An error detection and recovery algorithm for compressed videosignal using source level redundancy

The motion compensation-discrete cosine transform (MC-DCT) coding is an efficient compression technique for a digital video sequence. However, the compressed video signal is vulnerable to transmission errors over noisy channels. In this paper, we propose a robust video transmission algorithm, which protects the compressed video signal by inserting redundant information at the source level. The proposed algorithm encodes every lth frame in the semi-intra frame (S-frame) mode, in which the redundant parity-check DC coefficients (PDCs) are systematically inserted into the compressed bitstream. Then, the decoder is capable of recovering very severe transmission errors, such as loss of an entire frame, in addition to detecting the errors effectively without requesting any information from external devices. The proposed algorithm is implemented based on the H.263 coder, and tested intensively in realistic error prone environment. It is shown that the proposed algorithm provides much better objective and subjective performances than the conventional H.263 coder in the error prone environment.     

Error-resilient video transmission using long-term memorymotion-compensated prediction

Long-term memory prediction extends the spatial displacement vector utilized in hybrid video coding by a variable time delay, permitting the use of more than one reference frame for motion compensation. This extension leads to improved rate-distortion performance. However, motion compensation in combination with transmission errors leads to temporal error propagation that occurs when the reference frames at the coder and decoder differ. In this paper, we present a framework that incorporates an estimated error into rate-constrained motion estimation and mode decision. Experimental results with a Rayleigh fading channel show that long-term memory prediction significantly outperforms the single-frame prediction H.263-based anchor. When a feedback channel is available, the decoder can inform the encoder about successful or unsuccessful transmission events by sending positive (ACK) or negative (NACK) acknowledgments. This information is utilized for updating the error estimates at the encoder. Similar concepts, such as the ACK and NACK mode known from the H.263 standard, are unified into a general framework providing superior transmission performance     

Layered Wyner–Ziv Video Coding

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks     

Layered Wyner-Ziv video coding.

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks.     

Spatially scalable video compression employing resolution pyramids

A spatially scalable video coding scheme for low bit rates is proposed. The codec is especially well suited for communications applications because it is based on motion-compensated predictive coding which provides the necessary low-delay property. The frames to be coded are decomposed into a Gaussian pyramid. Motion estimation and compensation are performed between corresponding pyramid levels of successive frames. We show that, to fulfill specific needs of spatial scalability, the motion compensation on each level must result in compatible prediction errors (displaced frame differences, DFD). Compatibility of the prediction errors means that the pyramid formed by independently obtained DFD's (the DFD pyramid) is close to a Gaussian pyramid decomposition of the DFD of the highest resolution level. From the DFD pyramid, a least squares Laplacian pyramid is derived, which is quantized and coded. The DFD encoder outputs an embedded bit stream. Thus, the coder control may truncate the bit stream at any point, and can keep a fixed rate. The motion vector fields obtained at the different resolution levels are also encoded by employing a pyramid approach. Simulation results show that the proposed coder achieves a coding gain compared to simulcast coding     

一种新的小波可视电话编码算法

针对极低比特率应用提出一种新的结合H.263与SLCCA的混合小波视频编码算法。在提出的算法中,首先,用基于H.263的微调运动估计减小时间冗余,用无遗漏覆盖块运动补偿保证运动补偿误差帧的连续性;第二,对运动补偿误差帧进行小波变换得到全局能量压缩;第三,用SLCCA组织和表示小波变换后的数据,最后,运动向量的水平和垂直分量分别用自适应算法编码,算法在A级测试序列Akiyo和B级测试序列Foreman（QFIF）上测试取得了良好效果。     

Error resilience in video and multiplexing layers for very lowbit-rate video coding systems

The transmission of audio-visual services on low-bit-rate, wireless telecommunications systems requires the use of coding techniques that are both efficient in their use of bits and robust against errors introduced in transmission. In this paper, we present efficient techniques for improving the error resilience of audio-visual services. These techniques are based on coding simultaneously for synchronization and error protection or detection. We apply the techniques to improve the performance of the multiplexing protocol (which combines the video and audio streams so that they can be transmitted on a single circuit), and also to improve the robustness of the coded video. We show through simulations that the techniques are efficient in their use of bits and effective against bursty errors common in wireless channels. For a simulation of the DECT channel at a bit-error rate of 10^-3, the techniques give an order of magnitude improvement in the probability of lost packets in the multiplexer layer over more conventional techniques. In the video layer, the techniques give an improvement of between 1-2 dB over ITU-T Recommendation H.263. The techniques proposed for the video layer also have the advantage of permitting simple transcoding with bit streams complying with H.263     

Scalable wavelet video coding using aliasing-reduced hierarchicalmotion compensation

We describe a spatially scalable video coding framework in which motion correspondences between successive video frames are exploited in the wavelet transform domain. The basic motivation for our coder is that motion fields are typically smooth and, therefore, can be efficiently captured through a multiresolutional framework. A wavelet decomposition is applied to each video frame and the coefficients at each level are predicted from the coarser level through backward motion compensation. To remove the aliasing effects caused by downsampling in the transform, a special interpolation filter is designed with the weighted aliasing energy as part of the optimization goal, and motion estimation is carried out with low pass filtering and interpolation in the estimation loop. Further, to achieve robust motion estimation against quantization noise, we propose a novel backward/forward hybrid motion compensation scheme, and a tree structured dynamic programming algorithm to optimize the backward/forward mode choices. A novel adaptive quantization scheme is applied to code the motion predicted residue wavelet coefficients, Experimental results reveal 0.3-2-dB increase in coded PSNR at low bit rates over the state-of-the-art H.263 standard with all enhancement modes enabled, and similar improvements over MPEG-2 at high bit rates, with a considerable improvement in subjective reconstruction quality, while simultaneously supporting a scalable representation.     

WAVELET－BASED FINE GRANULARITY SCALABLE VIDEO CODING

This letter proposes an efficient wavelet-based fine Granularity Scalable(FGS)coding scheme,where the base layer is encoded with a newly designed wavelet-based coder,and the entancement layer is encoded with Progressive Fins Granularity Scalable(PFGS)coding.This algorithm involves multi-frame motion compensationk,rate-distortion optimizing strategy with Lagrangian cost function and context-based adaptive arithmetic coding.In order to improve efficiency of the enhancenent layer coding,an improved motion estimation scheme that uses both information from the base layer and the enhancement layer is also proposed in this letter.The wavelet-based coder significantly improves the coding efficiency of the base layer compared with MPEG-4 ASP(Advanced Simple Profile)and H.26L TML9.The PFGS coding is a significant improvement over MPEG-4 FGS coding at the enhancement layer.Experiments show that single layer coding efficiency gain of the proposed scheme is about 2.0-3.0dB and 0.3-1.0dB higher than that of MPEG-4 ASP and H.26L TML9,respectively.The overall coding efficiency gain of the proposed scheme is about 4.0-5.0dB higher than that of MPEG04 FGS.     

Drift controlled scalable wavelet based video coding in the overcomplete discrete wavelet transform domain

Traditional video coders use the previous frame to perform motion estimation and compensation. Though they are less complex and have minimum coding delays, these coders lose their efficiency when subjected to scalability requirements. Recent 3D wavelet coders using lifting schemes offer high compression efficiency and scalability without significant loss in performance. The main drawback of 3D coders is that they process several frames at a time. This introduces additional delay, which makes them less suitable for real time applications.In this work, we propose a novel scheme to minimize drift in scalable wavelet based video coding, which gives a balanced performance between compression efficiency and reconstructed quality with less drift. Our drift control mechanism maintains two frame buffers in the encoder and decoder; one that is based on the base layer and one that is based on the base plus enhancement layers. Drift control is achieved by switching between these two buffers for motion estimation and compensation. Our prediction is initially based on the base plus enhancement layers buffer, which inherently introduces drift in the system if a part of the enhancement layer is not available at the receiver. A measure of drift is computed based on the channel information and a threshold is set. When the measure exceeds the threshold, i.e., when drift becomes significant, we switch the prediction to be based on the base layer buffer, which is always available to the receiver. We also developed an adaptive scheme with additional computation overhead at the encoder to decide the switching instance. The performance of the threshold case that needs fewer computations is comparable with the adaptive scheme. Our coder offers high compression efficiency and sustained video quality for variable bit rate wireless channels. This proves that we need not completely eliminate drift and decrease compression efficiency to get better received video quality.     

A low-complexity rate allocation algorithm for joint source-channel video coding

The problem of enabling robust video transmission over lossy networks has become increasingly important because of the growing interest in video delivery over unreliable channels such as wireless networks. The more the coding process relies on an intensive use of prediction to improve the coding gain, the more the reconstructed sequence proves to be sensitive to information losses. As a matter of fact, it is necessary to introduce some redundant data in order to increase the robustness of the coded bit stream. A possible solution can be found filling a matrix structure with RTP packets and applying a Forward Error Correction (FEC) code on its rows. However, the matrix size and the chosen FEC code affect the performance of the coding system. The paper proposes a novel adaptation technique that tunes the amount of redundant information included in the packet stream and differs from previously proposed solutions since it relies on the percentage of null quantized transform coefficients in place of the activity or the Mean Square Error (MSE). This strategy is then integrated in a joint source-channel coder rate allocation algorithm that shares the available bits between the H.264/AVC coder and the channel coder according to the significance of the frame in the decoding process. Experimental results show that the presented approach significantly improves the quality of the reconstructed sequences at the decoder with respect to activity-based strategies and requires a low computational complexity.     

Perceptual feedback in multigrid motion estimation using animproved DCT quantization

In this paper, a multigrid motion compensation video coder based on the current human visual system (HVS) contrast discrimination models is proposed. A novel procedure for the encoding of the prediction errors has been used. This procedure restricts the maximum perceptual distortion in each transform coefficient. This subjective redundancy removal procedure includes the amplitude nonlinearities and some temporal features of human perception. A perceptually weighted control of the adaptive motion estimation algorithm has also been derived from this model. Perceptual feedback in motion estimation ensures a perceptual balance between the motion estimation effort and the redundancy removal process. The results show that this feedback induces a scale-dependent refinement strategy that gives rise to more robust and meaningful motion estimation, which may facilitate higher level sequence interpretation. Perceptually meaningful distortion measures and the reconstructed frames show the subjective improvements of the proposed scheme versus an H.263 scheme with unweighted motion estimation and MPEG-like quantization.     

H.263: video coding for low-bit-rate communication

This article provides an overview of H.263, the new ITU-T Recommendation for low-bit-rate video communication. H.263 specifies a coded representation for compressing the moving picture component of audio-visual signals at low bit rates. The basic structure of the video source coding algorithm is taken from ITU-T Recommendation H.261 and is a hybrid of interpicture prediction to reduce temporal redundancy and transform coding of the prediction residual to reduce spatial redundancy. The source coder can operate on five standardized picture formats: sub-QCIF, QCIF, CIF, 4CIF, and 16CIF. The decoder has motion compensation capability with half-pixel precision, in contrast to H.261 which uses full-pixel precision and employs a loop filter. H.263 includes four negotiable coding options which provide improved coding efficiency: unrestricted motion vectors, syntax-based arithmetic coding, advanced prediction, and PB-frames     

H.263甚低速率图像编码的全局判决实现方法

本文对Ｈ．２６３编码算法的现有实现方法作了深入的分析,首先发现变换部分存在大量无效运算,提出了在变换前加判决的前变换判决的编码方案,以压缩无效的变换运算;其次发现运动估计部分由于忽略了图像场景的分级运动而存在一定的无效搜索运算,提出了基于分级运动的可变搜索域法来压缩无效的搜索运算;最后将前变换判决方案与运动估计的可变搜索域法有机地结合在一起,提出了全局判决编码方案,从而比较全面地改进了现有实现方法,因而能大幅度地提高编码器的编码速度．     

Fast multi-frame motion estimation for H264/AVC system

Advanced video compression standard, H264/AVC, with multi-frame motion estimation, can offer better motion-compensation than the previous coding standards. However, the implementation of real-time multi-frame estimation for an H264/AVC system is difficult due to heavy computations. In this paper, a fast algorithm is proposed in an effort to reduce the searching computation for motion estimation with five reference frames. The fast multi-frame motion estimation consists of the adaptive full-search, three-step search, and diamond search methods using the content adaptive control process. Efficient control flow is proposed to select the searching algorithm dependent on video features. The adaptive algorithm can achieve better rate-distortion and lower computation for H264/AVC coding. The experiments indicate that the speed-up is 6–15 times compared with the full search method, while the image quality slightly degrades.     

Image coding with robust channel-optimized trellis-codedquantization

This paper presents a wavelet-based image coder that is optimized for transmission over the binary symmetric channel (BSC). The proposed coder uses a robust channel-optimized trellis-coded quantization (COTCQ) stage that is designed to optimize the image coding based on the channel characteristics. A phase scrambling stage is also used to further increase the coding performance and robustness to nonstationary signals and channels. The resilience to channel errors is obtained by optimizing the coder performance only at the level of the source encoder with no explicit channel coding for error protection. For the considered TCQ trellis structure, a general expression is derived for the transition probability matrix. In terms of the TCQ encoding rat and the channel bit error rate, and is used to design the COTCQ stage of the image coder. The robust nature of the coder also increases the security level of the encoded bit stream and provides a much more visually pleasing rendition of the decoded image. Examples are presented to illustrate the performance of the proposed robust image coder     

H．264中快速多参考帧选择算法研究

为了提高编码效率,H．264中采用了多参考帧搜索策略,其参考实现中提供了全搜索的多参考帧选择算法,这一策略的运用显然会大大增加H．264编码器的复杂度,且其复杂度的增加基本上和所使用的参考帧数戍线性增长,文中提出了一种更加快速的多参考帧选择算法,该算法可根据所得到的运动信息及编码所使用的模式信息快速确定参考帧的数量,对一些明显不可能的模式直接忽略掉了其最佳参考帧选择,其编码的性能与全搜索算法非常接近,但编码的速度却比全搜索算法快了许多。     

Speech and channel coding for digital land-mobile radio

The joint development of a medium bit-rate speech coder along with an effective channel coding technique to provide a robust, spectrally efficient, high-quality mobile communication system is described. A subband coder operating at 12 kb/s is used; in the absence of channel errors, it provides speech quality comparable to current analog land-mobile radio systems. The coder design incorporates a unique coding of the side information to facilitate the use of forward-error-correction coding without the need to code the entire bit stream. The use of excessive overhead for redundancy is avoided while the harsh effects of frequent channels are mitigated. These techniques have been used in an experimental FDMA (frequency-division multiple access) digital land-mobile radio system. The combined speech and channel coder operates at 15 kb/s and provides intelligible speech at fading channel error rates up to 8%     

H.264视频编码系统中多参考帧的选择算法研究

H.264/MPEG-4 AVC中引入多参考帧运动补偿来提高视频编码性能,由此产生的多参考帧运动估计(MRF-ME)却带来了巨大的运算代价.本文提出一种基于快速分层特征匹配的运动估计策略(HFM-ME)来加速多参考帧的匹配过程.HFM-ME策略通过引入一种符号截断特征(STF)将块匹配被分解为均值匹配和二进制相位匹配.实验结果表明,与传统的块匹配ME相比,HFM-ME在保持匹配性能的同时显著提高了运算速度.     

Low bit rate video coding using robust motion vector regenerationin the decoder

In this paper, we present a novel coding technique that makes use of the nonstationary characteristics of an image sequence displacement field to estimate and encode motion information. We utilize an MPEG style codec in which the anchor frames in a sequence are encoded with a hybrid approach using quadtree, DCT, and wavelet-based coding techniques. A quadtree structured approach is also utilized for the interframe information. The main objective of the overall design is to demonstrate the coding potential of a newly developed motion estimator called the coupled linearized MAP (CLMAP) estimator. This estimator can be used as a means for producing motion vectors that may be regenerated at the decoder with a coarsely quantized error term created in the encoder. The motion estimator generates highly accurate motion estimates from this coarsely quantized data. This permits the elimination of a separately coded displaced frame difference (DFD) and coded motion vectors. For low bit rate applications, this is especially important because the overhead associated with the transmission of motion vectors may become prohibitive. We exploit both the advantages of the nonstationary motion estimator and the effective compression of the anchor frame coder to improve the visual quality of reconstructed QCIF format color image sequences at low bit rates. Comparisons are made with other video coding methods, including the H.261 and MPEG standards and a pel-recursive-based codec.