You can certainly do this kind of thing using javascript, but there are some problems. Firstly, you do not know how long it will take the media files to download; everyone's connection speed is different. Secondly, this kind of javascript may well be disabled in the user's browser. HTML is not really for this; HTML is about layout, it is not about time sequencing and animation. That is why Flash (and other similar plugins) were created. In your case, Flash is probably the way to go.