What Is HTML5?

This is an installment in our ongoing series of "What Is...?" articles, designed to offer definitions, history, 以及围绕在线视频行业的重要术语和问题的背景.

Executive Summary

随着苹果决定放弃Flash并使用HTML5技术向iPad传送视频，HTML5迅速蹿升至风口. Actual HTML5 usage, however, 由于html5兼容浏览器的普及率较低而减慢了速度, the need to encode video into two or three formats for complete HTML5 compatibility, and the lack of feature parity with Flash, 主要基于插件的技术，用于在网络上观看视频.

HTML5需要出现在所有流媒体生产商的雷达屏幕上, but switching over to HTML5 does not appear to be a short-term priority as of this writing.

HTML5 the Specification

HTML stands for HyperText Markup Language, HTML是制作大多数网站的主要语言. HTML是由万维网联盟(World Wide Web Consortium, WC3)维护的标准。, a group that includes browser developers and other interested technology companies. HTML5是w3c将引入的HTML的最新版本.

In 2004, a group called the HTML Working Group (HTMLWG) was formed by employees of Apple, the Mozilla Foundation, and Opera Software, 因为这些公司“越来越关注W3C在XHTML方面的方向”, lack of interest in HTML, 而且明显无视现实世界作者的需求.” Later, the WC3 recognized the HTMLWG, and tasked it with providing (among other deliverables):

从HTML4演变而来的一种语言，用于描述万维网上文档和应用程序的语义. 这将是一个完整的规范，而不是增量规范.
该小组将为HTML规范创建一个全面的测试套件.

To a degree, this dual control has led to two specifications of HTML5 (see, for example, “The two specifications of HTML 5.0: WHAT WG vs W3C,”) or at least the appearance of two specifications. Here’s an explanation from the WHATWG FAQ.

Which group has authority in the event of a dispute?

编辑将每个人的反馈都考虑进去，而不是为了技术论据而查看这些论据的来源.

W3C HTML工作组有一个升级过程，在某些情况下会导致做出的决定与编者对某个主题的原始决定不同. So far, whenever this has happened the WHATWG has gone along with the W3C's request; nothing of especially big importance has been changed in this manner so far (it's mostly been editorial issues or mostly minor technical issues). 一般来说，只要W3C小组没有出现任何严重的判断失误，WHATWG就会确保规范的规范内容(对作者和实现者的要求)保持不变.

On January 18, 2011, the W3C revealed an HTML5 logo (Figure 1), complete with t-shirts and stickers, and on February 14, 2011, W3C announced that HTML5 would be finalized in mid-2014.

HTML5 Logo

Figure 1. The HTML5 logo.

In contrast, on January 11, 2011, in a blog post entitled “HTML is the new HTML5,” the WHATWG announced 他们正在转向一种“新的开发模式”，消除HTML5版本号，使现有的HTMLWG规范成为一种“生活标准”.ww3和WHATWG标准的编辑Ian Hickson评论道:

S因为W3C仍然专注于让HTML5走到最后, I'll maintain a WHATWG copy of the HTML spec that matches what the W3C HTML WG is working on:

http://www.whatwg.org/specs/web-apps/html5/

I've updated the FAQ's explanation of what specs exist, 如果你想得到一个概述(它变得有些复杂)!):

http://wiki.whatwg.org/wiki/FAQ#What_are_the_various_versions_of_the_spec.3F

So, HTML5 is dead from the WHATWG perspective, but you can buy an HTML5 t-shirt from the WC3. This complexity notwithstanding, 该规范的war3和WHATWG版本在如何处理视频标签方面是一致的, discussed next. For the sake of clarity, we’re going to continue to call the spec HTML5 in this article.

The HTML5 Video Tag

HTML5 is a sweeping specification, with multiple new features and capabilities. From a streaming media perspective, however, HTML5特别有趣的地方在于，它包含一个视频标签，使浏览器能够在页面内本地播放视频, obviating the need for plug-ins like Flash, Silverlight, and QuickTime. 当苹果在2010年初推出不支持Flash的iPad时，这一特殊的问题就出现了, with video playback accomplished via HTML5.

To support this feature, however, browser vendors must directly implement codec playback capabilities in their browsers. Originally, 有两种视频编解码器被考虑用于HTML5: Ogg Theora, which is open source, and H.264, which bears royalty obligations. 虽然该规范的最初目标是指定一种可以在所有浏览器上工作的视频编解码器, this goal proved unreachable. Here’s a quote from a June 29, 2009 Ian Hickson post to the WHATWG message list:

After an inordinate amount of discussions, both in public and privately, on the situation regarding codecs for

因此，我删除了HTML5规范中需要编解码器的两个小节, and have instead left the matter undefined, as has in the past been done with other features like and image formats, and plugin APIs, or Web fonts and font formats.

The current situation is as follows:

Apple refuses to implement Ogg Theora in Quicktime by default (as used by Safari), 理由是缺乏硬件支持和不确定的专利前景.
Google has implemented H.264 and Ogg Theora in Chrome, but cannot provide the H.264编解码器许可给Chromium的第三方分销商, 并表示相信Ogg Theora的每比特质量还不适合YouTube处理的音量.
Opera refuses to implement H.264，理由是相关专利许可的高昂成本.
Mozilla refuses to implement H.264, as they would not be able to obtain a license that covers their downstream distributors.
Microsoft has not commented on their intent to support

从那以后，谷歌收购了On2并开源了VP8编解码器 WebM，该功能已在Google Chrome (version 6)中实现.0+) and the Opera browser (version 10.6+) and will be supported in Mozilla Firefox 4.发布时为0(目前在测试版中可用). Google also announced their intention to drop H.264 support from Chrome.

Safari has not implemented any codec other than H.264. Microsoft implemented H.264 in Internet Explorer 9, but later stated that their new browser will support “VP8 video when the user has installed a VP8 codec on Windows.”

虽然没有一种HTML5编解码器可以在所有浏览器中工作, by using alternative tags like those shown in Figure 2，网站可以完全支持所有兼容html5的浏览器.

Jilion's Implementation of HTML5

Figure 2. Jilion使用多个标签和文件来完全支持HTML5.

It should be noted that some of these codec limitations can be avoided via downloadable plug-ins. For example, on January 14, 2011, Google promised to release plug-ins that enable WebM support in Safari and Internet Explorer 9 via the HTML standard

Invasion of the Patent Trolls

Meanwhile, issues of patent infringement reared their ugly heads with both Ogg Theora and WebM. 通过后台，MPEG LA管理H的专利池.264 and a number of other technologies. In an interview with Streaming Media on March 4, 2010, MPEG LA CEO Larry Horn commented “市场上的任何人都不应该有这样的错误印象，即Theora等其他编解码器是免专利的. Virtually all codecs are based on patented technology, and many of the essential patents may be the same as those that are essential to AVC/H.264. Therefore, 用户应该意识到，使用他人开发的这些技术可能需要许可和支付适用的版税, too.”

In April, 2010, when Steve Jobs was asked why Apple used H.264 instead of Ogg Theora据报道，他回答说:“所有视频编解码器都受专利保护. A patent pool is being assembled to go after Theora and other “open source” codecs now. Unfortunately, just because something is open source, 这并不意味着或保证它不会侵犯他人的专利.”

MPEG-LA never took any formal action against Ogg Theora, most likely because it was largely supplanted by WebM. Regarding WebM, however, Microsoft attributed its decision not to implement WebM directly in Internet Explorer 9 to Google’s refusal to indemnify, or pay the costs of patent infringement, 微软会因为使用WebM而被起诉侵犯专利权吗?

For example, will Google indemnify Mozilla, a PC OEM, a school, a Web site, a chip manufacturer, a device company, or an individual for using WebM? Will they indemnify Apple? Microsoft? 他们会赔偿全球范围内的任何或所有这些当事人吗? 如果谷歌真的有信心这项技术不会侵权，也不会受到任何专利的阻碍, wouldn’t this indemnification be easy?

On February 10, 2011, MPEG-LA issued a call for patents essential to WebM这可能导致任何使用这项技术的人都要支付版税. On March 4, the Wall Street Journal reported that the Justice Department is investigating MPEG-LA 以确定它是否“不公平地试图扼杀谷歌公司支持的免费在线视频技术竞争对手”."

To be fair, licensing H.264与MPEG-LA不保证第三方不包括在H.264 patent pool won’t assert intellectual property rights against companies using H.264, with the AVC/H.264 FAQ stating "No assurance is or can be made that the License includes every essential patent." However, at this point, WebM的用户比H的用户遭受第三方版税索赔的风险似乎要大得多.264

Using HTML5: Practical Issues

With this as background, let’s examine some practical issues relating to using HTML5.

HTML5-Compatible Browser Penetration

According to NetMarketShare, as of March, 2011, html5兼容浏览器的比例远低于46%. This is shown in Figure 3, 排名前四的浏览器中有三个是旧版本的ie, comprising 54% of the total, were not HTML5 compatible. 从市场份额来看，排名前30位的浏览器中有40%是HTML5兼容的, while 59% were not.

Market Share of HTML5-Compatible Browsers

Figure 3. Browser usage stats as of March, 2011.

Now that a release candidate of Internet Explorer 9 is shipping, you would expect these numbers to change dramatically over the next twelve months. On the other hand, NetMarketShare also reports that Windows XP users comprise 55.09% of the installed base of all operating systems, and IE9 won’t run on Windows XP. 当然，这些旧版本ie的用户可以安装其他HTML5兼容的浏览器, 但早在ie9发布之前，他们就可以做到了, and most didn’t. One would have to assume that either these desktop users didn’t care about HTML5, were on locked down corporate, government or education desktops, or both.

Note that it’s possible to create HTML5 syntax that displays video first using HTML5 if available, and then falls back to Flash, Silverlight or other plug-in for legacy browsers. This approach should work well for most simple, video in a window, playback applications. However, as a new technology, HTML5并没有提供Flash或Silverlight等替代平台所具备的许多功能, at least not in proven, cross-browser compatible form.

HTML5 Feature Deficits

For example, though YouTube has made an HTML5 player available 自2010年1月起，YouTube仍然默认使用Flash Player. On June 29, 2010, YouTube addressed why in the YouTube API Blog, where the company stated that the video tag doesn’t currently meet all of YouTube’s needs. 需要改进的领域包括缺乏标准的视频格式, robust video streaming, content protection, Encapsulation and Embedding, Fullscreen Video ,and Camera and Microphone access.

正如YouTube博客所说，许多领域正在取得进展. For example, Wowza Media Systems (Figure 4) has previewed a version of Wowza Media Server that streams live HTML5 video with WebM, 虽然它需要一个兼容WebM的浏览器来播放. Anevia is also showing a WebM-based live, adaptive streaming solution, though this requires a WebM-compatible browser as well. Flumotion has also implemented live streaming with WebM.

Wowza's Live HTML5 Video Demo

Figure 4. Wowza媒体服务器流直播WebM视频到WebM兼容的浏览器.

At the second annual W3C Web and TV Workshop, held in Berlin in February 2011, 有关于HTTP自适应流和内容保护的会议, though standards have yet to be proposed or adapted, 这表明基于标准的解决方案需要几个月的时间, if not years, away.

In this regard, 区分适用于iOS设备的基于HTML5的技术和通用HTML5技术是很重要的. That is, while Apple has created solutions for live, iOS平台的自适应流媒体和数字版权管理, these won’t work in other browsers. For example, Apple HTTP Live Streaming, which enables live and on demand, single file or adaptive streaming, only runs on “iPhone, iPad, and iPod touch (requires iOS version 3.0或更高版本)或安装了QuickTime X或更高版本的任何设备.” (). QuickTime X is available only for Mac OS X Snow Leopard, and not for Windows computers.

HTML5 Adoption To Date

The most high profile adaption of HTML5 to date has been by Apple with the iPad, though as mentioned, many components of this solution are Apple specific, and all videos are in H.264格式，所以不会在目前大多数HTML5浏览器上播放. 虽然许多商业和广播网站支持iPad, very, very few (if any) fully support all HTML5 browsers with the required three formats of video.

Multiple UGC sites, including YouTube and Vimeo, have HTML5 compatible players，不过两者都需要用户选择是否加入才能查看HTML5页面. At the time of this writing, YouTube (a Google subsidiary) is still producing HTML5 compatible files in both H.264 and WebM formats, with no word if H.264 will be dropped. Neither site encoded video into Ogg format, so the only way for Firefox users, 它们占据了HTML5兼容市场的50%, 浏览这些网站的内容是通过Flash播放器.

Otherwise, Kaltura和Brightcove等多个服务提供商正在提供HTML5兼容的解决方案, though the most common applications are for HTML5 video support on iOS devices. 许多第三方都在为游戏开发和其他基于HTML5的应用发布兼容HTML5的播放器和工具包.

At WebM’s launch on May 19, 2011, Adobe宣布:“我们很高兴在即将发布的Flash Player中包含VP8视频编解码器, 这将帮助用户在所有联网设备上无缝访问高质量的视频内容.Flash Player的WebM兼容版本也没有发布, or announced, as of the time of this writing. On August 31, 2010, Adobe发布了Adobe Dreamweaver CS5 HTML5 Pack，它为Adobe流行的HTML创作程序添加了许多与HTML5相关的新功能.