How do you synchronise the content of a directory on the computer with the mediaplayer.
Not sure how you can synchronize a folder on your computer to the media player. However, you can share that folder with your files on your network and using the media player, you will be able to access those files.
See if the following link helps:
How to share a folder in Windows that can be viewed with the WD TV Live, Live Streaming, Live Hub, or Live Plus