Record resolution and recording frame rate are the most important specification for any DVR. Both of them determined the quality of video.
For real-time recording, the frame rate is 30fps, it's fixed for every DVR. the highest recording speed for a 4 channel DVR is 120fps, 8 channel DVR is 240fps, 16 channel is 480fps, 24 channel DVR is 720fps, 32 channel DVR is 960fps.
(Note: At 3-5 frames per second recording, you will not omit any activity, there is no real need to record in real time unless there are regulatory reason.)
Now the processors in most of DVR can not recording all the channels in realtime.
Typically most of DVR provides recorded resolution as QCIF, CIF, 2CIF, and D1, 960H