you would have to look at your audio plugin to see if there is a "playback start" event listener. Most have this.
You would then set an interval to move your image1 pixel by pixel across the screen until it reaches its final position (you can divide the amount of pixels it needs to move by the seconds it should take to get there and set your values accordingly). Once it reaches that position you would change image 2 from display:none to display:inline.
None of it's that complicated, but finding that event listener would be my first step.