视频流点播Dynamic Batched Patching算法研究

本文提出了一个新的视频流点播传输策略,用以解决现有传输策略中存在的系统资源利用率低,QoS较差等问题.该策略的思想是服务器根据用户请求到达时刻,按动态批处理的方式来接纳并服务请求用户,每组用户必须同时从一个或两个信道接收视频内容.文中对本策略的性能进行了理论推导与定量分析,并与现有传输策略作了性能比较,最后采用仿真实验对前面的理论分析与比较进行了验证.理论分析及实验结果表明该策略是一个简单高效的传输策略,适合任意规模的点播应用.     

基于IIS平滑流式处理的移动流媒体系统

针对当前流媒体传输协议在无线网络中的不足,采用IIS平滑流式处理技术设计了基于服务器/客户端模式的移动流媒体系统。详细讨地论了微软的IIS平滑流式处理协议,采用该协议传输音/视频数据,搭建了基于IIS7 Web服务器的流媒体服务,设计了一款基于Windows Phone 7智能手机的流媒体播放器客户端。通过在WiFi网络环境下测试该系统,在直播和点播两种播放模式下,客户端播放的视频画面清晰流畅。通过仿真无线网络带宽的变化,验证了IIS平滑流式处理根据客户端的可用带宽实时调整传送到客户端视频流的质量的特性。     

基于无线视频服务器自适应带宽算法

针对无线网络上行带宽有限的情况,提出了无线视频传输带宽的自适应算法。采用双卡发送采集的视频流数据,这样大大增加了无线视频传输带宽。解决了公共无线网络带宽资源有限的问题。使得无线视频传输码率能够达到500～900 kbit/s。在接收端采取双缓冲区的设计,在客户端能够得到清晰、流畅的视频图像。从而解决了无线视频传输和带宽不足的问题。     

有限带宽网络视频流传输速率控制策略研究

为促进公共视频监控领域新技术的开发和应用,立足解决工程实际问题,提出了一种有限带宽网络下视频流传输速率的控制策略。系统可以根据数据包丢失率、传输时间和时限等动态参数对网络带宽进行估测,并对实时视频的发送速率进行自适应调整,实现稳健控制,很好地解决了网络的传输带宽与视频流码率不匹配等问题。仿真实验表明,系统在降低视频时延和包丢失率、减少网络拥塞、提高带宽利用率和改善视频质量等方面效果明显。     

HLS直播流媒体传输系统的冗余优化

对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件存在较大的冗余,造成网络带宽开销增大。提出一种可行的改进方案,在.m3u8文件中添加一个#EXT-X-MEDIA-SEQUENCE-LAST标签,并使服务器和客户端都对该标签进行识别。通过对网络占用率的对比分析,改进后的方案对网络带宽的占用率明显减小,进而验证了该改进方案的可行性。     

直播流媒体传输系统的冗余优化

摘 要: 对HTTP Live Streaming深入研究之后,发现该协议在直播流媒体传输过程中存在视频流索引文件重复传送的问题。详细阐述了服务器与客户端之间的交互过程,并通过对网络监控软件的使用,检测到交互过程中服务器传输给客户端的视频流索引文件存在较大的冗余,造成网络带宽开销增大。提出一种可行的改进方案,在.M3U8文件中添加一个#EXT-X-MEDIA-SEQUENCE-LAST标签,并使服务器和客户端都对该标签进行识别。通过对网络占用率的对比分析,改进后的方案对网络带宽的占用率明显减小,进而验证了该改进方案的可行性。     

IPv6视频组播系统研究与设计

为了解决大数据量的视频数据在网络上传输的拥塞问题,提高网络带宽的利用率,文中基于微软的Directshow 技术,研究和实现了一种IPv6网络协议下的视频组播系统.该系统通过TCP建立服务器与各个客户端之间的连接管理,并利用RTP实时流媒体协议传输视频数据.根据测试结果分析,此设计不仅有效地节约了网络带宽,而且可以保证视频画面的实时性及准确性,具有一定的实用价值.     

基于Android的视频流自适应算法设计

随着网络的快速发展,对高质量视频的实时传输提出了更高的要求,然而由于智能手机处理能力低、内存小等硬件配置因素,使得嵌入式媒体播放器中的视频数据无法自适应网络状况,最终导致视频数据在传输过程中大量丢失,降低接收到的视频图像质量。在此提出基于Android的视频流自适应算法,该算法可动态探测网络带宽,自动适应网络拥塞状况,制定平滑的数据传输带宽,缓解网络拥塞．根据传输带宽控制视频编码和视频传输速率,提高视频传输质量。     

一种基于优化可变间隔的视频流传输的带宽探测方法

为解决视频传输中的带宽探测问题,本文提出一种基于可变包间隔的视频流传输带宽探测方法.这种方法利用传输的视频流进行带宽测量,通过视频流发送过程中设置不同的报文,组合可变的包间隔,探测时变的网络传输带宽.由于利用视频流传输进行带宽测量可能导致丢包、拥塞等情况,降低视频接收质量,因此本文在提出利用视频流进行带宽测量的基础上,...     

一个基于速率控制的Internet视频流服务方案

由于视频流服务对于网络服务质量有着较高的要求,而现有的Internet所提供的是尽力而为的服务,无法保证数据的实时传输。该文设计了一个用于Internet上视频流的端到端传输方案.整个方案设计的目的是在网络本身缺乏服务质量保证的条件下尽可能达到最好的视频传输质量。根据可用带宽估计和网络信息反馈,系统对发送速率进行调整,并提供两种视频流服务:存储视频和实时视频。仿真结果表明方案的性能良好,能满足Internet视频流的需求。     

Partial video sequence caching scheme for VOD systems withheterogeneous clients

Video on demand (VOD) is one of the key applications in the information era. A hinge factor to its widespread use is the huge bandwidth required to transmit digitized video to a large group of clients with widely varying requirements. This paper addresses issues of heterogeneous clients by proposing a program caching scheme called the partial video sequence (PVS) caching scheme. The PVS caching scheme decomposes video sequences into a number of parts by using a scalable video compression algorithm. Video parts are selected to be cached in local video servers based on the amount of bandwidth that would be demanded from the distribution network and central video server if it was only kept in the central video server. We also show that the PVS caching scheme is suitable for handling vastly varying client requirements     

Video staging: a proxy-server-based approach to end-to-end videodelivery over wide-area networks

Real-time distribution of stored video over wide-area networks (WANs) is a crucial component of many emerging distributed multimedia applications. The heterogeneity in the underlying network environments is an important factor that must be taken into consideration when designing an end-to-end video delivery system. We present a novel approach to the problem of end-to-end video delivery over WANs using proxy servers situated between local-area networks (LANs) and a backbone WAN. A major objective of our approach is to reduce the backbone WAN bandwidth requirement. Toward this end, we develop an effective video delivery technique called video staging via intelligent utilization of the disk bandwidth and storage space available at proxy servers. Using this video staging technique, only part of a video stream is retrieved directly from the central video server across the backbone WAN whereas the rest of the video stream is delivered to users locally from proxy servers attached to the LANs. In this manner, the WAN bandwidth requirement can be significantly reduced, particularly when a large number of users from the same LAN access the video data. We design several video staging methods and evaluate their effectiveness in trading the disk bandwidth of a proxy server for the backbone WAN bandwidth. We also develop two heuristic algorithms to solve the problem of designing a multiple video staging scheme for a proxy server with a given video access profile of a LAN. Our results demonstrate that the proposed proxy-server-based approach provides an effective and scalable solution to the problem of the end-to-end video delivery over WANs     

A multiplexing scheme for H.323 voice-over-IP applications

Voice communications such as telephony are delay sensitive. Existing voice-over-IP (VoIP) applications transmit voice data in packets of very small size to minimize packetization delay, causing very inefficient use of network bandwidth. This paper proposes a multiplexing scheme for improving the bandwidth efficiency of existing VoIP applications. By installing a multiplexer in an H.323 proxy, voice packets from multiple sources are combined into one IP packet for transmission. A demultiplexer at the receiver-end proxy restores the original voice packets before delivering them to the end-user applications. Results show that the multiplexing scheme can increase bandwidth efficiency by as much as 300%. The multiplexing scheme is fully compatible with existing H.323-compliant VoIP applications and can be readily deployed.     

High-performance prefetching protocols for VBR prerecorded video

We describe several high-performance prefetching protocols for the transport of VBR prerecorded video over a shared channel. The protocols are particularly well suite for offering video on demand over a residential cable network, a residential ADSL network, or over a shared satellite channel. We advocate the use of VBR-encoded video instead of CBR video because, for the same image quality, VBR-encoded video can have a significantly lower average rate. However in order to exploit the efficiency of VBR encoding, it is necessary that the VBR scheme multiplex and prefetch streams so that near 100 percent link utilizations are achieved. Our protocols are based on the observation that there are frequent periods of time during which the network bandwidth is under utilized. During these periods the server can prefetch frames from any of the ongoing videos and send the frames to the buffers in the appropriate clients. Simulation results based on MPEG-encoded traces show that the discussed prefetching protocols compare favorably with other VBR transport protocols     

A bandwidth assignment algorithm on a satellite channel for VBR traffic

Variable bit rate (VBR) video is currently by far the most interesting and challenging real-time application. A VBR encoder attempts to keep the quality of video output constant and at the same time reduces bandwidth requirements, since only a minimum amount of information has to be transferred. On the other hand, as VBR video traffic is both highly variable and delay-sensitive, high-speed networks (e.g. ATM) are generally implemented by assigning peak rate bandwidths to VBR video applications. This approach may, however, be inefficient in a satellite network based on a TDMA scheme. To overcome this problem, we have designed a demand assignment satellite bandwidth allocation algorithm in TDMA, named V2L-DA (VBR 2-Level Demand Assignment), which manages the VBR video traffic according to a dynamic bandwidth allocation algorithm. In this paper we discuss how to tune the proposed algorithm in order to optimize network utilization when MPEG-1 VBR video traffic is being transmitted. Our results indicate that most of the time only 40% of the peak rate bandwidth is needed to satisfy the VBR source, so the remaining 60% of the peak rate bandwidth can be used to transmit the datagram traffic queued in the network stations. © 1997 John Wiley & Sons, Ltd.     

Bandwidth renegotiation for VBR video over ATM networks

A scheme for delivery or variable bit-rate (VBR) video over asynchronous transfer mode (ATM) networks where bandwidth can be renegotiated during the duration of a call between the video source and the network is considered. Renegotiation can be initiated by either the video source or the network. The video bandwidth requirement is characterized by a usage parameter control (UPC) consisting, in general, of peak rate, burst length, and sustained rate. A baseline design is outlined where rate-control adjusts the source's rate while a new UPC is requested from the network. When granted, the new UPC allows the source to maintain its target quantization and delay requirements. Rate control epochs may be extended when the network blocks UPC requests or sets a lower UPC value to temporally deal with congestion. Simulation results are presented for VBR MPEG video. The results show that with a moderate renegotiation rate the scheme tracks the bandwidth requirements of the source. As a result, the video quality and bandwidth efficiency can be maintained     

Optimal multicast smoothing of streaming video over the Internet

A set of applications such as Internet video broadcasts, corporate telecasts, and distance learning require the simultaneous streaming of video to a large population of viewers across the Internet. The high bandwidth requirements and the multi-timescale burstiness of compressed video make it a challenging problem to provision network resources for streaming multimedia. For such applications to become affordable and ubiquitous, it is necessary to develop scalable techniques to efficiently stream video to a large number of disparate clients across a heterogeneous Internet. In this paper, we propose to multicast smoothed video over an application-level overlay network of proxies, and to differentially cache the video at the intermediate nodes (proxies) in the distribution tree, in order to reduce the network bandwidth requirements of video dissemination. We formulate the multicast smoothing problem as an optimization problem, and develop an algorithm for computing the set of transmission schedules for the tree that minimize the peak rate and rate variability, given buffer constraints at different nodes in the tree. We also develop an algorithm to compute the minimum buffer allocation in the entire tree, such that feasible transmission to all the clients is possible, when the tree has heterogeneous rate constraints. We show through trace-driven simulations that substantial benefits are possible from multicast smoothing and differential caching, and that these gains can be realized even with modest proxy caches.     

基于多路并行的3G视频传输系统设计与实现

针对3G视频传输时低带宽、高丢包以及不稳定的特点,本文提出一种利用WCDMA和CDMA2000多张网卡并行传输720P高清视频的方案。该方案通过测试WCDMA和CDMA2000两种3G上行带宽,分析了3G上行的特点,确定了使用3G网卡的数量;提出了一种带宽自适应方案和一种换路丢包重传算法。测试结果显示,本方案能够很好的聚合带宽、增强传输鲁棒性、将丢包控制在1%以下并且能够流畅的传输视频。     

视频失真优化的分布式视频点播服务系统及性能分析

本文提出一种用于分布式视频点播服务系统的速率分配算法和实现框架。在考虑负载均衡与满足服务器带宽限制的前提下,速率分配能将以失真为度量的全局视频质量最优化。确定各服务结点的输出码率被建模成一个最优化问题：优化目标是最小化多个视频总失真,限制条件为最低可接受视频质量、服务器带宽限制以及发送速率对客户端TCP流量的友好性。根据优化算法的计算结果,视频节目使用可变码率编码,由多个视频分发服务器同时向客户端传输;同时服务器检测与客户端之间端到端链路的时变特性和估计网络拥塞情况,使优化速率分配结果适应网络状态的变化。本方案应用跨层设计的思想,将应用层视频质量建模为网络层参数的函数,当网络状态波动时,动态调整编码码率和发送速率以适应带宽变化,提前避免链路拥塞,降低接收端解码器丢包率,从而使总体视频质量得到提升。     

Transporting compressed video over ATM networks with explicit-ratefeedback control

We propose a scheme for transmission of variable bit rate (VBR) compressed video for interactive applications using the explicit-rate congestion-control mechanisms proposed for the available bit rate (ABR) service in asynchronous transfer mode networks. Compressed video is inherently bursty, with rate fluctuations over both short and long time scales. This source behavior can be accommodated by the ABR service, since the explicit-rate scheme allows sources to request varying amounts of bandwidth over time. Moreover, when the bandwidth demand cannot be met, the network provides feedback indicating the bandwidth currently available to a connection. In our scheme, the video source rate is matched to the available bandwidth by modifying the quantization level used during compression. We use trace-driven simulations to examine how effective the enhanced explicit-rate scheme is in “rate matching” between the network and the source and the effect on end-to-end delay. We also look at the sensitivity of the proposed scheme to the estimates of the network round-trip times and to inaccuracies in the rate requests made by sources