基于分层编码的流媒体传输技术研究

本文将分层编码技术应用于P2P视频点播中,能提高整个系统的健壮性,还可加快接收端对流媒体数据的接收速度,在固定播放启动时延条件下提高接收端的播放质量。     

TFAMCC:TCP友好的自适应分层多播拥塞控制机制

满足接收端异构性的分层多播传输机制,源端一般只用于编码及各层数据流的传输,而拥塞控制主要在接收端来完成。这里提出一种源端与接收端协同作用共同完成多播的拥塞控制机制。源端根据接收端的反馈调节多播层次数目及各层传输速率,接收端根据TCP吞吐量模型计算本地允许带宽,进行层次的接收及形成对源端调节的反馈。经试验证明,此机制具有TCP友好性、接收端带宽充分利用及良好的可扩展性。     

H.264视频码流分级传输和抗误码性能的研究

网络异构性是面向网络传输的视频编码面临的最大挑战之一,而分层可扩展性编码则在一定程度上解决了这一问题。作为最新的视频编码标准,H.264/AVC很好地继承和发展了该项技术,本文在研究各种分层编码在H.264/AVC标准中的应用情况的基础上,结合差错非均匀保护(UEP-UnequalErrorProtection)技术提出了一种联合可扩展性编码及网络传输方案,实验结果表明该方案提供了更宽范围的可扩展性并具有良好的抗误码性能。     

基于凸优化和遗传算法的分层多播自适应优化

针对无线网络上视频多播效用优化问题，提出了一种新的结合自适应调制编码的分层多播自适应优化方法。具体做法是将视频的各层对应传输于不同的自适应调制编码模式，并对各视频层分配合适的带宽，如果效用函数为凸函数，则系统效用的优化问题转换成凸优化问题，若效用函数无凸性限制，并考虑实际因素，即视频分层编码的层数限制以及有限的、可选择的各层速率之后，新的系统优化问题则通过遗传算法求解。仿真结果证明了该方法的有效性。     

一种分层多描述编码的动态带宽分配策略

针对无线流媒体业务带宽资源有限的特点,提出一种基于分层多描述编码的动态带宽分配策略LMDBA.该策略利用了分层多描述编码的特性实现动态带宽分配,并采用QoS升降级策略,在保证用户QoS的前提下,尽可能地降低系统阻塞,提高系统带宽资源利用率.并对QoS升降级策略进行了公平性分析.仿真实验结果表明,在提供一定用户QoS保证下,提出的新策略比传统固定带宽分配策略在带宽资源利用率和系统阻塞上有显著的改善.     

基于缓冲技术的网络带宽自适应码流控制策略

码流控制是网络多媒体服务中需要解决的主要问题之一.该文依据码流控制的主要影响因素--网络带宽,提出了一种基于网络带宽自适应的缓冲技术方案,先在接收端实时探测网络带宽反馈给网络服务发送端,按照网络带宽选择编码不同的数据分层,并进行了缓冲处理,然后输出传送码流,使得网络服务在适应网络不同带宽需求上具有灵活性.实验表明,使用该文带宽自适应缓冲技术方案,提高了预编码的MPEG视频流的传输质量.     

视频实时传输中的速率控制研究

视频在互联网上的实时传输常因其要求高带宽、低延迟而造成网络拥塞。传统TCP基于窗口的拥塞控制已经不适用于实时传输中的拥塞控制,该文讨论了基于速率的网络拥塞控制方法,它采用自适应码率和分层的视频编码技术,详细说明了基于源端和收端的各种速率控制方法。     

OpTrans:一个率失真优化的MC-EZBC转换编码算法

可伸缩性视频转换编码算法是大型分层视频组播系统层次化代理自适应机制的核心技术.好的转换编码算法不仅要满足拥塞速率控制的要求,而且要使分层视频组播流中的增强层数据以率失真优化的方式进行截断,以提高接收者的接收效能.本文对可伸缩三维小波编码算法MC-EZBC视频转换编码的联合率失真目标函数和优化算法进行了深入研究,提出了率失真优化的MC-EZBC转换编码算法及其分层速率控制方法.对比实验结果表明,采用了联合率失真优化后的转换编码码率控制方法比原有的按顺序截断方法可提高平均视频质量PSNR0.3-0.5dB,进而可优化大型分层视频组播系统的整体效能.     

异构环境下层次编码多视频源多共享信道分层组播

视频组播是许多当前和将来网络服务的重要组成部分,如视频会议,远程学习、远地展示及视频点播,随着网络传送基础设施的改善和端系统处理能力的增强,组播视频应用日益变得可行,组播视频传输中存在的主要问题是网络送资源的异构性和动态性,其使得视频流的多个接收方都达到可接受的流量特性变得异常困难,目前该问题的一个有效解决方式就是利用自适应的分层视频传输机制,在该机制中,各源产生层次媒体流,并在多个网络信道中传输。对视频会议类的多点到多点视频组播应用,信道往往被所有潜在的发送方共享,任何发送方都可在任何一个共享信道中发送其视频层次。在该多点到多点、共享信道、分层视频组播模型下,一个关键问题就是如何动态确定各视频源层次到各共享组播信道的映射,映射策略直接影响到会话整体视频接收质量和网络带宽利用率。典型的方式是顺序映射,该映射方式同等对待各发送方,但利用该方式,随源数目的增加,在各共享网络信度上会出现带宽可伸缩性问题,而且顺序映射方式无法适应网络传送资源和会话状态的动态变化。为此,该文设计了一种基于接收方反馈信息的自适应的层次映射算法,接收方周期性地将其当前感兴趣的发送方及接收速率的信息反馈给某控制节点,而控制节点就利用当前反馈信息动态地调整映射策略。经证实,该算法始终能比顺序层次映射算法获得更高的整体视频接收质量,并具有高的带宽利用率和很小的复杂度。     

面向移动网的可分层Web服务自适应发布方法

提出一种面向移动网的可分层Web Service(LWS)的自适应发布方法--LSA(Layered Self-Adaptive)方法,目标是克服移动网的带宽局限性、多样性和不稳定性,实现通过移动网智能地、无缝地访问可分层Web Service。在研究可扩展性视频分层算法的基础上,提出一系列数值化计算方法,通过数值化计算得出最适合当前网络环境的Web Service。     

多描述可分级编码的研究进展

多媒体及Internet的迅速发展促使视频编码不仅要有较好的容错性能，而且要根据网络带宽和接收设备的特性而自适应地进行调整和传输。多描述编码可以提高视频传输的容错性能但不具有网络自适应性；可分级编码能够根据网络带宽和接收设备的特性而自适应地进行调整和传输但不具有容错性能。综合了多描述编码和可分级编码优势的多描述可分级编码，则不但具有网络带宽的自适应性，同时具有很好的容错性能。在分析了多描述编码和可分级编码的各自局限性的基础上，重点介绍了多描述可分级编码的产生和几种实现策略。     

一种不同租借带宽用户公平性解决方法

为解决具有不同接入带宽用户在共享链路上的公平性问题，提出了一种多门限随机早期检测(RED)队列方法。该方法对RED队列进行改造，即在共享链路输出队列上为每一个接入用户设置一个RED最大门限，同时测量各接入用户所获得的实际吞吐率，并根据此测量值动态调整这一系列最大门限值，从而控制对各用户数据分组的丢弃概率,达到调整实际吞吐率比例的目的。实验表明，所提出的解决方法不仅保持了RED队列的优点，同时能够保证接入用户在共享链路获得公平带宽。     

码率可分级小波视频编码算法的研究

对于多种视频传输业务,传统的分层可分级性已不能很好地满足要求,编码器需要提供码率可分级性.采用改进的零树小波编码算法生成了高性能的嵌入式码流,实现了一个码率可分级视频编解码器.而在码率可分级编解码算法中,同一码流需要在较大的码率范围内保持编码效率.目前的解决方案在目标码率提高时,重建图像的质量得不到有效的改善.指出了码率可分级编码算法不仅要考虑误差扩散问题,还要考虑帧间依赖关系,并提出了一种新的算法.实验结果表明,该算法使同一码流能在多种码率下提供更好的重建图像的质量,而且所提算法可用于其他采用运动补偿算     

LION: Layered Overlay Multicast With Network Coding

Recent advances in information theory show that the throughput of a multicast session can be improved using network coding. In overlay networks, the available bandwidth between sender and different receivers are different. In this paper, we propose a solution to improve the throughput of an overlay multicast session with heterogeneous receivers by organizing the receivers into layered data distribution meshes and sending substreams to each mesh using layered coding. Our solutions utilize alternative paths and network coding in each mesh. We first formulate the problem into a mathematical programming, whose optimal solution requires global information. We therefore present a distributed heuristic algorithm. The heuristic progressively organizes the receivers into layered meshes. Each receiver can subscribe to a proper number of meshes to maximize its throughput by fully utilizing its available bandwidth. The benefits of organizing the topology into layered mesh and using network coding are demonstrated through extensive simulations. Numerical results indicate that the average throughput of a multicast session is significantly improved (up to 50% to 60%) with only slightly higher delay and network resource consumption.     

Fine-Grained Scalable Video Caching for Heterogeneous Clients

Much research has focused on caching adaptive videos to improve system performance for heterogeneous clients with diverse access bandwidths. However, existing rate-adaptive caching systems, which are based on layered coding or transcoding, often suffer from a coarse adaptation and/or a high computation overhead. In this paper, we propose an innovative rate-adaptive caching framework that enables low-cost and fine-grained adaptation by using MPEG-4 fine-grained scalable videos. The proposed framework is both network-aware and media-adaptive; i.e., the clients can be of heterogeneous streaming rates, and the backbone bandwidth consumption can be adaptively controlled. We develop efficient cache management schemes to determine the best contents to cache and the optimal streaming rate to each client under the framework. We demonstrate via simulations that, compared to nonadaptive caching, the proposed framework with the optimal cache management not only achieves a significant reduction in the data transmission cost, but also enables a flexible utility assignment for the heterogeneous clients. Our results also show that the framework maintains a low computational overhead, which implies that it is practically deployable.     

Internet上图象渐进传输的研究

在Internet环境中,每个用户所占用的网络带宽是不同的,并且随着网络状况的动态变化而变化,不同用户对图象的质量要求也不一样,因此要求服务器端的图象编码器必须具有高度的适应性。1993年,Shapiro提出的小波零树编码算法是一种非常有效的基于小波变换的图象编码方法,该算法编码器输出的比特流是按基重要性排序的,是对原图象一种渐进的二进制表示。在该算法的基础上,提出了一适合Internet环境下的静态图象渐进传输解决方案,最后给出了实验结果。     

Seamless switching of scalable video bitstreams for efficient streaming

Efficient adaptation to channel bandwidth is broadly required for effective streaming video over the Internet. To address this requirement, a novel seamless switching scheme among scalable video bitstreams is proposed in this paper. It can significantly improve the performance of video streaming over a broad range of bit rates by fully taking advantage of both the high coding efficiency of nonscalable bitstreams and the flexibility of scalable bitstreams, where small channel bandwidth fluctuations are accommodated by the scalability of a single scalable bitstream, whereas large channel bandwidth fluctuations are tolerated by flexible switching between different scalable bitstreams. Two main techniques for switching between video bitstreams are proposed. Firstly, a novel coding scheme is proposed to enable drift-free switching at any frame from the current scalable bitstream to one operated at lower rates without sending any overhead bits. Secondly, a switching-frame coding scheme is proposed to greatly reduce the number of extra bits needed for switching from the current scalable bitstream to one operated at higher rates. Compared with existing approaches, such as switching between nonscalable bitstreams and streaming with a single scalable bitstream, our experimental results clearly show that the proposed scheme brings higher efficiency and more flexibility in video streaming.     

Optimal Coding of Multilayer and Multiversion Video Streams

Traditional video servers partially cope with heterogeneous client populations by maintaining a few versions of the same stream with different bit rates. More recent video servers leverage multilayer scalable coding techniques to customize the quality for individual clients. In both cases, heuristic, error-prone, techniques are currently used by administrators to determine either the rate of each stream version, or the granularity and rate of each layer in a multilayer scalable stream. In this paper, we propose an algorithm to determine the optimal rate and encoding granularity of each layer in a scalable video stream that maximizes a system-defined utility function for a given client distribution. The proposed algorithm can be used to compute the optimal rates of multiversion streams as well. Our algorithm is general in the sense that it can employ arbitrary utility functions for clients. We implement our algorithm and verify its optimality, and we show how various structuring of scalable video streams affect the client utilities. To demonstrate the generality of our algorithm, we consider three utility functions in our experiments. These utility functions model various aspects of streaming systems, including the effective rate received by clients, the mismatch between client bandwidth and received stream rate, and the client-perceived quality in terms of PSNR. We compare our algorithm against a heuristic algorithm that has been used before in the literature, and we show that our algorithm outperforms it in all cases.     

基于预测机制的云媒体网络自适应视频流选择算法

研究移动网络中,如何进一步提高云媒体服务带宽利用率的问题,提出一种基于预测机制的云媒体网络自适应视频流选择算法。该算法包含可用带宽预测模型和视频流决策模型。在带宽预测模型中,根据带宽评估结果把当前的网络状态划分为三个模式,每个模式对应不同的带宽预测方法,并且不同的模式能够相互转化。在视频流决策模型中,利用预测的可用带宽,结合可伸缩视频编码技术为用户自适应的调整视频质量。根据实验,在不同网络环境下,该方法能够有效的利用带宽,并提高媒体服务质量。