As has been mentioned, there's no easy way to go about building a web application like that without rewriting it. Is there a particular reason it has to be a web application as opposed to a downloadable exe?
Dealing with copyright issues over music can be a hassle in the long run thats relatively easy to avoid. There's no shortage of CC music around like from the Big List of Free Sounds here or one of the many random music generators floating around the net, just be sure to read and the licensing terms (attribution, etc). If at some point you want some custom tracks you can also ask around for rates from the various musicians floating around here.