Before buying a DVR ensure the following features.
1. Check the DVR compression ( H.264, MPEG4, MJPEG, JPEG 200) Price and Quality is high for H.264 goes asceding order JPEG200 is the cheapest.
2. Check FPS rate : Frames per second higher the rate is better 4 channel DVR for best quality recording it needs 100FPS, 8 Channel requires 200 FPS and 16 Channel 400 FPS.
3. Real time : Make sure there are two types of real time one is live display should be real time normally most of the DVRs got this feature. Second one is real time recording this is important part this will shows lot of difference in pricing.
4. Network: Check it can support for LAN for internet, if so check whether it supports to static IP only or DDNS. DDNS supporting is best so without additional cost you can view on internet.
5. Rcording resolution: higher the rate is better