Hey!

Is there some way I could detect if the device/browser that is viewing my page supports flash?
If is does not I would like to output some simple HTML... If it does I would like to output my swf...

Could I do this with PHP? Or do I have to do it with a client side language such as javascript?

Thanks in advance!

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There are various Flash detection javascripts, but of course if javascript is disabled they will not work. Some of them also rely on activeX being enabled when testing MSIE. In addition you may have to test which Flash plugin version the browser has installed.

Do you mean you want to serve a different page altogether or just add a few lines on the current page? If the latter, the OBJECT element has this functionality built in.
http://htmlhelp.com/reference/html40/special/object.html
If you also use EMBED it gets a little trickier, because NOEMBED fires only if EMBED isn't supported, not if Flash isn't.

More about this here:
http://www.alistapart.com/articles/flashembedcagematch/