H.264視頻壓縮標(biāo)準(zhǔn)的日益普及已使H.264成為視頻監(jiān)控行業(yè)內(nèi)公認(rèn)的“流行語(yǔ)”。H.264使得我們談到的所有可能的增強(qiáng)功能脫穎而出。Optelecom-NKF 公司的Kate Huber, Peter de konik and Piet Nieuwets在接下來文章當(dāng)中的前三段首先為大家呈現(xiàn)了這個(gè)流行的標(biāo)準(zhǔn)真正的好處和缺點(diǎn)。

　　H.264像風(fēng)暴一樣席卷視頻流媒體世界

　　星期六的晚上，當(dāng)你坐在電視機(jī)前的時(shí)候，比起看一座橋自動(dòng)升起或者一個(gè)交通攝像頭拍下的闖紅燈的畫面，或許不會(huì)對(duì)視頻流媒體標(biāo)準(zhǔn)有什么想法。但是是視頻流使得可以從控制中心安全的開通橋梁，以及讓盡可能多的街道變得安全，使得你可以抬起你的腳并暫時(shí)忘記你最喜歡的電影。

　　H.264已經(jīng)成為安防產(chǎn)業(yè)選擇的壓縮標(biāo)準(zhǔn)

　　自1995年以來，電視廣播和DVD視頻選擇的視頻流媒體標(biāo)準(zhǔn)一直是MPEG-2.它的繼任者，MPEG-4第二部分，在1998年擴(kuò)大了MPEG-2的可能性，創(chuàng)造了一個(gè)現(xiàn)今已被計(jì)算機(jī)產(chǎn)業(yè)廣泛采用的流媒體標(biāo)準(zhǔn)。但是現(xiàn)在視頻流媒體世界的流行語(yǔ)是H.264，又稱為MPEG-4第10部分。人們現(xiàn)在正在開發(fā)或傳播編解碼器要么已經(jīng)支持它要么很快也要支持它。但是到底H.264是什么，它有什么特別之處呢?

　　開創(chuàng)了一個(gè)新的視頻壓縮標(biāo)準(zhǔn)—H.264簡(jiǎn)史

　　H.264是一種國(guó)際合作的產(chǎn)物

　　簡(jiǎn)單來說，H.264是一種視頻壓縮標(biāo)準(zhǔn)。它是定義流媒體技術(shù)基本準(zhǔn)則的三大組織，國(guó)際標(biāo)準(zhǔn)組織(ISO)和國(guó)際電工委員會(huì)(IEC)以及國(guó)際電信聯(lián)盟-電信標(biāo)準(zhǔn)部門(ITU-T)，合作的產(chǎn)物。ISO和IEC的成員與1988年五月成立了一個(gè)運(yùn)動(dòng)圖像專家組(MPEG)，它以20世紀(jì)90年代發(fā)布MPEG-2和MPEG-4第二部分視頻和音頻壓縮與傳輸標(biāo)準(zhǔn)而聞名。2001年，MPEG和ITU-T的分支組織視頻編碼專家組(VCEG)，成立了一個(gè)新的工作組—聯(lián)合視頻組(JVT)。JVT在MPEG-2/4標(biāo)準(zhǔn)的基礎(chǔ)上，創(chuàng)造了新的H.264視頻壓縮標(biāo)準(zhǔn)，并于2003年發(fā)布。[nextpage]

　　一個(gè)靈活的視頻壓縮標(biāo)準(zhǔn)

　　H.264視頻壓縮標(biāo)準(zhǔn)為格式化壓縮視頻設(shè)立了要求，以保證在提高視頻質(zhì)量的同時(shí)比以往的標(biāo)準(zhǔn)比特率更低。但是，它實(shí)際上并沒有明確編碼器應(yīng)該如何進(jìn)行視頻流編碼。它只定義了可能用到的解碼器的功能、工具以及機(jī)制，這使得這個(gè)標(biāo)準(zhǔn)無與倫比的靈活，并允許開發(fā)者角逐最有效的編碼機(jī)制。

　　不過，H.264并不是與它的前輩完全不同的壓縮標(biāo)準(zhǔn)。與MPEG-2/4相似，開發(fā)者必須要為特定的用途選擇一個(gè)特定的配置文件。以H.264為例，有三種配置文件：基線，主要和擴(kuò)展?；€配置文件由于在解碼器上的要求較少，為可視電話、視頻會(huì)議、無線通信、筆錄電視裝置所優(yōu)化。主要配置在視頻廣播和視頻存儲(chǔ)中更好用，而處理能力要求較少的更嚴(yán)格的應(yīng)用程序可以使用到擴(kuò)展配置文件。

　　像以前的MPEG-2/4一樣，H.264也使用基于模塊的編碼機(jī)制。這意味著H.264采用運(yùn)動(dòng)估計(jì)、變換、量化以及熵編碼(注：熵編碼是在編碼過程中按熵遠(yuǎn)離不丟失任何信息的編碼)來進(jìn)行視頻壓縮，并方向進(jìn)行這些進(jìn)程來進(jìn)行圖像解碼以便觀看。

　　基于模塊的編碼所涉及的步驟

　　一個(gè)卓越的視頻壓縮標(biāo)準(zhǔn)?

　　H.264視頻壓縮標(biāo)準(zhǔn)為格式化壓縮視頻設(shè)立了要求，以保證在提高視頻質(zhì)量的同時(shí)比以往的標(biāo)準(zhǔn)比特率更低。

　　總之，H.264是基于MPEG-2/4視頻壓縮標(biāo)準(zhǔn)并通過運(yùn)動(dòng)估計(jì)、變換、量化、熵編碼的基于模塊的編碼步驟。然而， H.264，通過其可變塊大小、四分之一分辨率、在循環(huán)中去塊以及在可變長(zhǎng)度編碼中的優(yōu)點(diǎn)來精簡(jiǎn)運(yùn)動(dòng)估計(jì)，被揭示作為新興的優(yōu)勢(shì)標(biāo)準(zhǔn)。

　　或許，大多數(shù)人會(huì)認(rèn)為MPEG-2/4已經(jīng)很好的應(yīng)用了好多年了，H.264也確實(shí)需要許多額外的處理能力。H.264仿佛也不會(huì)那么快成為潮流。那么為什么還要糾結(jié)在這種新的視頻壓縮標(biāo)準(zhǔn)上呢?

　　然而，它是當(dāng)前最佳最有效的視頻流標(biāo)準(zhǔn)。這就是為什么H.264從家庭娛樂發(fā)展到監(jiān)控系統(tǒng)，已經(jīng)擴(kuò)大到龐大的SD和HD視頻流應(yīng)用。除了以更低的比特率獲得高質(zhì)量的視頻，H.264壓縮標(biāo)準(zhǔn)的靈活性允許工程師剪裁H.264編碼器來用到特殊應(yīng)用上，這是MPEG-2/4所不能比擬的。此外，一個(gè)有著能進(jìn)行運(yùn)動(dòng)估計(jì)的高質(zhì)量的H.264編碼器將能進(jìn)行卓越的編碼。所以，即使升級(jí)可能會(huì)增加一些額外的成本，但實(shí)施H.264長(zhǎng)遠(yuǎn)來講可以顯著的節(jié)省你的流壓力。

        原作者：

        Kate Huber　　Optelecom - NKF技術(shù)作家

　　Peter de Konink　　Optelecom - NKF編解碼器/分析產(chǎn)品線經(jīng)理

　　Piet Nieuwets　　Optelecom - NKF高級(jí)硬件工程師

        翻譯：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