I've been able to read most of information stored in this file. However, as you probably know, recordings are probably encrypted now. I believe this wasn't always the case - I have some recordings more than a year old now and they can be played back with VLC (not correctly, but still they can be).
I wasn't able to extract even those non-encrypted recordings, so basically I'm giving up. If anyone wants to pickup, where I've left off, be my guest. My source code (C#) is in the attachment.
You'll need Gibbed.IO (http://svn.gib.me/public/gibbed2/trunk/Gibbed.IO/) library and ObjectListView (http://objectlistview.sourceforge.net/cs/index.html) library (well, technically you don't need that, because I only used it to display some info about dvr.mrt file).
I've not commented source code very well, so if anyone has questions about the format of dvr.mrt, please ask.