Dash Cam = DVR. I think that is what the OP is talking about.
If you look at the company Echo Master or its parent you may see some things there, however nothing that can "tap" into current cameras as they will be speaking their own language.
Also, you want a battery based dash cam (dvr) if you live in a hot area (ie AZ), as the ones that use capacitors will stop working once they get too hot. The battery (capacitor) is used to "save" the last file it was recording when turned off (or in an accident and power is removed).
Good luck.
//KMac