H.264视频压缩标准的日益普及已使H.264成为视频监控行业内公认的“流行语”。H.264使得我们谈到的所有可能的增强功能脱颖而出。Optelecom-NKF 公司的Kate Huber, Peter de konik and Piet Nieuwets在接下来文章当中的前三段首先为大家呈现了这个流行的标准真正的好处和缺点。

　　H.264像风暴一样席卷视频流媒体世界

　　星期六的晚上，当你坐在电视机前的时候，比起看一座桥自动升起或者一个交通摄像头拍下的闯红灯的画面，或许不会对视频流媒体标准有什么想法。但是是视频流使得可以从控制中心安全的开通桥梁，以及让尽可能多的街道变得安全，使得你可以抬起你的脚并暂时忘记你最喜欢的电影。

　　H.264已经成为安防产业选择的压缩标准

　　自1995年以来，电视广播和DVD视频选择的视频流媒体标准一直是MPEG-2.它的继任者，MPEG-4第二部分，在1998年扩大了MPEG-2的可能性，创造了一个现今已被计算机产业广泛采用的流媒体标准。但是现在视频流媒体世界的流行语是H.264，又称为MPEG-4第10部分。人们现在正在开发或传播编解码器要么已经支持它要么很快也要支持它。但是到底H.264是什么，它有什么特别之处呢?

　　开创了一个新的视频压缩标准—H.264简史

　　H.264是一种国际合作的产物

　　简单来说，H.264是一种视频压缩标准。它是定义流媒体技术基本准则的三大组织，国际标准组织(ISO)和国际电工委员会(IEC)以及国际电信联盟-电信标准部门(ITU-T)，合作的产物。ISO和IEC的成员与1988年五月成立了一个运动图像专家组(MPEG)，它以20世纪90年代发布MPEG-2和MPEG-4第二部分视频和音频压缩与传输标准而闻名。2001年，MPEG和ITU-T的分支组织视频编码专家组(VCEG)，成立了一个新的工作组—联合视频组(JVT)。JVT在MPEG-2/4标准的基础上，创造了新的H.264视频压缩标准，并于2003年发布。[nextpage]

　　一个灵活的视频压缩标准

　　H.264视频压缩标准为格式化压缩视频设立了要求，以保证在提高视频质量的同时比以往的标准比特率更低。但是，它实际上并没有明确编码器应该如何进行视频流编码。它只定义了可能用到的解码器的功能、工具以及机制，这使得这个标准无与伦比的灵活，并允许开发者角逐最有效的编码机制。

　　不过，H.264并不是与它的前辈完全不同的压缩标准。与MPEG-2/4相似，开发者必须要为特定的用途选择一个特定的配置文件。以H.264为例，有三种配置文件：基线，主要和扩展。基线配置文件由于在解码器上的要求较少，为可视电话、视频会议、无线通信、笔录电视装置所优化。主要配置在视频广播和视频存储中更好用，而处理能力要求较少的更严格的应用程序可以使用到扩展配置文件。

　　像以前的MPEG-2/4一样，H.264也使用基于模块的编码机制。这意味着H.264采用运动估计、变换、量化以及熵编码(注：熵编码是在编码过程中按熵远离不丢失任何信息的编码)来进行视频压缩，并方向进行这些进程来进行图像解码以便观看。

　　基于模块的编码所涉及的步骤

　　一个卓越的视频压缩标准?

　　H.264视频压缩标准为格式化压缩视频设立了要求，以保证在提高视频质量的同时比以往的标准比特率更低。

　　总之，H.264是基于MPEG-2/4视频压缩标准并通过运动估计、变换、量化、熵编码的基于模块的编码步骤。然而， H.264，通过其可变块大小、四分之一分辨率、在循环中去块以及在可变长度编码中的优点来精简运动估计，被揭示作为新兴的优势标准。

　　或许，大多数人会认为MPEG-2/4已经很好的应用了好多年了，H.264也确实需要许多额外的处理能力。H.264仿佛也不会那么快成为潮流。那么为什么还要纠结在这种新的视频压缩标准上呢?

　　然而，它是当前最佳最有效的视频流标准。这就是为什么H.264从家庭娱乐发展到监控系统，已经扩大到庞大的SD和HD视频流应用。除了以更低的比特率获得高质量的视频，H.264压缩标准的灵活性允许工程师剪裁H.264编码器来用到特殊应用上，这是MPEG-2/4所不能比拟的。此外，一个有着能进行运动估计的高质量的H.264编码器将能进行卓越的编码。所以，即使升级可能会增加一些额外的成本，但实施H.264长远来讲可以显著的节省你的流压力。

        原作者：

        Kate Huber　　Optelecom - NKF技术作家

　　Peter de Konink　　Optelecom - NKF编解码器/分析产品线经理

　　Piet Nieuwets　　Optelecom - NKF高级硬件工程师

        翻译：Kunny Lau[nextpage]

【英文原文】

　　The rising popularity of the H.264 video compression standard has established H.264 as ‘the buzzword' within the video surveillance industry. With all this talk of the possible enhancements brought to the fore by H.264, Kate Huber, Peter de konik and Piet Nieuwets of Optelecom-NKF present the true benefits and shortcomings of this popular standard in the first of a three-part review.

　　H.264 takes the world of video streaming by storm

　　A Saturday night in front of the TV maybe doesn't make you think of video streaming standards any more than watching a bridge go up automatically or getting caught on a traffic camera for running a red light do. But video streaming is what makes it possible to safely open bridges from a control center and secure the streets as much as it is what lets you put your feet up and forget the world for awhile with your favorite film.

　　H.264 has become the compression standard of choice in the security industry

　　Since 1995, the video streaming standard of choice for TV broadcasting and DVD video has been MPEG 2. Its successor, MPEG-4 part 2, expanded the possibilities of MPEG-2 in 1998, creating a streaming standard that has largely been adopted by the computer industry. But the buzzword in the world of video streaming these days is H.264, a.k.a. MPEG-4 part 10. Everybody developing or distributing codecs either already supports it or will very soon. But just what exactly is H.264 and what is so special about it?

　　Creating a new video compression standard- a brief history of H.264

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　　H.264 is a product of international cooperation

　　Simply said, H.264 is a video compression standard. It is a product of the cooperation between the the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) which have been working together to define the basic criteria for streaming technologies. Members of ISO and IEC formed a workgroup in May of 1988 called the Moving Picture Experts Group (MPEG), which is known for the MPEG-2 and MPEG-4 part 2 video and audio compression and transmission standards, published in the 1990s. In 2001, MPEG and a subgroup of ITU-T, the Video Coding Experts Group (VCEG), founded a new workgroup called the Joint Video Team (JVT). Basing their work on the MPEG 2/4 standards, JVT created the H.264 video compression standard, first published in 2003.

　　A flexible video compression standard

　　The H.264 video compression standard sets the requirements for formatting compressed video so as to provide improved video quality at lower bit rates than preceding standards. However, it doesn't actually specify how codecs should go about encoding video streams. It only defines how decoders should function and the tools and mechanisms that may be used, giving this standard unparalleled flexibility and allowing developers to contend for the most efficient encoding.

　　Still, H.264 isn't all that different from its compression predecessors. Similarly to MPEG-2/4, developers have to select a particular profile defined for specific uses. In the case of H.264, there are three: Baseline, Main, and Extended. The Baseline Profile is optimised for videotelephony, videoconferencing, wireless communications, and CCTV installations since it is less demanding on the decoder. The Main Profile works better in television broadcasting and video storage, while more exacting applications that are less concerned with processing power requirements can make use of the Extended Profile.[nextpage]

　　Like MPEG-2/4 before it, H.264 also uses block-based encoding. This means that H.264 employs motion estimation, transform, quantisation, and entropy encoding to compress video, and it inverses these processes to decode image data for viewing.

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　　The steps involved in block-based encoding

　　A superior video compression standard?

　　The H.264 video compression standard sets the requirements for formatting compressed video so as to provide improved video quality at lower bit rates

　　In conclusion, H.264 is based on the MPEG-2/4 video compression standards and similarly goes through the block-based encoding steps of motion estimation, transform, quantisation, and entropy encoding. However, H.264 reveals itself as the up-and-coming superior standard through its streamlining of motion estimation with variable block sizes, quarter pixel resolution, and in loop deblocking as well as its advancements in variable-length encoding.

　　Yet, most would agree that MPEG-2/4 have been working great for years, and H.264 does require a lot of extra processing power. So why bother with this new video compression standard? It isn't as though H.264 will suddenly make video streaming a Saturday night on the couch.

　　Still, it is the finest and most efficient video streaming standard to date. That's why H.264 is already expanding into a vast array of SD and HD video streaming applications from home entertainment to surveillance systems. Besides getting better quality video at a lower bit rate, the flexibility of the H.264 compression standard allows engineers to tailor H.264 encoders to specific applications in a way that MPEG-2/4 can't possibly compete with. Moreover, a quality H.264 encoder with competent motion estimation will provide preeminent encoding. So, even if an upgrade may add a few extra costs, implementing H.264 will save you a significant amount of streaming stress in the long run.

　　Kate Huber　　Technical Writer　　Optelecom-NKF

　　Peter de Konink　　Product Line Manager, Codec/Analytics　　Optelecom-NKF

　　Piet Nieuwets　　Senior Hardware Engineer　　Optelecom-NKF