I HAVE FOUND A SOLUTION!
We have similar DVRs at our company, and I would have had to manually convert over 2000 files of an incident. After days of searching, and trying everything I can, it turns out the AVI MP4 Converter made by Hoo Technologies works perfectly. It even will convert them all to one MP4 file!!!
http://www.avi-mp4.com/avi/h264-to-avi.htm
Saved me days of wanting to hit my head on the desk, manually converting DVR files!
For reference our .264 files were off a Kguard DVR.
Cheers,
Shaun Brookman