COMPUTATIONAL COMPLEXITY REDUCTION OF INTRA-FRAME PREDICTION IN MPEG-2/H.264 VIDEO TRANSCODERS Gerardo Fern ndez-Escribano, Pedro Cuenca, Luis Orozco-Barbosa and Antonio Garrido Instituto de Investigacin en Infor tica Universidad de Castilla-La Mancha, Ca pus Universitario, 02071 Albacete, SPAIN ,gerardo,pcuenca,lorozco,antonio-.info-ab.ucl .es ABSTRACT 1 :ualit1 video at about 1/3 to 1/2 of the bitrates offered b1 the MPEG-2 is the most widely digital video-encoding standard in MPEG-2 for at. 2hese significant band0idth savings open the use nowadays. It is being widely used in the development and ar5et to ne0 products and services, including 6423 services deployment of digital T services, D D and video-on-demand at lo0er bitrates. Further ore, given the relativel1 earl1 stage of services. However, recent developments have given birth to the video services in obile phones, obile phones 0ill be one of H.264/A C, offering better bandwidth to video )uality ratios the first ar5et seg ents to adopt 6.278 video. 6o0ever, these than MPEG2. It is expected that the H.264/A C will take over gains co e 0ith a significant increase in encoding and decoding the digital video market, replacing the use of MPEG-2 in most co pleAit1 ,3-. digital video applications. The complete migration to the new Bhile the 6.278 video standard is eApected to replace video-coding algorithm will take several years given the wide MPEG-2 video over the neAt several 1ears, a significant a ount scale use of MPEG-2 in the market place today. This creates an of research needs to be done in developing efficient encoding important need for transcoding technologies for converting the and transcoding technologies. 2he transcoding of MPEG-2 video large volume of existent video material from the MPEG-2 into to 6.278 for at is particularl1 interesting given the 0ide the H.264 format and vice versa. However, given the significant availabilit1 and use of MPEG-2 video no0ada1s. Further ore, differences between the MPEG-2 and the H.264 encoding there is a clear industr1 interest in technologies facilitating the algorithms, the transcoding process of such systems is much igration fro MPEG-2 to 6.278. 2he coeAistence of these more complex to other heterogeneous video transcoding technologies until the co plete adoption of 6.278 creates a need processes. In this paper, we introduce and evaluate a novel for technologies to transcode fro the MPEG-2 into the 6.278 intra-frame prediction algorithm to be used as part of a high- for at and vice versa. 6o0ever, given the significant differences efficient MPEG-2 to H.264 transcoder. ,ur evaluation results bet0een the MPEG-2 and the 6.278 coding algorith s, show that the proposed algorithm considerable reduces the transcoding is a uch ore co pleA tas5 co pared to the tas5 complexity involved in the intra-frame prediction- a key involved in other heterogeneous video transcoding architectures operation in the transcoding process. ,8-8-. 2he 6.278 e plo1s a h1brid coding approach si ilar to that of MPEG-2 but differs significantl1 fro MPEG-2 in ter s of 1. INTRODUCTION the actual coding tools used. 2he ain differences areC 1D use of an integer transfor 0ith energ1 co paction propertiesE 2D an No0ada1s, the MPEG-2 video coding for at ,1- is being 0idel1 in-loop debloc5ing filter to reduce bloc5 artifactsE 3D ulti-fra e used in a nu ber of applications fro digital 23 s1ste s to references for inter-fra e predictionE and 8D intra-fra e video-on-de and services. 2he use of MPEG-2 technolog1 prediction. 2he 6.278 standard introduces several other ne0 represents billions of dollars of invest ent in the MPEG-2 coding tools ai ing to i prove the coding efficienc1. infrastructure alread1 or currentl1 being deplo1ed. In this paper, 0e focus our attention on the intra-fra e 4uring the last fe0 1ears, technological develop ents, such predictionC one of the ost stringent tas5s involved in the as novel video coding algorith s, lo0er e or1 costs, and encoding process. A co plete overvie0 of the 6.278 can be faster processors, are facilitating the design and develop ent of found in ,9-. 2he rest of the paper is organized as follo0s. highl1 efficient video encoding standards. A ong the recent Section 2 provides a brief overvie0 of the intra-fra e prediction 0or5s in this area, the 6.278 video encoding standard, also process used b1 the 6.278 encoding standard. In Section 3, 0e 5no0n as MPEG-8 A3C occupies a central place ,2-. 2he 6.278 introduce a fast intra-fra e prediction algorith suitable for the standard, 9ointl1 developed b1 the I2U-2 and the MPEG transcoding of MPEG-2 into 6.278. In Section 8, 0e carr1 out a co ittees, is highl1 efficient offering perceptuall1 e:uivalent perfor ance evaluation of the proposed algorith in ter s of its co putational co pleAit1 and rate-distortion results. Finall1, 2his 0or5 0as supported b1 the Ministr1 of Science and 2echnolog1 of Spain under Section 5 concludes the paper. CICY2 pro9ect 2IC2003-08158-C07-02, the Council of Science and 2echnolog1 of Castilla-La Mancha under pro9ect PBC-03-001 and FE4ER. 0-7803-9332-5/05/$20.00 ©2005 IEEE 2. INTRA -FRAME PREDICTION IN H.264 3. SPEEDING -UP THE INTRA -FRAME PREDICTION 6.278 incorporates into its coding process, an intra -picture prediction (defined 0ithin the piAel do ainD 0hose ain ai is to i prove the co pression efficienc1 of the intra -coded Our approach si plifies the intra -fra e prediction b1 a5ing pictures and intra -MBs. Intra prediction can result in significant use of the 4C coefficients available fro the decoding process savings 0hen the otion present in the video se:uence is of the MPEG -2. 6o0ever, due to the presence of t0o different ini al and the spatial correlations are significant. 2hroughout sizes of bloc5 s used b1 the 6.278, na el1 8 x8 and 17 x17, and the paper, 0e 0ill illustrate the principle of ope ration of the that the MPEG -2 standards use bloc5s of 8 x8, the evaluation of intra -fra e prediction odes as applied to the lu inance bloc5s. the prediction ode involves and inter ediate scaling process. It is understood that a si ilar procedure has to be applied to the In the follo0ing, 0e describe one b1 one the ain steps of our chro inance bloc5s. algorith . Bhile acro bloc5s (MBD of 17 x17 piAels are still used, St p 1: predicting a MB fro the previou sl1 encoded MBs in the sa e picture is ne0 in 6.278. An MB a1 a5e use of 8 x8 and 17 x17 In an MPEG -2/6.278 video transcoder, once having decoded the bloc5 prediction odes, referred to as Intra_8 x8 and MPEG -2 video, besides the unco pr essed video, the 4C Intra_17 x17, respectivel1. 2here are nine 8 x8 possible bloc5 coefficient of the 8A8 bloc5s is readil1 available to the 6.278 prediction directions and four 17 x17 bloc5 prediction directions. video encoder. Since the MPEG -2 a5es use of onl1 8 x8 bloc5 s, Figure 1 depicts the nine and four prediction directions for the 0e need to devis e a echanis allo0ing us to properl1 co pute 8A8 and 17A17 prediction odes, respectivel1 . 2hese intra the 4C coefficients of the 8x8 and 17 x17 bloc5s. Figures 1a and prediction odes include a directional prediction greatl1 1b depict the procedure for co puting the 4C coefficients of the i proving the prediction in the presence of directional four 8 x8 bloc5s and the one associated to the 17 x17 bloc5. structures. Bith the intra -fra e prediction, th e I -pictures can be encoded ore efficientl1 than in MPEG -2, 0hich does not support intra -fra e prediction. Inverse I age space 4C2 4C2 do ain 8A8 8A8 bloc5 8 8A8 bloc5 (aD 8A8 bloc5 8A8 bloc5 Inverse I age space 4C2 4C2 do ain 17A17 17A17 bloc5 8A8 bloc5 8A8 bloc5 (bD (aD Figure 2. Straightfor0ard ethod. (aD 8 x8. (bD 17 x17. As seen fro Figure 2 a, the process to obtain the four 8 x8 bloc5s involves first appl1ing the inverse 4C2 to each 8 x8 bloc5 of the decoded MPEG -2 picture. 2his step regenerates the 8 x8 bloc5 in the spa ce do ain. 2hen, the 4C2 has to be applied to each 8A8 bloc5 in order to obtain the 4C coefficients of each (bD one of the . 2his process has to be applied to each and ever1 Figure 1. Prediction Modes. (aD 8 x8 bD 17 x17. 8x8 bloc5. In order to speed -up this process, 0e propose using the follo0ing resoluti on conversion ethod introduced in ,10-C For each MB, one prediction ode and one prediction T direction is 5ept. 2he 6.278 encode r selects the best /0 1 2 A / 1A (1D co bination ode/direction b1 using the .um of Absolute Errors (SAED. 2his i plies, that for each eAisting direction of each ode, the predictor 0ithin the piAel -do ain is created fro 0.71 0.78 0 0.22 0 0.15 0 − 0.13 the boundar1 piAels of the current partition and the SAE costs 0 0.29 0.71 0.56 0 − 0.25 0 − 0.20 are evaluated. 2he best co bination of ode/direction is 0 − 0.05 0 0.36 0.71 0.54 0 − 0.27 deter ined corresponding to the one eAhibiting the ini u 0 0.02 0 − 0.07 0 0.35 0.71 0.61 A = SAE cost.