基于WINDOWS平台的多媒体文件格式转换原理与实现

主要分析了多媒体文件格式转换需要的技术,提出了一种解析多媒体文件的方法。介绍了几种典型的多媒体文件系统,视频数据的压缩方法和标准。介绍了DirectShow的体系结构,编码器和解码器的工作原理和插件机制。分析了如何使用第三方插件来完成编码解码,并提供了测试一个编码解码方案有效性的方法。最后,以MP4 文件转换为ASF文件为例,说明了如何利用DirectShow中的组装插件技术来构建格式转换方案,以及如何编程实现这个方案。     

DirectShow技术在音频格式转换及音视频分离方面的应用

目前语音识别系统的输入都是线性PCM格式的音频文件,然而在实际应用中,需要识别各种格式音频文件以及视频流中的音频,在开始识别前,需要进行音频格式转换并从视频流中进行音频提取.因此,音频格式的转换和从视频中分离出音频信号已成为语音识别系统一种必需的预处理过程.文中介绍了一种将Microsoft的DirectShow技术应用于Windows平台的多种压缩音频格式转换为Windows PCM WAV格式以及从多媒体视频中分离音频信号的方法,并分析了常见音频压缩编码格式经转换后对语音识别系统性能的影响.这对于语音识别技术在实际中的应用有着重要的意义.     

应用DirectShow和Codec技术录制屏幕

介绍了如何应用DirectShow技术进行电脑屏幕和音频的录制,并应用Codec压缩音/视频数据为多媒体文件,并可通过第三方多媒体播放器进行回放。可以通过实践了解DirectShow和Codec技术的基本使用方法。     

扩展格式AVI文件播放的编程方法

在阐明扩展格式AVI文件格式和DirectShow编程技术原理的基础上，给出了一种基于扩展格式AVI文件的动态图像文件播放程序的设计和实现方法，该播放程序使用Visual C 6.0编写，使用了DirectShow技术，可以在Windows环境下实时播放扩展格式AVI文件。     

视频转码技术在网络多媒体传输中的应用

视频文件数据量大、网络带宽有限,针对这一特点,提出了一种将视频文件进行转换为低码率的MPEG-4格式的文件后分帧传输的方案。在实际工程中表明基于该方案设计的采用视频转码技术的网络多媒体传输系统可以使传输效率提高5~10倍。文中重点对方案中涉及的压缩转码过程进行了讨论分析,根据分析给出了在压缩编码过程中涉及到的一些参数,并进一步指出了视频转换编码模块的灵活性。     

视频转码技术在网络多媒体传输中的应用

视频文件数据量大、网络带宽有限，针对这一特点，提出了一种将视频文件进行转换为低码率的MPEG-4格式的文件后分帧传输的方案。在实际工程中表明基于该方案设计的采用视频转码技术的网络多媒体传输系统可以使传输效率提高5～10。文中重点对方案中涉及的压缩转码过程进行了讨论分析，根据分析给出了在压缩编码过程中涉及到的一些参数，并进一步指出了视频转换编码模块的灵活性。     

基于FFMPEG的视频转换与发布系统

近年来数字视频工业得到了快速的发展,数字视频摄像机也成为了人们日常生活的一部分,但是同时也增加了视频的格式和编码方式.因此,如何能够从一种格式转换成另一种更适合的格式也成了一种迫切需求,而FFMPEG为音视频的转换提供了强大的支持.主要讨论了如何在Linux操作系统下,进行FFMPEG的安装、编译,利用FFMPEG平台对视频的格式进行转换,以及视频的上传与发布.     

基于DirectShow的远程视频展示实现

在分析了DirectShow技术的基础上,该文提出基于DirectShow技术的远程视频展示系统。构建了系统的框架,设计了视频采集、视频编解码、视频发送和视频接收的实现方案。     

基于DirectShow设计视频加密Transform Filter

实现了基于DirectShow技术开发视频加密TransformFilter。首先介绍了视频加密的原理和方案,分析了Di-rectShow的体系结构,然后研究了基于DirectShow技术如何实现视频加密TransformFilter,并给出了试验结果和结论。试验结果表明该Filter可以对实时视频进行加密,加密速度快,效果好。     

虚拟摄像头开发模式及其应用研究

随着多媒体通信技术的发展,如何通过普通摄像头有效传输特效视频数据成为当前的一个研究热点。针对该问题,本文提出了一种基于DirectShow和WDM技术的虚拟摄像头开发模式,并详细讨论了实现过程中的关键技术,最后介绍了一个典型的应用方案。     

分布式系统Hadoop 平台的视频转码

在研究了目前主流的视频转码方案基础上,提出了一种分布式转码系统。系统采用HDFS（Hadoop Distributed File System）进行视频存储,利用MapReduce思想和FFMPEG进行分布式转码。详细讨论了视频分布式存储时的分段策略,以及分段大小对存取时间的影响。同时,定义了视频存储和转换的元数据格式。提出了基于MapReduce编程框架的分布式转码方案,即Mapper端进行转码和Reducer端进行视频合并。实验数据显示了转码时间随视频分段大小和转码机器数量不同而变化的趋势。结果表明,相比单机转码,提出的系统在采用8台机器并行转码时,可以节约80％左右的时间。     

MSC: a multi-version shared caching for multi-bitrate VoD services

Recently, many Video-on-Demand (VoD) service providers try to attract as many users as possible by offering multi-bitrate video streaming services with differentiated qualities. Many researches focus on video layered coding (e.g., scalable video coding, SVC). However, SVC is not widely used in VoD industry. Another solution, multi-version videos, can be classified into online transcoding and pre-stored multi-version videos. Online transcoding is a CPU-intensive and costly task, so it is not suitable for large-scale VoD applications. In this paper, we study how to improve caching efficiency based on pre-stored multi-version videos. We leverage the sharing probability among different versions of the same video and propose a multi-version shared caching (MSC) method to maximize the benefit of caching proxy. If the desired version is not in the cache while the higher neighbor version is in, MSC transmits the higher version streaming to user temporarily. In this case, MSC can make full use of the caching resources to improve the cache hit ratio and decrease users’ average waiting time. Simulation results show that MSC outperforms the others in the cache hit ratio and the average waiting time.     

Utility-Based Video Adaptation for Universal Multimedia Access (UMA) and Content-Based Utility Function Prediction for Real-Time Video Transcoding

Many techniques exist for adapting videos to satisfy heterogeneous resource conditions or user preferences, whereas selection of the best adaptation operation among various choices usually is either ad hoc or inefficient. To provide a systematic solution, we present a conceptual framework based on utility function (UF), which models video entity, adaptation, resource, utility, and the relations among them. In order to support real-time video adaptation, we present a content-based statistical paradigm to facilitate the prediction of UF for real-time transcoding of live videos. Instead of modelling the UF through analytical models, as in the conventional rate-distortion framework, the proposed approach formulates the prediction as a classification and regression problem. Each video clip is classified into one of distinctive categories and then local regression is used to accurately predict the utility value. Our extensive experiment results based on MPEG-4 transcoding demonstrate that the proposed method achieves very promising performance - up to 89% accuracy in choosing the optimal transcoding operation (in both spatial and temporal dimensions) with the highest quality over a diverse range of target bit rates     

Efficient segment-based video transcoding proxy for mobile multimedia services

To support various bandwidth requirements for mobile multimedia services for future heterogeneous mobile environments, such as portable notebooks, personal digital assistants (PDAs), and 3G cellular phones, a transcoding video proxy is usually necessary to provide mobile clients with adapted video streams by not only transcoding videos to meet different needs on demand, but also caching them for later use. Traditional proxy technology is not applicable to a video proxy because it is less cost-effective to cache the complete videos to fit all kinds of clients in the proxy. Since transcoded video objects have inheritance dependency between different bit-rate versions, we can use this property to amortize the retransmission overhead from transcoding other objects cached in the proxy. In this paper, we propose the object relation graph (ORG) to manage the static relationships between video versions and an efficient replacement algorithm to dynamically manage video segments cached in the proxy. Specifically, we formulate a transcoding time constrained profit function to evaluate the profit from caching each version of an object. The profit function considers not only the sum of the costs of caching individual versions of an object, but also the transcoding relationship among these versions. In addition, an effective data structure, cached object relation tree (CORT), is designed to facilitate the management of multiple versions of different objects cached in the transcoding proxy. Experimental results show that the proposed algorithm outperforms companion schemes in terms of the byte-hit ratios and the startup latency.     

边缘计算中面向多码率视频的缓存、转码和传输联合优化策略

结合边缘缓存技术与流媒体传输技术能有效提升视频服务质量,为降低视频内容提供商的边缘资源租赁成本,提出一种视频缓存、转码和传输联合优化策略.首先,综合考虑视频的缓存、转码、边缘传输和云端传输的成本,以最小总租赁成本为目标建立整数规划模型,并证明其NP-complete性质;其次,根据历史请求数估计视频流行度变化,并对流行视频进行缓存;最后,基于视频的缓存状态,为用户的请求选择成本最低的响应方式.仿真实验表明,所提策略与现有策略相比,可提升请求命中率并有效降低内容提供商的资源租赁成本.     

A platform for transcoding heterogeneous markup documents using ontology-based metadata

As new standards, markup languages, protocols, and client devices continue to emerge, the main problem of existing transcoding systems is the lack of intelligence to cope with the heterogeneous effects, including various transcoding policies, markup documents, device constraints, and server platforms. This study proposes a new approach, called hybrid transcoding, to combine the traditional transcoding technologies based on ontology-based metadata to improve these heterogeneous problems. Additionally, the heterogeneous markup document transcoding (HMDT) platform, based on the proposed hybrid transcoding and web services technologies, is also presented to serve as a transcoding service broker to facilitate interoperability between distributed heterogeneous transcoders. To demonstrate the feasibility of HMDT platform, an application scenario of hybrid transcoding is implemented to convert HTML forms into various client devices.     

A weighted segment-based caching algorithm for video streaming objects over heterogeneous networking environments

Traditional caching technology is not applicable to cache video streaming objects over heterogeneous networking environments. The popularity of mobile devices in the heterogeneous networking environments make the access of Internet content become a common phenomenon. To support different mobile devices in the heterogeneity networking environments, a transcoding proxy is used to transcode different versions of the streaming videos according to clients’ requests. In this paper, we propose a weighted caching replace strategy for video streaming objects over heterogeneous networking environments. A new caching algorithm with static weight transcoding graph and dynamic caching relation tree is introduced. The proposed algorithm is compared with LRU, LFU, CP and PF cache algorithms in three parts: hit ratio, byte hit ratio, and average transmission delay. Experimental results show that the proposed algorithm outperforms than traditional LRU, LFU, CP and PF cache algorithms.     

MPEG-2到H.264转码中的运动矢量优化算法

在视频转换编码技术中,通常利用输入码流中的运动矢量等信息来降低转码处理的计算量。该文介绍一种MPEG-2到H.264的转码器,针对MPEG-2和H.264标准中运动估计算法的不同特点,提出用于转码处理的运动矢量优化算法,并对不同算法进行分析比较。结果表明该优化算法可以在保证转码质量的前提下,降低转码处理的计算量。     

视频转码应用分析

在视频会议系统中还有日常拍摄处理视频时,需要利用视频转码技术对传统和新兴视频流进行格式转换。使用转码的意义在于可以在不损失任何视频质量的前提下节省高达50％的网络带宽。转码的分类按照媒体格式可分为音频转码、视频转码,视频转码比较出名的有暴风转码、格式工厂,音频转码用大众的千千静听就能满足使用需要。本文以转码应用为研究对象,进一步分析软件转码技术的应用。     

Video watermark application for embedding recipient ID in real-time-encoding VoD server

A previously developed system for embedding watermarks in video content in real time has been improved by incorporating real-time transcoding, which enables embedding of watermarks specific to the recipient. That is, watermarks are used as fingerprints. When a play command is received from a customer, the system decodes the requested video content into frame images in the server. The frame images are then watermarked, encoded, and streamed to the customer in real time. Prototype testing demonstrated that use of this watermarking method is feasible for video-on-demand service; that is, up to 20 individually watermarked videos can be concurrently streamed to customers. Visibility testing showed that the quality of the watermarked images was practical to some degree. Robustness testing showed that the embedded watermarks were practically robust against encoding. Use of this system should help deter the illegal copying and distribution of video content.