Ondemand audio file transcoding (ffmpeg, linux)

We require an application which will transcode mp3 files ondemand (probably using ffmpeg) in such a way that they appear to already exist on a linux server. For example if we have a real mp3 called [login to view URL] on a server in one folder we want to be able to call a virtual file in another folder called [login to view URL] which will appear to be a transcoded version of [login to view URL] We need to do this so that an ondemand streaming server such as wowza media server could receive the request to stream [login to view URL] and the data would be streamed to it just as though [login to view URL] actually already existed on the server. This would also need to be able to support byte range requests to allow the streaming of [login to view URL] to be seekable. The filename would be used to pass through some encoding settings such as the bitrate and format. The application would need to support aac and mp3.