I'm working on a site for someone where they are inviting their music artists to submit their MP3s for others to pick up and use in their own work - for a price of course. To prevent the artists track from being ripped off by unscrupulous individuals - my plan is to loop a vocal track underneath the 'preview' version and make it useless... and then serve up the clean version to people who have paid for the rights.
I'm using PHP & running on a Linux server - and it seems like a pure PHP solution is not the way to go, with the preference being using an exec() of a command line program to mix the tracks at the point of upload. I need something quick and reliable.
Unfortunately I don't know of any such tools and my searching has come up blank. Can anyone suggest where I might find something? It doesn't have to be free, but it has to be reasonable - and more importantly - simple to work with via PHP.