ALGORITHM FOR H.264/AVC

ISSN 1392 124X INFORMATION TECHNOLOGY AND CONTROL, 2010 Vol. 38, No. ISSN 1392 124X INFORMATION TECHNOLOGY AND CONTROL, 2011, Vol.40, No.3 1, 5 7 A NOVEL Novel Varance-Based VARIANCE-BASED Intra-FrameINTRA-FRAME Rate Control Algorthm RATE for CONTROL H.264/AVC ALGORITHM FOR H.264/AVC Fu-Chuang Chen, Y-Pn Hsu Insttute of Electrcal Control Engneerng, Natonal Chao Tung Unversty P.O. BOX 25-92, Hsnchu 30099, Tawan, ROC. e-mal: fcchen@cc.nctu.edu.tw, hsuypn@gmal.com http://dx.do.org/10.5755/j01.tc.40.3.631 Abstract. To enhance mage qualty and retan a lmted bt budget, ntra-frame n the frame type selecton plays a sgnfcant role n vdeo codng systems because the frame s treated as a key frame for temporal doman reference. Ths paper presents an algorthm to predct accurate quantzaton parameters by developng varance-based dstorton measurements. Frstly, the ntra-frame rate control n JVT-G012 s analyzed before dscussng possble drawbacks. Current algorthms ncludes JVT-G012 and Yan s algorthm based on mean square error metrcs for ntra-frame rate controls are compared to show that the proposed dstorton metrc s useful to estmate quantzaton parameters. Expermental results show that the proposed algorthm can sgnfcantly mprove vdeo qualty up to 0.19 db and 1.28 db, compared wth the algorthm JVT-G012, whch s mplemented n the H.264 reference software JM 15.0 and Yan s algorthm. Keywords: ntra-frame, JVT-G012, quantzaton parameter, rate control, JM15.0. 1. Introducton Image qualty s a sgnfcant ssue n multmeda applcatons, such as vdeo streamng and survellance technologes. To acheve hgher mage qualty n vdeo encodng systems, the rate control method must frst be mplemented, and for an accurate fttng of the mage qualty, a large number of ntra-frame must be nserted n each mage groupng. The purpose of a rate control s to predct a sutable quantzaton parameter (QP) for ntra-frame under the specfed bts target. However, the work s dffcult, one man reason beng that the mage content s tmevared, and the fxed QP cannot ft for all mages. In the H.264/AVC vdeo codng standard, the QP specfes the quantzaton step sze, whch subsequently nfluences mage qualty and bt budget. The QP also affects rate-dstorton optmzed mode-decson and moton-estmaton process. The QP can be used to control the bt stream, thereby maxmzng the codng effcency wthout overflow or underflow channel rates. L et al. [1] proposed an approxmated quadrc model n JVT-G012; a one-pass rate control method to predct a possble QP for H.264/AVC, and a lnear model to predct dstorton by utlzng the mean absolute dfference (MAD) to solve the chcken-andegg ssue. In the quadrc model, whch was derved n Chang and Zhang [2], because the QP s a typcal closed-form, t can be acqured drectly. Due to ts effcency, JVT-G012 has been adopted n H.264/AVC reference software. The MAD predcton must be precse to attan a quadratc form, rendng the observatons above partcularly noteworthy. Encodng the current P-frame mght cause a possble ssue wth JVT-G012 because the bt budget and buffer constrant are gven. Therefore, provdng an estmate of the QP s dffcult because the quadratc model s nadequate when the MAD s not precse and the complexty of the current frame s not utlzed. Ths ssue hghlghts the necessty for desgnng a rate control algorthm that ncludes frame-complexty for H.264/AVC. Overall, rate control strategy can be dvded nto two parts: ntra-frame and nter-frame. However, the mplementaton of an effcent rate control algorthm should help acheve the balanced allocaton between mage qualty and the assgned bts budget, due to the lmted bandwdth n a wreless envronment. Several rate control methods for H.264/AVC are ether ntraframe or nter-frame, especally the nter-frame rate control methods [3]-[8] and the ntra-frame rate control methods [5],[12]-[14]. The frst method conssts of the optmal rate control combnng a rate model and a dstorton model [3]-[5], and the other method conssts of the real-tme rate control [6]-[8]. The orgnal quadratc model s based on statstc dstrbuton, and the rate-dstorton theory s appled to generate an R-Q(rate-quantzaton)/R-D(ratedstorton) model. The method of selectng the dstrbuton model, rate model, and dstorton model s becomng a sgnfcant topc. A new rate dstorton model combnng several logarthmc functons and adjustng the boundary of each functon has been proposed n We et al. [3]. Ths algorthm s based on vdeo sequence statstcs durng the encodng process. 227

6 Fu-Chuang Chen, Y-Pn Hsu F. -C. Chen, Y. -P. Hsu The Lagrange method has also been used to construct a new R-D model n Lu et al. [4] and Wang and Kwong [5]. These studes propose an R-D optmzed rate control algorthm wth an adaptve ntal QP determnaton scheme that s unlke the JVT- G012 quadratc form. Though these studes present new models, calculatng the MAD requrement stll requres lookng to prevous MAD values. Even f these models are excellent and robust enough to determne the QP shft, the decdng the fnal QP stll nvolves predctng the MAD. Secondly, the models n [6]-[8] use a quadratc form as the man skeleton to more accurately modfy MAD predcton. Studes n Jang and Lng [6] and n Wang and Yan [7] propose adaptve MAD predctons. Frame complexty, whch combnes a buffer status operaton, s the man consderaton n ths approach, and the MAD rato and emprcsm are used to change the QP. Expermental results n Kwon et al. [8] show that the estmaton error of the quadratc model can be sgnfcantly reduced to perform a smplfed and effcent form. The orgnal quadratc model can drop second-order term wthout sacrfcng any consderable performance, and a model parameter can modfy the frst-order term, much lke orgnal quadratc model. The order of power can also be changed to a dfferent frame type. In the current vdeo codng standard H.264/AVC, for nter-frame rate control, estmatng the QP requres the quadratc equaton when the assumed source s the Gaussan source dstrbuton model expressed by the Taylor seres. A more effcent scheme n vdeo codng systems comprses the ntra-frame encodng. Because the ntra-frame s treated as a reference frame for post P-frame or B- frame encodng, the two processes of moton estmaton and compensaton accordng to reference frame wll nfluence the results of bts consumpton and PSNR degree. If the QP for an ntra-frame s too small, a large number of bts are overspent to encode the ntra-frame, and the subsequent nter-frame cannot allocate enough target bts. The ntra-frame rate control algorthm has been embedded n the reference software JM 15.0 [9], whch s based on bts per pxel (BPP), frame rate, and the bts budget to decde QP. Although the BPP can provde a reference QP value for ntra-frame encodng, the mage-complexty property and the wde range of QP are not utlzed to enhance overall vdeo qualty. In Wang and Kwong [5] and n Wu and Km [12], accordng to mage and larger vdeo tranng, obtanng an approxmate equaton s necessary to estmate the QP value. For actual applcaton, the nformaton of mage densty and gradents s used n Wang and Kwong [5], and an mage dstorton such as MAD s also employed n Wu and Km [12] as the ndcator, to calculate the fnal QP value. In Hsa and Wang [13], mage edge characterstcs and BPP are appled to construct an equaton for QP estmaton. The mage edge characterstc apples a Laplacan matrx of Gaussan (LoG) operators. In Zhou et al. [14], accordng to extensve expermentaton results, the combnaton of mage gradents and hstograms, both ncludng lumnance and chromnance coeffcents, s extremely useful to represent QP estmaton under the exponent-based equaton. To acheve correct QP estmaton for ntra-frame rate control, ths study proposes an algorthm based on varance-based dstorton measurements, ntegrated on the current vdeo encodng system JM15.0. The proposed model uses varance between the current and prevously reconstructed MB to acqure dfferent dstorton n off-lne tranng wth a specfed QP range. After obtanng the model parameters, the study mplements them for real vdeo sequence n the ntra-frame rate control. The remander of the paper s organzed as follows: Secton 2 revews the ntra-frame rate control n JVT-G012 for QP computaton. Secton 3 ntroduces the proposed ntra-frame rate control algorthm wth a varance-based dstorton. Secton 4 evaluates the proposed algorthm and presents smulaton results. Fnally, Secton 5 offers conclusons. 2. Intra-frame rate control analyss n JVT-G012 Each frst frame n a pcture group s a crtcal reference frame for post processng. In JVT-G012 [1], the algorthm of ntra-frame QP selecton s formulated as follows: 35, BP P L 1 25, L QP = 1 < BP P L 2 (1) 20, L 2 < BP P L 3 10, BP P > L 3 R BP P = (2) F W H where R s the assgned bt rate, F s the frame rate, and W and H connote mage wdth and heght, respectvely. The set of three parameters {L 1, L 2, L 3 } are predefned as {0.1, 0.3, 0.6} for QCIF vdeo sequences and {0.2, 0.6, 1.2} for CIF vdeo sequences, respectvely. However, unsutable BPP leads to uncontrollable bts allocaton and mage qualty because the mage content s not consdered. The large QP s selected n the formula (1) when a large budget R s appled n the formula (2). However, f the mage con- 228

A Novel Varance-Based Intra-Frame Rate Control Algorthm for H.264/AVC 7 tent s complex the QP should be slghtly reduced to mantan complete mage qualty. bts n the front vdeo sequence, the status of bts underflow occurs n the hnd vdeo sequence. Though the large number of bts s used to encode frames between the 1 st and 5 th frame when a small QP s appled, the ncrease n mage qualty s barely notceable. Durng the nterval between the 61 st and 99 th frame, the mage qualty s large reduced to balance the target bts budget, resultng n unsmooth vsualzaton. In summaton, the two drawbacks comprse the uncontrollable bts allocaton and notceable decay n mage qualty. Thus developng an effcent rate control algorthm for ntra-frame s an essental strategy. 3. Proposed varance-based ntra-frame rate control algorthm (a) Ths secton comprses three parts: the mean square error (MSE)-based dstorton measurement, the varance-based dstorton measurement performed va theoretcal deducton to analyze the dstorton property, and the varance-based ntra-frame rate control algorthm. 3.1. Analyss of MSE-based dstorton measurement Wang and Kwong [11] verfed the relaton between MSE and quantzaton step (Q step ). Obtanng Q step requres estmatng MSE from the prevous frame. A real applcaton equaton s expressed as follows: Q step = ρ MSE (3) where ρ s the varable for dfference vdeo sequences. To ft Q step estmaton more accurately, however, Yan and Wang [10] have proposed a gradentbased equaton to modfy the formula (3) as follows: Fgure 1. (b) Comparson of the bts consumpton and correspondng PSNR are shown n "News", "Brdge-close" and "Foreman" vdeo sequences. To prove the condton of unsutable QP estmaton n L et al. [1], the "News", "Brdge-close" and "Foreman" vdeo sequences n Fgure 2 are selected for evaluaton. For the man parameters comprsng 300 Kbps for the target bt rate, 30 fps frame rate, the encodng structure s IPPPPIPPPP, and JVT-G012 decdes the entre ntra-frame QP s constant by L et al. [1]. The presence of an unbalanced bt allocaton s worth notng. Because several frames consume more Q step = η MSE prev ( Gradcurr MG 1 BF prev + θ) + ε (4) 1 Buffer Sze Where η, θ and ε are varables for dfference vdeo sequences. MSE prev s the prevous frame MSE and BF prev s the prevous buffer fullness after encodng the th group of pcture (GOP). Grad curr s the gradent value of the current frame, and MG s the average gradent value of the prevously encoded I-frame n ths sequence. Accordng to varous encodng test sequences, the relatonshp between Q step and the gradent value s quas-lnear. Ths study also consders the buffer fullness to further mprove the 229

8 Fu-Chuang Chen, Y-Pn Hsu F. -C. Chen, Y. -P. Hsu QP estmaton and avod the buffer overflow or underflow. The mage complexty and bts buffer status are used to adaptvely modfy Q step because the MSE cannot accurately reflect QP estmaton. Accordng to the above analyss, the dstorton wll prmarly nfluence Q step the estmaton; thus, attemptng to dscuss the relaton between dstorton and QP becomes an mportant topc. Dstorton s performed va the quantzaton process n the vdeo encodng system. Accordng to the theoretcal defnton, the MSE can be expressed as follows: MSE x Quan ) 2 xcurr QP )2 ) 2 (1 QP 1 ) 2 (5) where N represents all the mage pxels, x Curr are the current mage and the quantzed and x Quan mage at the th pxel, respectvely. In the formula (5), the MSE s nfluenced by mage content and QP value. The ncrease n QP enlarges the MSE when the mage content s constant, and vce versa. 3.2. Deducton and analyss of the varance-based dstorton measurement The theorem n [9] provdes the orgnal defnton of the rate-dstorton form used n ths study. Ths secton dscusses several necessary aspects for enhanced modelng operaton. The relaton between rate (R) and dstorton (D) can be formulated as follows: R(D) = s D + Q(u) ln(λ(u))du (6) where s 0, d(u, v) s an error metrc measurement, D and λ(u) are defned as follows: D = λ(u) = [ λ(u)q(u)p (v)e sd(u,v) d(u, v)dudv P (v)e sd(u,v) d(u, v)dv] 1 (7) Consder a source, Q(u), that outputs an ndependent Gaussan random varable. The orgnal source can be treated as P (v), whch s also an ndependent Gaussan random varable, wth the assumpton that a squared-error dstorton measure s d(u, v) = (u v) 2. Suppose the terms σ and β represent the standard devaton of the output Q(u) and nput P (v) source, respectvely. Takng Q(u) and substtutng P (v), nto the formula (7) yelds the followng relaton: D = α2 β 2 α 2 + β 2 + ( α 2 α 2 + β 2 )2 α 2 (8) where α 2 = 1 2S. Therefore, α2 s drectly related to the parameter S, whereas β 2 s unrestrcted. Thus β 2 s chosen to satsfy α 2 + β 2 = σ 2, producng the followng relaton on S: D = α 2 = 1 2S The expresson for R(D) then becomes (9) R(D) = 1 2 ln(σ2 D ) (10) The formula (10) s a well-known equaton that can be expressed va the Taylor seres to perform a close-form equaton for QP estmaton n the current H.264 rate control scheme. Accordng to the aforementoned observatons n the formula (9), the dstorton s evdently arbtrarly varable. The condton α 2 +β 2 = σ 2 and the formula (9) lead to the followng equaton: D = σ 2 β 2 (11) The analytc result (11) s an analytc and novel equaton to estmate dstorton. Ths equaton s used to develop an effcent rate control algorthm. Ths study performs a new varance-based dstorton measurement. The formula (12) shows a detaled deducton process for evaluatng the dstorton: D = σ 2 β 2 M α ) 2 1 N M α ) 2 1 N (x Quan M β ) 2 QP M α ( xcurr M α ) 2 (1 QP 2 ) QP )2 (12) 230

where N comprses all the mage pxels, x Curr and x Quan are the current mage and the quantzed mage at the th pxel, respectvely. The terms M α and M β are the mean value of the current mage and quantzed mage. Ths dstorton, D, comprses two tems to compare wth the formula (5): the frst tem s the consderaton of the mage mean, and the other s the new QP equaton. 3.3. The study s proposed ntra-frame rate control algorthm In past approaches Wang and Kwong [11], the estmated QP could be obtaned va dstorton, and the relatve parameters are obtaned va pre-tranng, the man reason beng that the QP estmaton of the frst frame n the vdeo sequence s not referental to any frame. Although the MSE can reflect actual QP estmaton, the precson s not accurate. Due to ths reason, the mage content s consdered n Yan and Wang [10] for adaptve QP modfcaton. The tranng procedure requres the lnear relatonshp between QP and the dstorton, but the ntrnsc problem s not clearly dentfed. To compare the formulas (5) and (12), the man effect tem s QP for dstorton obtanment. Explanng the QP effect necesstates settng the bt rate to 400 kbps and the range of Q step from 6.5 to 64 (QP s between 20 and 40) to plot the relatonshp. Fgure 2 shows the selecton of two dfferent varables to present the gan magntude. Results demonstrate that the lnear mappng property n Gan1 s a better ft than Gan2, and the vbraton s also small because ths property can perform a more accurate QP estmaton n the tranng procedure than the nonlnear mappng property [12]-[14]. Thus, selectng a varance-based dstorton for QP estmaton s more sutable than selectng an MSE-based dstorton. When the varance-based dstorton utlzes ether of the two parameters, the lnear mappng property s also sustaned. The QP parameter s more sutable than Q step for constructng the quantzatondstorton (Q-D) relaton equaton, as follows: QP = γ D + δ (13) Where γ and δ are varables for dfference vdeo sequences. The formula (13) also ncludes the mage complexty through the varance nformaton to more accurately reflect the QP estmate. To ntegrate the ntra-frame QP estmaton n JVT-G012, the descrpton of the algorthm s represented as follows: f the nput frame s frst n the entre vdeo sequence, QP value estmaton can be acheved va the formula (1), restorng the reconstructed mage varance. If the nput frame s the frst frame n the next GOP, the ds- (a) (b) Fgure 2. Comparson of the dfference quantzaton gan s shown n two dfferent equatons: (a) usng the Q step varable, and (b) usng the QP varable. torton could be calculated va current frame varance and the prevous ntra-frame varance. Accordng to the dstorton, the estmated QP value can be obtaned by the formula (13). The QP estmaton for the nterframe s calculated by the JVT-G012 quadrc closeform, whch s also mplemented n JM15.0. A whole vew of the ntra-frame rate control s depcted n Fgure 3. 4. Expermental results Ths study used H.264/AVC reference software JM15.0 [9] to evaluate the proposed rate control algorthm. The conducted evaluaton requred usng the frst 100 frames of fve QCIF test sequences. The test 231

10 Fu-Chuang Chen, Y-Pn Hsu F. -C. Chen, Y. -P. Hsu Fgure 3. Integraton of JVT-G012 and varance-based ntra-frame rate control. target bt rate s 300 Kbps for " Foreman," and " News," and 400 Kbps for "Brdge-close," "Hghway," and "Grandma." Each sequence was coded at 15 fps accordng to the IPPPPIPPPP structure. The reference frame was set to 5, and the search wndow was set to 15. CAVLC, RDO, and rate control were also enabled. The study equally selected other relatve parameters for JM15.0 [1], Yan and Wang [10], and the proposed algorthm. To obtan the model parameters n the off-lne operaton, fve QPs were attempted, ncludng 20, 25, 30, 35, and 40 n the frst frame of the vdeo sequence, and ther respectve dstortons D were recorded. Va lnear regresson and recorded dstortons D, the good Q-D performance curve was constructed. Table 1 lsts the model parameters of γ and δ on varous test sequences. Fgure 4 shows the frame-by-frame PSNR comparson of three algorthms for the "Hghway" vdeo sequences. Snce the JVT-G012 algorthm n the ntra-frame QP estmaton s not adaptve, all the ntra-frames utlze the same QP. Yan and Wang [10] predcted that QP can sometmes be unsutable; for example, a dsadvantage s that the nter-frame only uses the large QP to preserve the target budget. Our proposed algorthm leads to mage qualty enhancement n the 65 th frame, 71 st frame, 75 th frame, 81 st frame, 85 th frame, 91 st frame and 96 th frame n Fgure 4 especally. The proposed algorthm sgnfcantly enhances the PSNR n ntra-frame and also holds sutable qualty n nter-frame when compared to JVT- G012 and Yan and Wang [10]. Fgure 5 dsplays the bts consumpton for "Foreman" and "News" test vdeo sequences. The fgure demonstrates that the proposed algorthm can mantan smoother and more sutable bts operaton than both JVT-G012 and Yan and Wang [10], because both use QP values whch are too small for prevous frames, consumng large numbers of bts. In our al- Fgure 4. PSNR comparson of JVT-G012, Yan and Wang [10] and our proposed algorthm on "Hghway" vdeo sequence. gorthm, bt allocaton s smoother, not only for ntraframes, but also for nter-frames because the ntraframe receves sutable QP and saves bt count for post nter-frame encodng. Our result sustans smooth mage qualty and s hghly sutable for lmted bandwdth networks. The proposed algorthm s more adaptve, producng smooth frame type changes, because t can adjust the QP by usng complexty measurements. Ths study adopts a formula n Wang and Kwong [5] to further evaluate the bt rate msmatch quantfcaton, as follows: R = R t R b R b 100% (14) where R t s the bt rate of the test algorthm and R b s the target bt rate. R represents the degree of msmatch n the produced bt rate, and the small R ndcates that the QP-produced bt rate s closer to the budget, and vce versa. Table 2 presents detaled numercal smulaton results, showng that the proposed algorthm can provde excellent performance, up to 0.19 db and 1.28 db better PSNR than JVT-G012 and Yan and Wang [10], respectvely, whle the output bt rate s also close to the target budget. Ths table also dsplays two gans, Gan 1 and Gan 2, to depct the performance mprovement over JVT-G012 and Yan and Wang [10], respectvely. Compared wth JVT- G012 and Yan and Wang [10], the proposed algorthm mproves results n all test sequences. These results show that the proposed algorthm produces lower R results than JVT-G012 for the News sequence. Table 2 also shows that the proposed algorthm s capable of controllng precson for the target bt rate. Moreover 232

A Novel Varance-Based Intra-Frame Rate Control Algorthm for H.264/AVC 11 Table 1. Model parameters of Q-D model wth dfferent vdeo sequences Vdeo Sequences γ δ Foreman 0.0465-67.3608 News 0.5885-40.2565 Brdge-close 0.4794-77.6881 Hghway 0.8383-135.2993 Gradma 0.9146-57.6692 can be appled to real-tme multmeda data streamng and can produce excellent mage qualty. (a) (a) (b) (b) Fgure 5. Bts consumpton comparson of JVT-G012, Yan and Wang [10] and the proposed algorthm, on two dfferent vdeo sequences: (a)"foreman" and (b)" News". the proposed algorthm presents better mage qualty than both JVT-G012 and Yan and Wang [10]. Furthermore, the bt rate varaton s near equal to JVT-G012 and Yan and Wang [10]. Thus, the proposed algorthm (c) Fgure 6. Vsual comparson of Yan and Wang [10] (left) and the proposed algorthm (rght) n three dfferent vdeo sequences: (a) "Foreman," (b) "News" and (c) "Hghway." The frame s n the 56 th, 91 st and 96 th locaton, from the top. Worth notng s that snce all the nter-frame QP estmates n Yan and Wang [10] are unsutable, the nter-frame should ncrease QP to balance the overall bts target. To further mprove fttng the algorthm to real vsualzaton applcaton, Fgure 6 shows the results of decodng frames wth the Yan and Wang [10] versus the proposed algorthm n three test vdeo sequences, the 56 th frame n "Foreman", the 91 st frame n "News," and the 96 th frame n "Hghway" respectvely. The movng objects nclude the face n Fgure 6(a), the dancer and reporter n Fgure 6(b), and 233

12 Fu-Chuang Chen, Y-Pn Hsu Table 2. F. -C. Chen, Y. -P. Hsu Performance of three algorthms n term of average PSNR, PSNR Std. devaton, bt rate and R Vdeo Sequences Method Average PSNR(dB) PSNR Std. Devaton Bt Rates (kbps) R Foreman JVT-G012 43.25 17.18 298.63 0.46 (300 kbps) [10] 42.87 18.17 298.97 0.34 Ours 43.39 17.16 298.34 0.55 Gan 1 +0.14 - - - Gan 2 +0.52 - - - News JVT-G012 47.26 19.09 299.50 0.17 (300 kbps) [10] 47.25 19.34 299.67 0.11 Ours 47.42 19.34 300.38 0.13 Gan 1 +0.16 - - - Gan 2 +0.17 - - - Brdge-close JVT-G012 41.76 16.48 399.81 0.05 (400 kbps) [10] 41.63 16.74 400.21 0.05 Ours 41.95 16.21 399.60 0.10 Gan 1 +0.19 - - - Gan 2 +0.32 - - - Hghway JVT-G012 44.23 17.58 400.08 0.02 (400 kbps) [10] 42.96 17.86 400.13 0.03 Ours 44.24 17.25 400.76 0.19 Gan 1 +0.01 - - - Gan 2 +1.28 - - - Gradma JVT-G012 47.93 19.45 400.69 0.17 (400 kbps) [10] 47.86 19.44 398.49 0.38 Ours 48.12 18.96 398.62 0.25 Gan 1 +0.19 - - - Gan 2 +0.26 - - - the road sgn n Fgure 6(c), though they are blurry, and the block effect s especally clear. The proposed algorthm can evdently mprove the mage qualty compared to the currently used algorthm. 5. Conclusons Ths paper presents a varance-based ntra-frame rate control for H.264/AVC. The purpose of ths paper s to make use of the advantage n the relatonshp between dstorton and QP, n order to develop a more effcent method for ntra-frame rate control. Expermental results show that the proposed algorthm can smultaneously mprove both the PSNR and the bt rate. Ths algorthm s also constructed on a one-pass scheme. Numerous smulaton results show that the proposed algorthm can also acheve a hgher average PSNR and lower bt rate msmatch. The balanced bt allocaton and control are sutable for strct network envronment. Thus, ths algorthm s better suted to H.264/AVC rate control than exstng algorthms. In further work, we shall attempt to develop an adaptve method for model parameter swtchng and dynamc tranng. References References [1] Z. L, F. Pan, and K. Lm. Adaptve basc unt layer rate control for JVT. n proc. Jont Vdeo Team (JVT) of ISO/IEC MPEG and ITU-T VCEG, JVTG012, 7th Meetng, Pattaya, Thaland, 2003. [2] T. Chang and Y. Q. Zhang. A new rate control scheme usng quadratc rate dstorton model. IEEE Trans. Crcut Syst. Vdeo Technol., 1997, 7, 246-250. [3] J. We, B. H. Soong and Z. G. L. A new ratedstorton model for vdeo transmsson usng multple logarthmc functons. IEEE Trans. Crcut Syst. Vdeo Technol., 2004, 11, 694-697. [4] Y. Lu, Z. G. L and Y. C. Soh. A novel rate control scheme for low delay vdeo communcaton of H.264/AVC standard. IEEE Trans. Crcut Syst. Vdeo Technol., 2007, 17, 68-78. [5] H. Wang and S. Kwong. Rate-dstorton optmzaton of rate control for H.264 wth adaptve ntal quantzaton parameter determnaton. IEEE Trans. Crcut Syst. Vdeo Technol., 2008, 18, 140-144. [6] M. Jang and N. Lng. Low-delay rate control for real-tme H.264/AVC vdeo codng. IEEE Trans. Multmeda, 2006, 8, 467-477. [7] M. Wang and B. Yan. Lagrangan Multpler Based Jont Three-Layer Rate Control for H.264/AVC. IEEE Sgnal Process. Lett., 2009, 16, 679-682. [8] D. K. Kwon, M. Y. Shen and C. C. Jay Kuo. Ratecontrol for H.264 vdeo wth enhanced rate and dstorton models. IEEE Trans. Crcut Syst. Vdeo Technol., 234

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