HTML5 is a cooperation between the World Wide Web Consortium and the Web Hypertext Application, it includes all the features from HTML 4.01, but it also adds several new and more powerful features. You may think of HTML as new tags and overall a new version of html, but it's not all about those new and interesting features and it's not the whole story.
You can use Html5 API to detect support for different video formats, play a video, pause, mute audio and everything else you need to build a rich user experience around the <video> tag. HTML5 supports all the form controls from HTML 4, but it also includes new input controls.
Whether you want to play video, design better forms, or build web applications that work offline, you’ll find that HTML5 is already well-supported. HTML5 is also a potential candidate for cross-platform mobile applications. Many features of HTML5 have been built with the consideration of being able to run on low-powered devices such as smartphones and tablets.
Html5 tries to reduces the need to external plugins, handle the errors better than before and be device independent to support all platforms. It offers new features that provide not only rich media support, but also enhance support for creating web applications that can interact with the user, his/her local data, and servers, more easily and effectively than was possible previously.
"HTML5 provides a number of features to allow web applications to run offline. Application Caches allow you to save a copy of all the assets and other files needed to run web applications locally, and Web SQL databases allow you to save a local copy of a web application's data. Together, these allow you to continue using an application when it goes offline, and then synchronize changes with the master version on the server when the network is available again. Web Storage: Cookies allow us some degree of local data storage, but their use is fairly limited. HTML5 Web Storage allows us to store a lot more data, and do a lot more with it."
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