Similar to sources.xml, but used to add custom network locations when browsing in the GUI for a path. Basically sources just for the "Browse for new share" window. mediasources.xml is only created when you "Add network location" from that window.
One example of meadiasources.xml is listed below:
<mediasources> <network> <location id="0">ftp://admin:firstname.lastname@example.org:21/Video</location> </network> </mediasources>