Does an NVR simply save the stream or does it re-encode the footage again using whatever codec it can handle.  I see many screenshots of the Dahua NVR and it lets you specify the bitrate, frame rate, resolution, etc. for each channel.  I'm assuming that it is re-encoding the stream to according to those settings.  I really want to avoid the NVR from encoding again a stream that's already highly compressed by the camera.   
  
My cameras are Vivotek IP8332 and they have been tested to work with ONVIF software.  I use it with Vivotek's own server software(ST7501).  The camera has 4 streams and the server can "record" from any stream.  It saves the stream directly onto the hard drive in .3gp format.  I want to use a standalone NVR to record from my cameras as I don't want to leave my power draining server up 24/7 just to record.