Because the xbox 360 only supports specific video/audio codecs, I'd like to write a utility that would look in a directory and convert files to specific formats as they are dropped in the directory.

In some cases, it would only need to convert the container format (ie, mkv to wmv or avi) and in some cases it might need to convert the actual movie.

Of course I don't want to write the code that does the actual conversions so I'm wondering if there are open source projects, or free libraries or event command line tools that can do this effiently that I can use in an automated way.