Dear Gerudo,
You can click "Insert Flash" or "Insert Media", it will embed flash or media file to edit area, the generated html code are as follows:
<object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" width="280" height="220" xcodebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab">
<param name="Movie" value="/CuteSoft_Client/CuteEditor/flashplayer.swf?videoUrl=http://cutesoft.net/uploads/barsandtone.flv&playerMode=simple&autoPlay=true" />
<param name="Quality" value="high" />
<param name="wmode" value="transparent" />
<param name="allowFullScreen" value="true" />
<embed src="http://cutesoft.net/CuteSoft_Client/CuteEditor/flashplayer.swf?videoUrl=http://cutesoft.net/uploads/barsandtone.flv&playerMode=simple&autoPlay=true" width="280" height="220" quality="high" wmode="transparent" allowfullscreen="true" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" ></embed></object></p>
You don't have to create customization button to embed a file.
When you click "Properties" for the embedded file, the file selection dialog is not supported. If you'd like to change the embedded file, you can remove current one, and click "Insert Flash" or "Insert Media", add a new one.
Thank you for asking