分布式视频编码关键技术及研究进展

系统地阐述了分布式视频编码(distributed video coding,DVC)技术框架的基本原理和近五年的发展历程;列举了国内外多个研究小组的基本思想研究现状;分析了分布式视频编码技术的发展趋势;揭示了技术的关键和研究热点;展望了该技术在信息安全、可伸缩编码、多描述编码以及光场编码中的应用前景.     

数字视频转码失真分析

在互联网视频应用领域中,视频在经过多次转码后相对于原始节目的失真难以控制,为此,提出一种对视频多次转码后的总失真进行估计的方法。首先,研究多次有损转码失真的叠加过程,找到了多次失真叠加后总体失真的下限;然后,用概率论的方法给出了总体失真的一个估计;最后,根据估计误差,采用最小二乘拟合对该估计进行修正。实验结果表明,经过修正后,Y、U和V三分量最终失真的平均估计误差仅为0.02dB,0.05dB和0.06dB,这说明该方法能够有效且准确地估计出视频转码的总体失真值。     

TES过程及其Matlab建模

详细介绍了TES过程的原理和建模方法，对高突发性业务流建模，仿真结果表明TES模型能够更好地捕捉到网络业务流的高突发性。     

Wyner-Ziv视频编码中边信息估计改进算法

首先简要介绍了分布式编码基本原理和一种典型的分布式编码方案——Wyner-Ziv视频编码。然后在Wyner-Ziv视频编码中提出了一种改进边信息估计算法,该算法中运动估计采用加权MAD准则。实验仿真结果表明,采用该文算法得到的运动矢量场更为准确,同时在相同输出码率时PSNR比原始算法平均提高0.7 dB。     

Prediction accuracy in estimating joint angle trajectories using a video posture coding method for sagittal lifting tasks

This study investigated prediction accuracy of a video posture coding method for lifting joint trajectory estimation. From three filming angles, the coder selected four key snapshots, identified joint angles and then a prediction program estimated the joint trajectories over the course of a lift. Results revealed a limited range of differences of joint angles (elbow, shoulder, hip, knee, ankle) between the manual coding method and the electromagnetic motion tracking system approach. Lifting range significantly affected estimate accuracy for all joints and camcorder filming angle had a significant effect on all joints but the hip. Joint trajectory predictions were more accurate for knuckle-to-shoulder lifts than for floor-to-shoulder or floor-to-knuckle lifts with average root mean square errors (RMSE) of 8.65°, 11.15° and 11.93°, respectively. Accuracy was also greater for the filming angles orthogonal to the participant's sagittal plane (RMSE = 9.97°) as compared to filming angles of 45° (RMSE = 11.01°) or 135° (10.71°). The effects of lifting speed and loading conditions were minimal. To further increase prediction accuracy, improved prediction algorithms and/or better posture matching methods should be investigated.

Statement of Relevance: Observation and classification of postures are common steps in risk assessment of manual materials handling tasks. The ability to accurately predict lifting patterns through video coding can provide ergonomists with greater resolution in characterising or assessing the lifting tasks than evaluation based solely on sampling with a single lifting posture event.     

多模式3维视频形状编码

目的 具有立体感和高端真实感的3D视频正越来越受到学术界和产业界的关注和重视,未来在3D影视、机器视觉、远程医疗、军事航天等领域将有着广泛的应用前景。对象基3D视频是未来3D视频技术的重要发展趋势,其中高效形状编码是对象基3D视频应用中的关键问题。但现有形状编码方法主要针对图像和视频对象,面向3D视频的形状编码算法还很少。为此,基于对象基3D视频的应用需求,提出一种基于轮廓和链码表示的高效多模式3D视频形状编码方法。方法 对于给定的3D视频形状序列逐帧进行对象轮廓提取并预处理后,进行对象轮廓活动性分析,将形状图像分成帧内模式编码图像和帧间预测模式编码图像。对于帧内编码图像,基于轮廓内链码方向约束和线性特征进行高效编码。对于帧间编码图像,采用基于链码表示的轮廓基运动补偿预测、视差补偿预测、联合运动与视差补偿预测等多种模式进行编码,以充分利用视点内对象轮廓的帧间时域相关性和视点间对象轮廓的空域相关性,从而达到高效编码的目的。结果 实验仿真结果显示所提算法性能优于经典和现有的最新同类方法,压缩效率平均能提高9.3%到64.8%不等。结论 提出的多模式3D视频形状编码方法可以有效去除对象轮廓的帧间和视点间冗余,能够进行高效编码压缩,性能优于现有同类方法,可广泛应用于对象基编码、对象基检索、对象基内容分析与理解等。     

高效视频编码中变换跳过模式的快速选择

目的新一代高效视频编码(HEVC)标准采用了灵活的块结构和大量新颖的编码工具,有效提高了视频编码效率。变换跳过模式作为一种新增加的模式,可以有效地提高编码效率,但是也显著地增加了编码的复杂度,增加了实时编码应用的难度。因此提出一种针对变换跳过模式的提前剪枝算法。方法通过分析不同率失真代价下是否选择变换跳过模式的残差块的分布情况,最终选取率失真代价的平方根作为阈值,并建立了量化参数与阈值之间的模型。之后可以根据量化参数提前计算得到阈值大小,减少变换跳过模式的编码次数,从而降低变换跳过模式的复杂度。结果由于最终只需要对少量的块进行变换跳过模式编码,并且使用模型得到经验阈值并不会额外增加复杂度,因此能减少编码器的计算复杂度。实验结果表明,与标准编码器相比,该算法对于不同场景的标准测试序列平均峰值性噪比和平均比特率变化都非常小,平均减少了70%的变换跳过模式编码的次数。结论该变换跳过模式的剪枝算法,选取率失真代价的平方根作为阈值,根据本文模型获取不同量化参数下的经验阈值,对是否需要进行变换跳过模式提前判断。实验结果表明,该算法能在保证视频编码质量的前提下有效地降低由于加入变换跳过模式增加的编码复杂度。     

频率域Wyner-Ziv视频编码算法的改进

为提高分布式视频编码压缩率,依据无线传感网络终端设备及Wyner-Ziv视频编码特点,针对Bernd Girod的频域Wyner-Ziv视频编码方案提出改进算法。该算法在编码端通过简单DCT运算提出将图像块分为Skip模式、低频模式和全频模式三种可选模式,在解码端根据相应的编码模式分别选择平均插值、自适应搜索运动估计插值和自适应搜索精细运动估计插值的边信息估算方法联合解码。该算法既能通过消除大量的帧间预测与熵编码实现低码率传输,又能以最小的解码代价获得更精确的边信息,从而有效地避免图像解码质量下降。实验结果表明,在相同峰值信噪比情况下,该算法的码率比Bernd Girod提出的频域Wyner-Ziv算法平均下降40%。     

分布式视频编码技术研究进展

介绍了分布式视频编码与传统视频编码方法思路的不同及各自适用的应用场景,阐述了分布式视频编码的理论基础和目前普遍采用的编解码框架,分析了分布式视频编码中的Wyner-Ziv编解码器设计、辅助边信息生成、虚拟相关信道建模等几项关键技术存在的问题及各自解决方案的最新研究进展,最后总结了分布式视频编码的发展与研究方向,并介绍了分布式编码在视频领域的其它应用.     

视频编码技术的若干新进展

对数字视频编码技术的新进展进行了综述。先对传统视频编码方法进行了分析,指出其存在的不足,然后对基于压缩感知理论的视频编码、分布式视频编码、基于视觉特性的视频编码和可分级视频编码这四种视频编码技术的新进展进行了介绍,最后对未来可能的发展方向进行了展望,可为视频编码技术的相关研究提供参考。     

基于Codebook背景建模的视频行人检测

针对视频序列,Codebook背景建模算法能检测出其中的运动物体,但却无法识别行人.而大部分基于支持向量机(SVM)训练的行人分类器,需要通过滑动窗口遍历图像检测行人.为加快行人检测的速度,提出将传统的行人分类器融入到Codebook背景建模算法中,通过背景建模算法为行人检测提供候选区域,减少搜索范围,降低了行人误检率;并根据行人的特点,构建临时块模型定期将满足条件的前景区域更新到背景模型中,解决了Codebook背景建模算法不能应对光照突变的问题.实验结果表明:所提算法能应对光照突变所带来的干扰,实现视频行人实时检测.     

全景视频双环带映射算法

针对全景视频映射过程中局部区域变形过大、冗余数据量极高的问题,提出了一种双环带映射算法（DRP）。首先,根据球面视频的几何特点,结合人眼视度（HVS）这一视觉特性,用两个相互正交的环形区域,将球面视频分割成14个大小相近的区域;然后根据空域采样定理,采用兰索斯插值法,将这14个区域对应的球面视频内容映射为14个大小相等的矩形视频;最后,根据最新视频编码标准的特点,重新排列这14个矩形视频,得到符合编码器标准的紧凑的全景视频。实验结果表明,与经纬图映射算法（ERP）、八面体映射算法（OHP）、二十面体映射算法（ISP）相比,DRP算法在视频压缩性能方面有良好的表现;其中同最流行的ERP算法相比,码率平均降低8.61%,明显提升了视频编码效率。     

A pixel-based outlier-free motion estimation algorithm for scalable video quality enhancement

Scalable video quality enhancement refers to the process of enhancing low quality frames using high quality ones in scalable video bitstreams with time-varying qualities. A key problem in the enhancement is how to search for correspondence between high quality and low quality frames. Previous algorithms usually use block-based motion estimation to search for correspondences. Such an approach can hardly estimate scale and rotation transforms and always introduces outliers to the motion estimation results. In this paper, we propose a pixel-based outlier-free motion estimation algorithm to solve this problem. In our algorithm, the motion vector for each pixel is calculated with respect to estimate translation, scale, and rotation transforms. The motion relationships between neighboring pixels are considered via the Markov random field model to improve the motion estimation accuracy. Outliers are detected and avoided by taking both blocking effects and matching percentage in scaleinvariant feature transform field into consideration. Experiments are conducted in two scenarios that exhibit spatial scalability and quality scalability, respectively. Experimental results demonstrate that, in comparison with previous algorithms, the proposed algorithm achieves better correspondence and avoids the simultaneous introduction of outliers, especially for videos with scale and rotation transforms.     

Auxiliary stream for optimizing memory access of video decoders

Due to the ever increasing resolution and frame rate of mainstream video sequences,memory access has become the main performance bottleneck of video decoding.To reduce the required of-chip memory,many decoders employ on-chip cache.However,they cannot distinguish whether a data block is reusable due to the lack of the information of undecoded Macro Blocks(MBs),thus often evicting reusable data from the cache and preserving non-reusable data in the cache,which will lead to a waste of of-chip memory bandwidth.In this paper,we manage to make full use of cache from a novel perspective,i.e.,auxiliary bitstream.Concretely speaking,since the memory access behavior of video decoding is determined in video encoding,the encoder can pack the memory access behaviors of video decoding as auxiliary bitstream,which can inform the decoder whether a data block will be reused by future MBs.Hence,such an auxiliary stream can enable optimal management of cache.To efectively reduce the size of auxiliary bitstream,we propose an Auxiliary Prior Information Coding(APIC)method complying with the current video standards.For future video standards,we introduce a Super Block scan Order(SBO)for MB organization to further reduce the bitrate overhead of auxiliary bitstream.The above ideas are evaluated on a number of representative video sequences.The additional prior information can reduce the required of-chip memory bandwidth for motion compensation by over 35%(for a 60 kB cache),while only causing less than 2.3%bitrate increase for high definition(HD)videos.     

TriMedia1300在视频会议中的应用

介绍和分析了Philips公司的TriMedia微处理器及其升级产品TriMedia1300的系统组成和特点。针对视频会议中存在的实时性问题,提出了一种基于TriMedia1300视频会议的简单、快速开发方案,并对TriMedia1300在视频和图像处理方面的性能与个人计算机进行了比较,给出了它们运算速度比较的结果。     

一种获得均匀图像质量的视频码率控制方法

在视频编码中,码率控制的目的是：在满足带宽约束的条件下,提高编码图像的质量。获得符合人眼视觉特性的均匀图像质量是码率控制的一个期望目标。根据信源的线性模型,考虑图像宏块的复杂度提出一种码率控制算法,此方法对宏块的量化参数具有平滑作用,可以使宏块量化参数和失真度分布更加集中,从而具有更加均匀一致的图像质量。仿真表明,该方法可以改善图像的峰值信噪声比,获得更好的主客观视觉质量。     

数据驱动的并行视频编码器的设计和实现(英文)

通用视频编码系统一般基于标准视频压缩算法, 比如 MPEG4 和 H.264。但这些标准算法包括如离散余弦变换和运动估计等高复杂度的计算,所以为了实现实时通信,编码系统通常采用以硬件为基础的实现方法。然而以硬件为基础的视频编码系统具有实施周期长、成本高、灵活性差等不足。文章介绍了一种基于低计算复杂度自适应块截短编码方案的数据驱动并行视频编码系统,实验结果验证了编码系统的有效性。     

用于虚拟现实的360度视频编码技术新进展*

随着虚拟现实技术不断发展,360度视频编码开始成为研究热点。应用于虚拟现实的360度视频与传统的视频相比分辨率更高,编码数据量更大,在实际应用中面临传输带宽有限的瓶颈,编码效率问题有待解决。归纳分析了国际标准组织联合视频研究组（joint video exploration team, JVET）正在制定的360度视频编码投影变换技术及其编码优化方法,综合对比了各变换技术的编码性能。根据当前最新研究成果,对下一步研究需要解决的问题进行了探讨总结,给出未来的研究方向和思路。     

Distributed video coding with adaptive two-step side information generation for smart and interactive media

Conventional video coding standards, such as MPEGx and H.26x, use a hybrid architecture of block-based motion compensation and discrete cosine transform (DCT) within the structure of a complex encoder and a simple decoder. Contrary to conventional video codecs, Wyner-Ziv (WZ) video coding, which is a practical application of distributed video coding (DVC) based on the Slepian-Wolf and WZ theorems, exploits the source correlation at the decoder, thereby allowing for the development of simpler encoders. However, the current WZ video coding algorithms cannot match the coding performance of conventional video coding. In order to improve the coding performance of transform-domain WZ video coding, an adaptive two-step side-information generation method is thus proposed for evaluation and analysis in this study. The proposed method uses decoded WZ frames in the down-sampled spatial resolution along with already decoded coefficients to successively improve rate-distortion (RD) performance as the decoding progresses. The experimental results show that the proposed method, compared to previous WZ video coding method, shows improved coding performance, particularly under critical conditions, such as cases with high motion content.