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Can HTML5 do most of what Flash does today?
I'm not necessarily for Apple, but I am sort of against the need for 3rd party vendors, if a browser can accomplish the same task, efficiently.
What are the advantages of HTML5 over HTML4, will there be a new XHTML, and will HTML5 have any interactive features that may replace Flash?
The biggest advantage is that the functionality is built into the browser, and doesn't require a 3rd party plugin.
Obviously newer browsers (chrome) have integrated flash, but that's an exception rather than the rule.
Interactivity will be dependant on Javascript, new CSS elements, as well as new HTML tags such as canvas.
FWIW, you can have pretty near the same level interactivity you have in todays flash, with today's Javascript, though javascript is limited to the browser sandbox, and flash is not (for instance Flash works well for video chat, Javascript not so much).
For the sake of objectivity, Flash does have some important advantages over HTML5.
Currently Flash has something like a 99% install rate. HTML5 wont reach that penetration level for a while (look at browser usage--many people still run IE6 [hell even IE5!]).
Flash also has a way (as does silverlight) to protect content. HTML5 does not currently provide a way to secure a video stream.
Flash is also a single plugin, not a standard open to interpretation. As any web developer will tell you, browsers take liberties with the HTML spec. They have gotten better, but the biggest browser by share (IE) still lags behind. Since flash is a runtime, you are nearly guarenteed that what you build is what you get, without having to worry much about cross browser compatibility.