So far I know that the file consists of 1795 frames of 496 bytes each, and that the 496 byte frame is defined by the 2nd set of 4 bytes in each frame. Also, the 4th set of 4 bytes counts up by 4 every frame, while the 3rd set counts up by 1 usually every 6 frames, but sometimes it takes 7 frames. The first set of 4 bytes almost always has a value of 2, but sometimes it's 10, and it's even more rarely 8, although at the end there's 54 consecutive frames where it's 8. I theorize this has something to do with what compression method/amount is being used in the current frame, but I'm not sure. I'm fairly certain everything after the first 16 bytes is the compressed data.
Most of this is educated guesswork, I'm not sure if this could really be cracked if the file spec isn't public. It might help a lot if you could say what brand and model DVR the file came from. Also, I think it's worth mentioning that, if my math is correct, the bitrate on this file is something like 23 or 24 kbps, which is pretty abysmal, but maybe that's not important in this case.
Anyway, if there's any more information you might be able to give me, I may be able to help you out, but otherwise it might be kinda tough.