I don’t think that developing a voice chat application with pure html5 is possible at the moment, as most browsers do not yet support audio recording. You will be able to use navigator.getusermedia ( W3C Draft ) for this purpose in the future, but AFAIK, this method is not supported by any main browser. Thus, I think you will have to abandon proprietary technologies, such as flash, to develop a web-based audio chat system that currently works for most users.
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