视频点播服务器中服务策略的研究*

研讨了同时为多个点播用户服务的轮转服务策略和比例服务策略,并提出了VOD(video-on-demand)服务器在不破坏各路点播流实时播放率的前提下,应用这些服务策略的方法.     

视频回取过程的数学建模

本文提出了从磁盘系统中读取连续媒体数据以缓冲器的一般回取框架，然后对基于服务循环的回取算法进行了深入的讨论、量化分析和数学建模。     

基于遗传算法的QoS选播流路由优化算法

选播是一种网络通信服务,在视频流点播等领域发挥重要作用。该文提出QoS选播流路由优化的问题模型,给出选播流路由端到端时延、服务器负载、网络流量等优化目标和QoS约束的遗传算法表达式,说明了算法求解的关键步骤和实现过程。实验结果表明,该算法在满足QoS约束的前提下可以实现选播路由的多目标组合优化。     

国防科大计算机学院工学博士学位论文摘要

连续媒体数据存储与回取技术的研究作者：刘衡竹（１９９９．６）导师：陈福接教授　　随着存储技术、通讯技术和视频压缩技术的高速发展,使得通过ＢＩＳＤＮ进行视频点播（Ｖｉｄｅｏ－Ｏｎ－Ｄｅｍａｎｄ）服务成为可能。ＶＯＤ服务器以压缩、数字化的形式存储视频数据,并为多个用户并发提供回取和传输服务。为了实现视频数据的优化存储与回取,本文对ＭＰＥＧ流的结构及传输特性进行了讨论,分析了现有磁盘系统的读取过程和延时特性,建立了用于对连续媒体回取过程进行分析的磁盘传输延迟模型。定义了与具体算法无关的用于连续媒体回取…     

一种基于节点可选度的P2P点播流媒体数据调度算法

当前的P2P(Peer-to-Peer)点播流媒体系统中数据调度算法未能充分利用每个用户节点自身的特性.在分析典型数据调度算法基础上提出一种基于节点可选度的数据调度算法(SSP算法).该算法一方面在调度下载数据块时综合考虑了邻居节点带宽能力及其所拥有的数据信息.另一方面对服务节点的请求处理过程进行了优化.SSP算法有利于提高用户节点播放视频的连续性,降低流媒体服务器的负载压力,从而改善P2P点播流媒体系统的整体服务质量.仿真结果和实际应用表明算法性能良好,适用于用户节点能力差异较大的P2P点播流媒体环境.     

连续媒体流的理论模型及缓冲对策研究

视频点播服务（ＶＯＤ）是当前交互式多媒体ＩＭＭ应用中的热门方向,而视频流的缓冲、控制策略是视频服务技术研究中相当关键的环节。本文试图采用全局的观点,利用恰当的数学工具建立了在网络并行下的请求流工作模型,并结合缓冲机制得到了一些关于媒体流服务的重要结论。同时,结合媒体服务的工作序列,给出了一些优化流控和数据缓冲的方法和策略,最后通过试验验证了该理论模型和结论的可行性。     

区分服务中基于彩票算法的公平带宽分配

区分服务是提供QoS的重要机制之一,但在区分服务中存在着汇聚流之间剩余带宽分配的不公平性问题。为解决该问题,本文提出了基于彩票算法的区分服务标记算法,该算法基于彩票算法,能够根据区分服务的优先级,调整标记各汇聚流的标记策略。它能以一种近似按比例的方式在各汇聚流之间公平地分配网络中的剩余带宽。仿真结果表明该算法是有效的。     

VBR视频在MZR磁盘上的比例安置

文章在分析了变位率（VBR）视频和多区记录（MZR）磁盘特性的基础上,提出了一种比例安置算法：视频数据块按尺寸、分比例安置到相应的记录区上。这种算法和其它算法相比简洁、更有效地利用了磁盘带宽和能支持更多视频流的同时检索。     

区分服务中一种公平的汇聚流标记算法

区分服务是提供QoS的重要机制之一,但在区分服务中存在着汇聚流之间剩余带宽分配的不公平性问题。为解决该问题,提出了动态数据包标记算法（DPMA）,该算法通过监测汇聚流的流速变化,能动态地调整标记策略,它能以一种近似按比例的方式在各汇聚流之间公平地分配网络中的剩余带宽。仿真结果表明该算法是有效的。     

远程教学中COD的组播实现

本文提出了一种集中式管理、点播服务器分布式放置的远程教学课件点播(Courseware On Demand-COD)系统。在这一体系结构下．采用了新的批处理信道调度策略，对用户实施多播流和补丁流相结合的组播服务。提高了网络带宽利用率，增加了可服务的点播并发流数，同时降低了课件播放延迟时间。     

一种新型VOD系统视频服务器的设计

本文提出了一种带有新颖的视频流分配方案的可伸缩ＶＯＤ系统视频服务器的设计方案,从系统的体系结构方面充分探讨了如何使用单个主机处理越来越多的同时发生的视频点播要求,以及如何利用视频节目的分配文件的存贮特性减少磁盘寻道行为。本文将详细讨论直流视频流泵、磁盘子系统的文件释放策略以及系统的可伸缩性。     

Digital video watermarking based on intra prediction modes for audio video coding standard

Digital video watermarking provides means for carrying information targeted for synchronization, error resilience or copyright protection. However, it is difficult to get a good trade-off between the embedding capacity, imperceptibility and efficiency. In this paper, a novel digital video watermarking algorithm based on intra prediction modes of AVS (audio video coding standard) is proposed. The algorithm hides one bit in each qualified intra 8 × 8 luma block by modifying intra 8 × 8 prediction modes based on the mapping rules between the modes and hidden bits. The specific positions of the host 8 × 8 blocks are determined by the features of every block and a position template indicated by the key. Watermark information can be retrieved by decoding the intra prediction modes from bitstream, requiring neither original media nor complete video decoding. Experimental results show that the proposed algorithm has little impact on video quality and video stream features. A comparatively high embedding rate is obtained with little impact on bit rate.     

结合帧率变换与HEVC标准的新型视频压缩编码算法

相比于之前主流的H.264视频压缩编码标准,HEVC在保证重建视频质量相同的前提下,可以将码率降低近50%,节省了传输所需的带宽.即便如此,由于一些特定的网络带宽限制,为继续改善HEVC视频编码性能,进一步提升对视频的压缩效率仍然是当前研究的热点.本文提出一种HEVC标准编码与帧率变换方法相结合的新型的视频压缩编码算法,首先在编码端,提出一种自适应抽帧方法,降低原视频帧率,减少所需传输数据量,对低帧率视频进行编解码;在解码端,结合从HEVC传输码流中提取的运动信息以及针对HEVC编码特定的视频帧的分块模式信息等,对丢失帧运动信息进行估计;最后,通过本文提出的改进基于块覆盖双向运动补偿插帧方法对视频进行恢复重建.实验结果证实了本文所提算法的有效性.     

{\cal SMDP}: minimizing buffer requirements for continuous media servers

Excessive buffer requirement to handle continuous-media playbacks is an impediment to cost- effective provisioning for on-line video retrieval. Given the skewed distribution of video popularity, it is expected that often there are concurrent playbacks of the same video file within a short time interval. This creates an opportunity to batch multiple requests and to service them with a single stream from the disk without violating the on-demand constraint. However, there is a need to keep data in memory between successive uses to do this. This leads to a buffer space trade-off between servicing a request in memory mode vs. servicing it in disk-mode. In this work, we develop a novel algorithm to minimize the buffer requirement to support a set of concurrent playbacks. One of the beauties of the proposed scheme is that it enables the server to dynamically adapt to the changing workload while minimizing the total buffer space requirement. Our algorithm makes a significant contribution in decreasing the total buffer requirement, especially when the user access pattern is biased in favor of a small set of files. The idea of the proposed scheme is modeled in detail using an analytical formulation, and optimality of the algorithm is proved. An analytical framework is developed so that the proposed scheme can be used in combination with various existing disk-scheduling strategies. Our simulation results confirm that under certain circumstances, it is much more resource efficient to support some of the playbacks in memory mode and subsequently the proposed scheme enables the server to minimize the overall buffer space requirement.     

适用于多通道视频流传输的循环线性2维表排序算法

多通道视频流传输的排序问题,在视频数据的传输领域有着重要的地位.提出了一种适用于多通道视频流的循环线性2维表排序方法,利用循环2维线性表的查表方式实现多通道的视频流分组进行排序处理.与传统的排序方法相比,它可以有效地消除时延不可控,排序复杂度过高,内存管理复杂等方面的缺陷.运用PC机对传统方法和该方法及其特点进行了测试,测试结果表明:传统排序方法在分组数量增加的条件下,排序时间呈指数式增长,而本文的方法的排序时间呈线性增长.与几种传统排序方法在排序时间的实验统计数据对比表明:在分组数量增加的情况下,该方法可以节约大量的排序时间.     

An efficient retrieval selection algorithm for video servers with random duplicated assignment storage technique

Random Duplicated Assignment (RDA) is an approach in which video data is stored by assigning a number of copies of each data block to different, randomly chosen disks. It has been shown that this approach results in smaller response times and lower disk and RAM costs compared to the well-known disk stripping techniques. Based on this storage approach, one has to determine, for each given batch of data blocks, from which disk each of the data blocks is to be retrieved. This is to be done in such a way that the maximum load of the disks is minimized. The problem is called the Retrieval Selection Problem (RSP). In this paper, we propose a new efficient algorithm for RSP. This algorithm is based on the breadth-first search approach and is able to guarantee optimal solutions for RSP in O(n²+mn), where m and n correspond to the number of data blocks and the number of disks, respectively. We will show that our proposed algorithm has a lower time complexity than an existing algorithm, called the MFS algorithm.     

基于密钥矩阵序列的视频乱序加密方法

提出RMSP(Random Matrix Sequence Permutation)方法,同时完成帧内宏块(MacroBlock,MB )之间、块内VLC(Variable Length Coding)码字之间双重互补的乱序加密,并利用随机序列生成随机乱序密钥矩阵序列,供每帧和每块依次用不重复的密钥矩阵对MB和VLC码字乱序.RMSP方法完全保持编码格式和压缩率,具有对应序列密码的抗攻击能力且明文信息完全隐藏的特点,速度快约四倍,适用于MPEG、H.26x及JPEG等主流编码信号加密,可制作单独模块.     

基于SVM和ICA的视频帧字幕自动定位与提取

视频字幕蕴涵了丰富语义,可以用来对相应视频流进行高级语义标注,但由于先前视频字幕提取考虑的只是如何尽可能定义好字幕特征,而忽视了分类学习机自身的学习推广能力.针对这一局限性,提出了一种基于支持向量机和独立分量分析的视频帧字幕定位与提取算法.该算法是首先将原始图象帧分割成N×N大小子块,同时将每个子块标注为字幕块和非字幕块两类;然后从每个子块提取能够保持相互高阶独立的独立分量特征去训练支持向量机分类器;最后结合金字塔模型和去噪方法,用训练好的支持向量机来实现对视频字幕区域自动定位提取.由于支持向量机能够在样本不是很多的情况下,具有良好的分类推广能力以及能使独立成分特征之间彼此保持高阶独立性,与其他视频帧字幕定位提取算法比较的结果表明,该算法具有明显的优点.     

An Animated GIF Steganography Using Variable Block Partition Scheme

The paper presents a novel Graphics Interchange Format (GIF) Steganography system. The algorithm uses an animated (GIF) file format video to apply on, a secured and variable image partition scheme for data embedding. The secret data could be any character text, any image, an audio file, or a video file; that is converted in the form of bits. The proposed method uses a variable partition scheme structure for data embedding in the (GIF) file format video. The algorithm estimates the capacity of the cover (GIF) image frames to embed data bits. Our method built variable partition blocks in an empty frame separately and incorporate it with randomly selected (GIF) frames. This way the (GIF) frame is divided into variable block same as in the empty frame. Then algorithm embeds secret data on appropriate pixel of the (GIF) frame. Each selected partition block for data embedding, can store a different number of data bits based on block size. Intruders could never come to know exact position of the secrete data in this stego frame. All the (GIF) frames are rebuild to make animated stego (GIF) video. The performance of the proposed (GIF) algorithm has experimented and evaluated based on different input parameters, like Mean Square Error (MSE) and Peak Signal-to-Noise Ratio (PSNR) values. The results are compared with some existing methods and found that our method has promising results.