视频转码技术

视频转码技术是多媒体通信领域新的研究热点。首先介绍了已有的几类转码算法，然后以MPEC—2到MPEG-4的转码为例，探讨了转码中的关键技术，并给出了转码参考结构，最后介绍了转码进一步的研究方向。     

一种自适应运动估值视频代码转换的新方法

针对窄带网络的视频信号传输问题,分析了传统视频代码转换帧速率转换时,由于运动矢量非最佳化所造成的图象质量下降的原因,并提出了一种基于量化误差的自自动化运动矢量模型,从而减小了搜索域,使最佳化输出运行矢量能进行快速运动估值;同时根据灰度系统理论,提出了一种有效的灰度预测搜索方法,另外,又根据DCT系数理论模型。采用自适应快速视频编码方法,进一步提高了编码速度,实验结果表明：该方法不仅改善了视频图象质量,而且计算复杂度也大大减小。     

重构内部宏块在视频转换编码中的应用

视频空间分辨率下变换转换编码过程的运算量较大,受实时性、输出码率的限制,转换后的图像质量会有一定程度的下降。为了改善转换后码流的质量,同时又不会大幅增加计算量和输出码率,提出了综合考虑相邻宏块的运动矢量的集簇状态及其残差信息的情况,判断下变换后宏块纹理信息和运动矢量的失真情况,然后动态地选择一种转换编码算法。实验结果表明,使用该方案进行转换编码后,码流的质量有一定提高,同时避免了进行大范围运动搜索和引入大量内部编码的宏块。     

视频转码应用分析

在视频会议系统中还有日常拍摄处理视频时,需要利用视频转码技术对传统和新兴视频流进行格式转换。使用转码的意义在于可以在不损失任何视频质量的前提下节省高达50％的网络带宽。转码的分类按照媒体格式可分为音频转码、视频转码,视频转码比较出名的有暴风转码、格式工厂,音频转码用大众的千千静听就能满足使用需要。本文以转码应用为研究对象,进一步分析软件转码技术的应用。     

分布式系统Hadoop 平台的视频转码

在研究了目前主流的视频转码方案基础上,提出了一种分布式转码系统。系统采用HDFS（Hadoop Distributed File System）进行视频存储,利用MapReduce思想和FFMPEG进行分布式转码。详细讨论了视频分布式存储时的分段策略,以及分段大小对存取时间的影响。同时,定义了视频存储和转换的元数据格式。提出了基于MapReduce编程框架的分布式转码方案,即Mapper端进行转码和Reducer端进行视频合并。实验数据显示了转码时间随视频分段大小和转码机器数量不同而变化的趋势。结果表明,相比单机转码,提出的系统在采用8台机器并行转码时,可以节约80％左右的时间。     

Low-Delay Low-Complexity Bandwidth-Constrained Wireless Video Transmission Using SVC Over MIMO Systems

We propose an efficient strategy for the transmission of scalable video over multiple-input multiple-output (MIMO) wireless systems. In this paper, we use the latest scalable H.264 codec (SVC), which provides combined temporal, quality and spatial scalability. At the transmitter, we estimate the decoded video distortion for given channel conditions taking into account the effects of quantization, packet loss and error concealment. The proposed scalable decoder distortion algorithm offers low delay and low complexity. The performance of this method is validated using experimental results. In our proposed system, we use a MIMO system with orthogonal space-time block codes (O-STBC) that provides spatial diversity and guarantees independent transmission of different symbols within the block code. The bandwidth constrained allocation problem considered here is simplified and solved for one O-STBC symbol at a time. Furthermore, we take the advantage of the hierarchical structure of SVC to attain the optimal solution for each group of pictures (GOP) of the video sequence. We incorporate the estimated decoder distortion to optimally select the application layer parameter, i.e., quantization parameter (QP), and physical layer parameters, i.e., channel coding rate and modulation type for wireless video transmission.      

面向无线视频传感器网络的低复杂度视频编码算法

针对无线视频传感器网络(Wireless video sensor networks,WVSN)时视频编码算法的具体需求,提出一种基于运动检测的低复杂度视频编码算法.该算法只对当前编码帧中的运动对象进行编码,并且以面向对象的结构输出码流.实验结果表明,与H.264全I帧编码相比,本文提出的算法编码速度提高了约3倍,编码性能提高了约2 dB.与H.264基本档次相比,虽然编码性能略有下降,但是编码速度平均提高了8倍左右.本文提出的算法可以在编码效率和编码速度之间获得很好的折衷,在一定程度上可以满足WVSN的需求.     

Effcient Mining of Heterogeneous Star-Structured Data

Many of the real world clustering problems arising in data mining applications are heterogeneous in nature. Heterogeneous co-clustering involves simultaneous clustering of objects of two or more data types. While pairwise co-clustering of two data types has been well studied in the literature, research on high-order heterogeneous co-clustering is still limited. In this paper, we propose a graph theoretical framework for addressing starstructured co-clustering problems in which a central data type is connected to all the other data types. Partitioning this graph leads to co-clustering of all the data types under the constraints of the star-structure. Although, graph partitioning approach has been adopted before to address star-structured heterogeneous complex problems, the main contribution of this work lies in an e cient algorithm that we propose for partitioning the star-structured graph. Computationally, our algorithm is very quick as it requires a simple solution to a sparse system of overdetermined linear equations. Theoretical analysis and extensive experiments performed on toy and real datasets demonstrate the quality, e ciency and stability of the proposed algorithm.     

视频转码技术研究现状与最新进展

简要回顾了视频转码技术的研究发展状况, 系统地归纳了各种转码方法, 分析了相关的转码算法的特点. 针对最新压缩标准 H.264 的出现, 文中特别介绍总结了最新出现的转码方面的研究成果. 最后, 分析了转码研究未来的发展和可能存在的难点和问题.     

一种改进的降尺寸视频转码算法

在Diversity &; Importance架构的基础上提出一种改进的空间降尺度视频转码算法,利用方差作为转码目标宏块的运动矢量测度因子,并通过自适应阈值的分类方法对不同视频序列选择合适的重编码模式。该算法比传统的运动矢量合成方法提高了约1dB的PSNR,在保持较高转码图像质量的同时有效地控制了编码长度,其转码后码流长度只相当于AMVR-DIM方法产生码流的40%~95%。     

Video Semantic Event/Concept Detection Using a Subspace-Based Multimedia Data Mining Framework

In this paper, a subspace-based multimedia data mining framework is proposed for video semantic analysis, specifically video event/concept detection, by addressing two basic issues, i.e., semantic gap and rare event/concept detection. The proposed framework achieves full automation via multimodal content analysis and intelligent integration of distance-based and rule-based data mining techniques. The content analysis process facilitates the comprehensive video analysis by extracting low-level and middle-level features from audio/visual channels. The integrated data mining techniques effectively address these two basic issues by alleviating the class imbalance issue along the process and by reconstructing and refining the feature dimension automatically. The promising experimental performance on goal/corner event detection and sports/commercials/building concepts extraction from soccer videos and TRECVID news collections demonstrates the effectiveness of the proposed framework. Furthermore, its unique domain-free characteristic indicates the great potential of extending the proposed multimedia data mining framework to a wide range of different application domains.     

恒定速率视频编码转换码率控制策略

分析了恒定速率视频编码转换缓冲区的状态，导出了编码转换缓冲区为防止解码器缓冲区下溢和上溢应满足的条件，建立了视频编码转换模型。并使用小波变换系数来表征图像特征，提出了基于图像特征的码率控制策略。模拟实验表明，该码率控制策略能有效地减少、避免缓冲器出现上、下溢的情况，使输出码率趋于稳定，提高了重建视频图像的信噪比。     

面向移动网络的实时视频转码系统

针对宽带IPTV视频源向移动网络和移动终端提供视频服务需要解决的视频转码问题,设计开发以软件方式实现的实时视频转码系统,可将MPEG-4格式的高码率、高分辨率节目源实时转换为适合移动网络和移动终端的低码率、低分辨率视频。在误差补偿转码框架的基础上,提出一种自适应的转码时延保证方法,解决了转码计算复杂性和转码质量均衡的关键技术问题,保证了转码系统的实时性。测试结果表明,实现的转码系统视频转换质量损失少、实时性高。     

降低空间分辨率视频编码转换方法

根据漂移误差与帧间编码块的运动活动性的关系,提出了一种自适应帧内刷新方法。该方法根据目标比特率和实际比特率的差值,动态地调整阈值,从而有效地减少了帧内编码的比特率,保持了对差错的鲁棒性,限制了差错的时间传播。同时,根据率失真定理,在保证失真最小的情况下,为帧内不同的宏块选用最佳的量化系数。仿真结果表明:文中提出的方法有效地平滑了缓冲器的输出,同时峰值信噪比也有所提高。     

降低空间分辨率视频编码转换方法

根据漂移误差与帧间编码块的运动活动性的关系，提出了一种自适应帧内刷新方法。该方法根据目标比特率和实际比特率的差值，动态地调整阈值，从而有效地减少了帧内编码的比特率，保持了对差错的鲁棒性，限制了差错的时间传播。同时，根据率失真定理，在保证失真最小的情况下，为帧内不同的宏块选用最佳的量化系数。仿真结果表明：文中提出的方法有效地平滑了缓冲器的输出，同时峰值信噪比也有所提高。     

恒定速率视频编码转换码率控制策略

分析了恒定速率视频编码转换缓冲区的状态,导出了编码转换缓冲区为防止解码器缓冲区下溢和上溢应满足的条件,建立了视频编码转换模型.并使用小波变换系数来表征图像特性,提出了基于图像特征的码率控制策略.模拟实验表明,该码率控制策略能有效地减少、避免缓冲器出现上、下溢的情况,使输出码率趋于稳定,提高了重建视频图像的信噪比.     

一种视频转码快速运动估计算法

提出一种基于输入码流信息的视频转码快速运动估计算法。该算法利用输入码流的运动矢量和系数信息合成预测运动矢量,分析当前宏块对应转码前区域宏块运动矢量的一致性,结合图像的运动活跃性,自适应地调整编码运动估计的搜索策略。实验结果表明,与菱形搜索算法相比,该算法能够降低20%以上的编码时间,同时保持良好的图像质量;与AMVR-DIM算法相比,其运算性能和图像质量均有所提高。     

一种用于视频编码的低复杂度整数变换

文中提出一种用于视频编码的低复杂度整数变换。与H．264标准中所采用的整数变换相比较,本整数变换非常接近于DCT变换,而且无需乘法计算,只需要16位的加法和移位操作,大大降低了编码的计算复杂度,因此特别适合于低端的处理器。试验结果表明,该变换能够最大获得1．56％的比特率节省和0．16dB的PSNR增益。     

Mining Effective Temporal Specifications from Heterogeneous API Data

Temporal specifications for Application Programming Interfaces (APIs) serve as an important basis for many defect detection tools. As these specifications are often not well documented, various approaches have been proposed to automatically mine specifications typically from API library source code or from API client programs. However, the library-based approaches take substantial computational resources and produce rather limited useful specifications, while the client-based approaches suffer from high false positive rates. To address the issues of existing approaches, we propose a novel specification mining approach, called MineHEAD, which exploits heterogeneous API data, including information from API client programs as well as API library source code and comments, to produce effective specifications for defect detection with low cost. In particular, MineHEAD first applies client-based specification mining to produce a collection of candidate specifications, and then exploits the related library source code and comments to identify and refine the real specifications from the candidates. Our evaluation results on nine open source projects show that MineHEAD produces effective specifications with average precision of 97.2%.