Limit user uploads by type or directory

Total user quota allows me to limit what an individual user can upload. It also takes into account files uploaded through means other than IMCE, like file fields. Can anyone suggest (a module?) how I might enforce quotas per user by either 1) the individual directories that the user has access to through IMCE or 2) the file types (extensions) the user uploads? The problem that I'm having is that I want to limit the images and videos the user uploads, but give the ability to upload unlimited MP3s.