Here is an example of code how to do this
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Let me do some comments for new people.
1) First of all I have to say that I used 1.5 version of swfobject instead of last one swfobject2.2. I'm planning to update it to 2.2 very soon. So please use 2.2 instead of 1.5, but anywhere approach is very similar.
- as you see DIV with ID FLV is used to be replaced with code that swfobject will generate to show SWF/FLV video.
- preview.swf is a player use want to use to show FLV video.
- your.flv is a FLV file you want to show.