Hi there, I can't think of anything of the peg, but if you wanted this sort of Hot Folder arrangement then dnotify would kick of a script that does the transcoding etc. I did something similar that processes images from my camera.
The trick with dnotify is that I couldn't make it report out the file that caused the trigger event, so what I have done is set up the script that gets called (in this case bash but it could be anything) to rename the files after it has processed them so they can be ignored on the next pass. Either that or you could have a "drop" folder that is separate to your "Processed" folder so you aren't trying to reprocess old files everytime a new one is dropped in.
Be aware though that it is very easy to run into issues when multiple files are dropped because your script will be queued for each new file, there are ways of changing this behavior.