【作者】 马强；

【导师】 于戈；

【作者基本信息】 东北大学 ， 计算机应用技术， 2005， 硕士

【摘要】 视频会议系统最早是由贝尔实验室研制出来的。由于其主要是以模拟方式传送声音和图像,对信号的进一步处理非常困难。而且其性能、价格和会议成本都不具有良好的推广条件。在网络技术、多媒体技术及编解码技术的研究取得了突破性进展和关于视频会议的一系列国际标准的相继出台后,视频会议系统的实用化才得到长足的发展。 本文重点讨论了如何实现一种能在未提供网络服务质量的网络平台上,在视频会议应用层仍能取得良好音频和视频效果的视频会议系统,同时要求其具有良好的差错控制能力。 首先,本文对视频会议系统本身的特性做了深入的分析。指出了视频会议系统的体系架构,传输的多媒体数据的特性以及数据帧的结构。同时也对视频会议系统的相关重要技术进行了介绍,包括网络状况评估技术和网络带宽的分配及调整技术。在对视频会议系统重要的相关技术的分析和研究的基础上,本文提出了一种能对当前网络状况自适应的视频会议系统,SAVC(Self-Adaptable Video Conferencing)系统,并给出了该系统的设计和实现细节,包括系统的体系结构,处理过程以及各个功能模块。 该系统由两部分组成:差错控制子系统和通讯带宽调整子系统。差错控制子系统采用了用RS码进行检错纠错的编/解码方式,并用SARQ(选择自动请求重传)方式进行数据帧的发送和接收。通讯带宽调整子系统是先对当前网络负载情况进行评估,包括当前网络的可用带宽、网络延时和网络抖动等重要参数,然后根据实时的网络状况适当的选择音频视频信号的质量级别(如视频分辨率,帧频等),从而为用户提供了一个稳定的视频会议环境。更多还原

【Abstract】 The video conferencing system is developed first by Bell Labs. Because it transmits audio and video mainly by analog signal method, it is very hard to process signal further. And also, none of its performance, price and conference cost has good popularity conditions. After the study of network techniques, multimedia techniques and encoding/decoding techniques had achieved tremendous progress and a series of international standard on video conferencing had been constituted sequentially, utilization of video conferencing system gets significantly progress.This thesis focuses on how to implement a video conferencing system that can achieve good audio and video effect at video conferencing system’s application level though it is based on the network platform which can not provide quality of service.At first, the thesis analyzes deeply the characteristics of a video conferencing system itself. It indicates architecture, transmitted multimedia data’s features and data frame’s structure of a video conferencing system. Meanwhile, it also introduces relative important technology of video conferencing systems, including network status estimating and network bandwidth assignment and adjustment. Based on the analysis and study of important relative technology on video conferencing systems, this thesis brings up a video conferencing system which can be self-adaptable to its current network status, named for SAVC (Self-Adaptable Video Conferencing) system. At the same time, the thesis describes the system’s design and details of implementation, including system’s architecture, procedure and each function module.The system is composed of two parts: error control subsystem and communication bandwidth’s adjustment subsystem. The error control subsystem adopts encoding/decoding method by the RS code to detect error and correct error. Also, it uses SARQ (Selected Automatic Repeat reQuest) method to send and receive data frames. The communication bandwidth’s adjustment subsystem estimates the current network load status first, including available bandwidth, delay and jitter which are important arguments. Then based on real-time network status it can select properly audiovisual signal’s quality level (for .example, video resolution, frame frequency etc.), so that it can provide a steady video conferencing environment for users.更多还原