摘要
信息化社会的到来以及IP技术的兴起,正深刻的改变着电信网络的面貌以及未来技术发展的走向。无线通信技术的发展为实现数字化社区提供了有力的保证。而视频通信则成为多媒体业务的核心。如何在环境恶劣的无线环境中,实时传输高质量的视频面临着巨大的挑战,因此这也成为人们的研究热点。
对于无线移动信道来说,网络的可用带宽是有限的。由于多径﹑衰落﹑时延扩展﹑噪声影响和信道干扰等原因,无线移动通信不仅具有带宽波动的特点,而且信道误码率高,经常会出现连续的﹑突发性的传输错误。无线信道可用带宽与传输速率的时变特性,使得传输的可靠性大为降低。
视频播放具有严格的实时性要求,这就要求网络为视频的传输提供足够的带宽﹑有保障的延时和误码率。为了获得可接受的重建视频质量,视频传输至少需要28Kbps左右的带宽。而且视频传输对时延非常敏感。然而无线移动网络却无法提供可靠的服务质量。基于无线视频通信面临的挑战,本文在对新一代视频编码国际标准H.264/AVC研究的基础上,主要在提高其编码效率和H.264的无线传输抗误码性能,以及如何在嵌入式环境下实现H.264解码器进行了研究。
结合低码率和帧内刷新,提出一种针对感兴趣区的可变帧内刷新方法。实验表明该方法可以使用较少的码率对感兴趣区域进行更好的错误控制,以提高区域图像质量,同时能根据感兴趣区及信道的状况自动调整宏块刷新数量,充分利用有限的码率。
为了有效的平衡编码效率和抗误码能力的之间的矛盾,笔者提出了一种自适应FMO(Flexible Macroblock Order)编码方法,可根据图像的复杂度自适应地选择编码所需的FMO模式。仿真结果表明这种FMO编码方式完全可行,且在运动复杂度频繁变化时效果更加明显,完全可应用在环境恶劣的无线信道中。
在对嵌入式PXA270硬件结构和X264研究的基础上,基本实现了基于H.264的嵌入式解码,在PXA270基础上进行环境的配置,定制WinCE操作系统,并编译、产生开发所用的SDK和下载内核到目标机。利用开发工具EVC实现在PC机上的实时开发和在线仿真调试,最终实现了对无差错H.264码流实时解码。
The advent of information society, as well as the emergence of IP technology, are profoundly changing the face of telecommunications networks and the future direction of technology development. Wireless communication technologies provide strong pledge for the realization of the development of digital communities. Video communication is the kernel of multimedia operation. The transmission of video content over wireless networks poses big technical challenge duo to the specific characteristics of wireless channel such as bad environment, so it becomes a hotspot for the research.
For the wireless channels, the available bandwidth is limited. Due to the multipath effect, multipath delay, multipath fading and some other reasons , the mobile communication has the characteristics that its bandwidth is undulate and high bit error rate, so some continuous and gusty error of transmission usually appears. The reliability of the transmission decrease because of the available bandwidth and the transmission rate are time-variant.
Video display needs well timeliness, this requires the sufficient bandwidth、guaranteed time lag and the bit error rate. In order to replay the video , we need at least 28 Kbits bandwidth. Video transmission is very sensitive to the time lag. But mobile network couldn’t provide credible services.
Based on the challenge of the wireless video communication, this paper dose some research on the H.264 , especially on how to well control error diffuseness and improve coding efficiency as well as how to realize the H.264 decoding on ARM platform.
In wireless communication system, there are many great challenges in transforming reliable video signals. So, how to effectively control bits error becomes urgent and significant. In this method is proposed to control bits error in low bit rate wireless transmission system. This method can use less overhead bits to control bits error of the interesting areas to improve the quality of the area of the image, and can automatically adjust the number of MB( Macroblock ) to make fully use of the limited bits rate according to the location, the size , and the shape of the interesting area.
In order to effective balance contradiction between coding efficiency and the anti-error code ability, the author proposed one auto-adapted FMO code method; could auto_adapted and choice FMO encoding pattern needed according to the image complexity.The simulation result indicated that this FMO encoding method is completely feasible, especially the effect is more obvious when movement complexity frequent change.It can apply in the bad wireless channel environment.
Based on the research on the hardware of the PXA270 and the X264, we basically realized decoding process on ARM platform. Do some environment setting on PXA270,customize WinCE Operation System,compile,produce SDK for application exploitation and download kernel into target ship. make use of exploit tool EVC ,make application program realtime and debug on line, finally realized realtime decoding for no error H.264 code.
引文
[1]毕厚杰,新一代视频压缩编码标准[M]. H.264/AVC人民邮电出版社. 2005(1): 197-198
[2] Thomas Wiegand and Gary J. Sullivan et al. Overview of the H.264/AVC video coding standard [J]. IEEE Transactions on Circuits and Systems for Video Technology, 2003,13(7):560-576
[3] Gary J. Sullivan, Pankaj Topiwala and Ajay Luthra. The H.264/AVC Advanced Video Coding Standard: Overview and Introduction to the fidelity range extensions [J].SPIE Conference on Applications of Digital Image Processing, 2004.
[4]候勇,赵巍,吐尔根·伊布拉音.视频编码标准H.264的主要技术特点及其应用前景[J].中国科技信息.2005,(10): 48～51
[5] Thomas Stockhammer, Miska M. Hannuksela, Thomas Wiegand. H.264/AVC in Wireless Environments[J]. IEEE Trans. on Circuits and Systems for Video Technology. 2003, 7:13～17
[6]王丽丰,牛建伟,肖晨等.基于H.264无线视频传输系统的研究.计算机应用与软件[J]. 2005,10:139～141
[7] T.Stockhammer,M.Hannuksela,S. Wenger.H.26L/JVT Coding Network Abstraction Layer and IP-based Transport[J]. IEEE ICIP, Rochester, NewYork, 2002,2:485～488
[8] Wenger, Stockhammr T,Hannuksemm M. H.264 over IP Framework[S]: Proposal H.264 NAL Normative Text. ITU-T VCEG-N72r1, VCEG(SG16/Q6).14th Meeting: Santa Barbara. CA, USA. 2001
[9]王文生,崔慧娟,唐昆.H.264前向/后向联合视频差错控制算法[J].清华大学学报.2005,(7):939～942
[10] Tihao Chiang,Ya-Qin Zhang.A New Rate Control Scheme Sing Quadratic Rate Distortion Model[J]. IEEE Trans.Circuit and Systems for Video Technology. 1997, 2(7):55～59
[11] R.Talluri,Y.Nag,G.Cheung.Error Concealment by Data Partitioning[J]. Signal Processing: Image Communication.1999,5(14):505～518
[12]周睿,崔慧娟,唐昆.高效的H.264时域误码掩盖算法[J].清华大学学报. 2005,(7):900～903
[13] Lius Ducla-Soares,Fernando Pereira.Error Resilience and Concealment Performance for MPEG-4 Frame-based Video Coding[J]. Signal Processing: Image Communication.1999,(14):447～472
[14] M.Flierl,B.Girod.Generalized B Picture and the Draft H.264/AVC Video Compession Standard.Trans.CSVT.2003,(13):587～597
[15] Jianfei Cai, et al. Error resilient video coding techniques[J]. IEEE Signal Processing Magazine, 2000,17(4):61~62
[16] Podolsky M, Vetterli M and McCanne S. Limited retransmission of real-time layered multimedia[J]. Processings of the IEEE Workshop on Multimedia Signal Processing, 1998, 591~596
[17] ITU-T, Draft for“H.263++”.Annexes U, V, and W to Recommendation H.263[J], 2000
[18] D.Chung, et al. Multiple description image coding using signal decomposition and reconstruction based on lapped orthogonal transforms[J]. IEEE Transaction on Circuits and Systems for Video Technology, 1999, 9(6):895~908
[19] Kwon D, et al. Error concealment techniques for H.263 video transmission[J]. IEEE Pacific Rim Conference on Communications, Computers and Signal Processing, 1999,276~279
[20] Brailean J. Wireless multimedia utilizing MPEG-4 error resilient tools[J]. Wireless Communications and Networking Conference,1999,104~108
[21] Wenger S, Knorr G, Ott J and Kossentini F. Error resilient support in H.263++[J]. IEEE Transactions on Circuits and Systems for Video Technology, 1998, 8(6):867~877;
[22] Moccagatta I, et al. Error-resilient coding in JPEG-2000 and MPEG-4[J]. IEEE Journal on Selected Areas in Communications, 2000, 18(6):899~914
[23] Ihidoussene D, et al. An unequal error protection using reed-solomn codes for real-time MPEG-4 video stream[J]. IEEE International Conference on High Speed Networks and Multimedia Communications, 2002, 254~258
[24] Martini M G, Chiani M. Proportional unequal error protection for MPEG-4 video transaction[J]. IEEE International Conference on Communications, 2001, 1033~1037
[25] Liao J and Villasenor J. Adaptive Intra Update for Video Coding over NoisyChannels[J]. Processing of ICIP, 1996, 3:763~766
[26]李勃,卓力,沈兰荪.基于Intra帧刷新的差错控制新方法[J].电路与系统学报. 2005年第10卷第6期
[27] Michael Gallant. Rate-Distortion optimized layered with unequal error protection for robust Internet video[J]. IEEE Transaction on Circuits and Systems for Video Technology, 2001, 11(3):357~372
[28] Horn U, Stuhlmuller K W, Link M and Girod B. Robust internet video transmission based on scalable coding and unequal error protection[J]. Signal Processing: Image Communication, 1999, 15(1~2):77~94
[29] Aravind R, et al. Packet loss resilience of MPEG-2 scalable video coding algorithms[J]. IEEE Transactions on Circuits and System for Video Technology, 1996, 6: 426~435
[30] Kondi L P, Ishtiaq F and Katsaggelos A K. Joint source-channel coding for motion-compensated DCT-based SNR scalable video[J]. IEEE Transactions on Image Processing, 2002, 11(9)1043~1052
[31] Cheung Gene and Zakhor A. Bit allocation for joint source/channel coding of scalable video[J]. IEEE Transaction on Image Processing, 2000, 9(3): 340~356
[32] Qian Zhang, Wenwu Zhu and Zhang Y-Q. Network-adaptive scalable video streaming over 3G wireless networks[J]. IEEE International Conference on Image Processing, 2001, er. nj. nec.2003
[33] Hong Man, et al. A family of efficient and channel error resilient wavelet/subband image coders[J]. IEEE Trans. On Circuits and Systems for Video Tech, 1999, 9(1):95~108
[34] Fredrik Ydenius. Scalable coding of video over IP-based networks. HTTP://citeseer. nj.nec, 2003
[35] Ramchandran K, Ortega A, et al. Multiresolution broadcast for digital HDTV using joint source-channel coding[J]. IEEE Journal on Selected Areas in Communication, 1993,11: 6~23
[36] Belzer B, Villasenor J D and Girod B. Joint source-channel coding of Images with trellis coded quantization and convolutional codes[J]. IEEE International Conference on Image Processing Letters, 1997, 4:72~81
[37] Lan T H and Tewfik A H. Power optimized mode selection for H.263 video codingand wireless communications[J]. IEEE International Conference on Image Processing, 1998, 113~117
[38] Pei Y and Modestino JW. H.263+ packet video over wireless IP networks using ratecompatible punctured turbo(RCPT) codes with joint source-channel coding[J]. IEEE International Conference on Image Processing, 2002, 541~544
[39] Bystrom M and Modestino J W. Combined Source-Channel Coding Schemes for Video Transmission over an Additive White Gaussian Noise Channel[J]. IEEE Journal on Selected Areass in Communications, 2000, 18(6):880~890
[40] Zhi Hai He, Cai J F and Wen C C. Joint source channel rate-distortion analysis for adaptive mode selection and rate control in wireless video coding[J]. IEEE Transactions on Circuits and Systems for Video Techology, 2002, 12(6):511~523
[41] Yao Wang, et al.视频处理与通信[M].侯正信等译.北京:电子工业出版社,2003
[42] Bhattacharyya K, et al. DCT coefficient-based error detection technique for compressed video stream[J]. IEEE International Conference on Multimedia and Expo, 2000,3: 1483~1486
[43] Sun H and Kwok W. Concealment of damaged block transform coded images using projections onto convex sets[J]. IEEE Transaction on Image Processing, 1995,4: 470~477
[44]王丽丰,牛建伟,肖晨等.基于H.264无线视频传输系统的研究[J].计算机应用与软件,2005,22(10):139-141.
[45]万里晴,李学明. H.264的差错控制与错误隐藏技术研究[J].计算机工程与应用,2007,43(16):53-57.
[46] Wenger S. H.264/AVC over IP[J].IEEE Trans Cir Syst Video Technol,2003,7(13):645-656.
[47] Wenger S,Horowitz M,Scattered slices:a new error resilience tool for H.26L,JVT-B027[S].2002-02.
[48] Valente S,Dufour C. An efficient error concealment implementation for MPEG-4 video streams[J]. IEEE Trans Consumer Electronics,2001,47(8):568-578.
[49]谢治平,郑更生.一种基于FMO的H.264容错编码[J].计算机工程与应用, 2006(31):200~2003.
[50] Wenger S,Horowitz M,Scattered slices:a new error resilience tool for H.26L,JVT-B027[S].2002-02.
[51]林都平,艾达. 3G视频传输中的抗误码技术研究[J].移动通信, 2004(9):68-71.
[52]王俊生.视频编码新标准H.264中抗误码技术的研究[J].中国有线电视, 2004(19/20): 15-18.
[53] Hannuksela M M,Wang Y K,Gabbouj M,Isolated regions in video coding[J]. IEEE Trans Multimedia,2004,6(2):259-267.
[54] Im S K,Pearmain A J. Unequal error protection with the H.264 flexible macroblock ordering[C]//Proc SPIE VCIP.Beijing,China:[s.n.],2005:1033-1040
[55]默罕莫德·默森,沈连丰,嵌入式视频监控服务器硬件设计与实现[D].东南大学. 2005: 43-46
[56]左书涛,马洪连.基于嵌入式系统的视频编码器的研究与实现[D].大连理工大学2006 :50-51