I have full control of my server, so I can install any plugins or whatever, but that software must be licensable for commercial use.
I want to create a "dulled" version (i.e. lower frequency and bit-rate) of the songs people upload, which will be used for a short while (maybe a few days at most) before being automatically deleted.
This can be done in real-time while it is downloaded, or when it is uploaded; I don't mind if it keeps an original copy on the server. I don't even mind just adding it to a database of items todo, and then just make a cronjob to crawl the todo items and then do it from there.
I don't have much of an understanding of making PHP running programs stored on the server, the most I do at the moment is run the MySQL backup script from PHP.