece o Asia-Pacific Sigal ad Iformatio Processig Associatio (APSIPA), Siem Reap, December 2014, pp P a, Z., S. K w o g, L. X u, Y. Z h a g, T. Z h a o. Predictive ad Distributio Orieted Fast Motio Estimatio for H.264/AVC. Joural of Real-Time Image Processig, Vol. 9, 2014, No 4, pp P a, Z., S. K w o g. A Directio-Based Usymmetrical-Cross Multi-Hexago-Grid Search Algorithm for H.264/AVC Motio Estimatio. Joural of Sigal Processig Systems, Vol. 7, 2013, No 1, pp