H.263极低码率窄带电信信道视频编码

介绍了码率低于６４ｋｂ／ｓ的窄带电信信道视频编码建议Ｈ．２６３及其推荐的四种编码改进方案。     

A layered coding system for very low bit rate video coding

Known coding techniques for transmitting moving images at very low bit rates are explained by the source models on which these coding techniques are based. It is shown that with motion-compensated hybrid coding, object-based analysis-synthesis coding, knowledge-based coding and semantic coding, there is a consistent development of source models. In consequence these coding techniques can be combined in a layered coding system. From experimental results obtained for object-based analysis-synthesis, coding estimates for the coding efficiency of such a layered coding system are derived using head and shoulder video telephone test sequences. It is shown that an additional compression factor of about 3 can be expected with such a complex layered coding system, when compared to block-based hybrid coding.     

Motion compensation for very low bit-rate video

A combination of spatial transformation and image segmentation is used to compensate for non-uniform intensity changes in moving scenes. The method efficiently tracks movements such that the motion vectors alone can be employed to represent a moving object with complex motion. Using fast transformation and interpolation algorithms, it is shown that while the compression efficiency of the presented method is far superior to that of the conventional full search block-matching motion estimation, its computational complexity is still affordable.     

Motion vector replensihment for low bit-rate video coding

A low bit-rate video codec based on motion vector replenishment is described. Motion vectors are used to update pictures at full frame rate. In addition, part of each frame is conditionally updated with a strip of interframe video data. The video data fill the remaining channel capacity not used for motion vectors. Thus under most conditions, each frame is fully updated by motion vectors and partially with interframe video data. This method has a comparable compression efficiency with that of the frame dropping method, but does not introduce any picture ‘jerkiness’. Finally the application of the proposed method to packet video networks is examined.     

MPEG-4自然视频编码技术

对MPEG－4自然视频编码的关键技术作了详细的分析和阐述。首先介绍MPEG－4频语法结构，并对视频编码的框架概要分析。接着分析了自然视频编码中涉及到的关键技术，包括：VOP的产生；二值和灰度级α平面的编码技术；运动估计和补偿方法；纹理编码；基于对象的时间分级和空间分级；MPEG－4提供的再同步和各种错误掩盖，刷新方法，精 编码技术和零树小波基的静止图像编码技术。指出MPEG－4和MPEG－1，MPEG－2等标准的异同，突出MPEG－4的三个主要特点。最后给出MPEG－4技术在网络视频传输中的应用，并给出测试和分析。     

视频编码比特率和重建图像显示的清晰度

以数字标准清晰度电视（ＳＤＴＶ）规定的范围为重点,讨论视频编码比特率与重建图像显示清晰度的关系。其中着重指出：在采用ＭＰＥＧ－１／２－进行视频压缩编码而且压缩编码的算法确定时,应该依据视频的比特率的大小来选取恰当的视频格式,便于猁所期望的重建图像显示的清晰度。     

Error concealment algorithms for robust decoding of MPEG compressed video

This paper provides some research results on the topic of error resilience for robust decoding of MPEG (Moving Picture Experts Group) compressed video. It introduces and characterizes the performance of a general class of error concealment algorithms. Such receiver-based error concealment techniques are essential for many practical video transmission scenarios such as terrestrial HDTV broadcasting, packet network based teleconferencing/multimedia, and digital SDTV/HDTV delivery via ATM (asynchronous transfer mode). Error concealment is intended to ameliorate the impact of channel impairments (i.e., bit-errors in noisy channels, or cell-loss in ATM networks) by utilizing available picture redundancy to provide a subjectively acceptable rendition of affected picture regions. The concealment process must be supported by an appropriate transport format which helps to identify image pixel regions which correspond to lost or damaged data. Once the image regions (i.e., macroblocks, slices, etc.) to be concealed are identified, a combination of spatial and temporal replacement techniques may be applied to fill in lost picture elements. A specific class of spatio-temporal error concealment algorithms for MPEG video is described and alternative realizations are compared via detailed end-to-end simulations for both one- or two-tier transmission media. Several algorithm enhancements based on directional interpolation, ‘I-picture motion vectors’, and use of MPEG-2 ‘scalability’ features are also presented. In each case, achievable performance improvements are estimated via simulation. Overall, these results demonstrate that the proposed class of error concealment algorithms provides significant robustness for MPEG video delivery in the presence of channel impairments, permitting useful operation at ATM cell-loss rates in the region of 10⁻⁴ to 10⁻³ and 10⁻² to 10⁻¹ for one- and two-tier transmission scenarios, respectively.     

极低码率视频压缩编码算法的改进方法

本文从系统结构出发，充分利用低码率系统的特点，提出一种基于自适应判断的改进方法，较之已报道的方法，本文算法在基本保证图像质量的同时，有效地避免了一些冗余计算。将系统的基本运算量需求（不计运动估值算法的影响）降低到原来的５０％，从而使系统速度提高。由于该方法改进的角度较为新颖、独立，如果和其他快速算法相补充、结合使用，可以获得更优的性能。因此，本文算法在视频压缩系统中有较广泛的发展前景。     

Spatiotemporal texture synthesis and region-based motion compensation for video compression

In this paper, a content-based approach for video compression is proposed. The main novelty relies on the complete texture analysis/synthesis framework, which enables the use of multiple algorithms, depending on texture characteristics. The idea comes from the efficient MPEG prediction based on a best mode selection. Existing synthesis algorithms cannot be efficient in synthesizing every kind of texture but a certain range of them.This approach is designed to be jointly used with current and future standard compression schemes. At encoder side, texture analysis includes segmentation and characterization tools, in order to localize candidate regions for synthesis: motion compensation or texture synthesis. The corresponding areas are not encoded. The decoder fills them using texture synthesis. The remaining regions in images are classically encoded. They can potentially serve as input for texture synthesis. The chosen tools are developed and adapted in order to ensure the coherency of the whole scheme. Thus, a texture characterization step provides required parameters to the texture synthesizer. Two texture synthesizers, including a pixel-based and a patch-based approach, are used on different types of texture, complementing each other.The scheme is coupled with a motion estimator in order to segment coherent regions and to interpolate rigid motions using an affine model. Inter frame adapted synthesis is therefore used for non-rigid texture regions.The framework has been validated within an H.264/MPEG4-AVC video codec. Experimental results show significant bit-rate saving at similar visual quality levels, assessed using subjective tests. The method can be coupled with the future HEVC in which blocks can be skipped by the encoder to be synthesized at decoder side.     

Error prevention and concealment for scalable video coding with dual-priority transmission

In this work, we present an efficient error resilient system against ATM cell loss using a hybrid error concealment and error propagation prevention (ECP) technique with dual-priority transmission scheme (DPTS). DPTS performs traffic policing to form dual-priority cells in ATM connections and manages to make most cell losses occur in a low priority layer. However, cell loss may still occur in the high priority layer if the bandwidth is not reserved enough for the usually variable bitrate video traffic. Therefore, the ECP technique can still be utilized to reduce the error damage and limit the impact of cell loss to the erroneous slices. Simulation results of two-layer MPEG-2 coding over DPTS in ATM networks demonstrate that ECP with feedback over DPTS can effectively isolate errors and reduce the damage to yield a satisfactory performance, even when the cell-loss rate is as high as 8%.     

Homography-based block motion estimation for video coding of PTZ cameras

Due to the constrained movement of pan-tilt-zoom (PTZ) cameras, two frames in the video sequences captured by such cameras can be geometrically related by a relationship (homography). This geometric relationship is helpful for reducing the spatial redundancy in video coding. In this paper, by exploiting the homography between two frames with optical flow tracking algorithm, we propose a novel homography-based search (HBS) algorithm for block motion estimation in coding the sequences captured by PTZ cameras. In addition, adaptive thresholds are adopted in our method to classify different kinds of blocks. Compared with other traditional fast algorithms, the proposed HBS algorithm is proved to be more efficient for the sequences captured by PTZ cameras. And compared to our previous work in ICME (Cui et al., 2011), which only deals with pan-tilt (PT) camera and calculates the homography with mechanical devices, in this extended work we compute the homography by using information on images instead.     

Methodologies used for evaluation of video tools and algorithms in MPEG-4

MPEG-4 issued two calls for proposals requesting submission of algorithms and tools relevant to standardization of MPEG-4. This paper reports on the evaluation of tools submitted for evaluation in November 1995 and January 1996. Complete video coding schemes submitted in January 1996 are also covered. The goal of the evaluation was to cluster the tools according to the technical areas they address, to evaluate them according to the issues relevant to the standardization process, and finally to suggest areas of core experiments to improve a video verification model (VM) as soon as the VM becomes available. Altogether, MPEG evaluated 87 tools and 19 complete coding algorithms, most of them highlighted in this paper. During the evaluation, 19 areas for core experiments were identified. Each core experiment is targeted at different functionalities like compression efficiency, content-based coding, error resilience, scalability. This definition of core experiments caused close collaboration and supported mutual fertilization between organizations working on similar tools, which allowed the VM to progress much faster than expected.     

基于反馈的自适应参考帧选择的率失真优化分析

为了提高数字视频实时传输的容差能力,该文提出了一种基于反馈的自适应参考帧选择方法。在传统参考帧选择优点的基础上,设计了一种新的通过率失真技术优化选择参考帧的帧间帧预测结构,分析了选择不同参考帧编码时的编码码率以及它对编码失真的影响。引入了信道代价均值的概念,探讨了信道误差的扩散过程及其对信道失真的影响。在联合信源和信道的率失真优化框架内,选择使得率失真代价最小的候选参考帧作为当前帧编码的参考帧,有效地改善了视频传输质量,并减少了编/解码器所需缓存的参考帧。仿真实验显示自适应参考帧选择的PSNR性能在不同码率和丢包率下均优于经典的ACK和NACK参考帧选择方法。     

Very low bit-rate video coding with DFD segmentation

A video coding system for applications requiring very low bit-rate is presented. This coding scheme uses an intraframe coder for the initial frame in the video sequence and subsequent frames are coded using an interframe coding method. A wavelet-based technique is used for intraframe coding. For interframe coding, displaced frame differences (DFD) are computed and coded using a segmentation-based method wherein the displaced frame difference is segmented into active and inactive regions using morphological operators. To meet the very low bit-rate requirements, the motion vectors are processed so as to reduce their contribution to the overall bit-rate. To reduce coding artifacts, a post-processing technique is developed for use at the decoder. Coding performance of the proposed coding scheme is evaluated at 16 kbit/s and 32 kbit/s using luminance component of several typical test sequences at QCIF resolution with a frame rate 8.3 frame/s.     

A new distortion measure for motion estimation in motion-compensated hybrid video coding

In the video coding standards MPEG-x and H.26x, a motion-compensated prediction technique is used for enhancing the coding performance of bitrate reduction or peak signal to noise ratio (PSNR) improvement. This technique takes advantage of the correlation between consecutive frames in the time domain, which is relatively higher than that between adjacent blocks in the spatial domain. In order to utilize the correlation between consecutive frames, the conventional video coding standards have used the motion estimation (ME) and compensation technique, where the Sum of the Absolute Differences (SAD) is usually used as the distortion measure. The ME estimates the reference block that could minimize the residual signal between the current and reference blocks. However, the SAD is not appropriate to the specific sequences that have global or local illumination changes. In addition, the high-resolution video sequences have higher spatial correlation than the low-resolution video sequences in general. Therefore, a new distortion measure that can consider spatial and temporal correlation simultaneously may be helpful to enhance the coding performance. The proposed distortion measure searches for a reference block that minimizes the motion-compensated residual signal when the DC-component is predicted. In our proposed algorithm, the maximum BD-rate improvement is up to 13.6% for illumination-changed video sequences, and the average BD-rate improvement is 6.6% for various high-resolution video sequences in the baseline profile.     

两种实时、低码率视频编码的运动估计搜索算法

先提出实时、低码率视频编码对运动估计搜索算法在运算时间和准确度上的要求，总结归纳了钻石搜索法和两步法的具体算法，通过与几种经典算法作比较，说明这两种算法更优，更适合用于实时，低码率视频编码，最后，以H．263的实现为例，说明了钻石搜索算法的具体实现。     

SSIM-based error-resilient rate-distortion optimization of H.264/AVC video coding for wireless streaming

The SSIM-based rate-distortion optimization (RDO) has been verified to be an effective tool for H.264/AVC to promote the perceptual video coding performance. However, the current SSIM-based RDO is not efficient for improving the perceptual quality of the video streaming application over the error-prone network, because it does not consider the transmission induced distortion in the encoding process. In this paper, a SSIM-based error-resilient RDO scheme for H.264/AVC is proposed to improve the wireless video streaming performance. Firstly, with the help of the SSE-based RDO, we present a low-complexity Lagrange multiplier decision method for the SSIM-based RDO video coding in the error-free environment. Then, the SSIM-based decoding distortion of the user end is estimated at the encoder and is correspondingly introduced into the RDO to involve the transmission induced distortion into the encoding process. Further, the Lagrange multiplier is theoretically derived to optimize the encoding mode selection in the error-resilient RDO process. Experimental results show that the proposed SSIM-based error-resilient RDO can obtain superior perceptual video quality (more structural information) to the traditional SSE-based error-resilient RDO for wireless video streaming at the same bit rate condition.     

A 3D-DCT video encoder using advanced coding techniques for low power mobile device

The three-dimensional discrete cosine transform (3D-DCT) has been researched as an alternative to existing dominant video standards based on motion estimation and compensation. Since it does not need to search macro block for inter/intra prediction, 3D-DCT has great advantages for complexity. However, it has not been developed well because of poor video quality while video standards such as H.263(+) and HEVC have been blooming. In this paper, we propose a new 3D-DCT video coding as a new video solution for low power mobile technologies such as Internet of Things (IoT) and Drone. We focus on overcoming drawbacks reported in previous research. We build a complete 3D-DCT video coding system by adopting existing advanced techniques and devising new coding algorithms to improve overall performance of 3D-DCT. Experimental results show proposed 3D-DCT outperforms H.264 low power profiles while offering less complexity. From GBD-PSNR, proposed 3D-DCT provides better performance by average 4.6 dB.