Kỹ thuật giảm lỗi lan truyền cho mã hóa video theo chuẩn h 264 dựa trên kỹ thuật FMO và kỹ thuật mã hóa intra

Tap chi Khoa hoc v^ Cong nghe 102 (2014) 050-056 A Novel Technique in Error Propagation Resilience for H.264 Video Coding Based on FMO and Intra Refresh Rate Ky thuat giam 16i Ian truyin cho ma hoa video theo chuSn H.264 diia tren ky thu^t FMO va ky thuat ma hoa Intra Dang Hoai Bac^*, Vu Huu Tien^ ' Electronics Engineering Department, Posts and Telecommunications Insntute ofTechnology, Hanoi Viet Nam ^ Multimedia Department, Posts and Telecommunications Institute ofTechnology Hanoi, Viet Nam Received: April 22, 2014; accepted- August 25 2014 Abstract In video coding, due to the references to neighboor frames while coding the current frame, if there is an error occuring in a neighboor frame, the current frame will be affected This error propagation phenomenon is one of issues in video coding needs to be resolved In this work, we propose an error resilience scheme for wireless video coding based on adaptive Frexible Macroblock Ordering (FMO) and intra refresh FMO explicit map is generated frame-by-frame using the estimated prior information The prior information involves the estimation of locations of guards and bursts of errors in the channel using three-state markov model and the estimation of the error propagation effects (EEP) from the current to the next frame Intra refresh is also used to reduce the dependency between frames therefore could stop error propagation ami a suitable intra refresh rate is selected based on channel state to reduce the effect of error propagation Experimental results show that our proposed method gains some improvements in terms of PSNR as compared to some other methods that have not taken channel condition and error propagation into consideration in generating FMO map Keywords: H,264, FMO, Intra Refresh Tom tat Trong qua trinh ma hoa tin hieu video, ma hoa mot khung thi khung hinh lan can dcrac tham chiiu S udc luiyng chuyin dong va dir doan khung hinh hien tai Vi vay tnrdng hap khung hinh tru^ bi loi thi khung hinh hien tai cung se bi anh hudng Hien tuang dirac goi la lan truyin loi giira cac khung hinh Trong bai bao nay, thuat toan dira tren ky thuat FMO va ky thuat ma hoa Intra coding dwac de xuat nhim giam anh hiK/ng cua idi lan truyin truyin tin hi§u video qua mang vo tuyin Thuat toan sifdiing phuong phap tao sa dd FMO cho tCrng frame dua tren viec du doan trang thai kenh truyin Di tao sa FMO, muc anh hudng cua Idi truyin lan duac su' diing di danh gia mire dd quan trt^ng cua tCrng /c/ioi anh khung hinh hi^n tai Dua v^o md hinh Markov ba trang thai, tr^ng thai kenh truyin duv^c du doan Cac khoi anh quan cua khung hinh se dwac truyin di kenh truyin d trang thai tot C^c kti6i anh it quan han dwac truyin di kenh truyin a trang thai bi anh htrang nhiiu bai fading Ngoai ra, mot s6 khdi anh quan nhit khung hinh se dtrac ma hda a chi Intra coding Kit qua rr\o phong da chi ring thuat toan dtrac di xuit cho hinh anh chat Iwang video sau giai m§ tdt han mot so thuat toan trwdc dd khdng xet din tinh trang idi truyin lan va tinh trang cua kenh truyin Ju khoa: H 264, FMO, Intra Refresh Introduction number of slice groups is limited to for each picture FMO [1], one ofnew techniques in H.264/AVC standard [2], is proposed with the aitn at reducing burst errors while transmitting video signal over error prone channel, FMO consists of deciding on which shce each macroblock of the image belongs Each macroblock can be assigned freely to a slice group using an MBAmap (MacroBlock Allocation map) Tbe MBAmap consists of an identification number for each macroblock of tbe image that specifies on which slice group that macroblock belongs The ' ° """""^ ""P''" ' ' " o ' : " " " " schemes B, ^ " ^ " " E » s " ' ^ " ' ^ MBAmap, the error MBs m fr"™ » « dispersed Consequently, the end concealment algonthm in decoder can recover the lost information from neighboring MB that is -^ In the previous approaches, to design slice group maps, an indicator is used to define the importance of an MB The indicators may be MB impact factor [1] and bh count [3], In these methods, a simple way is used to generate FMO map in which MBs with h i ^ importance are arranged consequently to slice groups However, it's not guaranteed that important * Corresponding author Tel: (+84) 903.284.728 Email' bacdh@ptit,edu Tap chi Khoa hoc va Cong nghe 102 (2014) 050-056 MBs are protected from error Due to variable length coding in a shce, if an MB standing before important MBs IS error, tbe next MBs are also affected Therefore these methods can only reduce number of loss important MBs In video coding, error propagation occurs due to the relationship between frames in a slice group To stop error propagation effectively, intra refresh algorithm is used However, the selecting a suitable intra refresh rate is a problem needed to be considered Intra MBs can effectively stop error propagation, but the number of intra MBs in a frame is limited by compression efficiency Coding efficiency will be reduced if the mfra refresh rate is high because of rate-distortion optimization Moreover, with limited target bit rate allocated for each frame, a frame with high number of intra MBs consumes high target bit and thus affects to the target bit of next frames Thus, it is necessary lo balance the benefit of reducing error propagation effect and the drawback of using a high number of intra coded MBs in a frame In the proposed method, instead of using model in bit level, three-state Markov model in packet level is used Figure I shows an example of the packet sequence for an error chaimel We define the following defmitions at packet level, similar to [6], [7] A guard section is defined as an error-free section and a burst section is defined as the section sandwiched between guard sections The minimum guard length is tbe minimum length of a guard section In this work, the minimum guard length of 10 packets is used as a result from empirical studies Thus, each guard section must be longer than ten consecutive error-free packets The run length is defined as a length from an error packet to the next error packet excluding the first error packet The first return probability P(t) is defined as the occurrence probability of each run length ( and the cumulative first return probability is obtained as the cumulation of the first return probability |< ft ' 0 0 0 - 0 i|oooooi|i|aoi Burst lens tti 0' Correcl packet Error packet There exist some researches focusing on resolving intra refreshment in the previous studies In [4], a fix number of MBs with the highest distortion in the current frame will be coded in intra mode Another study in [5] chooses the suitable MBs for intra coding by computing cost for each type of coding mode However, the algorithm has to try all possible mtra and inter modes and thus may cause delay in real-time appheations In this work, the method of FMO map generation in [8] is referred However, the method for estimating importance of MB is improved to evaluate MB more exactly The final results of proposed method are compared with the results in [8] to show the evidence of improvement The remainder of the paper is organized as follows Three-state Markov model and proposed method to estimate positions of guard and burst sections are introduced in Section II Section III presents the proposed method to generate FMO explicit map Section IV provides the simulation results and discussions Finally, conclusions are given on Section V Error Burst Location Estimation 2.1 Three-state Markov Fig Packet sequence for an error charmel Fig.2 Three-state Markov Model Figure shows the transition probabilities of a three-state Markov model where C; and Cz show error-free states which are state and state 2, and E shows the error state which is state Ci shows errorfree state in a guard section while C2 and E show error-free and error state in a burst section p„„i is probability of transition from state n to state m p„,„''^ is the probability of the case in which there are (i-2} consecutive transitions from state n to state n The first return probabilities are computed as shown in Eq.(I), ni) =p