MPEG-4的RTP封装技术及其应用

宽带网络的迅速发展,为网络流媒体应用提供了广阔的前景,MPEG-4具有的高压缩率、强交互性和灵活分级扩展的特性,使之特别适合网络流媒体应用。首先对MPEG-4在网络流媒体应用中的关键问题的RTP封装技术进行深入研究,然后将其应用到视频点播系统中。     

Supporting constant-bit-rate-encoded MPEG-2 transport over local ATM networks

As one of the fast-developing switch-based high-speed networks, asynchronous transfer mode (ATM) is a promising network standard which may satisfy various requirements of multimedia computing. The Moving Picture Experts Group (MPEG) standard was designed to support full motion video stored on digital storage media at compression ratios up to 200:1. MPEG-2 is the second development phase of the MPEG standard and is designed for higher resolutions (including but not restricted to interlaced video) and higher bit rates (up to 20 Mbits/s). In this paper, the ATM adaptation layer type 5 (AAL-5) protocol was used to encapsulate constant-bit-rate-encoded MPEG-2 transport packets because of AAL-5's general availability. However, there is a mismatch of size between MPEG-2's transport packets (188 bytes) and ATM AAL-5's protocol data units (up to 65 535 bytes). In this paper, we examine and analyze four different packing schemes, 1TP, 2TP, nTP-Tight, and nTP-Loose (the scheme we propose), which encapsulated a certain number of MPEG-2 transport packets into one AAL-5 PDU. nTP-Loose scheme is proposed to have (1) better end-to-end performance than schemes 1TP and 2TP, (2) better error-recovery capability than scheme nTP-Tight, and (3) the same buffer requirement as scheme 2TP. A Power Macintosh ATM platform was used to identify the range of possible ways of packing MPEG-2 transport packets into one ATM AAL-5 PDU, when schemes with more than two MPEG-2 transport packets are chosen. Based on the test results, 10 or 12 MPEG-2 transport packets, which can yield throughputs of 70.36 and 78.98 Mbits/s, respectively, are recommended. Fast forward and backward playing of MPEG-2 movies (several times the video display speed) can be easily achieved via ATM networks.     

基层层次光流的半自动时空视频分割技术

在新一代MPEG-4视频编码标准中，为了支持面向对象编码和实现基于内容的应用，视频的半自动分割成为关键技术之一，为此提出了一种基于层次光流的半自动时空视频分割算法。该算法由空域分割和时域分割组成。在空域分割中，提出的基于点的图形用户界面（PBGUI），在用户的协助下，能够精确地定义需要分割的视频对象（VO）。时域分割根据空域分割的结果采用层次光流算法对视频对象进行边界和整体跟踪。实验结果表明，利用该算法，能够精确地分割出视频对象。     

基于层次光流的半自动时空视频分割技术

在新一代 MPEG- 4视频编码标准中 ,为了支持面向对象编码和实现基于内容的应用 ,视频的半自动分割成为关键技术之一 ,为此提出了一种基于层次光流的半自动时空视频分割算法 .该算法由空域分割和时域分割组成 .在空域分割中 ,提出的基于点的图形用户界面 (PBGU I) ,在用户的协助下 ,能够精确地定义需要分割的视频对象 (VO) .时域分割根据空域分割的结果采用层次光流算法对视频对象进行边界和整体跟踪 .实验结果表明 ,利用该算法 ,能够较精确地分割出视频对象 .     

Simple intra prediction algorithms for heterogeneous MPEG-2/H.264 video transcoders

Recent developments have given birth to H.264/AVC: a video coding standard offering better bandwidth to video quality ratios than MPEG-2. It is expected that the H.264/AVC will take over the digital video market, replacing the use of MPEG-2 in most digital video applications. The complete migration to the new video-coding algorithm will take several years given the wide scale use of MPEG-2 in the market place today. This creates an important need for MPEG-2/H264 transcoding technologies. However, given the significant differences between both encoding algorithms, the transcoding process of such systems is much more complex to other heterogeneous video transcoding processes. In this work, we start by analyzing the methods defined in the H.264 video coding standard for the intra prediction: a central element of every H.264 encoder. We then introduce and evaluate six fast intra mode decision algorithms which should enable the development of MPEG-2 to H.264 transcoders. Having evaluated all the proposed methods, we have come out with a high-efficient method, namely DC-ABS pixel. Our results show that our algorithm considerable reduces the complexity involved in the intra prediction with respect the mode decision algorithms used in H.264 JM reference software, while exhibiting a slight degradation on the RD function.. Finally, we analyze a comparative study with two of the most prominent fast intra prediction methods presented in the literature. The results show that the proposed DC-ABS pixel method achieves the best results for video transcoding applications.

A systematic rate controller for MPEG-4 FGS video streaming

This paper proposes a systematic rate controller (SRC) for content-aware streaming of MPEG-4 FGS video over the Internet. An active layer dropping technique is proposed to provide both coarse-grain and fine-granularity scalability of smooth quality adaptation to bandwidth fluctuations and bit-rate variations of streamed video over a general time-scale. The smooth quality adaptation is realized through the mode and state transition of a state machine that implements the SRC. The SRC effectively uses available bandwidth and client buffer by forward-shifting the FGS video stream. It provides protection to video segments with important content by introducing a content-aware priority-based layer model for the MPEG-4 FGS video stream. RID="*" ID="*" The work reported in this paper was performed when this author was working at Microsoft Research Asia as a research intern.     

基于MPEG-7的视频语义检索系统

设计和实现一个支持语义的分布式视频检索系统:"语寻"。该系统利用一个改进的视频语义处理工具(该工具基于IBM VideoAnnEx标注工具,并增加镜头语义图标注和自然语言处理的功能)对视频进行语义分析和标注,生成包含语义信息的MPEG-7描述文件,然后对视频的MPEG-7描述文件建立分布式索引,并同时分布式存储视频文件;系统提供丰富的Web查询接口,包括关键字语义扩展查询,语义图查询以及自然语句查询,当用户提交语义查询意图后,便能够迅速地检索到感兴趣的视频和片段,并且可以浏览点播;整个系统采用分布式架构,具备良好的可扩展性,并能够支持海量视频信息的索引和检索。     

Video protection for MPEG-4 FGS with watermarking

The MPEG-4 fine granularity scalability (FGS) video coding standard offers flexible adaptation to varying network bandwidths and different application needs. This paper presents a MPEG-4 FGS video CODEC based watermarking scheme to embed watermark during encoding. Watermark is embedded into base layer, and can be extracted from both base layer and enhanced video through eliminating the influence of enhancement layer on watermark. This scheme eliminates error propagation caused by watermark for normal video, and utilizes error propagation caused by watermark adjustment to protect the video content. This scheme provides dual protection for intellectual property rights (IPR): watermark and video content protection utilizing error propagation in temporal motion compensation prediction. Watermark is embedded into I-VOP, and is adjusted before I-VOP is reconstructed as reference VOP. Only customers with authorization can adjust the watermark correctly during decoding to get good video quality. Illegal customers can also access the video, but with bad quality. This scheme has the virtue of providing dual protection with a little expense. Theoretical bounds of watermark embedding strength to keep watermark invisibility and of watermark adjustment strength to get enough protective effect are calculated. Some experimental results are given and analyzed.

From MPEG-7 user interaction tools to hanging basket models: bridging the gap

The content–user gap is the difference between the limited range of content-relevant preferences that may be expressed using the MPEG-7 user interaction tools and the much wider range of metadata that may be represented using the MPEG-7 content tools. One approach for closing this gap is to make the user and content metadata isomorphic by using the existing MPEG-7 content tools to represent user (as well as content) metadata (Agius and Angelides 2006, 2007). Subsequently, user preferences may be specified for all content, without omission. Since there is a wealth of user preference and history metadata within the MPEG-7 user interaction tools that can usefully complement these specific content preferences, in this paper we develop a method by which all user and content metadata may be bridged.

MPEG-4 Simple Profile视频网络的传输

给出了一个利用MPEG-4技术在网络上进行视频的流式传输方案。指出了MPEG-4技术的优越性，说明它是符合流媒体技术的要求的。给出总体设计的模块图，并对其中的视频编解码、SL层打包和解包、基于DMIF的网络子系统分别给予详细的阐述。     

基于AT2401的MPEG-4嵌入式视频监控系统的实现

MPEG-4标准是目前视频监控应用中最先进的压缩方法。本文在对MPEG-4编码原理进行研究后，提出了一种基于MPEG-4标准的视频处理芯片AT2401的嵌入式视频监控系统的实现方法，并详细介绍了该嵌入式视频监控系统的主要功能、硬件设计和软件设计流程。该系统完全由硬件进行视频的实时压缩，通过网络可实现多路视频的远程监控。经实际应用证明，该系统稳定可靠，可满足视频监控的需求。     

MPEG-4流媒体系统中的视音频同步

流媒体系统中视音频同步是非常重要的。首先简要地介绍了MPEG 4的相关概念,分析了流媒体系统中影响视音频同步的因素,提出了一套相应的解决方案,最后,给出了一个基于MPEG 4的视频监控系统的实现。     

基于MPEG-4用户数据域的视频抗误码方法

文章根据MPEG-4视频流语法定义,针对视频流当中不同的信息内容采用不同强度的FEC进行抗误码保护,同时利用MPEG-4视频流定义中的用户数据域(user_data)标识编码器所采用的FEC,并利用user_data反馈解码错误信息,使编码端可以动态调整FEC,达到能够自适应调整纠错能力和防止误码扩散的目的。实验结果表明,在高误码率环境下使用该文提出的抗误码方法可以大大提高视频恢复的质量,并且该方法与MPEG-4标准语法兼容,在没有增加过多信道负载和运算复杂度的前提下,具有一定的实用价值。     

基于移动计算的开放式教学系统的设计与实现

结合移动计算及流媒体技术在远程教学中的应用，设计一种基于移动计算的开放式教学系统，利用MPEG-4对视频信号进行编码，使用无线网络进行音频或视频信号传输，并基于Xscale架构的嵌入式系统自主开发设计了用户移动终端，最后实现了一个原型系统。系统具有良好的实时性、交互性和可扩展性。     

Mobile cinema: canonical processes for video adaptation

Nowadays, users not only want to watch digital videos on a PC but also use mobile devices to play back multimedia content. Video adaptation algorithms enable the visualization of recorded videos on mobile devices. Based on our Mobile Business system, we have developed a video adaptation application called Mobile Cinema which considers several characteristic features of mobile devices like screen resolution, bit rate or color depth of a display. The functionality of this system is high and it would be much easier to understand the system if the analysis and the design of the algorithms and the communication interfaces are based on predefined processes which we call canonical processes for media production. The definition of these processes would also make the comparison of two video adaptation applications or the exchange of modules between different systems much easier. In this paper, we describe the functionality and requirements of our existing video adaptation application and map them to the canonical processes for media production.     

基于MPEG-4关键技术的视频医疗系统

通过对MPEG-4视频编码关键技术及原理的分析,利用MPEG-4视频技术实时、高效无线视频传输的特性,开发、设计并实现了基于JMF技术、应用于智能化社区的视频医疗系统。在视频医疗系统中,由JMF提供一个统一的架构和通信协议来管理基于时间媒体的获取、处理和传输。采用实时传输协议/实时传输控制协议(RTP/RTCP)很好的保证了视频传输过程中的实时性,并在JMF中引入了MPEG-4压缩算法插件进行视频压缩。MPEG-4压缩算法压缩比高,并且具有良好的网络适应性。     

基于MPEG-4视频流的QoS映射研究

基于XVID和实时传输协议(RTP)提出了一种MPEG-4视频流的服务质量(QoS)映射管理方法。分析了MPEG-4视频流特点、编解码软件和QoS分层管理方法,提出了基于RTP协议的QoS管理逻辑结构、不同层次上的QoS参数,即应用层和系统层QoS参数,以及应用层到系统层QoS参数的映射算法。在模拟网络环境下的实验结果表明这种QoS参数的映射算法能够保证MPEG-4视频流的服务质量。     

战场电视侦察系统中视频压缩技术及其DSP实现

数字视频压缩是多媒体应用中的关键技术。该文针对战场电视侦察系统的需求提出了一种可行的MPEG-4视频编解码方案,阐述了基于数字信号处理器ADSP21160、数字视频采集芯片Bt829、数字视频合成芯片ADV7175的硬件设计电路以及MPEG-4视频压缩标准的软件程序的算法及其实现。实验表明该文提出的MPEG-4视频编解码器设计方案是可行的。     

基于XMT的MPEG-4场景视频制作及系统设计

介绍了MPEG-4标准中的二进制格式的场景描述，基于XML的两种可扩展文本格式的描述框架：XMT-A和XMT-Ω及其支持的节点、属性、域与BIFS流的映射关系；给出了MPEG-4标准场景视频制作及发布系统的功能结构和基于XMT的系统层次分析。利用该系统制作和发布的多媒体交互式场景视频，可以进行网上教学的节目制作和远程点播。系统建立在MPEG-4标准上，提高了远程教学的质量，满足了用户与场景视频的交互需求；利用XMT作为中间描述格式，满足了相同场景在MPEG-4、SMIL、VRML等标准间的内容交换及互操作功能。