一种提高MPEG-4解码器性能的错误定位技术

提出一种基于MPEG-4标准容错措施反向可变长编码RVLC（Reverse variable length coding）的错误发现定位方法（Improved RVLC,IRVLC）.IRVLC方法充分利用数据帧的局部信息,对I帧和P帧采用不同的错误再定位策略,克服了标准RVLC策略对可能错误宏块进行保守性丢弃的缺点.IRVLC通过一个适应函数对RVLC不能恢复的宏块进行错误再定位性选择,减少丢弃标准RVLC策略定位范围中的错误宏块数,从而缩小错误扩散的区域,提高解码质量.通过与标准RVLC方法比较可得,IRVLC方法得到了较好的解码质量,平均峰值信噪比（Peak signal-noise rate,PSNR）提高了1～2 dB,证明了IRVLC方法的有效性,且与MPEG-4标准完全兼容.     

Recovering Connected Error Region Based on Adaptive Error Concealment Order Determination

Parts of compressed video streams may be lost or corrupted when being transmitted over bandwidth limited networks and wireless communication networks with error-prone channels. Error concealment (EC) techniques are often adopted at the decoder side to improve the quality of the reconstructed video. Under the conditions of a high rate of data packets that arrives at the decoder corrupted, it is likely that the incorrectly decoded macro-blocks (MBs) are concentrated in a connected region, where important spatial reference information is lost. The conventional EC methods usually carry out the block concealment following a lexicographic scan (from top to bottom and from left to right of the image), which would make the methods ineffective for the case that the corrupted blocks are grouped in a connected region. In this paper, a temporal error concealment method, adaptive error concealment order determination (AECOD), is proposed to recover connected corrupted regions. The processing order of an MB in a connected corrupted region is adaptively determined by analyzing the external boundary patterns of the MBs in its neighborhood. The performances, on several video sequences, of the proposed EC scheme have been compared with those obtained by using other error concealment methods reported in the literature. Experimental results show that the AECOD algorithm can improve the recovery performance with respect to the other considered EC methods.      

A data embedded video coding scheme for error-prone channels

We propose a novel data embedding scheme for fractional-pixel based video coding algorithms such as H.263 and MPEG-2. By modifying the motion estimation procedure at fractional-pixel precision, two bits data can be embedded in a motion vector (MV) for an inter-mode coded macroblock (MB). For half-pixel precision motion estimation, the resulted bitstream is compatible with the current video coding standards. Performance of the proposed data embedding scheme in terms of compression efficiency is also studied. As an application example of the proposed data embedding scheme, an error-resilient video coding scheme is also presented where some redundant information, which is used to protect MVs and coding modes of MBs in one frame, is embedded into the MVs in the next frame. When errors occur in one group of blocks (GOB), the decoder can exactly recover the MVs of the corrupted GOB if the next frame can be received correctly. Simulations show that the proposed scheme has better performance than standard H.263 coding scheme for transmission over error-prone channels     

Header Detection to Improve Multimedia Quality Over Wireless Networks

Wireless multimedia studies have revealed that forward error correction (FEC) on corrupted packets yields better bandwidth utilization and lower delay than retransmissions. To facilitate FEC-based recovery, corrupted packets should not be dropped so that maximum number of packets is relayed to a wireless receiver's FEC decoder. Previous studies proposed to mitigate wireless packet drops by a partial checksum that ignored payload errors. Such schemes require modifications to both transmitters and receivers, and incur packet-losses due to header errors. In this paper, we introduce a receiver-based scheme which uses the history of active multimedia sessions to detect transmitted values of corrupted packet headers, thereby improving wireless multimedia throughput. Header detection is posed as the decision-theoretic problem of multihypothesis detection of known parameters in noise. Performance of the proposed scheme is evaluated using trace-driven video simulations on an 802.11b local area network. We show that header detection with application layer FEC provides significant throughput and video quality improvements over the conventional UDP/IP/802.11 protocol stack     

Robust transmission of scalable video stream using modified LT codes

LT codes are convenient and popular kind of rateless codes that could easily tolerate different patterns of loss in erasure channels. In this paper an LT code with unequal packet protection (UPP) property is proposed. The proposed code could provide unequal packet recovery to any importance-sorted data packets. Simulation results indicate the enhanced performance of the suggested scheme and its ability to increase the probability of early decoding of more important parts of data rather than the rest. Also it is shown that the proposed scheme could provide comparable bit error rates in comparison to the one of the well known previous methods. The code with modified encoding graph has been utilized for transmitting of the scalable data-partitioned video stream. Simulation results also illustrate the performance of the suggested approach in early delivery of the most important parts of a video sequence.     

Error resilient video coding with priority data classification using H.264 flexible macroblock ordering

Flexible macroblock ordering (FMO) is a new error resilience feature in the H.264 (MPEG-4 part 10) video coding standard. The paper exploits FMO to offer a new classification algorithm for prioritised video transmission. Instead of using the default mapping structures of FMO, an optimisation algorithm in which the more important macroblocks (MBs) are categorised in a separate slice group (SG), which corresponds to high-priority packets for transmission, is proposed. The importance of each MB is determined based on its eventual influence on picture quality. This is assessed by considering the fact that the successful transmission of an MB not only enhances the quality of the associated pixels, but also improves the quality of its adjacent lost MBs by improving the efficiency of error concealment. It is assumed that the network can offer a prioritised service for successful transmission of the high-priority SG. Based on this, a vulnerability factor for each MB is determined, and a certain proportion of high-vulnerability MBs at each frame to limit the impact of temporal error propagation is intra-updated. It is shown, where the proposed mapping algorithm outperforms the default mappings of the H.264 codec, that this prioritised transmission will improve the subjective and objective video quality in situations with a high probability of transmission errors.     

用于H.264的Turbo码非均等译码保护策略

从最新的H．264视频压缩标准出发，提出一种基于H．264的数据分类和Turbo码的非均等译码保护的策略。针对Turbo码译码的特点译码迭代次数越多，纠错能力越强，但带来更多的译码复杂度和时延即消耗较多的功率。对于H．264三种数据分类，按照信息比特重要性的不同进行非均等译码保护，重要的数据给予更多的迭代次数的译码，次重要的数据给予较少的迭代次数的译码，以实现性能和功耗的折衷。仿真结果表明，本文算法不仅能提高解码质量，而且在实时中能减少时延和复杂度及功耗，特别适用于视频手机和手持设备业务。     

MPEG-4视频解码模块的设计与优化

基于OMAP5910双核处理器设计了一个MPEG-4视频解码模块，对其进行了优化，使之具有实时解码处理的能力。介绍了MPEG-4简单框架的解码过程以及在DSP平台上代码优化过程的重点部分。算法的编写符合TI XDIAS算法标准，通用于C5000系列的DSP平台。该解码过程与优化方法对视频处理以及在OMAP平台开发其他应用有借鉴价值。     

Wyner-Ziv coding of video: an error-resilient compression framework

This paper addresses the problem of video coding in a joint source-channel setting. In particular, we propose a video encoding algorithm that prevents the indefinite propagation of errors in predictively encoded video-a problem that has received considerable attention over the last decade. This is accomplished by periodically transmitting a small amount of additional information, termed coset information, to the decoder, as opposed to the popular approach of periodic insertion of intra-coded frames. Perhaps surprisingly, the coset information is capable of correcting for errors, without the encoder having a precise knowledge of the lost packets that resulted in the errors. In the context of real-time transmission, the proposed approach entails a minimal loss in performance over conventional encoding in the absence of channel losses, while simultaneously allowing error recovery in the event of channel losses. We demonstrate the efficacy of the proposed approach through experimental evaluation. In particular, the performance of the proposed framework is 3-4 dB superior to the conventional approach of periodic insertion of intra-coded frames, and 1.5-2 dB away from an ideal system, with infinite decoding delay, operating at Shannon capacity.     

MPEG-4错误检测和定位技术研究

如何在低带宽和高噪声信道环境下传输压缩视频和改善接收到的视频质量是当前视频技术研究的一个热点问题.简要介绍MPEG-44种错误恢复工具的基本原理,讨论了错误数据恢复的3个步骤.由于错误检测和定位是错误恢复的基础,因此,将重点讨论错误检测和定位的几种主要方法,并详细介绍一种基于数据隐藏的错误检测与定位技术.     

互联网上的MPEG-4视频解码自适应控制研究

针对互联网上的多媒体应用,提出了有限的系统资源条件下的MPEG-4视频解码控制方案。该方案既能保证视频流的解码,又能有效地利用网络带宽,从而实现了有服务质量保证的网络上的MPEG-4码流的实时传输和解码。     

基于自适应叠加的H.264时域错误隐藏算法

为了减小视频传输错误对解码端重建视频质量的影响,根据H.264标准的特点,提出一种基于多模式自适应叠加的时域错误隐藏算法。该算法以不同分割模式对丢失宏块进行4次隐藏,得到4个隐藏块,并计算各模式的绝对帧差和,使该值最小的2个隐藏块自适应加权叠加作为最终的替代块。仿真结果表明,与传统方法相比,该算法的错误隐藏性能得到较大提高。     

Video protection for MPEG-4 FGS with watermarking

The MPEG-4 fine granularity scalability (FGS) video coding standard offers flexible adaptation to varying network bandwidths and different application needs. This paper presents a MPEG-4 FGS video CODEC based watermarking scheme to embed watermark during encoding. Watermark is embedded into base layer, and can be extracted from both base layer and enhanced video through eliminating the influence of enhancement layer on watermark. This scheme eliminates error propagation caused by watermark for normal video, and utilizes error propagation caused by watermark adjustment to protect the video content. This scheme provides dual protection for intellectual property rights (IPR): watermark and video content protection utilizing error propagation in temporal motion compensation prediction. Watermark is embedded into I-VOP, and is adjusted before I-VOP is reconstructed as reference VOP. Only customers with authorization can adjust the watermark correctly during decoding to get good video quality. Illegal customers can also access the video, but with bad quality. This scheme has the virtue of providing dual protection with a little expense. Theoretical bounds of watermark embedding strength to keep watermark invisibility and of watermark adjustment strength to get enough protective effect are calculated. Some experimental results are given and analyzed.

Watermarking of MPEG-4 video objects

The recent finalization of MPEG-4 will make this standard very attractive for a large range of applications such as video editing, Internet video distribution, wireless video communications. Some of these applications are likely to get great benefit from watermarking technology, since it can enable a number of innovative services, such as conditional access policies, data annotation, data labeling, content authentication, to be implemented at a low price. One of the key points of the MPEG-4 standard is the possibility to access and manipulate objects within a video sequence. Thus object watermarking has to be achieved in such a way that, while a video object is transferred from a sequence to another, it is still possible to correctly access the data embedded within the object itself. The algorithm proposed in this paper embeds a watermark in each video object by imposing a particular relationship between some predefined pairs of quantized discrete cosine transform (DCT) coefficients in the luminance blocks of pseudo-randomly selected macroblocks (MBs). Watermarks are equally embedded into intra and inter MBs. Experimental results are presented validating the effectiveness of the proposed approach.     

基于子块运动估计补偿的视频误码块掩饰

视频数据在传输过程中存在着信道误码或丢包等现象,为了达到提高视频误码掩饰的目的,可利用子块运动估计方法,预测出在时间方向上的相关信息,通过运动补偿进行误码掩饰,同时为了消除子块补偿的边缘效应,进一步利用重叠块运动补偿方法以提高掩饰效果。     

应对反应攻击的级联中密度准循环奇偶校验码公钥方案

基于中密度准循环奇偶校验（QC-MDPC）码的McEliece公钥密码（PKC）方案具有较小的密钥量,利于存储,是一类在抵抗量子攻击上发展前景良好的公钥密码体制。然而目前存在一种反应攻击对其安全性产生了较大威胁。攻击者选取特殊的错误图样对大量消息进行加密以获得接收者反馈的译码失败情况,然后通过分析译码失败率与私钥结构的关系从而破解出私钥,该攻击被称为密钥恢复攻击。为应对此攻击,提出了一种将QC-MDPC码与喷泉码进行级联的公钥方案。该方案利用喷泉码的“无码率性”生成大量的加密包来取代反馈重发（ARQ）结构,使攻击者无法获取反馈信息。分析结果表明,所提出的方案能有效抗击密钥恢复攻击,同时还能保证在其他攻击下的安全性。     

H.264高清视频解码实时错误掩盖算法

针对IP网络丢包条件下的H.264高清视频实时解码问题,分析高清视频码流的特点,提出一种实时错误掩盖算法。该算法利用丢失片的边缘宏块信息,以垂直距离为权值加权平均预测得到错误宏块的运动矢量,进而完成错误掩盖。实验表明,与Joint模型中的错误掩盖算法相比,该算法提升了重建图像的主观质量和客观质量,计算复杂度较低,错误掩盖效果较好,适用于高清实时解码。     

基于柯西RS编码的网络丢包恢复算法研究

为提高多媒体系统中视频数据包的丢包恢复率,在传统柯西RS编码和对角交织的基础上,提出对多帧视频数据包进行二次柯西RS编码的优化算法。通过动态选取适当的柯西矩阵,用一次矩阵运算实现对视频源数据包的二次柯西RS编码,并对对角交织进行变形以适应视频数据包的特点。实验结果表明,与传统柯西RS编码算法相比,该算法在相近的解码性能、解码延时和校验包数情况下,能明显提高丢包恢复率。     

Hybrid error concealments based on block content

We present a novel error-concealment method for MPEG-2 video decoders. Imperfect transmission of block-based compressed images may result in the loss of blocks, degrading the quality of the received video signal. Since an I-picture is used as a reference picture for forward and backward predictions of neighbouring pictures, transmission errors in an I-picture are propagated both spatially in the I-picture and temporally to P-/B-pictures, and thus may severely degrade the video signal, compared with the errors in P-/B-pictures. To minimise the quality degradation of the video signal, error concealment has been performed in I-pictures through adaptive spatial and temporal interpolations in the respective domains. Using edge information extracted from the neighbourhoods of the erroneous macroblocks, we categorise each erroneous macroblock (MB) based on the characteristics of neighbouring MBs. The categorised MB is reconstructed by the spatial or temporal error concealment methods selected by the category-dependent criteria reflecting the properties of the block content. The proposed technique solves blocky artefacts and blurring problems of existing error concealment methods and thus effectively conceals the lost blocks in an error video signal. Through computer simulations on damaged images, we show that the proposed method is robust to image characteristics and obtains better subjective quality than other error concealment methods.     

一种新型的基于离散化宏块及螺旋扫描的视频数据打包算法

在研究传统视频数据打包算法中所采用的光栅扫描方式的局限性基础上，融合离散化宏块和螺旋扫描，融合这两种算法提出了一种新的视频数据打包算法，该算法首先按照某种规则离散化编码宏块，然后再从人眼感兴趣的中心区域开始，螺旋形步进打包．理论和试验都证明了这种新型的打包算法一方面可以有效地提高数据包抗丢包、抗误码的性能，另一方面可以使得数据包具有一定的可伸缩性，该算法比传统的打包算法在解码输出质量上具有明显的提高。