What you're talking about requires to be client side. Long story short, it just doesn't work that way. You can find a flash mp3 player that you can load-up on your page. But actually coding an mp3 player on an ASP.NET page is just physically impossible.
You need not to customize your media player ,Asp.Net framework provide inbuilt medial player control ,Just drag and drop from toolbox, Set property and use it.