I have studied the file a bit more now and here's what I've found.
The main script has a timed loop that cycles between two different background clips (countdown is in the foreground).
First background clip, entitled 'Nico' in the actionscript, plays that deep rumbling gong-sound (not to be confused with the short countdown sound!) and displays cyan-colored weird glyph-like symbols fading in and out (doesn't Ico actually have glyphs like this on the tombs in the room at the beginning?! I also remember Ico official site had glyphs kinda like these)
Second background clip entitled 'Genji', plays the short melody played on the string instrument, like some Japanese sounding harph, and it shows petals flying across the screen.
Obviously these two are the hints representing some kind of the style of the games to be announced.