Despite the appearance in Dreamweaver, even when previewed in a browser, the FLV should appear and play OK once the files have been uploaded to the remote server.
Many people have complained that embedding FLV files in Dreamweaver CS4 "doesn't work". It does work, but the code generated by Dreamweaver CS4
relies on three external files: FLVPlayer_Progressive.swf, swfobject_modified.js, and expressInstall.swf.
The first of these files is inserted in the same folder as the page in which the FLV is embedded. The other two are installed in a folder called Scripts, which
Dreamweaver creates in the root of your site if it doesn't already exist.
All three external files MUST be uploaded to your remote server for the FLV to be displayed correctly. Forgetting to upload these files is the most common cause of FLV files failing to run correctly in a web page.
Because of the way the external files work, you cannot use Preview in Browser to test a page with an embedded FLV UNLESS you have defined a testing server in your Dreamweaver site definition. Normally, you require a testing server only if you are developing pages with ASP, ColdFusion, or PHP
If you are building websites that use only HTML, and haven't defined a testing server, pressing F12/Opt+F12 produces a jumble of skin controls
onscreen. This is nothing to worry about. Upload the page, the FLV file, and the three external files to your remote server, and test it there. As long as your browser has the Flash Player plugin, everything should display correctly.
Adobe Community Expert, Dreamweaver
Although I have just opened CS4, and inserted a FLV in to an html page without defining a testing server, and the flv previewed OK.
Tried it in a site with setting of 'links relative to site root' (as opposed to document) and the flv won't preview.