Live Data Feeds

Hi all,
Was just wondering if anyone knows much about how live data and transmission works.

By this i mean within a browser. When i think of this sort of thing i think of the use of AJAX methods, but for a browser to run AJAX code so often does not seem feasible.

Can anyone delve into the mechanics of this for me, or point me in the right direction?

What type of source are you using for video? Do you intend to stream something like a live feed from a camera equipped with firewire or what?

EDIT: Few more questions...what's the server OS? Are you on your own dedicated machine?

No not any form of media...maybe i explained very wrong.

What i mean is data in the form of say an instant chat for example.

When person 1 (Jenny) starts typing the person 2's(jake) IM client says
"jenny is typing a message..."

For this to happen within a web page chat rather than a IM client Jakes page would have to constantly be checking for updates to the database would it not??

If so for things to happen almost seamlessly jakes browser would be running an awful lot of querries.

Is there a way that the database can push data through to jakes page when requested to by jennys page?

I hope this made sense. It did to me. :-\

Ooh, my bad here. I was assuming video. Sorry.

In a nutshell, you wouldn't have to communicate the message from one user to the other directly. The 'typing' user would just have to notify the server and the other users would receive the message from polling the server.

Work up a few google searches surrounding the Comet methodology. It's spawned off a couple of solutions like cometd and Orbited (cool demo) that are worthy of a look.

If you're into something more hands-on, then start off by googling something like 'PHP Ajax polling' (of course, substitute the language of your choice in for PHP). You may have to filter out results dealing with polls. You can try adding the -poll switch to your query and see what that does for you as well.