HTML 5 is the newest version of HTML. It is still under development and browsers do not fully support it yet but this is rapidly changing.
HTML 5 is an attempt to update and clean up the hodgepodge of codes and conventions that have evolved over the years for delivery of content via the Web. It's authors are working to arrive at a single markup language that:
Is easily readable by humans
Is consistently understood by devices (computers, smart phones, browsers)
Adding video to Web pages has historically involved various kludges because HTML 4 was not designed to accommodate it. Fortunately, HTML 5 is but a certain amount of redundancy is still necessary in order to get video to work in all browsers and platforms.
The reason for this is that, of the three widely-used video formats, browser support is not uniform:
Browser
MP4
WebM
Ogg
Internet Explorer 9
YES
NO
NO
Firefox 4
NO
YES
YES
Google Chrome 6
YES
YES
YES
Apple Safari 5
YES
NO
NO
To address this issue, HTML 5 covers all the bases by allowing you to reference as many video types as you want and letting the browser play the first one it comes to that it supports.
Your browser does not support the video tag.
</video>
Web page:
Audio
Because there was no standard for playing audio prior to HTML 5, adding audio to Web pages has often involved third-party plug-ins such as Flash. Fortunately, HTML 5 cleans that up similiarly to the way it does video.
As with video, the three widely-used video formats are not uniformly supported by browsers:
Browser
MP3
Wav
Ogg
Internet Explorer 9
YES
NO
NO
Firefox 4
NO
YES
YES
Google Chrome 6
YES
YES
YES
Apple Safari 5
YES
YES
NO
Using the same approach it does for video, HTML 5 allows you to reference as many audio types as you want and the browser plays the first one it comes to that it supports.